# Rotary Table Questions



## Susquatch (Sep 14, 2021)

A few years ago, I hobbed a spur gear to repair my old mill/drill. I used a gear cutter hobb and rotary angle indexer with an er30 collet to hold the work. It worked and the gear was a complete success.

However, I had wished I had a rotary table instead. I recently made an adapter plate for a new motor for my Hartford mill. Again, I found myself wishing I had a rotary table.

I took a quick look on Ali, Amazon, BusyBee, Accusize, and KBC. They seem to come in 2" increments from 4 up to 20. All are also expensive. So I made search bots for both Kijiji & eBay and I'll see what comes up. I'm in no rush.

My questions here are looking for advice.

What size do you think is optimum?

What features are desirable?

Is an add-on chuck essential?

Are there any add-on accessories that ARE essential or at least highly useful?


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## RobinHood (Sep 14, 2021)

I have an OE 12” BP for my mill. It can only be mounted flat on the table - some of the newer/other brands can be mounted both horizontally & vertically. I think that would be an advantage.

They are heavy (well, the older ones anyway). My RT is quite low profile and very accurate (It divides the circle into degrees, minutes, and seconds. Used it yesterday to set a 39.45* (39* 27”) angle either side of a ref line to bore two 24.05mm holes. Worked great.

I would get the largest RT you can afford - for your mill size 12”+. Why, because if you have an 8” work piece there are only 2” all around for clamping - that is not a lot of room for strap clamps.

I bolt chucks onto it as required. I don’t have any “dedicated“ ones. Pulled the backing plate off of an 8” lathe chuck in the past because it was the best option. I do have some “spare” chucks that I try to use if I can (4J, 3J & 3J independent).

Fixture plates are nice to have for small stuff - you can make one from a chunk of alu sheet.


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## Brent H (Sep 14, 2021)

@Susquatch : I have a 12” rotary table used on my (same as your) Bridgeport mill.  It is huge and can sit vertical or Horizontal- although I need to make a base mount for it so the existing slots line properly.
I purchased indexing plates for it and it came with an 8” bison 3 jaw chuck.   The chuck only has the one jaw set which sucks but it would be nice to have a 4 jaw and outside jaws - then you can clamp some big parts.  With the 12” table you can really mill some large pieces and secure things down.  Given the mass of the table it is very solid when machining.  
I have made gears and other items and it works great.  
In a perfect world having the 12” table AND a smaller, say 6”to 8” indexing head would be sweet.  I missed out on one at auction that included gearing to tie back into the power feed for making helical gears - bummer


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## PeterT (Sep 14, 2021)

Some more points to ponder
- some but not all RT's will allow a tooling plate to be mounted to RT with through bolts into T-slots, thus buying you more available real estate. But some RT's have a ledge or casting that limits so evaluate some pictures
- ability to be horizontal and vertical isvery important in my mind, otherwise you need a dividing head
- adding chuck to RT usually involves a home brew intermediary adapter plate. I have posted some piics so do a search. But be aware the whole thing starts to stack up like a wedding cake & you may run out of vertical room depending on your mill, tooling, part etc.
- trying to make self centering chucks concentric to the RT MT hole can be somewhat futile depending on accuracy you are after. Adapting a 4J chuck vs a 3J gives you ability to dial it in regardless.
- whatever RT you buy, consider teh plates &tailstock while you're at it. Sometimes its harder to reconstruct the accessories years later
- watch Stefan video where he dissects an Asian RT. Like most things they vary in quality


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## John Conroy (Sep 14, 2021)

I have a Vertex CS8 Super spacer which is basically a rotary table with a 8" chuck instead of  table. I got it used for a good price but it had a worn out gear and it took a while to find a preplacement. I made a 12" table for it using a 12" brake rotor for a GM truck and a 12" round steel plate that I drilled with a pattern of threaded holes for hold downs. With the chuck mounted it weighs 175 LBS so these things are pretty heavy so best to find a way to load it onto the mill table without lifting. It can be mounted vertical or horizontal and I have the indexing plates for it. Used ones are pretty hard to find but if you are patient you'll find one.

























As Peter mentioned they do fill the available vertical space between spindle and table pretty fast especially when you add a drill chuck or boring head. That was the main reason I added a 6" riser block to my mill.


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## Susquatch (Sep 14, 2021)

Thanks @Brent H, @PeterT, @RobinHood, @John Conroy. 

OK, the largest I can get. Preferably 12+.

Vertical & Horizontal if possible.

About the dividing heads. I have a few pieces already. See photos below. The easiest one to use is the 5C Collet Head. But the 3 jaw chuck head will do angles off the table and is slick even if it is a bit complicated.















Do they change anything?


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## Brent H (Sep 14, 2021)

@Susquatch : the 5C collet indexer is great for fast machining on dimensional stock.  Accurate but not super strong.  

the Indexing head with the chuck - beauty!   Solid, lots of options and just as fast as the collet indexer once you set things up.  

your three jaw (can change out to 4 jaw) size would be my next purchase.  I don’t think I would get a 5C indexer as that requires more collets and the fast operations I can handle with a hex/square collet chuck 

the big rotary table will allow you to do some pretty cool things the other 2 machines cannot.

I made my own tailstock for the 12” - it is somewhere on here. Works great


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## RobinHood (Sep 14, 2021)

All good points that I forgot to mention, fellows.

Apropos using up space fast even on a 12” table - here is a 200 mm hand wheel being machined. Not much room for clamps.


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## PeterT (Sep 15, 2021)

Usually people buy the RT size they need & that's the end of it. But as table diameter grows, usually so does thickness. Not always depending on the model but something to check.

What I was saying about some RT's can accommodate larger diameter tooling plates (or the extending part footprint for that matter) is kind of depicted by these pics. Its hard to judge based on catalog pictures where the dial or casting upright may intercept, but anyways this is what I was driving at.


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## Susquatch (Sep 27, 2021)

Thanks for all your input guys! 

I found a 10" Sowa RT at a really good price in A1 condition. It's not 12", but I'm hoping it will meet my needs.


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## Dabbler (Sep 30, 2021)

My 10" table is about 1/2 the weight of my friend's 12" table...  Small win for the 10" table.  My 8" table weighs about the same as the 10" - go figure...


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## Susquatch (Sep 30, 2021)

Dabbler said:


> My 10" table is about 1/2 the weight of my friend's 12" table...  Small win for the 10" table.  My 8" table weighs about the same as the 10" - go figure...



I am told this one weighs over 100 pounds. I'll find out when I pick it up next week.


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## Susquatch (Oct 11, 2021)

Picked up the 10" rotary table enroute to Barrie. Here are some photos.

It has 4 degrees per turn of the crank and 5 minutes per division with a vernier scale to find the nearest minute of 5.

As far as I can tell, it has zero backlash but that's with no load. I'll have to test it with a load to see what it really is.











I have no idea what the knurled rings (one inner and one outer) are for. Any ideas?






Also, the dial zero and vernier are located oddly. I think they can be rotated by loosening the tiny set screw, but I'm hesitant to play with it.

Lastly, there are two screws on the  outside of the crank handle. The center one is probably a retainer, but what is the outer one for? An index adjustment or a rotation stop??






It doesn't have a 90 degree stand, but I have other tools (see separate post above) for that so I'm not worried about it. If I ever need it, I can always make a separate stand.

Lastly, it seems to have this very odd crank disengagement mechanism. You loosen the little T-handle and then you roll the entire crank assembly (prolly a worm gear) out of engagement.


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## Dabbler (Oct 11, 2021)

The vernier and the disengagement are on the same mechanism on both of mine.  You have a typical rotary table: 90  turns per revolution, so any indexing plate set will work, once you have it mounted.  (rotary indexers are 40 turns per revolution, FYI.

The disengagement mechanism is to permit it to use indexing plates.


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## Susquatch (Oct 11, 2021)

Dabbler said:


> The vernier and the disengagement are on the same mechanism on both of mine.  You have a typical rotary table: 90  turns per revolution, so any indexing plate set will work, once you have it mounted.  (rotary indexers are 40 turns per revolution, FYI.
> 
> The disengagement mechanism is to permit it to use indexing plates.



Cool! I have a set of 4 indexing plates that came with my semi-universal dividing head. Any Chance that they can be used with the dividing head? Or is all that kind of stuff proprietary?


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## Susquatch (Oct 11, 2021)

Dabbler said:


> The vernier and the disengagement are on the same mechanism on both of mine.  You have a typical rotary table: 90  turns per revolution, so any indexing plate set will work, once you have it mounted.  (rotary indexers are 40 turns per revolution, FYI.
> 
> The disengagement mechanism is to permit it to use indexing plates.



Just thinking out loud.....  Why would you want to disengage the worm in order to use dividing plates? I would have thought that the plates need the worm too......


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## Brent H (Oct 11, 2021)

I think you can disengage the worm so you can rotate the table without the handle spinning. - mine does the same thing - I will have to check it out.
The indexing plates typically fit standard.


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## Dabbler (Oct 11, 2021)

A dividing head plate is calibrated for 40 turns per revolution, not 90, so to use one in a straightforward way... no.  But on some divisions, it can still be useful with a little math - perhaps an engineer? 

On a dividing head like mine I have to disnegage the clockwork to use dividing plates.  On both my RT's the worm gear is always engaged, both plates and manual handle...

I think I 'spoke' poorly in my above post on the matter.  Sigh.  English! sorry.  I think I said it backwards!


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## Susquatch (Oct 11, 2021)

Brent H said:


> I think you can disengage the worm so you can rotate the table without the handle spinning. - mine does the same thing - I will have to check it out.
> The indexing plates typically fit standard.



Ah yes, that makes sense. Who wants to crank around to 180° manually. Better to disengage spin and re-engage.

I will have to check my plates to see if they will fit.


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## RobinHood (Oct 11, 2021)

On my BP RT, the worm needs to be engaged at any point in the circle that is divisible by 4 and the handle needs to be in the UP position. Otherwise the markings on the hand wheel and table are out of sync no matter what you set the dial to and thus the set angles won’t be correct.

Yours might be different, but there are RTs where it matters where you engage the worm.


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## Susquatch (Oct 11, 2021)

Dabbler said:


> A dividing head plate is calibrated for 40 turns per revolution, not 90, so to use one in a straightforward way... no.  But on some divisions, it can still be useful with a little math - perhaps an engineer?
> 
> On a dividing head like mine I have to disnegage the clockwork to use dividing plates.  On both my RT's the worm gear is always engaged, both plates and manual handle...
> 
> I think I 'spoke' poorly in my above post on the matter.  Sigh.  English! sorry.  I think I said it backwards!



No worries..... Backwards usually works too...... Lol!

In my case, the worm gear seems to disengage and works as @Brent H suggests.

I think that means I just replace the handwheel with the dividing system.

A mathematician wouldn't bother with a dividing disk. They would just add the increment to the previous number and dial it in. Non-mathematicians can't do that because they can't handle addition in a base 60 numbering system. Assuming that is correct, I'd prefer to avoid mistakes which is what the dividing disks are supposed to do. (I think).

Why can't both trig, time and number bases all be in octal?

Which reminds me of another story. When one of my previous bosses retired, I was tasked with getting him a good gag gift. He was a member of Canada's metrication committee (the dummies who believed the US would follow Canada's lead and go metric too.). He was also an avid clock maker. 

I decided to get him a metric clock. 10 hours in a day, 10 minutes in an hour, 10 seconds in a minute, etc. 

There were none. Apparently the decimal base system doesn't apply to time or angles. Go figure! 

So I designed a kit and bought all the gears and parts needed to make one and that's what we gave him! I don't know if he ever built it. Didn't matter. It was hilarious.


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## Susquatch (Oct 11, 2021)

RobinHood said:


> On my BP RT, the worm needs to be engaged at any point in the circle that is divisible by 4 and the handle needs to be in the UP position. Otherwise the markings on the hand wheel and table are out of sync no matter what you set the dial to and thus the set angles won’t be correct.
> 
> Yours might be different, but there are RTs where it matters where you engage the worm.



Yup, that's mine. I discovered that myself when I noticed that zero on the crank marks could not be aligned with zero on the table itself. But by disengaging the worm, I could turn it a bit such that they could be aligned.


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## Susquatch (Oct 11, 2021)

I think I fixed the goofy markings on the crank that only short people could see. Loosening the little tiny Allen key allows the whole assembly to be turned so that all the markings are easily viewable from above. After that, another alignment of the worm gear and its good to go.

I'll play with my dividing plates tomorrow.


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## Brent H (Oct 12, 2021)

https://www.sowatool.com/img/catalogue_downloads/USCAT17_Sec7_Accessories .pdf

might be of some use to you?


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## Susquatch (Oct 12, 2021)

Brent H said:


> https://www.sowatool.com/img/catalogue_downloads/USCAT17_Sec7_Accessories .pdf
> 
> might be of some use to you?



I'll take a good look! Thanks @Brent H!


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## Susquatch (Oct 12, 2021)

So here is my RT with the crank handle and front dial removed.






In the process I discovered that the outer screw on the handle is a lock for the front dial.

Obviously, it is already setup for divider plates. The three threaded holes bear witness to that.

Unfortunately, not mine...... My divider plates have a smaller inside ID and a smaller bolt circle and the index bar will never reach.

Nonetheless, I think I can make a bushing that fits the existing stub, attaches with long machine screws at the 3 existing plate mount holes, and then provides a new 2 screw mounting stub out closer to the handle pin for my plates. There isn't a lot of axial room for them to the handle stub, but if need be, I can extend the stub too.

The other alternative is to buy a new plate kit that fits as is.


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## Brent H (Oct 12, 2021)

@Susquatch - that plate kit is crazy hard to find in Canada.  Seems to be a UK or Australia thing - I located plates for my 12” RT in the US for $119 but they wouldn’t ship to Canada.  Had to find a mule. It will probably be easier to mod the plates you have on hand.  Plates for the larger RT’s are sometimes double sided and 1/2” thick.













The triangle of holes seems to be about 1.400” between centres.
Holes go from 26 to 99 on 2 plates double sided.  If I had a 127 hole plate—— soon - soon


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## RobinHood (Oct 12, 2021)

Brent H said:


> If I had a 127 hole plate—— soon - soon



Or an universal dividing head with differential dividing capabilities like a B&S #3; that would also work...


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## Dabbler (Oct 12, 2021)

Re 127 plate...

You can print on paper a 127 section pie chart with fine lines and get within .004 on the 8" diameter.... or you could 3DPrint a plastic one....

or, do you have a 127 division gear on your lathe that can help?


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## Brent H (Oct 12, 2021)

@Dabbler the 127 plate would be to make the gears for the old Utilathe  

couple more pressing projects and then I will crank out a plate of 127 for all to behold .


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## Susquatch (Oct 12, 2021)

Brent H said:


> @Dabbler the 127 plate would be to make the gears for the old Utilathe
> 
> couple more pressing projects and then I will crank out a plate of 127 for all to behold .



Wow, I'm impressed...... Not with making the gear. But rather with making the dividing plate to make the gear with!


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## Dabbler (Oct 12, 2021)

Stefan Gotteswinter made one by doing a radial plot of 127 divisions on a laser printer and used his lathe and a loupe for indexing.  He felt he could differentiate up to .002 on the diameter.  I think the gear was for metric transposing on his Enco lathe.

You can find a 127 dividing plate for a rotary table in thingiverse for 3d printing.  this one is configurable it might do what you want:  https://www.thingiverse.com/thing:1908993

In any event, it isn't too advanced to design and build one in Fusion360 for printing.


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## George (Oct 13, 2021)

Nigel at go create hobby machine shop on YouTube does a video about making gears and makes a dividing plate


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## Susquatch (Oct 13, 2021)

Dabbler said:


> Stefan Gotteswinter made one by doing a radial plot of 127 divisions on a laser printer and used his lathe and a loupe for indexing.  He felt he could differentiate up to .002 on the diameter.  I think the gear was for metric transposing on his Enco lathe.
> 
> You can find a 127 dividing plate for a rotary table in thingiverse for 3d printing.  this one is configurable it might do what you want:  https://www.thingiverse.com/thing:1908993
> 
> In any event, it isn't too advanced to design and build one in Fusion360 for printing.



Despite being a Pioneer in 3D printing during my career, I don't have a 3D printer myself ..... I've thought about it many times though..... 

I'm just going to make an adapter to use my existing plate set. 

For most jobs though, I'll prolly just "do the math". Besides, after fiddling around and measuring all my parts, I cannot imagine that a plate can be as accurate as manually setting the Rotary Table. Even with a plate done with 1 thou precision, there is the pin load, pin play, arm play, and stop interference to contend with. I watched a few you tube videos of people (Including a few pros) using divider plates. What a mess they made of the backlash and movement in the parts! One fellow even had to move the stops back and then held them with his fingers after that - did he get it right? 

Assuming I am correct about all that, it seems to me that a mission critical job would be better done using math to create a table of angles and just dial them in. I am blown away by the low backlash on my RT. But even so, taking up backlash is no big deal to anyone who uses machines regularly and the plates do not look after backlash anyway. If anything, they add some! 

I also have a rotary spindle with a 1 degree adjusting system and 5C Collets. 






I used it and some math to make a small gear to raise and lower the head on my mill/drill. Till then I had to lock it, and reindex the old gear every 270 degrees to compensate for two missing teeth!


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## RobinHood (Oct 13, 2021)

When you talk about making dividing plate(s) for the RT, are you referring to plates that would fit here?





That would make use of the “indirect indexing” method of dividing the circle.

If you need to have 127 divisions, indirect indexing will never work with a 127 hole plate unless your worm/worm gear ratio is 1:1. I believe the standards are either 40:1 or 90:1 for RTs and Dividing Heads.

I think you are planning on using “direct indexing”. The plate is mounted to the rotating member (spindle or table) and moves in unison (ie. 1:1), then it will work. How are you going to mount the dividing plate to the RT? It would have to be an awfully large ring to fit over the OD of the table.

In the picture below of your B&S #2 dividing head, the red arrow points to the direct indexing plate (they are removable) and the green arrows are all your indirect indexing plates.





If you are planning the use the dividing head, you need to make a direct indexing plate with 127 holes.

You are concerned about accuracy and backlash. If you make your template large (like 12” or so) and the gear you are cutting is only ~ 6”, your error will be reduced greatly as your are only cutting half way up the radius of the template. Your gear tooth spacing will be plenty close enough for slow speed threading.


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## RobinHood (Oct 13, 2021)

Little bit off topic - but I’d does relate to accurately positioning holes on a circle (note the year this experiment was done!):


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## Susquatch (Oct 13, 2021)

RobinHood said:


> When you talk about making dividing plate(s) for the RT, are you referring to plates that would fit here?
> 
> 
> 
> ...



Yes, that's exactly what I am planning to do and that's exactly where I want to mount them - albeit with an extended bushing to get the plates out closer to the crank and fit the smaller ID of my existing plates.

I guess I made a few assumptions about all of this. I assumed that one turn on my crank moves the table 4 degrees. So any indexing plate with "N" holes in it moves the table 4/N degrees for each indexing hole. All those tables that machinists use just simplify that math. How many holes a given plate has just breaks the 4 degrees into bigger or smaller increments  

To be honest with you, I'm not all that sure I even want them. That's kind of what I was getting at in my previous posts. When I stand back and look at the big picture of what is going on MY TABLE, I realize that my 10" table provides pretty amazing precision all on its own without plates! Furthermore, the plates might actually reduce its precision! 

You are absolutely correct, the bigger the table, the better the angular precision that CAN BE achieved. 



RobinHood said:


> You are concerned about accuracy and backlash. If you make your template large (like 12” or so) and the gear you are cutting is only ~ 6”, your error will be reduced greatly as your are only cutting half way up the radius of the template. Your gear tooth spacing will be plenty close enough for slow speed threading.



I'm not really concerned about backlash. My table seems to have zero backlash. At that huge radius, it's easy to see it physically move when the crank is turned. I still have to measure it though. When I do, I bet I'll find a little backlash. 

I only mentioned backlash (and other errors) for the purpose of discussing the negative side of using a divider plate VS just using the tables own basic rotary system. My basic table will discern minutes of angle. At a 4" radius, that's only a thou or so. (didn't do the math just guessing). 

But I suspect, adding all the movement (backlash, bending, play, error, etc) that is inherent in a dividing plate system will end up much worse than just using the tables built in scale. 

As @Dabbler said a few posts ago, all this stuff is really just math. As long as I understand what the parts are all really doing, I can do the math as well as needed. 

All that said, I like convenience as much as the next guy. If I can add a plate system to my table with very little expense, why not? It will certainly be faster than the math and less error prone too (I think).


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## Susquatch (Oct 13, 2021)

RobinHood said:


> Little bit off topic - but I’d does relate to accurately positioning holes on a circle (note the year this experiment was done!):
> 
> View attachment 17674



Very cool story!

Back in my day, we would have fired any engineer who required that kind of precision in a part though. Stacked tolerances and low cost are much more important than absolute precision.

An interesting story. One our suppliers made brake parts for lots of OEM's. They once told me that the Japanese auto companies had much more stringent specifications than we did. Not for the regular quality tests but rather for the endurance specs. We would typically specify minimum endurance requirements. So did the Japanese. But the Japanese ALSO specified maximum endurance! For most parts, we only cared if it lasted as long as the life of the vehicle. If it lasted longer that was a bonus. But apparently the Japanese were fanatics about controlling costs any anything that lasted too long was obviously too expensive!


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## RobinHood (Oct 13, 2021)

Great story!

So it is no coincidence that components start to fail right after the warranty is up. Who would have guessed that?

Look at this fellow’s quest for a precision dividing head (it is a two part series). Alex is on a whole other level of precision…


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## Susquatch (Oct 13, 2021)

RobinHood said:


> When you talk about making dividing plate(s) for the RT, are you referring to plates that would fit here?
> View attachment 17672
> 
> That would make use of the “indirect indexing” method of dividing the circle.
> ...



Just a few additional observations. 

My universal dividing head is 9 degrees per revolution of the crank handle. 1 in 40 as per your note.

My RT is 4 degrees per revolution. 1 in 90 as per your note. 

My collet indexer is direct only and is setup to do only whole degrees.

I'm still struggling to understand the value of all this numbered hole stuff or even why it's called 1 in 40 instead of 9 degrees per turn. It seems plainly obvious to me that 9 holes on a dividing plate for my universal head would yield 1 degree per hole. 18 holes would be a half degree or 30 minutes. 36 holes would be 15 minutes each, and 540 holes would be 1 minute each. 

I have 3 plates (that fit it) and one that is a misfit. The three range from 15-20, 21-33, & 37-49 with a few skipped on each plate except the first. They all have six sets. 

As far as I have seen, there are no plates with 540 holes, so there are no plates with 1 minute resolution.  Yet, the regular crank handle on my RT will resolve 1 minute - with near zero backlash! There is wayyyy more backlash and error using those plates........ So why are they so popular? Surely it can't be just the convenience! 

The more I think about it, the more I want a working set of dividing plates, and the more pathetic I look in the mirror......... Sheshhhh


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## Susquatch (Oct 13, 2021)

RobinHood said:


> Great story!
> 
> So it is no coincidence that components start to fail right after the warranty is up. Who would have guessed that?
> 
> Look at this fellow’s quest for a precision dividing head (it is a two part series). Alex is on a whole other level of precision…



Typical German Engineer....... I recognize his type in the mirror too......


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## Dabbler (Oct 13, 2021)

@Susquatch , you might want to talk to @Johnwa about his spin indexer conversion.  It might be easier, given your background.  He built an electronic addition to get any number of divisions, and far less error prone than doing it manually!  A work of art, really...


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## PeterT (Oct 13, 2021)

I was just going to suggest the same. The electronic systems I've seen installed on RT's are actually very slick. Enter any angle & it magically goes there. No plates, no sector arms, no notepad scribbles... Quite a few documented installations & kits. The electronics is above my pay grade but you seem to be familiar with this stuff.


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## YYCHM (Oct 13, 2021)

Dabbler said:


> @Susquatch , you might want to talk to @Johnwa about his spin indexer conversion.  It might be easier, given your background.  He built an electronic addition to get any number of divisions, and far less error prone than doing it manually!  A work of art, really...



This one? https://canadianhobbymetalworkers.com/threads/rotary-table-indexer.687/#post-6451


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## PeterT (Oct 13, 2021)

I've come across a few links (including John's mentioned above). Here is one of them 

https://www.homemodelenginemachinist.com/threads/arduino-rotary-table-for-dummies.26744/


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## Johnwa (Oct 13, 2021)

PeterT said:


> I've come across a few links (including John's mentioned above). Here is one of them
> 
> https://www.homemodelenginemachinist.com/threads/arduino-rotary-table-for-dummies.26744/



That is where I first found it.  The original version in that thread had a couple of issues.  I rewrote some of the code to address those issues.  Another member of HMEM made some more changes including adding acceleration which allows for faster stepper speeds.  I have a copy of his code but am still using my version.


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## Susquatch (Oct 13, 2021)

Johnwa said:


> That is where I first found it.  The original version in that thread had a couple of issues.  I rewrote some of the code to address those issues.  Another member of HMEM made some more changes including adding acceleration which allows for faster stepper speeds.  I have a copy of his code but am still using my version.



I looked at your project briefly and made a comment there about your battery. 

The project is very cool! I'll review it in more detail shortly.

One thing I have noticed in my short time on this forum. All you guys seem to spend more time making tools for your tools than making parts. I always thought I was the only one who did that......


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## Susquatch (Oct 15, 2021)

I was looking for index plate info and saw the post below on practical machinist. Its an old post about rotary tables so I didn't want to jump in. But it raises some questions. First off, I don't think it's correct but I can see how they got their numbers.

*QUOTE FROM PRACTICAL MACHINIST*
_*40:1 is 9 turns for 360°
60:1 is 6 turns
72:1 is 5 turns
90:1 is 4 turns*_
*120:1 is 3 turns*

I am told that mine is a 90:1 RT. I believe that those who told me that are correct. What I also know for certain is that my table turns 4 degrees for every full turn of the crank not 4 turns per 360. In my case, it takes 90 turns of the crank to turn the table 1 turn. So I think 90:1 is correct, but that is the crank to table ratio, not all those other terms that I see elsewhere including on this post. In my world all drive ratios are specified as input to output. I've never seen otherwise.

So, what's the real deal with this and why all the confusion out there? Am I missing something?


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## Dabbler (Oct 15, 2021)

I don't know what the 'Practical Machinist' guy was thinking.  I have 2 RTs and a B&S indexer. 

-- I think that in an effort to make things simple, they made it waaay harder.

Einstein said:  "Make thing as simple as possible, but no simpler"


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## RobinHood (Oct 15, 2021)

I agree with you that there is a problem with their table. I think it should read:


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## PeterT (Oct 15, 2021)

Susquatch said:


> Just a few additional observations.
> As far as I have seen, there are no plates with 540 holes, so there are no plates with 1 minute resolution.  Yet, the regular crank handle on my RT will resolve 1 minute - with near zero backlash! There is wayyyy more backlash and error using those plates........ So why are they so popular? Surely it can't be just the convenience!



Dividing plates are mostly a convenience to position the chuck/table/whatever 'output' to some target angular increment. For example if I need to cut a 27 tooth gear, I can:
1) mount the plate which has a 27 hole circle, crank (1 turn + 13 holes), cut the tooth, rinse & repeat.
2) turn the RT wheel the exact amount. So 360/27= 13.333333 degrees, so crank to 13-deg plus corresponding degree-minute-second graduation to 0.33333 remainder. Cut the tooth, then repeat that 26 more times without a math error or inadvertent division slip up.

On simple, nominal divisions it might be quicker to use the RT dial but that's because the graduation readily aligns. On more complex combinations, as long as you can count & stick it in the hole (LOL), it removes the math. So the fact that an interim hole division happens to works out to some very fine angular remainder (what you all resolution) is just a secondary artifact of the math, not really the purpose of the plate IMO. So the likely reason is there are no super high hole count plates is a) hard to fit that many holes on a small diameter plate b) equates to gears or splines that are so fine they are generally uncommon in most  everyday mechanisms.

Been a long time since I looked at this stuff, but I wrote a spreadsheet where I can input the gear ratio & the desired tooth count (or angle which is related) & it spits out the plate/hole combination. There are tables on the internet but I wanted to figure it out. So a few things are evident. The gear ratio & plate must be known because they work in conjunction with one another. A 40:1 will have a different hole combination than a 90:1. And different plates may yield the same angle with different hole combinations. And some tooth count/angle combinations are not possible because non-evenly divisible. And I guess if you ever wanted to use a different worm/gear/plate combination, maybe there is a new & exciting gear tooth you could achieve! LOL

https://cdn.shopify.com/s/files/1/0424/4249/0019/files/Final_-_Combined.pdf?v=1623448375

Lastly, I think backlash is backlash whether you are using method 1 or 2. You must always advance in one direction. You can pause but you cannot overshoot & backup, otherwise backlash is introduced. If you go slightly past the target hole on a plate & then jiggle it in, that's technically a no-no. But no different than inadvertently going past the target dial increment & reverse creeping to the target.


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## Dabbler (Oct 15, 2021)

@PeterT a very nice elegant little spreadsheet. It was what I was trying to say 'with math' you can find plate/tooth combinations to do what you need...   Of course, I hadn't seen all the way to your solution - you are brilliant!


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## Susquatch (Oct 15, 2021)

Thanks guys. Sometimes I think I am going crazy. Things have to make sense to me but they often don't. The internet has become a crazy place with too much crap out there.

@Dabbler - Einstein was an amazing man. I wish I could have met him or even just sat and listened to him once. Yes, "make it as simple as possible, but no simpler......." a worthy goal indeed. But not one I am very good at. That said, I accept your point. It sits very comfortably in my mind. And no worries, I believe I did understand what you were trying to say. 

@RobinHood - Perfect! I agree totally! I feel better now.

@PeterT - I've seen others on-line talk about spreadsheets to do this stuff and I've tried unsuccessfully to find one. Looking at your results tells me I don't need to find one. I'm very comfy with the math. Your first paragraph says it all nicely. It's just easier and less error prone to use the plate. The only quibble I have with that is the result of watching others use a plate in their videos. Almost all fail to account for backlash (just as you describe), and I've yet to watch anyone execute the simple process without screwing up in moving the arms or making the indexer fit the right hole correctly. What should have been simple and error free - simply wasn't. 

I guess I'll have to try both approaches to see what I really prefer to do myself. Making the adapter to use my existing plates will be a labour of love so why not?  Easy to write my own spreadsheet and create my own charts. Also easy to hand calculate a list of target settings.

Either way, it's easy to check the results too. It either ends up at 360 with the right number of increments or I screwed up and it doesn't........ 

Thanks guys.....


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## RobinHood (Oct 15, 2021)

Susquatch said:


> Almost all fail to account for backlash (just as you describe), and I've yet to watch anyone execute the simple process without screwing up in moving the arms or making the indexer fit the right hole correctly. What should have been simple and error free - simply wasn't.



I hear you on that point.

Most dividing heads / RTs have the ability to en/disengage the worm from the worm wheel. The backlash can be “totally“ eliminated by snugging the two components tightly together. One gets away with this (unlike in other gear trains where you need a certain amount of clearance) because it is a very slow speed system. So, the “only“ source of backlash comes from overshooting the hole in the plate. Turning it back to engage the hole will cause the spindle to rotate backwards. On good quality DHs/RTs, the pin engaging the hole is tapered. It will find center.

Another thing to remember is that any error in positioning is reduced by the ratio of the worm to worm gear.

I tend to leave on the lock so it just drags a bit. Makes it very easy to find the center of the hole in the chosen direction.

Some sector arms also have a ramp. If you carefully position them, the pin can slide down the ramp and never miss the hole.

The above comments are only valid when either direct indexing or indirect indexing. Using differential dividing is a different animal as now there is a gear train involved (and they need a tiny bit of backlash). Dragging the brake helps a lot in the case. If you overshoot, no problems: just turn the crank a good turn back and then forwards and hopefully this time don’t miss the hole.

When I made the 127T gear for the SM1340 metric to imperial conversion, it worked very well, albeit it took a long time to make.


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## Dabbler (Oct 15, 2021)

@Susquatch  I wanted to grow up to be like Einstein when I was little.

@RobinHood As the sector is usually used,  the ramp is on the wrong side of the backlash, but - as you say, is easily corrected.

Using a RT with even several thou out on any single tooth will never make a difference on any gear, especially on a 127 tooth (or larger) gear.


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## Brent H (Oct 16, 2021)

I use this on line program to calculate the turns I need for making gears - works great:

http://www.bilar.co.uk/cgi-bin/division-calculator.pl


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## Dabbler (Oct 16, 2021)

based on your calculator, the only way to get to 127 on a RT is with direct indexing on a 127 plate.


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## PeterT (Oct 16, 2021)

I haven't looked at my xls in years now but a couple of spot checks looks like same result as Brent online program. 

I was wondering about the 127 tooth myself, That works out to 2.834645669... degrees. @RobinHood did you accomplish this by directly dialing in each angular setting, or? 
I know exactly why 127 is a sought after gear, so it comes up often. Discussed here. 
https://www.hobby-machinist.com/threads/127-hole-plate-for-b-s-bs0.21342/page-2

another post
https://bbs.homeshopmachinist.net/forum/general/10991-gear-cutting#post248476

I think the conclusion is with either so called common 40:1 or 90:1 ratio, there is no plate/hole combination <127 holes that satisfies exact solution? Maybe its related to prime numbers or some such concept?

My spreadsheet has my own index plates hole count pre-loaded, but I can input any arbitrary hole count in to see if a solution is possible. My next step was to enter a target gear & have it solve for the closest solution & leave it to you to decide if its close enough. But where's the fun in that when I could just draw it in CAD with hole spacing accurate to 20 decimal places & export to CNC guy who hopefully can drill it to 3 decimal places LOL


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## Dabbler (Oct 16, 2021)

Exactly. If one had a 127 plate made, then set the sector arms for 90 holes, there you have it.


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## RobinHood (Oct 16, 2021)

PeterT said:


> I think the conclusion is with either so called common 40:1 or 90:1 ratio, there is no plate/hole combination <127 holes that satisfies exact solution? Maybe its related to prime numbers or some such concept?



Yes, because 127 is a prime number.

I have an “Universal” dividing head (B & S #2 type). It has external change gears to allow “differential division”. I my case, the formula called for 11 holes movement on a 33 hole plate; 24T gear on the input shaft, 56T on the spindle shaft, and 40T & 44T between them to make up the space and cause the reference shaft to rotate in the correct orientation.

Edit: my universal dividing head is a B & S #2 - which is the universal dividing head. B & S only made three types: the 0, 1 and 2.


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## PeterT (Oct 16, 2021)

_Exactly. If one had a 127 plate made, then set the sector arms for 90 holes, there you have it._
Attached. What else can I help you with this morning? LOL

This probably illustrates another thing. I sketched this at 6" OD, 127 pin holes x 0.100" diameter just as a visual. Its getting rather tight spacing. And there could be a limitation as to how large the plate diameters can be depending on the device & installation. But this illustrates why you don't see plates available with super high hole count in order to hit minute-second angles.

I wish there was a plug-n-play electric add-on accessory for RTs. I can solder but I'm lost in the programming. If the stepper motor could be counted on to reliably increment to this kind of resolution, it would be so much easier to type in a number & watch it rotate. That's even better than a DRO display which just passively displays where you are at. Well somehow we got along with plates for the past hundred years or more. I think the reason the electronics stuff is mostly in the domain of creative hobbyists is because CNC makes quick work of this stuff. Either the mill head moves or its a 4-axis, either way digitally driven.


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## RobinHood (Oct 16, 2021)

100% agree with your observation regarding CNC, or the use of affordable electronics in the small shop. Oh, and the problem with lots of holes on a small diameter plate…

If the universal DH had not come with my mill, that is exactly what I would have done. But since I have it, and all the change gears, it was just waiting for me to use it. Worked exceptionally well.


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## PeterT (Oct 16, 2021)

807 USD ouch
https://www.sherline.com/product/8700-cnc-4-rotary-table-indexer/

Where can I buy just the electronic stuff.... for say... $100 lol


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## PeterT (Oct 16, 2021)

RobinHood said:


> Yes, because 127 is a prime number.
> I have an “Universal” dividing head (B & S #3 type). It has external change gears to allow “differential division”. I my case, the formula called for 11 holes movement on a 33 hole plate; 24T gear on the input shaft, 56T on the spindle shaft, and 40T & 44T between them to make up the space and cause the reference shaft to rotate in the correct orientation.



Ah! I get it now, thanks. Yes, change gears would add more versatility than worm/wheel style.


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## RobinHood (Oct 16, 2021)

So in “indirect” dividing, the plate is fixed to the DH and only the crank handle moves the appropriate number of holes.

In “differential“ dividing, the plate is on a geared shaft. It rotates in either the same direction as the crank or in the opposite direction to make up the “difference” that the crank moves the spindle either too far or not enough for each division. The “difference” being a function of (and controlled by) the change gears feeding back to the hole plate.

It basically solves fractions using gear ratios - very ingenious.


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## PeterT (Oct 16, 2021)

I don't have a requirement, but at least I know what they look like if I ever see one.

This issue gets discussed a lot at model engineering levels. Probably same issue - oddball gear teeth and/or angles. I've seen plans & kits. Maybe like this? Although I'm not quite clear if 'versatile' means quite the same thing as differential (with intermediate gears).
http://www.myford-lathes.com/accessories8.html
https://www.martinmodel.com/products/versatile-dividing-head-3-piece-casting-set


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## Brent H (Oct 16, 2021)

It “should” be easy enough to couple a stepper motor to the handle of the RT and then use a computer to drive the motor for the required angle for each gear tooth or hole?  Yes?/No?


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## Dabbler (Oct 16, 2021)

@PeterT   that is what the Universal Head looks like with differential gears.  Like mine and @RobinHood - we both have the same unit, but mine was made in Poland.  I've never taken the gears out of the cosmoline!  (shame, shame!)


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## Dabbler (Oct 16, 2021)

Brent H said:


> It “should” be easy enough to couple a stepper motor to the handle of the RT and then use a computer to drive the motor for the required angle for each gear tooth or hole? Yes?/No?



yes - but.  Many of the add on libraries for arduino and raspberry pi have decent motion control, but as @Johnwa found out, one can do a lot better by custom programming.


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## Johnwa (Oct 16, 2021)

Brent H said:


> It “should” be easy enough to couple a stepper motor to the handle of the RT and then use a computer to drive the motor for the required angle for each gear tooth or hole?  Yes?/No?


The indexer that I made will also work with a RT.  There is a menu to change the “gear” ratio to match the ratio of the RT.


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## Brent H (Oct 16, 2021)

@Johnwa : did you post the build on here?  Any plans? Etc.


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## Susquatch (Oct 16, 2021)

As has been said, 127 is a prime number. IMHO the indivisability of a prime number is no big deal to the end result. Using extreme decimal places only to demonstrate, one finds that:

360/127 = 2.834645669 degrees
                 = 2 degrees 50.07874014 minutes
                 = 2 degrees 50 minutes 4.7244084 seconds

4.7244084 seconds of arc is just 0.001312336 degrees which is just 0.000022905 inches at 1" radius
    Half that at 1/2" radius
    Twice that at 2" radius
In fact, the radius must be 43" (diameter is 86 inches) before the seconds of arc become one thou. 

In other words, it is meaningless for all intents and purposes. Just set your table to the degrees and rounded minutes and go. 

N     RT setting
0      0 degrees
1      2 degrees 50 minutes
2      5 degrees 40 minutes 
3      8 degrees 30 minutes
4      11 degrees 20 minutes
5      14 degrees 10 minutes
6      17 degrees even

          Etc all the way to

126  357 degrees 10 minutes
127  360 degrees even
             (same as 0)

The formula is:

(360/127) x tooth number = degrees
     Subtract whole degrees
     Multiply remainder x 60 = minutes
     Round minutes to nearest whole number
Dial in the degrees and rounded minutes
Cut the gear tooth. 

Consider for a moment the precision of the plate hole. Does anyone here really believe that any of those holes on that 4" plate is within 0.000004 of an inch from the correct location? Then there are all the other errors too. Just lining up that hole pin and stressing the mechanism being a huge one....... 

IMHO, rounded minutes of angle using a plain old calculator, a programmable calculator, or a spreadsheet are no doubt more accurate than the plate despite its magical prime number membership. 

That all said, if I had a plate w 127 holes in it, I'd prolly use it. As much as I believe the actual error using a plate would be greater than rounded minutes, they are probably still inconsequential to the quality of the gear being cut. 

Just my two cents for whatever they are worth to others here.


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## Susquatch (Oct 16, 2021)

Brent H said:


> @Johnwa : did you post the build on here?  Any plans? Etc.



I love the idea too. Just got a few Arduino's. They are still in their static proof bags. But I can hear one of them screaming about wanting to turn my RT crank for me! It will have to round off the minutes first though...... LOL!


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## Johnwa (Oct 16, 2021)

@Susquatch I followed the build described in HMEM by BMac2  @PeterT gave a link to that in post #45.  A number of us took stabs at resolving issues with the Arduino code.  I believe kquiggle’s version is the last one.


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## Susquatch (Oct 16, 2021)

RobinHood said:


> I hear you on that point.
> 
> Most dividing heads / RTs have the ability to en/disengage the worm from the worm wheel. The backlash can be “totally“ eliminated by snugging the two components tightly together. One gets away with this (unlike in other gear trains where you need a certain amount of clearance) because it is a very slow speed system. So, the “only“ source of backlash comes from overshooting the hole in the plate. Turning it back to engage the hole will cause the spindle to rotate backwards. On good quality DHs/RTs, the pin engaging the hole is tapered. It will find center.
> 
> ...



I believe I understand your points and I agree to the extent that others are able to do what you do. 

But I'm not sure they can. 

I spent a fair bit of time looking at the dividing plate mechanism on my universal dividing head. (yes, I know it isn't the same). In particular I was interested in understanding it's limitations. How well does it minimize stress related errors. How well does the point truly engage the hole. How often does it have to be wiggled into position. How does the user have to adjust it to minimize these errors. I ended up concluding that I would never be able to set the angular position of my RT nearly as well with a divider plate as I could just using the crank manually with backlash in mind. 

Perhaps your unit is better than mine. But it's difficult for me to see how a sliding pointer on a spring loaded drum on a relatively weak arm can really hold to a minute of angle. 

Perhaps a test is in order..... But I don't have a clue right off hand how to do that! 

In any event, I suspect that debating which is better is largely just an interesting academic exercise. 

The most important thing that both you and I do agree on is that it's important not to delude ourselves about how much accuracy is really needed to cut an awesome gear. 

I think there is an old saying for this. "Never let the perfect be the enemy of the good." 

I have no real fear of using either approach to make a great gear.


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## Susquatch (Oct 16, 2021)

Johnwa said:


> @Susquatch I followed the build described in HMEM by BMac2  @PeterT gave a link to that in post #45.  A number of us took stabs at resolving issues with the Arduino code.  I believe kquiggle’s version is the last one.



Yes, I noticed that. 

I wish I could do just this and nothing else. I'd get it done yet this week. But that isn't the reality of my life right now. 

Nonetheless, I do want to do this. I may or may not use kquiggle's latest version to do so. I've always enjoyed customizing such things and in particular I'm looking forward to mixing Arduino code with machine language code for the atmega chip.  That is a big step, but as they say,..... We will see.


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## Johnwa (Oct 16, 2021)

One of the chief advantages of the index plate method is that once you have the sector arms set then you really have to bugger up to get a misplaced tooth.  You don’t have to count holes or match your dials up with a long list of numbers, just move the plunger and sector arms.

I don’t know if using dials or an index plate is more precise.  Fortunately any error with either one is divided by the table ratio.


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## Johnwa (Oct 16, 2021)

@Susquatch the thing I liked the best about BMac‘s write up was that he had his wife wire one up based on his instructions.  That was enough of a kick in the butt to get me to build mine.


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## Johnwa (Oct 16, 2021)

Johnwa said:


> @Susquatch I followed the build described in HMEM by BMac2  @PeterT gave a link to that in post #45.  A number of us took stabs at resolving issues with the Arduino code.  I believe kquiggle’s version is the last one.


This should have been in reply to @Brent H question.


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## Susquatch (Oct 16, 2021)

Johnwa said:


> This should have been in reply to @Brent H question.



No problem. My answer still applies. 

My Arduino Nanos just arrived and I can't wait to start playing with them.


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## RobinHood (Oct 16, 2021)

@Susquatch, I do agree with your statements about accuracy.

Lots of gear trains have enough backlash that the gears can have some tooth form error (spacing differences, profile tolerances, and run out allowance). Plus I think most systems also have a run-in period where the elements in a gear train wear in as they mesh with each other for the first time.

Here is the test report of my Japanese made Yamatokoki Co. ‘NEWS‘ Universal dividing head from 09/ Sep/1968:





As you can see, the dividing accuracy of the worm drive is +/- 46”.

This is a very well made precision DH and probably would cost you in excess of $5000 today. The “News” brand of tooling was a division of YUASA.

If you have to force the crank handle so that it would bend in order for the spindle to turn, it is time for a serious inspection of the tool. There should be very little to no resistance whith the lock released.

The plain bearings are in very good condition and ride on a very thin film of oil. If the handle had a bit more mass, it would keep turning if you gave it a good spin - like it does on my BP 12” RT. The handle runs on for about one turn after being released. (Unfortunately I don’t have a report sheet for the BP RT).

You mention plunger play - there is no discernible radial play on the DH. The parts seem lapped together. There was just some dried out lubricant preventing smooth operation when I got it. Careful disassembly, cleaning, lube and reassembly took care of that.

The plates are a very close sliding fit onto the crank spindle. There are countersunk fasteners that guarantee zero play attaching.

The crank itself is keyed. There are two lash eliminating screws to reduce play to zero after installation.

I already mentioned the adjustable worm/worm wheel arrangement.

They went to great lengths to make this as precise as possible.

I fully trust this tool. As stated above, if I did not have one, I would certainly consider electronics together with a RT to address my dividing needs.


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## Susquatch (Oct 16, 2021)

@RobinHood - As always, I write things with what I mean in my head and then others read something else in them. 

I didn't mean that the crank handle bends. I meant the handle for the plate pin is thinner than the regular round crank. All metals no matter how big or small bend. But the smaller they are the more they bend. Stress is metal bending in response to force. Steel is strong, but it bends too. No matter how smooth the table is or how little friction the bearings have, the handle has to be bent to retract the plunger against its spring force. I'd bet there is a few thou of bending associated with that. A few thou is quite a bit more than a minute of arc at that radius. 

I like your calibration print out. I'm certainly impressed to see a precision under a minute of arc. Mine is certainly not that good. At best, +/- one minute ASSUMING no other errors. But that is for the main worm drive in both our cases. I believe that's as good as it can get and any indexing or secondary driving system will probably be worse. 

I don't understand how anything can slide without some clearance to allow it. The total length on my plunger assembly is about 2 inches with about half an inch in the spring sliding mechanism. It's loose enough to slide freely. I doubt it's lapped. But even if it was, there is going to be a little movement. Any movement (no matter how small) is a deterioration from the direct indexing of the direct drive system. 

I'm not saying it's terrible. I'm just saying I believe the dividing plate system is not as good as the direct drive system. But both are perfectly usable for any gear making activity. 

It's important to understand why I was writing about this in the first place. It wasn't meant to knock dividing plates - although I can easily see why others might think so. It was meant to say there is no reason to be concerned about the accuracy of the regular crank system. In my mind, plates are not a requirement, they are a convenience. The standard drive angular measurement system is not worse. In fact, as I described, it is actually a bit better. But not meaningfully so. 

I too would totally trust either system to make a gear.


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## Susquatch (Oct 16, 2021)

PeterT said:


> 807 USD ouch
> https://www.sherline.com/product/8700-cnc-4-rotary-table-indexer/
> 
> Where can I buy just the electronic stuff.... for say... $100 lol



I think the thread got a bit mixed up on your question. But in case you missed it..... 

Replace that calculator looking thingy with an Arduino Nano the size of a thumb drive and an input reostat to generate two or three digits for the number of divisions, some clever programming, and voila - your desired system for well under a hundred bucks. 

I'm gunna do it too. 

@Johnwa - I can't seem to find the latest version of that software that you mentioned. Could you please link to it or help me find it?


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## PeterT (Oct 16, 2021)

Susquatch said:


> Does anyone here really believe that any of those holes on that 4" plate is within 0.000004 of an inch from the correct location? Then there are all the other errors too. Just lining up that hole pin and stressing the mechanism being a huge one.......IMHO, rounded minutes of angle using a plain old calculator, a programmable calculator, or a spreadsheet are no doubt more accurate than the plate despite its magical prime number membership.



I don't think anyone has suggested hole plates are more accurate. I suspect the intent is more about reducing operator error. And maybe that's debatable if you personally favor aligning a Vernier scale 127 times vs rotating a sector arm & pinning a hole 127 times. Both are mind numbing if you ask me. There are entire textbooks written about jig design principles pertaining to the human element (typically assembly line work).  So I'd guess someone has studied this long before we came along & concluded plates are a good thing, otherwise why bother. And if you want to talk about accuracy then its probably prudent to consider all other factors that contribute to the final part production - alignment & concentricity of the blank, cutter tool geometry... Its an interesting topic. When you see videos of how industrial precision gears are made, those machines look nothing like what is in our shops. For one thing they typically are hardened & ground. Cutting or hobbing are usually roughing operations before they go in the oven.

Another thing I was just thinking about (always dangerous). How accurate is the worm & gear inside the RT? I'm not talking backlash or diminished effect of gear ratio, I mean the gear train accuracy itself. Yes, you have visually aligned the vernier scale all right, but does that position really equate to an angle accurate to arc seconds? By analogy, I can turn the knob on my 20$ Chinese micrometer so the vernier 10ths mark lines up & choose to believe its measuring 1.0000". But I'm pretty sure if I compared it to gage block it could read 0.999 to 1.001 on a good day. So much for tenths. What kind of barrel screw thread was I expecting for that price LOL. Maybe for fun & excitement you should rig up a repeatable stop on the RT table referenced to a zeroed DTI. Crank rotate the table 10 times & terminate at the same DTI reading. If its exactly 360 degrees c/w zero arc seconds, we have a winner. If Its 357 degrees or 362 degrees, well now we know more about our gears & true angular resolution on the scale.


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## Susquatch (Oct 16, 2021)

PeterT said:


> I don't think anyone has suggested hole plates are more accurate. I suspect the intent is more about reducing operator error. And maybe that's debatable if you personally favor aligning a Vernier scale 127 times vs rotating a sector arm & pinning a hole 127 times. Both are mind numbing if you ask me. There are entire textbooks written about jig design principles pertaining to the human element (typically assembly line work).  So I'd guess someone has studied this long before we came along & concluded plates are a good thing, otherwise why bother. And if you want to talk about accuracy then its probably prudent to consider all other factors that contribute to the final part production - alignment & concentricity of the blank, cutter tool geometry... Its an interesting topic. When you see videos of how industrial precision gears are made, those machines look nothing like what is in our shops. For one thing they typically are hardened & ground. Cutting or hobbing are usually roughing operations before they go in the oven.
> 
> Another thing I was just thinking about (always dangerous). How accurate is the worm & gear inside the RT? I'm not talking backlash or diminished effect of gear ratio, I mean the gear train accuracy itself. Yes, you have visually aligned the vernier scale all right, but does that position really equate to an angular position accurate to arc seconds? By analogy, I can turn the knob on my 20$ Chinese micrometer so the vernier 10ths mark lines up & choose to believe its measuring 1.0000". But I'm pretty sure if I compared it to gage block it could read 0.999 to 1.001 on a good day. So much for tenths. What kind of barrel screw thread was I expecting for that price LOL. Maybe for fun & excitement you should rig up a repeatable stop on the RT table referenced to a zeroed DTI. Crank rotate the table 10 times & terminate at the same DTI reading. If its exactly 360 degrees c/w zero arc seconds, we have a winner. If Its 357 degrees or 362 degrees, well now we know more about our gears & true angular resolution on the scale.



Bang on. 

You are singing my song now!

And yes, I did feel like some were saying (or implying) that a dividing plate was a requirement to achieve certain angles. Which I did not agree with. 

But I do agree with every point you have made. 

Now, let's get on with that stepper motor design. Which will be even worse but still will make great gears! 

And for what it's worth, I think making a gear is mind numbing regardless of what method is used to set the angles! However, the resulting gear is almost always a thing of pride!


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## Susquatch (Oct 16, 2021)

@PeterT - I forgot to mention the 127 hole plate you drew up. I was glad to see that. In my minds eye it was even worse. 

But it did make me wonder. Why couldnt one make a plate with say three separate pins that are offset radially such that they would align with three circles of holes instead of just one. "Divide" the beast up so to speak. I'm having a bit of trouble visualizing that too since you cannot divide 127 by 3. But I assume it could still be done by skipping a few holes on one or more of the circles and a bit of dancing on the sequence.


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## Johnwa (Oct 16, 2021)

Kquiggle‘s documentation and code is avaiable at
https://sites.google.com/site/lagadoacademy/miscellaneous-projects/stepper-motor---accelstepper-h

I’m using the code I posted in message 149 of the HMEM thread.
I intend to migrate to Kquiggle‘s version but I want to add a rotary encoder that will at least give an error or possibly even correct for missed steps. 
I have  an $5 encoder that can be easily mounted on a stepper.  The specs suggest it should be accurate to 0.1 degree but my test show it’s more like 0.3.  With a 90:1 rotary table it would be fine but with my 4:1 indexer its a bit large.


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## Dabbler (Oct 16, 2021)

@Johnwa now that hybrid stepper motors and controllers are getting so cheap, perhaps someone starting out new might use one?  Just a thought...


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## Susquatch (Oct 17, 2021)

Dabbler said:


> @Johnwa now that hybrid stepper motors and controllers are getting so cheap, perhaps someone starting out new might use one?  Just a thought...



I was thinking exactly that!

Based on a quick review of stepper technology late last night (a welcome break from the stress of moving my mother), I found myself disappointed with what the regular and even half step Motors could do. (1.8 degrees and 0.9 degrees per step.) a far cry from the one minute my RT can do mechanically. But then again, maybe enough...... LOL!

The hybrid system were also interesting, but I couldn't find anything that said they worked with static systems - only low speed applications. More research needed. 

That got me wondering about alternatives and of course also thinking about the many issues that any stepper system would have to address.

I wondered about a gear drive to improve stepper resolution, and stumbled onto a 5:1 sun gear stepper on Amazon that struck me as an obvious improvement and only $60. That's at least in the 10 minute neighbourhood. Maybe there are 10:1 or even finer Motors out there too. I don't know - I didn't look.

https://www.amazon.ca/dp/B075KCC1QS/ref=cm_sw_r_apan_glt_i_Q5PJNESBRNRH2J74QEA9?_encoding=UTF8&psc=1

The encoder problem is a big one too. Again, I wondered why a stepper motor doesn't always include that built in right off the starter blocks? Maybe some do.....

I think I already mentioned this, but it seems to me that a simple reostat could be used to dial in a number of steps displayed the same way as an rpm readout - or maybe a bump up/down button.

To your point, when I was still working, we would routinely throw a newbie at a project just to see what whacko ideas they might come up with that might be better than what people who "always did it that way" might do.

But sometimes it's also good to be lazy and just do it the old way cuz it works. Take the good where you find it and weed out the bad.


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## Dabbler (Oct 17, 2021)

Almost all of the stepper drivers will microstep to at least 16 microsteps, and the better ones lock correctly up to 64 microsteps.  Most 3D printers use the TM220x series stepper motor drivers that do all of that, and silently.  Doing the correct torque/current calcs woth appropriate acceleration/deceleration factors it would be very rare to ever lose a step...


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## Johnwa (Oct 17, 2021)

Hybrid Stepper motors would certainly be an improvement.  Loose set screws and slipping couplers can still get you though.@#$&!!!!

If my calculations are correct a stepper(at 200 steps) directly driving a 90:1 table will give positional error of less than 0.001” on a 1 inch diameter gear.  That’s more than adequate for me.


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## Susquatch (Oct 17, 2021)

Johnwa said:


> Hybrid Stepper motors would certainly be an improvement.  Loose set screws and slipping couplers can still get you though.@#$&!!!!
> 
> If my calculations are correct a stepper(at 200 steps) directly driving a 90:1 table will give positional error of less than 0.001” on a 1 inch diameter gear.  That’s more than adequate for me.



My calculations support yours. At a half inch radius, one full cog error is only +/- a half a thou. I'd sure be happy with that too.


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## Susquatch (Oct 18, 2021)

As a result of dreaming about stepper motors, I did a little more research. Here is what I thought was a really good evaluation. 

https://hackaday.com/2016/08/29/how-accurate-is-microstepping-really/

In particular, I loved the idea of mounting a laser on the motor spindle to evaluate arc accuracy at a distance to magnify any error. This could be applied equally well to the Rotary Table itself to calibrate it. I would use green instead of red (for visibility in daylight conditions) and could probably get a 20ft radius inside my shop or 100 yards out the barn door to the forest. Basically lots of space to do a downtown evaluation. I'll have to do some math to see what is really required to do a proper evaluation. 

Anyway, I thought some of you might find the article as interesting as I did.


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## Susquatch (Oct 18, 2021)

Or how about a rifle scope? Even better than a laser. They are typically setup to provide 1/4 moa adjustments (1/4 inch at 100 yards). It would be easy to mount a scope on the RT and sight on a piece of calibrated paper outside the shop door. At 100 yards, 1 MOA is approximately 1 inch. At 50 yards it is 1/2 inch, etc. If I put a scale on the target paper, I don't even need to go for a walk. The scope will provide the required magnification to read it right from the Rotary Table.


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## RobinHood (Oct 18, 2021)

Susquatch said:


> Or how about a rifle scope? Even better than a laser. They are typically setup to provide 1/4 moa adjustments (1/4 inch at 100 yards). It would be easy to mount a scope on the RT and sight on a piece of calibrated paper outside the shop door. At 100 yards, 1 MOA is approximately 1 inch. At 50 yards it is 1/2 inch, etc. If I put a scale on the target paper, I don't even need to go for a walk. The scope will provide the required magnification to read it right from the Rotary Table.



If you are going to go to that length of evaluating your RT, you could also use a surveyor’s theodolite - kind of like Alex does here…


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## Susquatch (Oct 19, 2021)

RobinHood said:


> If you are going to go to that length of evaluating your RT, you could also use a surveyor’s theodolite - kind of like Alex does here…



I happen to have a good digital theodolite so I did consider that approach just a few cerebral farts after the rifle scope idea. But I quickly concluded that a good scope has much better optical quality and the cross hairs are finer. That said, I also thought that the RT and scope might be a good way to calibrate the theodolite! 

After discussing the pros and cons of dividing plates with you, I found myself insanely curious about all this stuff. I want to know more than I do if for no other reason than to confirm for myself that it either does or doesn't have any practical impact on my own applications. As it is, I suspect it's all pretty academic.


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## RobinHood (Oct 19, 2021)

Here is my take on dividing plates: they have been around a very long time. Dividing heads (and RTs) were the only means of making accurate divisions of a circle for many decades. Remember, even the DROs were not available - so no bolt circle function. Parts still needed to be produced in large quantities to certain accuracy levels (depending on what the end use of the part was). So workers in factories were tasked with the monotonous work of cutting gears, for example. Probably to reduce the number of spoiled parts, dividing plates were used to keep the parts within tolerances and reducing errors vs setting a bunch of angles (numbers) read out of a table.

I think either method can be as accurate as the other given the right size of dial scale and fine enough graduations or accurately spaced holes on a hole circle. The rest is down to the operator.

Electronics changed everything. I bet you if stepper motors were available before the first RT or DH with vernier scales / hole plates were invented, we’d only see steppers and the associated electronics.

I think the same can be said about theodolites vs electronic (gps) surveying equipment. Why bother with super precise and hugely expensive Wild Heerbrugg or Leica manual instruments if the same can be done with electronics but only better? Because the electronic ones came later.

So for no other reason than that, I had my manual BP RT (with a dial vernier to arc seconds) and my News Universal DH with plates before I got any other circle dividing device.

Very good discussion indeed. As stated previously, I can foresee an electronic 4th axis for my mill - especially after seeing Tom Lipton cut his spiral fluted plastic drill with such ease. Very cool.


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## Susquatch (Oct 20, 2021)

Yup. I think you are absolutely right about all of that. 

Maybe because I spent the early part of my career researching and designing electronic sensors and systems to control or replace mechanical systems in cars and trucks, I might have a slightly different perspective of what is more reliable though. I like electronics as much or more than most people. One look at my electronics lab and all my electronic gadgets would quickly tell you how much I love electronics. But with knowledge also comes contempt. Ya, it's possible to do things electronically that you cannot do mechanically. But I just don't trust electronics nearly as much as I trust good old fashioned mechanical systems. Most of my distrust results from my experiences with the skill set of the programmers and circuit designers. The vast majority have zero or very low experience or knowledge of the mechanical systems they seek to emulate or control electronically - alternatively, some are experts mechanically but know little about the electronics side. With few exceptions, skilled mechanical people don't do electronics or programming. The result is often amazing but garbage in is still garbage out. 

And perhaps equally troublesome is the gullability of us users. If it's digital and has a number we can read, too many of us trust it as if our life depended on it. Me, not so much. 

I have a saying that I love to use for electronic devices. "Trust is earned, not given". Of course that saying applies equally well to many other things including a lot of people! 

Btw, does your RT really read arc seconds or was that a typo and you meant minutes? If it really is seconds, I'd love to know more about how it does that. 

Anyway, I don't mean to come across as down on electronics. I'm really not. Good designs can do absolutely amazing things that would be impossible otherwise. I guess it would be better to say that I don't have blind faith. 

Yes, spiral milling would be one of those absolutely amazing things wouldn't it!


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## RobinHood (Oct 20, 2021)

Susquatch said:


> Btw, does your RT really read arc seconds or was that a typo and you meant minutes? If it really is seconds, I'd love to know more about how it does that.



Amazingly, yes it does.

To 5 arc seconds on the vernier divisions (with some interpolation accurately to at least 2.5 arc seconds).

One turn on the dial is 3*. Hard to take a picture because the dial is so large, but I think you can just see the 0* mark on the right and the 1* mark on the left with the 60 minutes division in between.


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## Susquatch (Oct 20, 2021)

RobinHood said:


> Amazingly, yes it does.
> 
> To 5 arc seconds on the vernier divisions (with some interpolation accurately to at least 2.5 arc seconds).
> 
> ...



Wow! Yes, I see the gradations you mention and I can also see the minutes, the 5 second vernier, and even the 2.5 second interpolation. That's one very impressive RT! 

Amazing what a big diameter dial can get you! 

More importantly, properly used with backlash properly handled, I would absolutely trust that! 

Bet you love it!

And ya, I'm jealous!


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## RobinHood (Oct 20, 2021)

Yes, it is very well made. Genuine Bridgeport 1967-ish vintage in top condition.

Only reason I say “1967-ish” is because I don’t exactly know the year it was made. It did come with the 1967 BP mill - so the mid to late 60s era should be reasonably close.


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## Susquatch (Oct 20, 2021)

All amazing what they all did before there were any computers (other than mainframes)......


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## Dabbler (Nov 4, 2021)

For those wanting to be able to cut 127 gears on the cheap-cheap,  Tom Lipton wrote an article on using a 5C spin indexer with a single custom plate to cut them.  His secret:  use 2 rows of holes.  

Here's the link to the original article, and then search for November 1 for the article in question:





__





						"Nothing Too Strong Ever Broke"
					

Ongoing journal of a life spent designing and building special tools, instruments and mechanical devices for the scientific, medical, metalworking and product development industries. Idea's turned into reality by the mechanical pursuits of Tom Lipton (OX)




					oxtool.blogspot.com
				




There's a trick he used that you need to know:  He used a DRO with the 'hole' function, but cut every other hole on the first pass (the 'even' pass, then cut the 'odd' holes on the inner circle on the second pass.


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## Susquatch (Nov 5, 2021)

Dabbler said:


> For those wanting to be able to cut 127 gears on the cheap-cheap,  Tom Lipton wrote an article on using a 5C spin indexer with a single custom plate to cut them.  His secret:  use 2 rows of holes.
> 
> Here's the link to the original article, and then search for November 1 for the article in question:
> 
> ...



Very cool! I thought we discussed two circles with alternating holes to make them fit on a smaller plate in another post on this thread, but maybe I was only thinking that in the foggy corners of my own mind!  LOL!

I do like the idea of using a spin indexer directly though instead of indexing plates on a rotary table crank.

I also liked Tom's comment on another users post about using three holes. I was surprised to see him discuss accumulating errors. That's the point I was trying to make (far less elegantly) on the RT thread here. I just can't see why an error of a thousandth or so here or there matters at all as long as the error is averaged out over the whole circle instead of accumulated one hole at a time. That thousandth (just an arbitrary small number) doesn't matter at all to the gear tooth spacing and besides, all the other errors from stuff bending probably add up to more anyway.

Good find! Thanks @Dabbler !


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