# Gear cutting and making gear cutters from scratch



## Brent H (Jan 27, 2021)

Hey folks, 

Has anyone on here made their own gear cutters?  There are a few guys on you tube that have made cutters.  Some are single point, fly type cutters, others are the HOBB type cutter and others (relatively few) have made the cutters for cutting the involute tooth into a single cutter and then cutting teeth followed by hardening and sharpening.

I have been going over the math and I am going to make up a spreadsheet to calculate the geometry of the cutter and work on doing some custom gear cutters.

Some of the pricing is crazy nuts on a single cutter and I cannot locate 20 degree Pressure angle cutters very easily - most are MOD and do not jive with my Diametral imperial pitch world - LOL.  

I am thinking I will just giver a go and see what I can mess up.  I cannot do much until I return home, but I will at least get the geometry figured and post my spread sheet of numbers for your enjoyment.


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## RobinHood (Jan 27, 2021)

I think another project just moved onto the top of your to do list: a relieving attachment for your lathe....


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## Brent H (Jan 27, 2021)

EUREKA!


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## RobinHood (Jan 27, 2021)

Yup, that’s the one....

Here is a video link of the tool:


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## Brent H (Jan 27, 2021)

Thanks Rudy,  Got the series downloaded and I own the Ivan Law book.  Have you made anything like these?  I have my tool sharpener and it is jigged out with the gear sharpener so that will be good.  Just trying to work out the math for the cutters and put it all into a self calculating spread sheet.


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## RobinHood (Jan 27, 2021)

No, I have not made a relieving attachment ( yet ).

I have a fair number of involute gear cutters. So no need to make my own just yet.


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## Brent H (Jan 27, 2021)

@RobinHood : Roger that - over the next days I will try to transfer the drawings over to Autocad and see about scaling them for 1" arbor cutters.

I will post as I get there.  I have the math working out for the button cutter build now with an excell spread sheet - just working on making it more user friendly and have it do both the imperial and metric math.  I transferred the numbers to an autocad drawing and all the angles came out bang on - that is at least a good start.

If the Eureka relieving attachment works out well, it will be a pretty cool addition to making some cutters.  It looks like by the time I am successful at making the cutters it will be about the same cost in time to buy them....but  there is no fun in that....LOL


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## JohnnyTK (Jan 27, 2021)

Gear cutting memorizes me, follow a few on Instagram


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## RobinHood (Jan 27, 2021)

I was actually thinking of modifying the Eureka so that the number of “teeth“ is adjustable. Maybe 12 is a standard for that size cutter?

Then is found this video:






It got me thinking that why not make gears using gear hobs? Only one hob is required for each DP or Module. It also does not matter if you are cutting a spur gear or a helical one - all use the same cutter.


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## Brent H (Jan 27, 2021)

@RobinHood - yes, I have a 12DP 20PA hobb I was hoping  to use to fine tune that tooth I welded onto my lathe bull gear..... sigh....

I guess I need a second lathe - haha 

linking in the hobb rotation to the cutter is quite the process. There are a few videos of guys doing quite well on a vertical mill with rotary table and a complex gearing selection.  

A few better options with a horizontal mill ...... will see what we can come up with.   I will post the drawings when I get them done and perhaps, Rudy, you can check them for errors if you have some time.


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## PeterT (Jan 27, 2021)

No sure if this is the same method. Look forward to your results!
http://mikesworkshop.weebly.com/designing-gear-cutters.html


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## Brent H (Jan 28, 2021)

@PeterT : yes bang on for making the button cutters that will cut the profile into the cutter blank.  

After a bunch of reading of Ivan Law book - the Mike’s workshop and John Stevenson, I was able to put 2 and 2 together.  
Then it was figuring out Excell and getting the formulas input correctly.  Next is getting my spreadsheet set so it is a “simple” matter of inputting the data  for the cutter you need and it will spit out the dimensions for the cutter buttons, spacing and depth of cut.  

The Eureka relief tool is designed to profile the cutter teeth for back side relief so the cutter doesn’t drag through your gear as it cuts.  As @RobinHood said the tool right now is designed for 12 cutter teeth.  Most cutters now have 14 if they are of the 1” keyed variety.  Things will get a bit “modified” to suit I should expect.


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## Hacker (Jan 28, 2021)

It took me over an hour to watch this and I still haven't figured it all out.  That is a very interesting video. It makes you want to build one just to cut gears even it you don't need them.  I was wondering if using cog belts on the tail stock drive instead of idlers would make for a quicker build and setup?


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## Brent H (Jan 28, 2021)

@Hacker : I think that is why it is called the Eureka!  It takes a few times to figure it out and then .....EUREKA!!!.....LOL...

The math part to do the calculations was driving me nuts and then I got things figured out after I learned that Excel calculates the angles in radians so you have to correct the Sin and Cos for this.  Then the drawing on AutoCad all worked out with the new measurements.

I will start drawing the Eureka out after I get some drawings set up for @YYCHobbyMachinist of the follow rest for the 9" Utilathe


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## RobinHood (Jan 28, 2021)

Hacker said:


> I was wondering if using cog belts on the tail stock drive instead of idlers would make for a quicker build and setup?



That’s exactly what I was wondering.

The change gear method is the traditional way - there is no possibility of getting “out of sync” because of the gear teeth. I think the modern cog belts / wheels have proven to be very reliable, just look at all the timing belts out there...

But first one needs to have a cutter...

The basic principle of the EUREKA attachment is to have a stationary tool and the work “lobes” in and out of the cut. Traditional relieving lathes are the opposite: the tool moves on the X-axis and the work rotates concentrically with the lathe’s Z-axis. The number of “reliefs” per rev is a function of the number of teeth the cutter has.

I am contemplating using the taper attachment mechanism (mostly the telescoping leadscrew) via a timed cam to move the cross slide. I would need the cam to rotate at the number of cutter teeth per one spindle rev. The cam profile would control the relief profile and the stroke length. This way, one could make cutters of various sizes & relief angles. Furthermore, if the cam drive was via a telescoping cardan shaft, one could use the lathe carriage and set up a desired Module or DP and make a gear hob. Gear hobs have straight flanks - eliminating the need to try and approximate the involute curve. And you only need one for all the gears, regardless of # of teeth.








Another thing, if the drive train to the cam was via a planetary, one could drive the ring gear “slower“ than the planet carrier and get a differential function. This would allow for helical cutters as long as the differential per rev is a function of the helix angle. (differential division is the mechanical principle behind an universal dividing head: with each rotation of the crank, the reference point moves backwards ((or forwards)) by the “differential amount” to allow the circle to be divided by a prime number, for example, without using a prime number hole circle plate [like 127]). I digress.

Maybe all this could be done on a Menziken M220? Hint, hint.... Joking aside, I think they fell victim to the CNC revolution, like so many other manufacturers of high quality manual machines.


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## Brent H (Jan 28, 2021)

Some kind of set up like this would work for your hobbing on the vertical mill - the execution  might need a bit of improvement but the concept is there


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## RobinHood (Jan 28, 2021)

You know, whatever works. If it gets the job done, why not?

Here is a relieving lathe in action. It’s the kind of set-up I was trying to describe above.


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## PeterT (Jan 28, 2021)

_>Next is getting my spreadsheet set so it is a “simple” matter of inputting the data  for the cutter you need and it will spit out the dimensions for the cutter buttons, spacing and depth of cut._

I was going to make the spur gears for my radial & was looking at the button method to make cutters. I ended up buying commercial gears & modifying them because they had to be thinned & modified on multiple fronts  so I went that route. But one thing I was always wondering about is how to properly attach the buttons to the toolholder. Ideally they should be made from tool steel & hardened if they are going to cut even mild r annealed tool steel gear blanks. I considered drilling a hole & securing with a screw kind of like an insert. But (depending on size) there isn't a lot of room. Possibly silver solder but now the chance of annealing the button hardness is likely. How were you planning on this aspect?  Its been a while since I read that Ivan book.


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## Brent H (Jan 28, 2021)

@PeterT : Ivan suggested loctite so you have a bit of open time to turn them so the cutting faces align properly with the relief on the tool holder


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## RobinHood (Jan 28, 2021)

If I am going the button route, I would use broken HSS or even broken carbide tooling and use the surface grinder with the spindexer or the T&C G with the spindexer. Use loctite and a slight press fit into the tool holder, or silver solder the buttons on. The distance between the buttons is controlled by the hole spacing. Then set the completed tool on the grinder again and deck off to the correct rake angle. Lap to finish the cutting edges.


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## RobinHood (Jan 28, 2021)

You could probably even use a Dremel or a tool post grinder on the lathe to make HSS buttons. Rough them out on the bench with an angle grinder and then finish grind them to size on the lathe.


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## Brent H (Jan 28, 2021)

I was planning on the same with respect to broken/old end mills etc and grind them to size on the Cincinnati No2 - I have the shaft grinder attachment and a wee 4 jaw chuck that fits it - can then do the faces to whatever desired angle


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## PeterT (Jan 28, 2021)

Ah that's right, I forgot he made his with a lower stem extension. That would add lots of rigidity


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## gerritv (Jan 28, 2021)

The original Balzer version (for which there is no patent) had variable tooth counts. The only etching found does not elucidate at all on how that was done. However, Taylor did describe a similar device, which is adjustable and for which there is a patent

Balzer did patent a relieving device, it was based on differential gearing. That of course assumes you can cut the gears on something first.

I built a Eureka device to make T2.5 timing belt cutter and a few others (not gears). Do not underestimate the load on your spindle and tailstock, it is substantial. For a cutter with 1" arbour I would recommend the approach of using a moving cross slide instead. Unfortunately I can't put my finger on which magazine I saw that in.

Ah, found it:
Model Engineer's Workshop, Feb 1999(#56) and April 1999(#57), issues 58,59,60 describe building a gear hobber. If I were to start cutting gears it would be with something along these lines: F. Cleff - YouTube. There is also an article coming out about using an Arduino to replace gear trains with steppers. I think that is in Digital Machinist but not sure.

Gerrit


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## Hacker (Jan 28, 2021)

RobinHood said:


> That’s exactly what I was wondering.
> 
> The change gear method is the traditional way - there is no possibility of getting “out of sync” because of the gear teeth. I think the modern cog belts / wheels have proven to be very reliable, just look at all the timing belts out there...
> 
> ...



Ok, you have me hooked. I went out to the shop this evening and pulled out the pieces that Horst and Konrad gave me for the lathe and laid it all out. I believe all the pieces are there to connect the drive mechanism to the cross slide. I will see about fitting it to the lathe tomorrow. I have the manual for this but it is in German and so I am hooped there. Would you know someone that could do some translating?

Were they bought out buy another outfit or did they just closed their doors. There seems to be quite a few in Europe yet. I guess the only reason this one is here is because of Horst.


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## RobinHood (Jan 28, 2021)

I am not 100% sure what exactly happened to Menziken. Horst is from Germany and Konrad from Switzerland. I am sure that played a big part why they got the M220. I can translate the manual for you, I speak the language fluently. Maybe send me a PM and we can arrange something?

That would be great if you could get the relieving attachment going and then we can all be green with envy as we watch you make gear hobs, gear cutters, etc.


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## Brent H (Jan 29, 2021)

> we can all be green with envy as we watch you make gear hobs, gear cutters, etc.



I second that motion!


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## Hacker (Jan 29, 2021)

Thanks for the support and encouragement. Every time I use the lathe I see that attachment on the back and wonder if I will ever figure out how to use it. I will PM the manual, I have some commitments over the next few days and have to get my auction goodies today but will try to get it to you this afternoon. If not will send it on Sunday. I have an e copy but it is in word and the file is huge so will have to make a PDF first. You can have a look at it and decide if you want to pursue this. Thanks!!


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