# Gear Hob Mandrel



## Susquatch (Nov 20, 2021)

Wondering why Gear Hob Mandrels have so many collars, washers, and sleeves. 






Why isn't it as simple as mounting a cutter on a key  between one collar and a nut and go?


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## Mcgyver (Nov 20, 2021)

Those aren't hobs, they're form cutters and the mandrel is a standard one - different spacers so different thicknesses of cutters can be used.  (although the manufacturer is rather optimistic given its R8  )


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## Susquatch (Nov 20, 2021)

Ok. I've only called them hobs cuz that's what I always thought they were called. Learned something new again. 

So what does a gear hob look like? 

If you think that is optimistic, my old MT3 shank for my own old hobs (sorry, I meant "Form Cutters") looks exactly the same! I have some fat and some skinny form cutters. All the extra sleeves, collars, and bushings live unused in the drawer. Still don't see why more than a nut and lock nut would be needed......


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## Brent H (Nov 20, 2021)

@Susquatch: see above


Using the arbor with the spacers you can move the cutter up and down depending on need to provide clearance, you can use two slitting saws spaced out, larger body cutters - the hob for example. 

Always good to have options


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## Mcgyver (Nov 20, 2021)

a hob has the rack form of the tooth wrapped around itself in a helix.....the hob and the work but rotate and are synchronized.  What I meant by optimistic was the manufacture making it so long  - I mean its not like on an R8 arbore you're going to have much luck using a cutter the whole length of that arbor.  Was just cracking off about the maker, It'll work fine for your cutters...sorry if I confused things



			https://upload.wikimedia.org/wikipedia/commons/thumb/3/3e/MillingCutterHobbingInvolute.jpg/1200px-MillingCutterHobbingInvolute.jpg
		


this shows it pretty well






.


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## Susquatch (Nov 20, 2021)

Never mind my question about a hobb. 

I found this on line:

Gear Hobbing​Gear hobbing is the process of generating gear teeth with a helical cutting tool, or hob. The gear blank and hob rotate continuously until all gear teeth are cut into the blank. The speed of this process makes it ideal for large production runs.

Gear Milling​The gear milling process uses a cutter, known as a form cutter, that moves axially to produce a gear tooth at the proper length and depth. After one tooth is cut, the cutter is withdrawn to allow the gear blank to rotate to the next position. Once the blank is rotated, the form cutter cuts the next tooth, and this process continues until all teeth are cut into the blank. This process is slower, making it a low production process.


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## Susquatch (Nov 20, 2021)

Hahaha..... I see both of you replied while I was drafting the above. Sorry about that. 

Ya, thanks @Brent H. That does make sense. I can see how clearance could be an issue up close to the spindle nose, and perhaps at the other end too!


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## Susquatch (Nov 20, 2021)

Mcgyver said:


> a hob has the rack form of the tooth wrapped around itself in a helix.....the hob and the work but rotate and are synchronized.  What I meant by optimistic was the manufacture making it so long  - I mean its not like on an R8 arbore you're going to have much luck using a cutter the whole length of that arbor.  Was just cracking off about the maker, It'll work fine for your cutters...sorry if I confused things
> 
> 
> 
> ...



Good explanation. 

Guess I never hobbed a gear after all. I only form cut one....... (insert pout face here). 

No biggie. One tooth at a time is fine for me. 

No worries on the R8 confusion. I like my R8 Spindle. I'm REALLY impressed by what an R8 on my bigger mills can do.


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## Mcgyver (Nov 21, 2021)

I like my R8 as well....but I wouldn't run a 2" wide horizontal mill cutting in it


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## Susquatch (Nov 21, 2021)

Mcgyver said:


> I like my R8 as well....but I wouldn't run a 2" wide horizontal mill cutting in it



I did try a BIG 50 thou side milling cut on my R8 Mill at 5Hz just to evaluate VFD low speed torque. I dunno what 2" would do but 1" worked just fine. I'm guessing 2" with a little more speed would work just fine. 



Susquatch said:


> Here you go Brent. 50 thou at 5hz side milling 1 inch thick mild steel was zero problem.
> 
> The top of the attached photo was cut at 5 hz on the back gear, the rest was cut at 5hz in direct drive.
> 
> ...


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## PeterT (Nov 21, 2021)

Those arbors come in different lengths & spacer kits BTW, you're not just stuck with that one. I guess short is generally preferred just from rigidity & runout reduction standpoint, but there may be times when the part/setup requires a longer arbor. Having a selection helps keep the bank account lean & trim. 

And just to add to confusion, there are arbors conspicuously like this sold as slitting saw / jeweler saw holders which may or may not be? Often times I wonder if some of these offshore places even know what they are selling or just leave it to you figure. Some still have a key but not all blades have a key slot & also the hole dimension can vary, particularly vs. N-Am blades. With these, you might have to reverse the process - examine the nominal dimensions of blades & see what arbors(s) fit. It can be a bit of money pit depending on what path you go down. Now what I'm finding is there is a whole world of metric slitting saws out there (but which necessitates matching tooling).


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## Susquatch (Nov 21, 2021)

PeterT said:


> Those arbors come in different lengths & spacer kits BTW, you're not just stuck with that one. I guess short is generally preferred just from rigidity & runout reduction standpoint, but there may be times when the part/setup requires a longer arbor. Having a selection helps keep the bank account lean & trim.
> 
> And just to add to confusion, there are arbors conspicuously like this sold as slitting saw / jeweler saw holders which may or may not be? Often times I wonder if some of these offshore places even know what they are selling or just leave it to you figure. Some still have a key but not all blades have a key slot & also the hole dimension can vary, particularly vs. N-Am blades. With these, you might have to reverse the process - examine the nominal dimensions of blades & see what arbors(s) fit. It can be a bit of money pit depending on what path you go down. Now what I'm finding is there is a whole world of metric slitting saws out there (but which necessitates matching tooling).



I hear you. Your explanation of all the bits on the arbor matches what @Brent H said. That makes sense to me. 

But I'll probably be dead before I need a metric slit saw...... LOL!


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## PeterT (Nov 21, 2021)

Well, maybe. The way I look at it is if all I need is 'a slit' of a +/- nominal size, then I'm impartial as to IMP vs MET. Thus far my slits don't have to mate anything of critical dimension. So whether its 1/16" or 1.5mm usually doesn't affect the part. But if one can get good quality metric tooling for same or lower price than N-Am, then the Hobby Buy-O-Matic needle starts to drift that way. My experience on domestic saws is the stuff from Europe is decent, but the stuff from India is crap. For example KBC carries some from Poland & eastern block Europe. The problem is, the next nominal size may be sourced elsewhere. Then you hop to Ali & see metric equivalents for less $ or even carbide for the price of HSS here. Whether the quality is there or not is the same old story - who knows. For example my carbide threading inserts/tools are clones of Carmex but at about 1/3 price. For my purposes they work great. I've switched over to metric parting tools/inserts for the same reason. Often times the domestic tool catalogs are cagey - they might list a width as X/64" but really all they are doing is converting mm.


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## Susquatch (Nov 21, 2021)

PeterT said:


> Well, maybe. The way I look at it is if all I need is 'a slit' of a +/- nominal size, then I'm impartial as to IMP vs MET. Thus far my slits don't have to mate anything of critical dimension. So whether its 1/16" or 1.5mm usually doesn't affect the part. But if one can get good quality metric tooling for same or lower price than N-Am, then the Hobby Buy-O-Matic needle starts to drift that way. My experience on domestic saws is the stuff from Europe is decent, but the stuff from India is crap. For example KBC carries some from Poland & eastern block Europe. The problem is, the next nominal size may be sourced elsewhere. Then you hop to Ali & see metric equivalents for less $ or even carbide for the price of HSS here. Whether the quality is there or not is the same old story - who knows. For example my carbide threading inserts/tools are clones of Carmex but at about 1/3 price. For my purposes they work great. I've switched over to metric parting tools/inserts for the same reason. Often times the domestic tool catalogs are cagey - they might list a width as X/64" but really all they are doing is converting mm.



Agreed on all counts.


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## Susquatch (Nov 21, 2021)

Mcgyver said:


> I like my R8 as well....but I wouldn't run a 2" wide horizontal mill cutting in it



So, I was straightening a big bracket on my 30 ton shop press and I noticed that one of my big steel reaction blocks was badly out of square. 

Hmmmmm says I! Nice chance to checkout 2" side milling on the Hartford. Actually it turned out to be 2-1/2 inches. Perfect job for my big 3" x 3/4" end mill. 

Chucked it up and had at it. Took 5 passes at 20 thou to get it square and one pass at 30 thou to try and make it complain. 

So this is 30 thou over 2.5 inches at just 5Hz on the VFD. It didn't whimper at all. Just got down to business and cut like butter.


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## Susquatch (Nov 21, 2021)

And here is 20 thou at 75hz just for shifs and giggles.


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## YYCHM (Nov 21, 2021)

Susquatch said:


> So, I was straightening a big bracket on my 30 ton shop press and I noticed that one of my big steel reaction blocks was badly out of square.
> 
> Hmmmmm says I! Nice chance to checkout 2" side milling on the Hartford. Actually it turned out to be 2-1/2 inches. Perfect job for my big 3" x 3/4" end mill.
> 
> ...



Chucked it up?


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## Susquatch (Nov 21, 2021)

YYCHM said:


> Chucked it up?



Ya sorry, nothing fancy, just my own shop slang for:

"I stuck a 3/4x3 inch four flute spiral end mill into a 3/4 inch R8 Collet, then shoved that assembly up the spindle, and then torqued up the draw bar."


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## Susquatch (Nov 21, 2021)

In case you are wondering, "Shifs" is code for low moisture content body waste. Gotta watch out for the forum security team.


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## YYCHM (Nov 21, 2021)

Susquatch said:


> Ya sorry, nothing fancy, just my own shop slang for:
> 
> "I stuck a 3/4x3 inch four flute spiral end mill into a 3/4 inch R8 Collet, then shoved that assembly up the spindle, and then torqued up the draw bar."



Ok, chucked up works.  I thought you were talking about the 1-1/2" thick steel reaction block


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## Susquatch (Nov 21, 2021)

YYCHM said:


> Ok, chucked up works.  I thought you were talking about the 1-1/2" thick steel reaction block



2-1/2 @YYCHM! Not 1-1/2!

Two point five, 2.5, two and a half.  

That was one very big cut for a home shop machine running at practically zero - just 5 hz. Nothing bent, nothing moved, nothing complained. I was sooooo impressed! And it's perfectly square too!


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## YYCHM (Nov 21, 2021)

Susquatch said:


> 2-1/2 @YYCHM! Not 1-1/2!
> 
> Two point five, 2.5, two and a half.
> 
> That was one very big cut for a home shop machine running at practically zero - just 5 hz. Nothing bent, nothing moved, nothing complained. I was sooooo impressed! And it's perfectly square too!



Oooops   Where the heck did you get a 3/4" endmill that has 3" long flutes?  Need to see a pic of that pls.


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## Susquatch (Nov 21, 2021)

YYCHM said:


> Oooops   Where the heck did you get a 3/4" endmill that has 3" long flutes?  Need to see a pic of that pls.



I got it with my mill drill when I bought that. All the goodies I got with that machine were worth three times what the machine was worth. It was a comical situation. When I picked up the mill/drill the fellow who sold it to me was moving - I think he said over seas. Anyway, he helped me put the machine in my pickup truck box. Then he just started loading other stuff in there too. I never knew I was getting anything but the mill/drill itself. The accessories included a strong metal stand, some measuring tools, a universal dividing head, a tailstock, a 5C rotary divider, two big vises, and boxes and boxes and boxes of tooling, Collets, Mandrels, arbours, gear cutters, slit saws, etc etc. My eyes just kept getting bigger and bigger. After a while I was starting to think he was gunna throw his wife in there too! 

The end mill is a big one for sure! It's almost 8 here now and the coyotes are howling. I'm scared of the dark. So I'll take a photo for you tomorrow some time after the sun comes up..... LOL!


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## Susquatch (Nov 22, 2021)

YYCHM said:


> Oooops   Where the heck did you get a 3/4" endmill that has 3" long flutes?  Need to see a pic of that pls.



Got to the shop for a bit before heading out into the fields.

Here is a photo.






I added the skinny tape measure and 1/8 end mill just because I know how much optical illusions like to follow you around...


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## Susquatch (Nov 22, 2021)

Or maybe this one is a bit more to your liking..... 







Sorry, devil made me do it....


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## Susquatch (Nov 22, 2021)

But just think @YYCHM ...... My Hartford actually turned that monster at just 5hz and carved (better choice of words than milled) off 30 thou over 2.5 inches in just one pass! The feed rate was not unreasonable either. 

I'm absolutely stunned and amazed! 

I'll prolly never do it again, but had to try it just to see what she could do! Obviously, since she didn't complain, she can prolly do much much more than that but...... That will certainly do!


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## Mcgyver (Nov 22, 2021)

Susquatch said:


> So, I was straightening a big bracket on my 30 ton shop press and I noticed that one of my big steel reaction blocks was badly out of square.
> 
> Hmmmmm says I! Nice chance to checkout 2" side milling on the Hartford. Actually it turned out to be 2-1/2 inches. Perfect job for my big 3" x 3/4" end mill.
> 
> ...




 I just did the bearings on my XLO last year.....expensive so my thought was fuelled mostly by not overtaxing the light nature of the spindle.  Point taken, there is no rule that because its a 2" cutter you can't just take super light cuts.  The comparison is a bit apples to oranges though as a 3/4 cutter needs less torque than cutter that'll fit on that arbor.

btw....that cut, how long did take and how many HP is the mill?


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## YYCHM (Nov 22, 2021)

Susquatch said:


> But just think @YYCHM ...... My Hartford actually turned that monster at just 5hz and carved (better choice of words than milled) off 30 thou over 2.5 inches in just one pass! The feed rate was not unreasonable either.
> 
> I'm absolutely stunned and amazed!
> 
> I'll prolly never do it again, but had to try it just to see what she could do! Obviously, since she didn't complain, she can prolly do much much more than that but...... That will certainly do!



Well... Ya, I'm impressed to.  But your machine is 6 times heavier than mine.  I'm finding my 1/2" carbide 4 flt endmill does well side milling as well.  I'd like to get some 3/4" carbide endmills with longer flutes, but where?  I don't think I'd have enough torque at 5hz to do anything, 20 seems to be the limit.


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## Tom Kitta (Nov 22, 2021)

Try auctions or aliexpress - a 3" long 3/4 new from a dealer carbide is going to be expensive.


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## PeterT (Nov 22, 2021)

I would have lost a 1 coffee bet that the big end mill would be spinning inside that R8 collet at that DOC removal rate. I guess one doesn't know till one tries.


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## YYCHM (Nov 22, 2021)

Susquatch said:


> But just think @YYCHM ...... My Hartford actually turned that monster at just 5hz and carved (better choice of words than milled) off 30 thou over 2.5 inches in just one pass! The feed rate was not unreasonable either.
> 
> I'm absolutely stunned and amazed!
> 
> I'll prolly never do it again, but had to try it just to see what she could do! Obviously, since she didn't complain, she can prolly do much much more than that but...... That will certainly do!



This 30 thou term confuses me, are we talking 0.03" ?  I go 0.05" or more all the time

My recent gear cutting exercise included a DOC to 0.13".


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## Susquatch (Nov 22, 2021)

Mcgyver said:


> I just did the bearings on my XLO last year.....expensive so my thought was fuelled mostly by not overtaxing the light nature of the spindle.  Point taken, there is no rule that because its a 2" cutter you can't just take super light cuts.  The comparison is a bit apples to oranges though as a 3/4 cutter needs less torque than cutter that'll fit on that arbor.
> 
> btw....that cut, how long did take and how many HP is the mill?



It is a 2HP VFD Rated motor. The cut wasn't fast like doing a half inch face cut, but no slouch either. I didn't time it. I'd say one or two minutes for a 5" pass. It wasn't throwing big huge swarf - just shavings. I could have pushed harder but that didn't seem wise.


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## Susquatch (Nov 22, 2021)

YYCHM said:


> Well... Ya, I'm impressed to.  But your machine is 6 times heavier than mine.  I'm finding my 1/2" carbide 4 flt endmill does well side milling as well.  I'd like to get some 3/4" carbide endmills with longer flutes, but where?  I don't think I'd have enough torque at 5hz to do anything, 20 seems to be the limit.



Some will debate this matter, but most motor/vfd combos are constant torque from the rated rpm down so available torque is unlikely to be an issue. The real issue is feed/metal removal rate. In other words, a slower cut should not really be an issue provided you have adequate motor cooling. 

But then again, why? I was deliberately testing my machine. Normally, I would make that cut at the recommended rate for the material, or as a rough guess, I'd prolly aim for 900 - 1000 rpm on a 3/4 bit and I wouldn't take off nearly that much in a single pass - maybe 5-10 thou or so. Im not in a race and time is not money for me. 

That's the simple version from my perspective anyway.


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## Susquatch (Nov 22, 2021)

YYCHM said:


> This 30 thou term confuses me, are we talking 0.03" ?  I go 0.05" or more all the time
> 
> My recent gear cutting exercise included a DOC to 0.13".


Ya, 30 thou is 0.030. And ya, one can go more or less depending. I just figured 30 thou was a very respectable cut that I could really test my machine at. Nothing more or less. 

Like you I have been routinely taking off a quarter inch at a crack on smaller end cuts.


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## Tom Kitta (Nov 22, 2021)

This is also function of sharpness of the EM & hardness of material - a dull carbide EM in 3/4 I usually go max 120 thou in single pass max in something like 4140 with around 900 rpm speed. Feed at 4ipm 4 flute giving me about 1+ thou cut per tooth. 
Yes technically I should have higher RPM and higher feed rate for the machine but I don't want it walk out the door  

This is with BP style machine.


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## Susquatch (Nov 23, 2021)

Tom Kitta said:


> This is also function of sharpness of the EM & hardness of material - a dull carbide EM in 3/4 I usually go max 120 thou in single pass max in something like 4140 with around 900 rpm speed. Feed at 4ipm 4 flute giving me about 1+ thou cut per tooth.
> Yes technically I should have higher RPM and higher feed rate for the machine but I don't want it walk out the door
> 
> This is with BP style machine.



Sounds a lot like experience talking. I'd be happy with that too!


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