# What is this tool for



## AGCB97 (Aug 18, 2017)

What kind of machine uses it. Does it have any value to a hobbyist?


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## T Bredehoft (Aug 18, 2017)

I suspect none of my machines would have the power to make chips with that. P & W is Pratt and Whitney, I expect this is a thread mill, but cannot imagine its use.


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## 09kevin (Aug 18, 2017)

Looks like it could be a serration cutter.


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## Bob Korves (Aug 18, 2017)

Whitworth thread mill.  My guess and I am sticking with it...


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## 682bear (Aug 18, 2017)

That is a B.F.T.

A big freakin' tap... lol!

It might make a good doorstop...

-Bear


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## projectnut (Aug 18, 2017)

It's a gear hobb:
http://www.star-su.com/cutting-tools/gear-cutting-tools/hobs/involute

They come in many different sizes.  They fit on a gear hobbing machine to cut various types of gears.  Here's a video of some extremely large gear hobbing machines in action:





The one you have more likely fits a machine of this size:http://www.ebay.com/itm/BARBER-COLM...228190?hash=item43d29bb35e:g:bXEAAOSwuMFUZkxA


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## Groundhog (Aug 18, 2017)

It's fer makin big stuff.


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## Billh50 (Aug 18, 2017)

Yep, that's a hob for making gears on a hobbing machine.


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## Mark_f (Aug 18, 2017)

Yes, it is a gear hob. unless you have a hobbing machine, it is only good for a paper weight or doorstop.


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## darkzero (Aug 18, 2017)

That would make one heck of a back scratcher.


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## Bill Gruby (Aug 18, 2017)

Judging by its size and stampings you have 1500 to 2000 dollars in your hand. Yes it's a hob.

 "Billy G"


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## Silverbullet (Aug 18, 2017)

Hang it over you mill and hope it grows up big and strong to use it. Or make a door knocker from it to your shop. I to am sure it's for hobbing gears .


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## Bob Korves (Aug 18, 2017)

Never saw a gear cutter with what appear to be 55-60 degree "V" teeth.  They are definitely not shaped like involute cutters.  The tips and the gullets of the Vs are rounded and the flanks look straight. And why does it show H-2, which is a thread class?  Also it says on it "6 P.I. Whit."  Six pitch per inch Whitworth?  Still guessing...


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## Ulma Doctor (Aug 18, 2017)

the v's look steeper than 60*


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## British Steel (Aug 18, 2017)

Bob Korves said:


> Never saw a gear cutter with what appear to be 55-60 degree "V" teeth.  They are definitely not shaped like involute cutters.  The tips and the gullets of the Vs are rounded and the flanks look straight. And why does it show H-2, which is a thread class?  Also it says on it "6 P.I. Whit."  Six pitch per inch Whitworth?  Still guessing...



Hi Bob,
Gear hobs don't have involute profiles - they generate them using a rack form (straight flank) cutter, and the flank angles can be anything the gear designer wants from 0* (square threads!) upwards - if the gears meshing are involute profiles they'll mesh whatever the PA, with the optimum sweet spot in the 10-30* range (the greater the PA the smoother they run but the greater the force pushing the two gears apart - in my experience, anyway).

The dead giveaways are that it's not marked with a thread size (e.g. 1&7/8") so not a tap and the marking for pitch angle, this is the hob's pitch, and in a hobber the hob and work aren't "square" to each other, one or the other (usually the hob) is offset at the pitch angle to generate straight-cut gears while allowing the helix to rotate the gear blank (free hobbing).

Gear hobs are a lot easier to make than a set of numbered involute cutters (even single-edge fly cutters) as the cutting edges are rack form which can be cut on the lathe (with a bit of calculating if you don't have charts of changegears / lever positions for Diametral or metric Module pitches) and the "threads" can be gashed like a tap - the thread flank angle will then become the gears' pitch angle, and a single hob will work with any number of teeth and still give the correct generated involute tooth form. Quicker than a single-tooth / multi-tooth gear cutter, too 

Dave H. (the other one)


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## Bob Korves (Aug 18, 2017)

British Steel said:


> Hi Bob,
> Gear hobs don't have involute profiles - they generate them using a rack form (straight flank) cutter, and the flank angles can be anything the gear designer wants from 0* (square threads!) upwards - if the gears meshing are involute profiles they'll mesh whatever the PA, with the optimum sweet spot in the 10-30* range (the greater the PA the smoother they run but the greater the force pushing the two gears apart - in my experience, anyway).
> 
> The dead giveaways are that it's not marked with a thread size (e.g. 1&7/8") so not a tap and the marking for pitch angle, this is the hob's pitch, and in a hobber the hob and work aren't "square" to each other, one or the other (usually the hob) is offset at the pitch angle to generate straight-cut gears while allowing the helix to rotate the gear blank (free hobbing).
> ...


Sounds like you know far more about it than I do, Dave.  Thanks for the education!  I still have a lot to learn about hobs.  I did know that it is not a tap...


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## AGCB97 (Aug 19, 2017)

British Steel said:


> Hi Bob,
> Gear hobs don't have involute profiles - they generate them using a rack form (straight flank) cutter, and the flank angles can be anything the gear designer wants from 0* (square threads!) upwards - if the gears meshing are involute profiles they'll mesh whatever the PA, with the optimum sweet spot in the 10-30* range (the greater the PA the smoother they run but the greater the force pushing the two gears apart - in my experience, anyway).
> 
> The dead giveaways are that it's not marked with a thread size (e.g. 1&7/8") so not a tap and the marking for pitch angle, this is the hob's pitch, and in a hobber the hob and work aren't "square" to each other, one or the other (usually the hob) is offset at the pitch angle to generate straight-cut gears while allowing the helix to rotate the gear blank (free hobbing).
> ...



Dave
What is the 6 PI spec for?
What info would I list on EBAY to sell this thing?
Thanks
Aaron


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## Bluedog (Aug 19, 2017)

Bill Gruby's post got you excited, didn't it!


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## Bill Gruby (Aug 19, 2017)

He won't get that for a used one. Those prices are for new. My friend Eric at Bryce Gear  pays those prices and sometimes nore.

  "Billy G"


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## Eddyde (Aug 19, 2017)

AGCB97 said:


> Dave
> What is the 6 PI spec for?
> What info would I list on EBAY to sell this thing?
> Thanks
> Aaron


IMHO you wont get anywhere near the above stated value. I would put it for auction starting at $20 and set your reserve at whatever your minimum price you would let it go for and see what happens.


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## Bill Gruby (Aug 19, 2017)

I agree, he wont, but then I never stated he would. I did not quote a price either. I just stated what they cost. Some are much less, some more. Please read my post above yours.

 "Billy G"


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## Eddyde (Aug 19, 2017)

Yep, you posted your response while I was writing mine...


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## projectnut (Aug 19, 2017)

I was going make another post on this subject last night.  After reading those already on the subject I decided what I had to offer had already been covered so I attempted to delete the one I had in progress.  Now every time I come to this thread my unfinished post appears asking if I want to post it.  I don't seem to be able to delete it so I edited it to ask how I can delete  a post in progress in the future.  What am I missing.


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## British Steel (Aug 19, 2017)

AGCB97 said:


> Dave
> What is the 6 PI spec for?
> What info would I list on EBAY to sell this thing?
> Thanks
> Aaron



My guess is it's 6 Circular Pitch (tooth pitch in teeth per inch measured around the pitch circle, rather than Diametral pitch where the pitch is in teeth per inch of the pitch diameter across it) - an advantage is if you come to cutting worm wheels, the worms driving them are straight TPI threads rather than DP threads with a factor of Pi in 'em... You can confirm with a thread gauge, if it's 6 TPI along the hob (or very close, allowing some Cosine error for the 3-degree lead, about a part in a thousand!) then it's 6 CP.

As for what to list on EvilBay, pass, I never manage to sell anything! Take a look at other gear hob listings for suggestions?

Dave H. (the other one)


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## AGCB97 (Aug 19, 2017)

I put it on EBAY auction like Eddyde said
http://www.ebay.com/itm/132300698765?ul_noapp=true
We'll see what happens!
Aaron


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## Bluedog (Aug 19, 2017)

Bill Gruby said:


> He won't get that for a used one. Those prices are for new. My friend Eric at Bryce Gear  pays those prices and sometimes nore.
> 
> "Billy G"



I know, I was just going on at the OP. Maybe the humor was missed. Most people are like me and wouldn't pay scrap price for it with no machine to use it. Maybe the OP can get lucky and get 20 bucks to spend on something useful and some buyer get a great deal as well. Win, win.


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## Bill Gruby (Aug 19, 2017)

I was not affended. One mans junk is another mans treasure.

 "Billy G"


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## benmychree (Aug 19, 2017)

Bob Korves said:


> Never saw a gear cutter with what appear to be 55-60 degree "V" teeth.  They are definitely not shaped like involute cutters.  The tips and the gullets of the Vs are rounded and the flanks look straight. And why does it show H-2, which is a thread class?  Also it says on it "6 P.I. Whit."  Six pitch per inch Whitworth?  Still guessing...


H2 likely is the type of HSS the tool is made of; this is a common marking for tools of this sort.


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## 4GSR (Aug 19, 2017)

That very well could be a thread hob for cutting internal/external threads.  This would be used on a old Lees Brander thread mill or a old Smalley-General thread mill.  

I'll stick with gear hob!


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## Chuck K (Aug 20, 2017)

682bear said:


> That is a B.F.T.
> 
> A big freakin' tap... lol!
> 
> ...


Not big enough for a doorstop.  Need something like this.....


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## projectnut (Aug 20, 2017)

benmychree said:


> H2 likely is the type of HSS the tool is made of; this is a common marking for tools of this sort.



It could also be the fit of the hob to the spindle.  If I recall correctly before the advent of hydraulic spindles gear hobs had different tolerance fits to the spindle much the same as thread classes.  I do recall some bobs being identified with a fit of H5 and H6.  The tighter the tolerance the lower the number.

This was more important for precision gears when all components of the machine were mechanical.  The hob had to fit precisely to insure proper depth and clearance.  Now that most machines have hydraulically controlled spindles they can keep uniform and constant pressure against the work piece so an .0005" difference in fit to the spindle can be compensated for.


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## Desolus (Aug 23, 2017)

It looks like a hammer to me...


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## Desolus (Aug 23, 2017)

mark_f said:


> Yes, it is a gear hob. unless you have a hobbing machine, it is only good for a paper weight or doorstop.



Or a huge ass mill with a huge ass servo drive spindle and a huge ass servo drive rotary table...


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## British Steel (Aug 24, 2017)

Desolus said:


> Or a huge ass mill with a huge ass servo drive spindle and a huge ass servo drive rotary table...



Spindle doesn't need to be servo drive, could just have an encoder on it and something like the electronic leadscrew controller (simple circuitry, Google should find it) for a stepper on the rotary table / dividing head? Would still need either the spindle or rotary canted at the hob's lead angle, but feasible for a home shop...

Dave H. (the other one)


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## DaveInMi (Aug 24, 2017)

mark_f said:


> Yes, it is a gear hob. unless you have a hobbing machine, it is only good for a paper weight or doorstop.



Some day I'm going to gash a gear blank and try to finish it with a hob (table slanted to lead angle?).  If one can use a tap or acme ready thread to make a worm gear, maybe the gash and hob would work.


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## Desolus (Aug 24, 2017)

British Steel said:


> Spindle doesn't need to be servo drive, could just have an encoder on it and something like the electronic leadscrew controller (simple circuitry, Google should find it) for a stepper on the rotary table / dividing head? Would still need either the spindle or rotary canted at the hob's lead angle, but feasible for a home shop...
> 
> Dave H. (the other one)



I looked into servos and steppers for a large machine I was considering building and if memory serves high rpm high torc servos are much cheaper than the stepper counterparts. It should also be noted that a motor + encoder is just a wireing difference away from a servo motor; abet a crappy one.

Edit: You know you want this on your spindle http://m.ebay.com/itm/262387139592?_trksid=p2141725.m3641.l6368 ...


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## Highsider (Sep 5, 2017)

It’s a thread cutting tool, used in toolmaking to cut the half round threads (or less than half round) on a quadrant shaped machine part that engages a threaded spindle piece, which controls the position of the quadrant.    It’s used much like a worm and quadrant gear set, but uses thread forms instead of gear tooth forms.


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