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What is this tool for

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AGCB97

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#1
What kind of machine uses it. Does it have any value to a hobbyist?

DSCF3280.JPG

DSCF3282.JPG
 

T Bredehoft

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#2
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.
 

682bear

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#5
That is a B.F.T.

A big freakin' tap... lol!

It might make a good doorstop...

-Bear
 

projectnut

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#6
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Silverbullet

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#12
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 .
 

Bob Korves

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#13
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...
 

British Steel

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#15
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)
 

Bob Korves

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#16
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)
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...
 

AGCB97

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#17
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)
Dave
What is the 6 PI spec for?
What info would I list on EBAY to sell this thing?
Thanks
Aaron
 

Bill Gruby

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#19
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"
 

Eddyde

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#20
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.
 

Bill Gruby

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#21
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"
 

Eddyde

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#22
Yep, you posted your response while I was writing mine...
 

projectnut

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#23
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.
 

British Steel

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#24
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)
 

Bluedog

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#26
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.
 

Bill Gruby

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#27
I was not affended. One mans junk is another mans treasure.

"Billy G"
 
Last edited:

benmychree

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#28
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.
 

4gsr

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#29
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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