What is this tool for

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 .
 
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...
 
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...
Click to expand...

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)
 
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).

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)
Click to expand...
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...
 
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).

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)
Click to expand...

Dave
What is the 6 PI spec for?
What info would I list on EBAY to sell this thing?
Thanks
Aaron
 
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"
 
AGCB97 said:
Dave
What is the 6 PI spec for?
What info would I list on EBAY to sell this thing?
Thanks
Aaron
Click to expand...
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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