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John Stevenson
11-16-2007, 06:57 PM
First a bit of background.

Commercially bevel gears are cut on exotic production machines like the Gleason. These take quite a bit of setting up as the various moves, slides etc are quite complex.
On a straight bevel gear the tooth parts converge to the cone point of the wheel which makes all the planes tapered.

The cutters on a Gleason are simple straight sided planing tools as they generate the involute which is the correct way to generate gear teeth.

It is possible to cut these on a milling machine with a Brown and Sharpe type cutter but it's a bit of a fudge as part of the tooth shape isn't correct and has to be dressed with a file.


Now we have easy access to CNC machines I have wondered for a while if it's possible to generate a geometrically correct bevel gear using a simple straight sided vee shaped cutter that is easily ground up.

The purchase of the machinable wax in another post is part of this project. The next part fell into place today when I was finishing a batch of stepper driver rotary tables off. As I had all the various bits and tooling out I dragged a small 4" tilting rotab that I have had kicking around for a while and connected this up to a small type 17 stepper. This only puts out about 36oz/in but runs it fine.

http://homepage.ntlworld.com/stevenson.engineers/lsteve/files/tiltingrotab.jpg

Still a bit of a lash up as regards cabling as I was testing it with my Divisionmaster before setting it up on the mill.

Hopefully once this is setup and the wax gears have been tried and again hopefully work then I think all the programming can be done inside Excel by getting Excel to work the formulae out and generate the G Code from Excel.

.

LES A W HARRIS
11-16-2007, 08:40 PM
Now we have easy access to CNC machines I have wondered for a while if it's possible to generate a geometrically correct bevel gear using a simple straight sided vee shaped cutter that is easily ground up.

John,
As you are probably aware, the cutter has to be thin enough to pass thru the "toe" end, and each side is set to the "Tooth Angle", not just straight thru on C/L, the "Tooth angle" is figured as a section on the pitch cone, the heel end being chordal tooth thickness. There were two ways of cutting, both cutters thru the space, and one cutter each side of the tooth. Larger pitches were gashed thru on C/L with a milling cutter, on machines such as G & E's muti spindles, two three or four parts at a time.
Then recut on the Gleason.

In the 60's the Face, Pitch and Root Cones WERE NOT co-insident.

"G" jobs Bevel drive gear for washing machine mangle rollers, were common; pack of 10 "Park Drive" ciggy's was the going rate, set up the machine, cut gear in slack time, "only on nights", no way on day shift.

Good luck with your venture, seems quite doable.
Cheers,

wierdscience
11-16-2007, 09:09 PM
Okay when will we see a hypoid being cut?:D

Seriously though,looks like a good setup.

Are those Sieg 4" Rotabs in the back?Got one myself I want to convert,how did you handle the eccentric adjustment?

Forrest Addy
11-16-2007, 11:04 PM
I sense another one of John's marvelous distillations of a complex shop procedure made into a simple and crystal clear series of photos and paragraphs is not too far off.