Subject: Hobbing Gears II

From: [email-masked] (Daryl Bender)
Date: 5 Jun 1995 21:02:18 GMT

I have a feeling (the more I think about it) that "freewheeling" could be
"ify". 

1) How do you gash the blank without driving it?
2) If you fudgingly reduce the pitch diameter slightly ie a 60 tooth gear
cut on a 59 tooth pitch diameter blank, (this is something I'll have to do)
do you just cut less deep as when using milling cutters? 

It certainly makes me want to see a real hobbing machine, the gear box
required to do every reasonable number of teeth would be MASSIVE. Therfore,
I thought I'd feel out the crowd on plan B.
I have a shaper, soooo if I ground some tool bit to make a rack tooth (or
rather space) form then used the shaper to generate a rack. Then use the
rack as a cutter for a blank mounted in an index head. For large numbers of
teeth I think it would work, you'd also get some generation since you cut
various parts of many teeth on each pass. The problem comes with low
numbers of teeth. The large curvature on the tooth profile would be only
roughly approximated. It seems the solution would be to rotate (or rock)
the rack cutter back and forth somewhat. My shaper can do this.

3) My question here is what is the center of rotation, the tooth space root
or the space pitch line? My gut tells me its the pitch line.

4) How much do you rotate, the angle subtended by two teeth?

5) Lastly, on an somewhat unrelated topic, how are elliptical gears cut?

Thanks
Daryl 
-- 
Working but not speaking for BNR