GearHeads Corner

A few years ago I made an XL timing gear 3 tooth cutter. (Published in Home Shop Machinist)
At the time I used a profile published for the belt of such a pulley. That was fairly accurate, but not exact. The most glaring error is that the depth is wrong. In the belt it is 0.050", but a pulley groove is closer to 0.060".
The effect is that while the cutter works, the machining is touchy as to depth of cut, diameter of pulley.
Since the cog of a belt is the same regardless of the pulley size, the groove (space between the teeth) of a pulley must be constant. Therefore a single cutter should work for all sizes of pulleys.
How/where can I get the exact dimensions of an XL pulley groove?
Ozzie

Generate one in Gearotic and analyse its tooth shape would be easiest.
The tooth shape itself should be in the dxf..

Art

I exported a dxf which I opened in Fusion 360. Unfortunately the curves seem to be unmeasurable; must be chords. I'm now remembering I had this problem before which might be why I used the belt specs.
However, since what I ultimately want is G-code, I should be able to get that from F360. Might be tricky because the path I want is on the inside of the profile.
Thanks,
Ozzie

Hi Ozzie:

  Gearotic only puts out line segments, so Fusion must be converting to curves on the
way in. .. I have heard that before.

Art

No, that's the problem, F360 IS bringing in segments, making it hard to measure the radii or their centers. I'm sure with a little trial and error I can approximate the size of the curves. Accuracy to tenths isn't needed.
I don't see a way to create a rack with XL profile. Is there a way?

Hi Ozzie:

  Ahh, I see. Vexx in future may be able to make them back into arcs for you to measure..

No, I never added a rack capability for pulleys.. gears are easy, just prssure angle lines, but the
pulleys would have required a bit of a job to do...not sure itd be worth it, to use a pulley as a rack
driver may as well swap the pulley to a gear..?

Art

I tried a thousand teeth and the closeup looks about rack like, good enough for me to get a profile and G-code.

I use my cnc lathe along with John Stevenson's method to make a three tooth relieved cutter. I never met him but I sure will miss him. He left us so much on the pages of machining sites; I'll think of him often.
Ozzie