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Posted by Robert Swinney on May 6, 2008, 4:14 pm
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Right on, Don. I should have known that but for some reason I couldn't get my
mind around it. Paul
answered it is in fact, pressure angle. If I have been reading everything right
and you make a rack
from the appropriate cutter, the sides of the teeth would be perfectly straight
and inclined on each
side at the pressure angle.
Bob (don't call me a gear head) Swinney
On Sun, 4 May 2008 21:59:43 -0500, "Robert Swinney"
>
>Paul, please elaborate a bit on your equations: BCR = PR*cos(PA) and TR =
tan(PA)*BCR In each,
>please explain what the term (PA) represents.
>
>
>Thank you,
>
>
>Bob Swinney
I'll bet PA represents pressure angle.
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Posted by Robert Swinney on May 4, 2008, 12:11 pm
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Sorry,
Make that "recently made some 56 DP gear cutters with the radius of a 3/32 end
mill. . ."
Bob Swinney
Paul sez: Now I'll have to get a copy of Law's book and see if my formulas
match his
numbers. Good go, Paul. While you're at it, see if you can dupe the math that
correlates the radii
of standard end mills with that of gear cutters. I haven't tried to reconcile
the math yet but I
recently made some 45 DP gear cutters (form) with the radius of a 3/32" end
mill. This was
according to a Jerry Keiffer article in Home Shop Machinist. I spoke briefly
with Jerry at the
Sherline booth at N.A.M.E.S. He put me onto the idea that most gear DPs can be
matched with the
radii of standard end mills. Thus far, I've only tried 56DP with a 3/32 end
mill. It runs
perfectly wtih the gears of my Sherline lathe.
Bob Swinney
>I have ivan Law's book, "Gears and Gear Cutting" and a copy of John
>Stevenson's paper, "Cutting
> involute Gears with Form Tools". In each are detailed instructions for
> making "button type" form
> tools for the fabrication of gear cutters. Choose any specific gear and
> pressure angle and the 2
> sets of instructions show different sizes of buttons, pin centers, and
> etc. Can anyone elaborate on
> why this is so? I would think the specifications for making precision
> gear cutters would be
> consistent among "authorities".
>
> Bob Swinney
Years back, as a mental exercise I worked out the math to duplicate
Stevenson's chart for 14 1/2 deg pa.
When I cross checked my math, I found some discrepancies with his 20 deg pa
chart. It wasn't much, but I lost interest and never followed it up. It
might have been a clearance issue or simply which tooth count is really the
average of the cutter range.
Paul K. Dickman
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>Paul, please elaborate a bit on your equations: BCR = PR*cos(PA) and TR =