On Jun 26, 3:18*pm, " wrote:
On Jun 26, 1:10*pm, "Ed Huntress" wrote:

It's also interesting that
Acme threads derived from a group of miscellaneous flat-bottom threads known
as "******* threads." The 29-degree angle, says Colvin, probably was chosen
because Brown & Sharpe published a simple method for laying out cutting
tools with 29-degree angles.

--
Ed Huntress

I think Colvin is wrong in this case. *My understanding is that the 29
degree angle is the strongest angle. *It is also the angle used for
gears *(14.5 degree pressure angle. *). *Brown and Sharpe came out
with involute gear cutters in 1858 so they are likely the source of
the angle. *Brown and Sharpe probably published a method for laying
out tools with 29 degree angles as that would be what is needed to cut
a rack using a shaper to work with 14.5 PA gears.

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Dan

The sine of 14.5 degrees is 1/4, so a patternmaker can accurately
construct the angle by linear measurement.

jsw