Originally Posted by kevinkoons  Looking at thread pitch charts I see the basic pitch for 1/4-20 listed as .2175 and what they list as "section at minor dia." in sq. inch as .0269. Was this person using the sq. inch value x 2 as the basis to arrive at 0.05 for the thread pitch or maybe I just don't understand!
Any thoughts on any of this??? |
there is pitch Diameter and Pitch lead.
.2175 is the pitch diameter of 1/4-20, it's a gage diameter measured 1/4 lead from centerline, a way to measure the threads with a number and not go/nogo.
the pitch you seek is the threads per inch, so 1/4-20 has 20 threads per inch (-20) so for every turn it travels 1/20 of an inch or .050.... a 1/4-28 has 28 threads per inch, so a turn is 1/28 of an inch=.03571. etc.. metric threads make it easy, say m6x1 the thread moves 1mm per turn.. m4x.75 moves .75mm per turn etc..
so on inch threads you use this Feed in inches per minute = RPM*(1/TPI) where TPI= threads per inch