Disclaimer: CNC Concepts, Inc. accepts no responsibility for the use
or misuse of techniques shown in this web page. We simply publish information
we feel will be of interest to CNC users. In all cases, the reader is totally
responsible for considering the implications, good and bad, of implementing one
or more of the techniques we show.
Calculating the lead of a twist drill
by Roger Levesque of Sanders
I see a lot of people use trig to calculate a drill tip or to calculate how
much deeper to go with the countersink. A quicker way to calculate a 118 degree
drill tip is to multiply the dia. by 0.3 i.e.: 0.250 X .3=0.075 The .3 is a
standard established by the fact that your answer would be .3 if it were trig'd
out for a 1" dia. Try it! You can do the same for different countersinks,
too. Use the value 0..575 (instead of 0.3) for an 82 degree countersink.