View Full Version : drill point angles
06-29-2001, 11:56 PM
This may sound dumb, but it's one of those questions I've never heard asked.....I guess everyone but me knows the answer. What's the difference between a 118-deg. drill point and 135-deg. drill (don't say 17 degrees). What are the advantages of one over the other? Thanks in advance.
06-30-2001, 05:14 AM
135 degree drills work better on tough materials than 118. Also, 135's typically have a "split point" design with cutting edges all the way to the center. 118's have sort of a chisel edge at the center. The split point cuts with less pressure, and with less tendency to "walk." However, regrinding split points requires special machinery, while ordinary points can be pretty successfully ground by hand given a simple gage, good eyesight, and a bit of practice. 135-split points cost about 10% more.
06-30-2001, 05:52 AM
The effective back rate increase with a decrease in angle, or is that an increase?
If you measure included lip angle, as the angle increases, as from 118 to 135, the effective back rake increases. With steel this is good, it makes the bit easier to feed, with softer materials it is bad.
That is the reason that there are different kinds of bits.
One can split the tip of a drill by hand, you have to have a sharply dressed wheel, or I should say a wheel with a sharply dressed corner. It takes pratice, but it's not too hard, most just simply thin the web if necessary, this is sometimes a trick if you don't have a good wheel.
Splitting the web of a drill is nothing new, I have a book by Colvin and Stanley that shows it, my copy was printed in 36, copyrighted before that.