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itselliott wrote: ↑Sat Dec 14, 2019 2:55 pm I wish I could hold a class on sharpening drills...………..As a tool & Die apprentice , years ago, I had 2 old German toolmakers drive me to tears "educating" me in the drill sharpening process...………..It is really super easy to sharpen a drill once you have got the process down.....

Agreed. As a machinist doing oilfield equipment repair (valve and BOP bodies), this is indispensable:



118deg for standard metals, 135 for hard stuff, like Inconel.

Also, keep your grinding wheels dressed and flat.

RJ Kyu……..
Exactly correct on both counts!

i have an easy to remember guide to help those who are unsure what spindle speed (rpm) to use for a particular size drill. I call it the “5 rule” and it works good for most drilling through mild steel. For a starting point or baseline I use a 1/2” drill which is .5” spinning at 500 RPM (notice the two fives). From there if you double the size of the drill you can divide the speed in half to 250 RPM. Again from the baseline of .5”, if you divide the diameter in half to a 1/4” drill you could double the speed to 1000 RPM.

Using this simple system one could extrapolate spindle speeds for most sizes of drills in mild steel. Of course this only helps if you have speed indication on the power tool you are using. Softer materials like aluminum can be run a bit faster.

I was taught (4 x the cutting speed)/diameter. Drill, mill, lathe, doesn't matter. Cutting speed for mild steel is 90, aluminum is 400. That's all I remember or routinely use. Values for other materials can be looked up.