Re: Drill bit sharpening help

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Posted by Tim Daley(MI) on July 20, 2018 at 05:28:42 [URL] [DELETE] :

In Reply to: Drill bit sharpening help posted by Beth and Allen on July 19, 2018 at 20:05:29:

Drill sharpening by hand is an art, almost a lost form nowadays what with devices like drill doctors and such. There are drill guide scales, or use to be, a 6 steel rule that had the 59 angled edge on one end with a scale and separate protractor so you could measure each side when sharpening by hand. Standard drill points are 118 included angle for most applications. For a more precise hole, and longer lasting drill, we used Parabolic Drills, at 140 included angle. Carbide is best, but more expensive that HSS. If you ever wondered what that V was for on your bench or pedestal grinder rest, it was a guide for sharpening drills. It cradled the bit at the correct 59 angle. Back in my machinist apprentice training days in 1975, I ran NATCOS (multi-spindle drill press machines), single spindle drill presses, and GANG DRILLS, and had to learn how to sharpen our own drills by hand. Ditto when I moved up to NC Turret Lathes. The hardest machining operation to perform is drilling a hole on a lathe. It will teach you how to correctly sharpen a drill and how to correctly set up the tool and machine. If the tool and the workholding device isnt solid and rigid, you will have problems with oversize holes, tool breakage, and drill walk. Carbide tools will chip or break easier than HSS and never should be used with a hand operated drill motor. The tool/drill must be aligned centered and square to the workpiece. On a precision NC (CNC now) lathe, the tool must be indicated in when set up. Total TIR should not exceed .001. Once you find center, it also must be aligned perpendicular, horizontally and up and down (vertically) so when it drills, it isnt cutting on an angle and cause a misaligned and/or oversize hole. Always use a center drill or better yet,a spotter drill. Using a spotter will give not only a center spot, but will leave a chamfer at the top of hole on the finished workpiece when set to correct depth. As stated, it is an art. Getting the web right, the lands right, and correct angle is so important. If you get stumped on sharpening larger drills, check out your local machine job shops and ask if they could sharpen them for you. Here is a LINK to some very good info on drills.


Tim Daley(MI)

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