Drill bit sharpening question

eac67gt

eac67gt

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When sharpening a drill bit how important is it what angle of the chisel point ends up. I am using a drill doctor because I am poor at hand sharpening. Some off the bits come out with the point slightly angled to the right and some to the left. I noticed new bits seem to be to the right when liking down on point. Thanks for your help and have a great day. Ed

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The cutting edge (the lips) need to be the highest point on the drill. This is the clearance (AKA relief angle) angle. You always want some positive angle here else the drill will rub. If it's negative, the drill won't cut at all.

The included angle looking at the bit from the side is the point angle. The point angle chosen depends on the material. From around 90 degrees for plastics to 135 or even 140 degrees for hard materials.

The chisel point angle is hard to describe, but a picture is worth a thousand words. Also, compare what you're getting to a known good bit. If the chisel point is the wrong angle, it usually resulkts from the relief angle being wrong. This happens because the drill doctor is very picky about how the drill is mounted in the chuck and what relief angle (not point angle) is chosen.

See here: http://www.americanmachinetools.com/images/4-11_drill_bit_geometry.jpg

John
 
Thanks John.
I see now after looking closer at them as that point angle comes around the relief increases on the lip. I have the bits in question mounted in holder correctly but they don't come out the same. There are some that come out perfect but others don't. I am trying to catch up on my sharpening so I have a pile to go through. I will have to play with those questionable ones and see what I can come up with. Does anyone know if the better models of the drill doctor perform better or different than the base model I am using, 350X. Thanks and everyone have a great day. Ed

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I think the one I have is the 750X. There are two things to set up... The point angle which is adjusted by adjusting the chuck cam in an arc with respect to the grinding wheel. The other adjustment is the relief angle which is adjusted by aligning a tab in the chuck when putting the chuck into the depth of cut adjustment thingy and clocking the bit to be held by the two spring steel gizmos. That's the adjustment that has to be right for the chisel point to come out correctly.

I've also found that if you've split the points on a drill, the spring steel thingys that align the bit in the chuck will never again position the bit correctly because they grab on the portion of the bit that's been split. That ends up clocking the bit incorrectly.

I can't remember whether the 350 can split points. If it doesn't, don't lose any sleep over it: the 750X does a poor job of splitting points on bits that are meant to be split; like the 135 degree cobalt bits with a thick web.

John
 
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