The bit is new and cuts extremely well, chips are long, continuous curls but the hole is slightly larger. the error is more than acceptable. The diameter of the fluted part is found to be accurate suggesting that the tip is not centered. I believe this is not uncommon and wonder how you guys deal with it. Toss it ? re-grind ?
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How would you deal with drill bits having the tip off center ?
- Thread starter compact8
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To toss it would be wasteful, definitely regrind it.
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I found grinding equal flute lengths and angles freehand was challenging so I made this very simple guide, and it’s now quite easy to get a good grind. It’s easy to touch up without completely messing up and having to restart. There are some threads on this kind of guide and how to use it.
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Toss or regrind depends on the value/need of the drill. Smaller sized are more difficult to sharpen cheaply and well. Smaller drills cost less to replace than larger drills. The tipping point depends on your equipment, skills, budget/cost, access to replacements and immediacy of need.
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Need to drill an oversize hole??? keep this trick in mind, just grind one flute a bit longer.
Need to drill under size??? Did you know drills are tapered? Remove an inch or two. Then use the drill as a reamer, make the drill point angle real sharp, like 80-90 degrees and run it down a predrilled hole the next size smaller. I find this trick useful when needing press fit roll pins and not having an undersized reamer on hand.
Need to drill under size??? Did you know drills are tapered? Remove an inch or two. Then use the drill as a reamer, make the drill point angle real sharp, like 80-90 degrees and run it down a predrilled hole the next size smaller. I find this trick useful when needing press fit roll pins and not having an undersized reamer on hand.
I am not aware of that. Just measured a quality 7.5 mm drill bit, the diameter at the tip is exactly 7.5 and reduces to 7.44 near the upper end of the flute. Very interesting. Thanks for the knowledge !
In fact that's what I have been doing but it seems that it's not a very popular practice. I dont have a grinder so regrinding is not an option for me. To use the off-center drill, I drill a slight smaller hole first and finish off with the off-center one. When used in that way, the hole will not be centering around the tip and the diameter is determined by that of the body of the drill hence accurate. The only risk is having the drill grab and wander causing the hole position to be off.
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Karl - thanks for the tip!
Just to explore this a bit, on a 7.5mm drill bit, (0.295") the flutes part would be approximately 75mm (nearly 3") or so out of a total 110mm (4.3") including shank. The difference is 0.06mm (0.0024") spread across the flutes length. If you take away (say) the first inch of the three, you have 0.04mm, or about 1.6 thousands, and if the hole you ream is less than about an inch deep, you have a diameter variation of less than a thousandth.
At a pinch, I would use this trick
, but I always know that a drill bit is a two-flute hole follower, and I like six flutes. I think I will continue to buy a single reamer as and when I need one. As with all things that cut, I always buy new. Unless it can be readily re-ground (by me), I see no point in buying pre-loved. I am amazed to see even used condition files put up for sale on eBay!