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Post by dialadad on Mar 24, 2011 21:32:05 GMT
This may sound stupid, but i have a load of drill bits that been modified beyond regrinding i think. Well the ends about 3/8 of an inch have been resized of different jobs, so i cant use them for their correct size.
What can be done with them or shall they go in scrap bin?
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ace
Statesman
Posts: 528
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Post by ace on Mar 24, 2011 22:06:20 GMT
Hi dialadad
I regrind old drills to make 'D' bits or regrind them to make short stub drills.
Steve
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Post by caseyjones82 on Mar 25, 2011 10:33:52 GMT
Gday,
If flutes are untouched and still visible right down to the shank they can still be re-sharpened, even if there's only 5mm worth of flute left. They make good sheet metal drills when correctly sharpened.
Cheers,
Alex
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jackrae
Elder Statesman
Posts: 1,333
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Post by jackrae on Mar 25, 2011 15:49:50 GMT
Do you mean the end is a smaller diameter than the main body of the drill. If so use a Dremel cutting wheel (reinforced type) to slice off the reduced length and then regrind what you have left. Just take care to a) not shatter the wheel and b) not over-heat the drill.
jack
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Post by denford on Mar 25, 2011 18:08:04 GMT
They could have been ground like that to make true counter bores for using socket head bolts or allen screws
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Post by goldstar31 on Mar 25, 2011 20:26:02 GMT
No! Ordinary HSS drill bits are tapered and the shanks are soft enough to be counter drilled.
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Post by caseyjones82 on Mar 26, 2011 0:02:29 GMT
No! Ordinary HSS drill bits are tapered and the shanks are soft enough to be counter drilled. Which part of the drill are you referring to? The inside diameter flute is slightly tapered yes, but the outside edge is most certainly not! Any drill that has a tapered outside would be completely useless. If it were and increasing taper as the drill gets deeper, then a tapered whole would be undesirably achieved, If a decreasing taper, the drill would have no support whilst drilling deeper holes and an oval shape hole would be the result. Unless of coarse you are referring to cheap drill bits....In which the quality control in china is extremely questionably and in which case the drill bits are useless. Cheers, Alex |
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Post by goldstar31 on Mar 26, 2011 7:35:54 GMT
No Alex, I am refering to diameter at BOTH ends of the drills. In this instance, the flutes don't come into the discussion. Might I suggest that you take a brand new drill of good quality and a decent micrometer and check my comments?
With a decent drill, put it in a collet -the wrong way round- and drill it as I have suggested.
Once you have done both exercises, you should find the simple reason for the clamped end being left soft. It is to avoid the damage caused by a spinning drill in a drill chuck's hardened jaws.
As for sheet metal drills to which you mentioned, these are twofold( well, in my book).
One is the special one to remove existing spot welds and the other is totally different to a conventional 118 degree jobber drill-- because of snatching.
Sorry, it doesn't appear in most books and the last thing is to 'talk down' to anyone.
Someone might avoid a torn hand working with sheet metal and my comments will have all been worthwhile.
As for silver soldering and extending drills, this is classic Northumbrian bagpipe method when a chanter has to be drilled 4.4mm dead parallel over a distance of some 19".
Regarding the comments about support and oval holes, this is a long, long subject than we have space for. Geo Thomas touches on it in his drilling of division plates when he uses stub-- and not jobber drills to avoid 'wandering'-- which I think that I am doing.
Cheers
Norman
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Post by bambuko on Mar 26, 2011 10:40:16 GMT
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Post by goldstar31 on Mar 26, 2011 10:56:52 GMT
Taper is t'other way. Mikes ahoy!
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