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Thread: Size markings on drill bits
08-22-2005, 01:26 PM #1
This question was first asked by my machinest neighbor 20 years ago, "Why do the manufacturers stamp the size on the very end of shank, instead of higher up near the flutes? If the drill grabs in the work, the marking can become un-readable."
No answer could be found. So now it is my turn to ask the same question.
08-22-2005, 01:30 PM #2
I have no real knowledge but if I could be permitted a guess, the cutting edges, flutes need to be hardened and it is hard to stamp on a hardened surface. The far end can be a lot softer and therefore easier to stamp. Of course, the softer area is also easier to bugger up if the drill slips in the chuck. SBT.
Another possible reason is that the upset area around the stamping may cause the drill to be a bit off center in the chuck. This effect will be less if it is at the far end. Not by a lot, but by a little bit. And if you wanted to cut it off to eliminate this effect, it is better at the end.
These reasons may not be relivant with modern day production methods but may just be carryovers from earlier days.
08-22-2005, 01:44 PM #3
Some manufacturers have replaced the stamping with etching or laser marking (Precision Twist http://www.precisiontwistdrill.com/ uses this type of marking)
It would seem both these processes could be done easily near the flutes, but convention dictates that they be placed near the end.
08-22-2005, 01:45 PM #4
Production methods? Nah.
The bean counters stayed up late figuring that if you couldnt read the numbers anymore, you'd be too impatient to run over and get a mic. Therefore, toss that bad boy out, and go get a new one from the tool crib, store, industrial supplier etc.
That is, until they ran into me, El Cheapo.
08-22-2005, 01:56 PM #5
Try Dormer drills. Their marking on drills over 1/4 is in black on a ground silvery band usually clear of the jaws. The markings usually outlast the drill. Funnily enough, they don't do this on the fancy TiN coated ones, just the steam tempered.
08-22-2005, 02:10 PM #6
I'm not thrilled with the etched ones either. Difficult to see depending on the lighting and I've seen a lot of taps that somehow had the etched size completely wiped or rubbed off.
08-22-2005, 04:17 PM #7
Here's a Dormer drill, as described by Greeno:-
08-22-2005, 06:25 PM #8
Ahh that is to give you practice with the micrometer when you dump 114 of the 115pc on the floor!
08-22-2005, 07:50 PM #9
Who cares if the size markings are spun off by the chuck? I got a micrometer eye. (I got a mike for a back-up)
08-22-2005, 08:23 PM #10