Thread: How to size used drills

I always measure at the very tip of the drill, right across the ends of the flutes with a vernier caliper. That is what matters most for the bore diameter.
Some of those drill shafts look pretty scored. Shafts are soft enough to be cleaned up in the lathe, just take a light cut across the shaft.

Hi Dale
Dont know if you have one but here is a list of drill sizes that I made a few years ago.

Roger

Originally Posted by bob ward

If you suspect you are measuring a non-metric drill, multiplying the millimetre size by 2.52 will give you the imperial size in 64ths. Not much help for letter size drills though.

never heard of that one before
but damn it, it works !

Originally Posted by janvanruth

never heard of that one before
but damn it, it works !

I thought the conversion factor between CM and Inch was 25.4 so why are we using 25.2 in this case? I'm not suggesting its wrong just want to understand.


Pity the Hare & Forbe EOFY sale has just passed



Is there anyone still producing Drill Tills? Especially a metric one as these don't seem to come up second hand.

Originally Posted by DSEL74

I thought the conversion factor between CM and Inch was 25.4 so why are we using 25.2 in this case? I'm not suggesting its wrong just want to understand..

Its not a conversion between mn and inches, but mm to 64ths of an inch

64/25.4 = 2.519685039

There are 64 divisions in 25.4 mm (1"), therefore there are 64/25.4 = 2.52 divisions in each mm. If you multiply that by the length in mm, you will get the measurement in 64th of an inch.

OK now that you explain it, it makes perfect sense