On 2010-09-27, DoN. Nichols wrote:
On 2010-09-27, Ignoramus24898 wrote:
Huot index with 8 USA HSS Silver and Deming drill bits, 1/2" shank,
9/16 to 1". All new except 3/4", which is almost new. $12.05

Nice!

USA made drill bit set, small sizes about up to 1/4" by 0.001 or 0.002
(I do not understand the principle), looks like all others, $5.

Are you sure that is not a number size (wire size) drill set?
60 drills ranging from something like 0.040" for the #60 up to 0.228"
for the #1.

Yes, it is very possibly that.

i

Don't expect them to be even sized steps. The sizes essentially
fill gaps left in the fractional inch sizes, so some skip over the
fractional in size. Also -- the size of the steps varies with the
overall size of the bit. For example, the #59 is 0.0410" and the #60 is
0.0400" -- so only 0.001" step size. But at the other end, the #1 is
0.2280" and the #2 is 0.2210" -- a step size of 0.007".

I believe that the sizes are related to the formation of wire by
drawing it through successively smaller holes -- with adjustments to
skip the fractional near misses. So you wind up with 0.1285" for a #30
and 0.1200" for a #31 -- skipping the 0.1250" for a 1/8".

Anyway -- don't expect the number sizes to fit a neat formula
for calculation. It is easier to implement a look-up table in your
program.

Here are the sizes:

http://sector7.xor.aps.anl.gov/tables/number_drill.html

The number series actually goes on down to #80 (0.0135") in a
separate smaller index. If you have one of the 115 bit Huot indexes
(fractional, number, and letter sizes) you may have noticed a bent up
hook in the letter size section. It turns out that this is just right
to hold the index for the #61-#80 bits. (I discovered this almost by
accident -- never read about it anywhere, but wondered what it was for,
and since I had a Huot #61-#80 index, I tried it for fit and was quite
pleased.

Enjoy,
DoN.