In article ,
Engineman1 wrote:

[ ... ]

Stupid question:
Has anyone ever tried to come up whith a more sensible set of sizes for drills
than numbers and letters?

How about metric? I've got sets of drills in 0.1mm steps from
1mm to 10mm. I use them in addition to the fractional, number, and
letter sizes to give more choices.

And I consider the number and letter drills to be intended to
fill the holes in the original fractional size sets, so you can get a
better size to drill holes to be tapped. The fractional sizes (in steps
of 1/64") are jumping something like 0.0156" per step, so there is a
need for smaller steps to fit various pitches of threads.

If so how come it never went over?

Because the extra sizes offered by whatever "rational" system
were simply absorbed as yet another way to get finer steps.

Probably, the most rational system (but a real pain to use)
would have each size 1% larger than the previous, as resistors area
available (also for coarser sets, 5%, 10%, and 20%).

An example, starting with 1 ohm, and 10% steps (a common set of
the carbon composition sets) would go (IIRC):

1.0
1.1
1.2
1.3
1.5
1.7
1.8
2.0
2.2
2.4
2.7
3.0
3.3
3.6
3.9
4.3
4.7
5.1
5.7
6.2
6.8
7.5
8.2
9.1
10.0

Note that the spacing in sizes grows with the size, which would work
find for finding reasonable tap drills for normal pitches, which also
get coarser with increasing size.

But -- it would still be a problem with extra-fine pitches.

1% increments wind up with really strange values, but they would
probably work nicely. Just pick some standard as the starting point,
e.g. 1.0", and use negative numbers for smaller, and positive for
larger.

And then, all you have to do is convince the world to re-tool
using your new system. :-)

Enjoy,
DoN.
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