Okay... I understand why fractional drill sizes and metric drill sizes
exist... They are common sense to me.

But... Why do number and letter drill sizes exist? Do they correspond to a
wire size or some other standard?

Regards,
Joe Agro, Jr.
(800) 871-5022
01.908.542.0244
Automatic / Pneumatic Drills: http://www.AutoDrill.com
Multiple Spindle Drills: http://www.Multi-Drill.com

V8013-R

--Well at least some of them are tap drills for various threads;
from memory: F = 5/16-18, G = 1/8" pipe (?), #21 = 10-32, etc. And then
there's the problem of over and undersize threads for various applications;
i.e. sometimes you'll want to use a drill that's a few thou over if you're
tapping a hole that's going to be anodized. I suspect that number and letter
drills 'evolved' to fill these sort of gaps.

--
"Steamboat Ed" Haas : Feeling like Bender in
Hacking the Trailing Edge! : a strong magnetic field...
www.nmpproducts.com
---Decks a-wash in a sea of words---

"steamer" wrote in message
...
--Well at least some of them are tap drills for various threads;
from memory: F = 5/16-18, G = 1/8" pipe (?), #21 = 10-32, etc. And then
there's the problem of over and undersize threads for various
applications;
i.e. sometimes you'll want to use a drill that's a few thou over if you're
tapping a hole that's going to be anodized. I suspect that number and
letter
drills 'evolved' to fill these sort of gaps.

That makes sense for some sizes... But it makes you wonder why the metric
system or even a fully decimal system doesn't take off...

Imagine simply saying that drills are available every thousanth up to a
certain size and then every 2 thousanths up to some larger size, so on and
so forth, etc.

I can see a supplier offering drills in .001" increments up to 1" and having
a market *IF* they became well known.

Regards,
Joe Agro, Jr.
(800) 871-5022
01.908.542.0244
Automatic / Pneumatic Drills: http://www.AutoDrill.com
Multiple Spindle Drills: http://www.Multi-Drill.com

V8013-R

"Joe AutoDrill" wrote in message
news:AnNOi.1698$d2.1149@trnddc08...
"steamer" wrote in message
...
--Well at least some of them are tap drills for various threads;
from memory: F = 5/16-18, G = 1/8" pipe (?), #21 = 10-32, etc. And then
there's the problem of over and undersize threads for various
applications;
i.e. sometimes you'll want to use a drill that's a few thou over if
you're
tapping a hole that's going to be anodized. I suspect that number and
letter
drills 'evolved' to fill these sort of gaps.

That makes sense for some sizes... But it makes you wonder why the metric
system or even a fully decimal system doesn't take off...

Imagine simply saying that drills are available every thousanth up to a
certain size and then every 2 thousanths up to some larger size, so on and
so forth, etc.

I can see a supplier offering drills in .001" increments up to 1" and
having a market *IF* they became well known.

The numbered and lettered drills filled in the gaps between some awkward
fractional sizes, at the smaller end of the range. Like many other things in
metalworking it was always explained to me as something resulting mostly
from a tradition.

I haven't kept up with this but 20 years ago the tension was between using
the traditional system that have known relationships to tap sizes and so on,
and going to a straight decimal system with a rational series of steps. Both
systems were in use in high volume production. Now, I don't know. Maybe
metrics have clouded the picture.

--
Ed Huntress

"Joe AutoDrill" wrote in message
news:fDLOi.1693$d2.1294@trnddc08...
Okay... I understand why fractional drill sizes and metric drill sizes
exist... They are common sense to me.

But... Why do number and letter drill sizes exist? Do they correspond to
a wire size or some other standard?

Regards,
Joe Agro, Jr.

The number sizes correspond to the "Stubs steel wire gage" a more or less
obsolete system of measurement.

However, it exactly matches the size and number of the holes in a recently
manufactured drawplate I have in the jewelry shop.

It may be a legacy of draw plate manufacture, but I suspect that the numbers
are based more on the amount you can reduce a wire in one pass, than on any
other number.(weight per ft, decimal steps)

I imagine that wire manufacturing started first, creating sizes that were
convenient to their process.

Later the drill sizes were created to match. This could be for 2 reasons. #1
to make holes that fit the wire, and #2 because the drill bits were made out
of wire, which was supplied in wire gage sizes.

I don't know about the letter series. I suspect that, as Ed says, they were
created to fill in awkward gaps in the decimal set.

Paul K. Dickman

I don't know about the letter series. I suspect that, as Ed says, they
were created to fill in awkward gaps in the decimal set.

Almost looks as if letter sizes were made to go beyond a #1 drill... In
other words in order from small to large: 4,3,2,1,A,B,C,D,...
--


Regards,
Joe Agro, Jr.
(800) 871-5022
01.908.542.0244
Automatic / Pneumatic Drills: http://www.AutoDrill.com
Multiple Spindle Drills: http://www.Multi-Drill.com

V8013-R

Joe AutoDrill wrote:

"steamer" wrote in message
...

--Well at least some of them are tap drills for various threads;
from memory: F = 5/16-18, G = 1/8" pipe (?), #21 = 10-32, etc. And then
there's the problem of over and undersize threads for various
applications;
i.e. sometimes you'll want to use a drill that's a few thou over if you're
tapping a hole that's going to be anodized. I suspect that number and
letter
drills 'evolved' to fill these sort of gaps.


That makes sense for some sizes... But it makes you wonder why the metric
system or even a fully decimal system doesn't take off...

Imagine simply saying that drills are available every thousanth up to a
certain size and then every 2 thousanths up to some larger size, so on and
so forth, etc.

I can see a supplier offering drills in .001" increments up to 1" and having
a market *IF* they became well known.

Regards,
Joe Agro, Jr.
(800) 871-5022
01.908.542.0244
Automatic / Pneumatic Drills: http://www.AutoDrill.com
Multiple Spindle Drills: http://www.Multi-Drill.com

V8013-R






1000 drill sizes on the shelf? I have ground down drills a couple of
thou once in a while when I didn't have the exact size I needed and I
had to finish the job.


John

"Joe AutoDrill" wrote in message
news:QoOOi.1702$d2.971@trnddc08...
I don't know about the letter series. I suspect that, as Ed says, they
were created to fill in awkward gaps in the decimal set.

Almost looks as if letter sizes were made to go beyond a #1 drill... In
other words in order from small to large: 4,3,2,1,A,B,C,D,...
--


Regards,
Joe Agro, Jr.
(800) 871-5022
01.908.542.0244
Automatic / Pneumatic Drills: http://www.AutoDrill.com
Multiple Spindle Drills: http://www.Multi-Drill.com

V8013-R


All I have read indicates that you are correct. Sizes (and things like
resistor values) often are in a geometrical progression. Each value is a
more or less constant percentage of the adjacent one. So the common
fractional drill series actually tends to create more sizes than are really
useful in the larger ones and not enough sizes in the smaller ones. Just as
useful thread pitches might include 4, 5, and 6 but probably would not
include 29, 30, and 31. A widely useful range of drill sizes might include
..001", .002", .003" (and probably some in between) but probably not .831",
..832", and .833".

Don Young

Joe AutoDrill wrote:
Okay... I understand why fractional drill sizes and metric drill sizes
exist... They are common sense to me.

But... Why do number and letter drill sizes exist? Do they correspond to a
wire size or some other standard?

Regards,
Joe Agro, Jr.
(800) 871-5022
01.908.542.0244
Automatic / Pneumatic Drills: http://www.AutoDrill.com
Multiple Spindle Drills: http://www.Multi-Drill.com

V8013-R




They fill in gaps that were left by the other sets.

Except the "E" drill, anyway.

Cheers
Trevor Jones

They fill in gaps that were left by the other sets.

Except the "E" drill, anyway.

Absolutely... But it doesn't explain why they are called out by numbers and
letters. It seems like someone created the idea and for some reason, a
bunch of people got together and supported the idea even though *someone*
had to be logical enough to see that a decimal based system would be easier
to track, understand, etc.
--


Regards,
Joe Agro, Jr.
(800) 871-5022
01.908.542.0244
Automatic / Pneumatic Drills: http://www.AutoDrill.com
Multiple Spindle Drills: http://www.Multi-Drill.com

V8013-R

On Oct 9, 9:46 am, "Joe AutoDrill" wrote:
Okay... I understand why fractional drill sizes and metric drill sizes
exist... They are common sense to me.

But... Why do number and letter drill sizes exist? Do they correspond to a
wire size or some other standard?

The number and letter sizes, just like wire gauges, represent a more
logarithmic distribution of sizes than you would get just going up by
say 0.1mm or say 128ths each and every step.
You need a finer step in your scale at the small sizes and a larger
step at the larger sizes. So at the #60 drill range the step size is
just one or two thousandths at each step, but by the time you get to
#10 you're stepping by two or three or four thousandths, and by the
time you're up at X or Y or Z you're stepping by 7 or 8 or 9
thousandths.

That said, there are some oddball spacings in the letter drill
sizes... e.g. M to N is a step of 7 thousandths, but N to O is a step
of 14 thousandths, so they aren't really logarithmically spaced
either. I'm guessing at some point in the distant past there was a
good reason to make M be 0.295 inches, N be 0.302 inches, and O be
0.316 inches, and there was no need for a drill in the 0.309 inch
step, but I can't explain the reasoning there!

Tim.

--Well that's why the boring head was invented, yes? I've got a pair
of Criterion boring heads and they get a *lot* of use, heh.

--
"Steamboat Ed" Haas : Feeling like Bender in
Hacking the Trailing Edge! : a strong magnetic field...
www.nmpproducts.com
---Decks a-wash in a sea of words---

--And don't forget we're talking drillbits not reamers; i.e. drills,
particularly larger ones, tend to cut oversize holes...

--
"Steamboat Ed" Haas : Feeling like Bender in
Hacking the Trailing Edge! : a strong magnetic field...
www.nmpproducts.com
---Decks a-wash in a sea of words---

Maybe somewhere in this archive ?

http://books.google.com/books?q=drills+sizes

or this one,

http://www.archive.org/search.php?qu...iatype%3Atexts

Here's Wikipedia's take,

http://en.wikipedia.org/wiki/Drill_bit_sizes

To get a definitive answer, you might have to search back into the archives
of SAE, ANSI, ASTM or Mil-Specs

David Merrill



"Joe AutoDrill" wrote in message
news:fDLOi.1693$d2.1294@trnddc08...
Okay... I understand why fractional drill sizes and metric drill sizes
exist... They are common sense to me.

But... Why do number and letter drill sizes exist? Do they correspond to
a
wire size or some other standard?

Regards,
Joe Agro, Jr.
(800) 871-5022
01.908.542.0244
Automatic / Pneumatic Drills: http://www.AutoDrill.com
Multiple Spindle Drills: http://www.Multi-Drill.com

V8013-R

Hum - think it was said before - the numbers .....80...1 were wire drills.
Based on the needs of the wire industry - Music uses a lot of wire!
The letter drills are large. I suspect they are cabinet and machine need drills.

Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
TSRA, Life; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal.
NRA Second Amendment Task Force Charter Founder
IHMSA and NRA Metallic Silhouette maker & member.
http://lufkinced.com/


Joe AutoDrill wrote:
They fill in gaps that were left by the other sets.

Except the "E" drill, anyway.

Absolutely... But it doesn't explain why they are called out by numbers and
letters. It seems like someone created the idea and for some reason, a
bunch of people got together and supported the idea even though *someone*
had to be logical enough to see that a decimal based system would be easier
to track, understand, etc.

----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

According to Joe AutoDrill :
Okay... I understand why fractional drill sizes and metric drill sizes
exist... They are common sense to me.

But... Why do number and letter drill sizes exist? Do they correspond to a
wire size or some other standard?

Mostly, they fill in the gaps in the fractional sizes, and came
into being before the Metric drills became easier to get here.

The number sizes are at least related to wire sizes -- the more
times through the drawing dies, the smaller the physical size. Letter
size seem to go the opposite direction, but again fill in gaps in the
fractional sizes, so it is easier to make a hole the size you actually
*need* (from strength details, rather than just to match whatever screw
you have handy -- or to make a hole which allows a specified amount of
liquid or gas to pass per unit time).

Of course, the number sizes and letter sizes often come closer
to being the optimum size for a tap drill for common Imperial screw
sizes. Metric sizes tend to work out pretty well with just the metric
set in 0.1mm steps.

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

To get a definitive answer, you might have to search back into the
archives
of SAE, ANSI, ASTM or Mil-Specs


Or Whitworth.
I thread standard, metric, BSF, BSP, BSC, and Whitworth (BSW) at work. That
makes some systems tricky to set up. I work on and make parts for vintage
Lotus race cars, along with a few similar marques.
I don't know why there are 3 sets of drills, but I won't be caught without
them. It's a lot easier to set up a bunch of 1/8 rivets in #30 holes that in
1/8holes.
--
Stupendous Man,
Defender of Freedom, Advocate of Liberty

Ed Huntress wrote:

The numbered and lettered drills filled in the gaps between some awkward
fractional sizes, at the smaller end of the range.
But, letter "E" is .250" exactly - that doesn't fill in a gap.

Jon

According to Jon Elson :
Ed Huntress wrote:

The numbered and lettered drills filled in the gaps between some awkward
fractional sizes, at the smaller end of the range.
But, letter "E" is .250" exactly - that doesn't fill in a gap.

No -- it gives you a spare for the bit which probably gets used
the most. :-)

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

On Oct 11, 12:59 am, Jon Elson wrote:
Ed Huntress wrote:

The numbered and lettered drills filled in the gaps between some awkward
fractional sizes, at the smaller end of the range.

But, letter "E" is .250" exactly - that doesn't fill in a gap.

I would say that the letter drills just *happen* to fill in a number
of gaps, but not all the gaps, in the fractional sizes. I don't think
they were chosen to fill the gaps in some uniform planned way.

In fact the letter sizes have some rather odd gaps themselves. Look at
the range from L through S and - in Sesame Street style - find the gap
that doesn't look like the others:

size gap
L 0.290
M 0.295 0.005
N 0.302 0.007
O 0.316 0.014
P 0.323 0.007
Q 0.332 0.009
R 0.339 0.007
S 0.348 0.009

Now, repeat the same table with 19/64, 5/16, 21/64, 11/32 filled in:

size gap
L 0.290
M 0.295 0.005
19/64 0.297 0.002
N 0.302 0.005
5/16 0.312 0.010
O 0.316 0.004
P 0.323 0.007
21/64 0.328 0.005
Q 0.332 0.004
R 0.339 0.007
11/32 0.344 0.005
S 0.348 0.004

You see the letters don't evenly fill in the gaps at all.

I think the letter drill sizes were just somebody else's idea,
actually generally a good idea at a geometric progression in sizes
despite a few odd gaps like N to O, and were not at all an attempt to
fill gaps between common fractions (although they are today used that
way).

Tim.

"Joe AutoDrill" wrote in message
news:QoOOi.1702$d2.971@trnddc08...
I don't know about the letter series. I suspect that, as Ed says, they
were created to fill in awkward gaps in the decimal set.

Almost looks as if letter sizes were made to go beyond a #1 drill... In
other words in order from small to large: 4,3,2,1,A,B,C,D,...
--


Regards,
Joe Agro, Jr.


Some more research indicates that the "Stubs steel wire gage" extended into
letters that exactly match the letter drills. They indeed extend fairly
neatly from the number series. The step to number 1 from A is pretty darn
close to the step from number 2 to number 1.

This supports my contention that in this chicken and egg problem, the wire
probably came first.

I also suspect that, in terms of twist drills, the number and letter sets
may predate the fractional series. For the most of metalworking history, we
made things to fit, not to dimension.

When we started making thing to dimension, fractions based on a power of 2
were a natural choice. If you had an inch standard, and a small enough set
of dividers, you could lay out a 1/64" rule.

Measuring things in thousandths is a fairly recent concept, attributed to
Henry Ford.

You could make drill bits in 1/1000 increments but you would be making then
in smaller steps than they accurately drill holes.

The system we have now functions reasonably well. The only improvement a
decimal series of drills would have, is that they are easier to remember.
Heck, I have enough useless information rattling around in my brain. when I
need to know a drill size, I look it up on the chart.


Paul K. Dickman

On Thu, 11 Oct 2007 12:30:05 -0500 in rec.crafts.metalworking, "Paul K.
Dickman" wrote,
This supports my contention that in this chicken and egg problem, the wire
probably came first.

But the wire was made by drawing it through holes in a plate;
and those holes had to be drilled.

"David Harmon" wrote in message
...
On Thu, 11 Oct 2007 12:30:05 -0500 in rec.crafts.metalworking, "Paul K.
Dickman" wrote,
This supports my contention that in this chicken and egg problem, the wire
probably came first.

But the wire was made by drawing it through holes in a plate;
and those holes had to be drilled.

No, they're punched.

Paul K. Dickman

"There's a hole in the bucket, dear Liza."

But the wire was made by drawing it through holes in a plate;
and those holes had to be drilled.

No, they're punched.

That's assault... G

Regards,
Joe Agro, Jr.
(800) 871-5022
01.908.542.0244
Automatic / Pneumatic Drills: http://www.AutoDrill.com
Multiple Spindle Drills: http://www.Multi-Drill.com

V8013-R

On Oct 11, 10:30 am, "Paul K. Dickman"
wrote:


Some more research indicates that the "Stubs steel wire gage" extended into
letters that exactly match the letter drills. They indeed extend fairly
neatly from the number series. The step to number 1 from A is pretty darn
close to the step from number 2 to number 1.

While Stubs wire gage was undoubtedly the source, my
American Machinists' Handbook says of twist drill gage sizes
"rod sizes by this gage should not be confused with
Stubs' Steel Wire Gage sizes. The difference betwen the sizes
of corresponding numbers in the two gates ranges from about
..0005 to .004 inch, the Stubs sizes being the smaller..."

#30 drill is 0.1285, and #30 Stubs' steel wire is 0.127, for example.

I suspect the Stubs' gages were measured as an afterthought from
some salesman's sample kit, but the number drill sizes were
designated in absolute measure (thousandths of an inch)
for an industry that could handle precision measurement.