Wire size drills

[PStechPaul]

See: https://en.wikipedia.org/wiki/American_wire_gauge

Wire sizes and the corresponding numbered drill sizes make sense because a very wide range of commonly used sizes can be defined with just a single or two digit number. A #36 drill is defined as 0.005" or 5 mils. Every three wire sizes is double or half the cross-sectional area, which is useful for determining wire size according to current carrying capacity. So a #10 AWG is good for 30 amps, #13 is 15 amps, and #16 is 7.5 amps.

For wire, each increment of size corresponds to about 12% difference in diameter, For drills, each increment of size corresponds to about 1.5% to 5% difference in diameter, which is useful for making holes just a bit larger or smaller. It is not so obvious what the next standard metric size might be, although unlike number drill sizes, there is a formula.

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

From 0.2 through 0.98 mm, sizes are defined as follows, where N is an integer from 2 through 9:

• N · 0.1 mm
• N · 0.1 + 0.02 mm
• N · 0.1 + 0.05 mm
• N · 0.1 + 0.08 mm

From 1.0 through 2.95 mm, sizes are defined as follows, where N is an integer from 10 through 29:

• N · 0.1 mm
• N · 0.1 + 0.05 mm

From 3.0 through 13.9 mm, sizes are defined as follows, where N is an integer from 30 through 139:

• N · 0.1 mm

From 14.0 through 25.0 mm, sizes are defined as follows, where M is an integer from 14 through 25:

• M · 1 mm
• M · 1 + 0.25 mm
• M · 1 + 0.5 mm
• M · 1 + 0.75 mm

[Georgineer]

Purely by chance I came across this today, in Machinery's Encyclopedia published in 1917:

The differences in the gages for small diameter twist drills and steel wire are a constant source of trouble to those who have to deal with drills and steel wire; and gage numbers mean nothing except if the name of the gage employed is specified. Some drill manufacturers are discouraging the use of gage sizes and are asking that the sizes of drills ordered be denoted in decimals of an inch. There are three well-known standards for twist drills and steel wire that are used at the present time. These are the Stubs steel wire gage, the gage used by the Standard Tool Co. and the gage used by other leading manufacturers, such as the Morse Twist Drill & Machine Co. and the Brown and Sharpe Mfg Co. The latter has been termed, in the accompanying tables, "the manufacturers' standard".

The Stubs steel wire gage is used for measuring steel wire and drill rod, but it is not used as much in the United States at the present time as in the past. The gage used by the Standard Tool Co. was originally adopted for drill sizes in the United States, but other manufacturers changed the numbers corresponding to certain sizes, while the Standard Tool Co. retained the original numbers, but interpolated half sizes in order to agree as to the actual diameters of drills furnished by other manufacturers. The Standard Tool Co.'s gage agrees with the "manufacturers' standard" for the sizes from Nos. 1 to 60, inclusive, but does not agree with the Stubs steel wire gage. From Nos. 61 to 80, inclusive, it agrees with the Stubs gage, half sizes being omitted. It also agrees with the manufacturers' standard, as far as the diameters used are concerned, but the numbers corresponding to given diameters are different.

As has been remarked elsewhere, the beauty of standards is that there are so many to choose from. I presume that what the encylopedia called the "manufacturers' standard" is the one that finally won. This isn't a problem that could have arisen with metric and fractional inch drills.

For the record, I keep number and letter drills as well as fractional inch and metric (in 0.1 mm increments up to 6 mm, 0.5 mm above that) so as not to be caught out.

George

[mixdenny]

I have a large collection of measuring rules and among them are the ones called timber rules. In principal they are straightforward. The thin, flexible, hickory rule has a hook or projection on one end and a handle on the other. You hook the far side of the butt of the log with the hook and look where the diameter falls. You can even do it while the log is floating and you are standing on it. It will have tables for various standard lengths of timber, 12 feet, 16 feet, etc. Run down the table at the log's diameter and it will read out how many board feet of lumber that can be cut from the log.

Except... everyone had their own set of calculations to calibrate the rule! Different parts of the country had their own favorite scale depending on the tree species and how fast it tapered. Some allowed for loss from branches, others required limbless trees. Some favored the buyer, some the seller, I imagine there were a few arguments during the sale with the two parties waving their respective timber rules at each other! Common names of these 'gauges' were Scribner, Doyle, the B-10, Southern Pine, the International, it goes on and on.

And you had to estimate the quality of the log as it floated, so you didn't want too many branches showing. Unscrupulous sellers would pound a couple of spikes in the bad side of a tree so it rotated underwater.

This is our measuring heritage, from King George's foot to how many round balls fit into the bore of a shotgun. Damn the metric system, full speed ahead!!

Dennis

[PStechPaul]

Something else to consider about drill sizes is that the hole produced can be -0.001" to +0.005" of stated size. And the diameter of the shank is not always the same as the size. The size of the drilled hole can vary due to inexact grinding of the cutting edges and chisel point, as well as expansion from heating and maybe some enlargement due to the drill untwisting along the flutes due to cutting forces. And while a drill lingers in the hole, some cutting will occur. There will also be some effect from the material being drilled.

[old mart]

In the UK number and letter drill sizes are pretty well obsolete. Googling them should get results though.

[Illinoyance]

I recall reading somewhere that the wire gauge numbers equaled the number of times the wire had to be drawn through a die to achieve that diameter.

[Rosco-P]

I recall reading somewhere that the wire gauge numbers equaled the number of times the wire had to be drawn through a die to achieve that diameter.

Exerted from: https://en.wikipedia.org/wiki/Wire_gauge

The origin of the Birmingham W.G. is obscure. The numbers of wire were in common use earlier than 1735. It is believed that they originally were based on the series of drawn wires, No. 1 being the original rod, and succeeding numbers corresponding with each draw, so that No. 10, for example, would have passed ten times through the draw plate.

The first attempt to adopt a geometrical system was made by Messrs Brown & Sharpe in 1855. They established a regular progression of thirty-nine steps between the English sizes, No. 0000 (460 mils or about 12 mm) and No. 36 (5 mils or about 0.13 mm). Each diameter was multiplied by 0.890526 to give the next lower size. This is now the American wire gauge (AWG), and is used to a considerable extent in the United States.

[CCWKen]

And those tapered square shank drills were the most awful invention ever. Who can use them now without cutting off the end?

But I gotta say, there were some smart people back then. I have a self-advancing portable bit-brace attachment from, I think, the 1800s. It has a chain that wraps around logs or metal stock, I'm guessing. All you do is turn the top shank and a drill bit will advance. Could be the starting idea for the Cole Drill.

[Paul Alciatore]

Who can use them without cutting the taper off? Well, all of us who have a lathe with a Morse taper in the tail stock.

And those tapered square shank drills were the most awful invention ever. Who can use them now without cutting off the end?

But I gotta say, there were some smart people back then. I have a self-advancing portable bit-brace attachment from, I think, the 1800s. It has a chain that wraps around logs or metal stock, I'm guessing. All you do is turn the top shank and a drill bit will advance. Could be the starting idea for the Cole Drill.

[Paul Alciatore]

Several above have tried to say the number system for drill sizes makes sense. But have they actually looked at the sequence of sizes for those numbered drills? I have and they jump around. One increase in the number may represent 7 or 10 thousandths decrease in the wire/drill size and the very next one may represent only 2 or 3. The sizes do not progress in a uniform manner. Now WHY is that? Give me the rational explanation for it.

[old mart]

I don't think a tapered "square" shank drill will fit very well in a morse taper.

[CCWKen]

Who can use them without cutting the taper off? Well, all of us who have a lathe with a Morse taper in the tail stock.

Your tail stock Morse taper is square?

[Rosco-P]

Something else to consider about drill sizes (editied as irrelevant to quote)......... And the diameter of the shank is not always the same as the size. The size of the drilled hole can vary due to inexact grinding of the cutting edges and chisel point, as well as expansion from heating and maybe some enlargement due to the drill untwisting along the flutes due to cutting forces. And while a drill lingers in the hole, some cutting will occur. There will also be some effect from the material being drilled.

We're discussing wire size or number drills here. Were did you get the idea that the diameter of the shank is not the same, as the size (of the bit)?

[Rosco-P]

And those tapered square shank drills were the most awful invention ever. Who can use them now without cutting off the end?

But I gotta say, there were some smart people back then. I have a self-advancing portable bit-brace attachment from, I think, the 1800s. It has a chain that wraps around logs or metal stock, I'm guessing. All you do is turn the top shank and a drill bit will advance. Could be the starting idea for the Cole Drill.

That would probably be a timber drill. Similar mechanical arrangement used in the Champion (and other) post mounted Blacksmith's drill presses.

[mklotz]

Several above have tried to say the number system for drill sizes makes sense. But have they actually looked at the sequence of sizes for those numbered drills? I have and they jump around. One increase in the number may represent 7 or 10 thousandths decrease in the wire/drill size and the very next one may represent only 2 or 3. The sizes do not progress in a uniform manner. Now WHY is that? Give me the rational explanation for it.

A long time ago I attempted to fit a polynomial to the number drill progression of sizes. I could never get a simple fit (ie less than four terms) that gave satisfactory accuracy. However, in the process I discovered that the progression agreed most closely with the Stubb's steel wire gage progression. My guess is that is where we got what we use in the USA today. Be careful; among the plethora of gages from which to choose (another problem with many nomenclature systems) there is a Stubb's IRON wire gage.

I also noticed, as you point out, that there were small, completely unexplained, variations of the number drill sizes from the Stubb's wire gage.

The idea that any of these idiotic nomenclatures derived from measures of convenience make sense or should be preserved as part of our mechanical heritage is pure bat guano. Humans make enough mistakes using rational systems; there is no need to introduce purposeful
confusion.