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Metric drill set types questions

Bill D

Diamond
Joined
Apr 1, 2004
Location
Modesto, CA USA
A general question about metric drill sets. In the USA we have fractional, number and letter size drills. There seems to be more consistancy about metric drill sizes. Are there different size ratios/patterns used for different set types. I am sure that below say. 1cm size jumps get smaller. I have never seen a micro size drill less then 1mm say.
Yes I know this is poorly worded.
I do know on many cars are the bolt heads are either odd or even mm. This makes it easy to eyeball what size wrench is needed. Do they make odd and even drill sets for metric or is that too limiting?
Bill D
 

eKretz

Diamond; Mod Squad
Joined
Mar 27, 2005
Location
Northwest Indiana, USA
A general question about metric drill sets. In the USA we have fractional, number and letter size drills. There seems to be more consistancy about metric drill sizes. Are there different size ratios/patterns used for different set types. I am sure that below say. 1cm size jumps get smaller. I have never seen a micro size drill less then 1mm say.
Yes I know this is poorly worded.
I do know on many cars are the bolt heads are either odd or even mm. This makes it easy to eyeball what size wrench is needed. Do they make odd and even drill sets for metric or is that too limiting?
Bill D

I don't know about general availability, but I have a Precision Twist Drill metric set that IIRC is 1 - 13mm by 0.5mm increments. Not sure what else might be commonly available in set form. Some of the tap drill sizes are outside that set's purview; requiring sizes like x. 6mm etc.
 

Benta

Hot Rolled
Joined
Mar 24, 2005
Location
Germany
Metric drills are completely consistent with regard to size:
They are always specified in mm.
Standard sizes are 1, 2, 3, 4... mm. Decimal fraction sizes are available in 0.1 mm steps from special tool stores, eg, 7.1 mm.
Exceptions are the drills used for threading: 2.5, 3.3, 4.2, 6.8, 8.5, 10.2 mm. Those are pretty standard.
Sub 1 mm drill are mostly for PCB drilling and watchmaking, you can get pretty much anything from 0.3 mm and up.
 

Benta

Hot Rolled
Joined
Mar 24, 2005
Location
Germany
Concerning bolt head sizes:
European cars normally use metric bolts with hex heads with odd size (11, 13, 17, 19 mm etc.)
Japanese cars use metric JIS bolts that have even head sizes (10, 12, 14, 18 mm etc.)
Mind you, that's just a rule-of-thumb, there's nothing fixed about it.
 

EPAIII

Diamond
Joined
Nov 23, 2003
Location
Beaumont, TX, USA
I have many sets of English (inch) sized drill bits as well as a couple of metric sets.

On the English (inch) sets the sequences vary. Fractional bits come in 1/64" steps or 0.0156". That is probably the best choice of all the sets. Number and letter sized bits seem to have NO real sequence. Some adjacent sizes in the number sizes are only 0.0002" (no error) apart while other, number sizes are as much as 0.0065" apart. And there is absolutely no discernible pattern. I am sure there is a reason for this awful sequence, but it is going to require a long, long explanation if you include all the details.

In the metric bits, one of my sets is in 1 mm steps and the other is in 0.5 mm steps. While this is a lot better than the number and letter sizes, it is by no means ideal. I checked and saw that metric bits are available in 0.1mm steps. That seems to cover the range from 1 or 2mm up to, perhaps 20mm fairly well. But I have not seen any index boxes for such a collection. Contrast this to the 101 bit sets of letter, number, and fraction bits which are fairly common.

There are two main types of sequence that seem to make sense here: arithmetic (constant difference/added amount) and logarithmic (constant factor - multiple). Each of these has it's advantages and drawbacks.

The arithmetic or constant difference sequence may be good at some sizes, but no matter how well you choose the starting point, it will always become difficult to follow at both larger and smaller ones. For instance, the 1/64" sequence of fractional sized bits may be quite good between 3/16" and 1" but comes to an abrupt end at the 1/64" size as it would be followed by 0". And who ever saw, even in catalogs, a 3 1/64" bit? Such a small size increase above 3" is never needed in most shops and almost useless. Many fractional bit sets may start with 1/64" increments at the low end, but switch to 1/32" or even 1/16" around the 1/4" size and end with 7/8" followed by 1" instead of 15/64". That is the nature of arithmetic sequences. When applied to practical matters, they fail at both ends (high and low).

On the other hand, a logarithmic sequence is difficult at almost all values. Consider: for both English and metric sizes a 0.5X or 2X (same thing, just different directions) jump would easily leave too much of a gap. 1/16", 1/8", 1/4", 1/2", 1", etc. or 1mm, 2mm, 4mm, 8mm, 16mm, etc. are both just too widely spaced to be of much use. A smaller multiple would be clearly needed. But WHAT would that be? A factor of 4/3X that starts at a nice, whole number like 1, would result in a sequence that almost never returns to whole numbers. 5/4X also rapidly goes into long decimal places at the low end: 1, 0.8, 0.64, 0.512, 0.4096, 0.32768, etc. 1mm, 0.8mm, may be OK, but 0,512mm or 0.32768mm? This is bad in two ways, horrible decimal values and gaps that are still too large. Who would want that? Clearly a smaller multiplier/divisor would be needed. BUT WHAT.

One place where a logarithmic ratio has been implemented with success is in the electronics field. Things like resistor values follow such a sequence. There are several logarithmic sequences that are used. And they actually have names: E6, E12, E24, E48, E96, etc. They are based on using a common factor (a logarithmic ratio) between sizes. The E12 is, perhaps the most common. Each value is 1.12X the previous one and it's values are 1, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2, and 10. That comprises one decade of values. Other decades are simply multiplies of 10 of those values" 10, 12, 15, etc. and 100, 120, 150, etc. and 0.1, 0.12, 0.15, etc. So the sequence is easily defined by just the numbers for a single decade. The numbers above are not the exact values given by the power equation that actually defines the sequence. They are rounded to the nearest two digits and that makes them a lot more acceptable to the users.

The other Exx sequences are sub-sets or super-sets of the E12. So the E6 sequence (a sub-set of E12) has every other value of the E12 sequence: 1, 1.5, 2.2, 3.3, 4.7, 6.8, and 10. And the E24 sequence, which is used for 5% resistor values, is: 1, 1.1, 1.2, 1.3 1.5, 1.6, 1.8, 2.0, 2.2, 2.4, 2.7, 3.0, 3.3, 3.6 3.9, 4.3, 4.7, 5.1, 5.6, 6.2, 6.8, 7.5, 8.2, 9.1, and 10. Again, the values are rounded to two places. In both the E12 and E24 sequences the rounding errors produce differences from the nominal values which are evenly spaced by factors of 1.12115... and 1.10069... respectively.

As a clue to how these numbers work in practice, you may notice that the E12 values are approximately at 12% internals while the E24 values are about 5% apart. Not surprisingly, the E12 values are called the 10% series and the E24 the 5% series. These values, when combined with the 10% or 5% specification, just about overlap. A 5%, E24 resistor that is marked 2.2 Ohms, +/-5% will have a value between 2.1 and 2.3 Ohms. The 2.0 Ohm, 5% ones will be between 1.9 and 2.1 Ohms and the 2.4 Ohm, 5% one between 2.3 and 2.5 Ohms. All of these ranges are about +/-5%. The practical result, at least for a manufacturer of resistors, is that any, EVERY resistor that comes off the manufacturing line can be sorted into one or another of the standard values in that (actually in any) standard sequence. There is zero waste as every item made is within +/-5% of one of the values. Or +/- 10% for the E12 values, etc. No matter how bad their equipment, materials, or methods they CAN NOT make a resistor that can't be accurately marked with one of the values. Smart, right?

But E6 is a very coarse sequence and even E12 would be too coarse for drill bit sizes. We would have to step up to an E24 or E48 to get a reasonable one. The E24 sequence, applied to metric drill bit sizes might be: 1, 1.1, 1.2, 1.3 1.5, 1.6, 1.8, 2.0, 2.2, 2.4, 2.7, 3.0, 3.3, 3.6 3.9, 4.3, 4.7, 5.1, 5.6, 6.2, 6.8, 7.5, 8.2, 9.1, and 10. Then 11, 12, etc. Probably still a bit too coarse for machinist use. So E48 may be the smallest sequence to consider here and that one is going to have three digit values. And if you look at a table of them, then you will see that those numbers do not have anything nice about them.

Also 10%, 5%, and probably 2% (the E48 sequence is referred to as 2%) values are not going to meet the accuracy needs of machinists. A 5mm bit +/- 0.1mm (+/- 0.002") is worse than even those routinely found at hardware store or home supply places.

I fear that no sequence that is based on any single, simple rule is going to meet our needs. But we can wish.

 

JDM-oldschool

Plastic
Joined
Jun 2, 2022
Standard metric sets usually come from 1-13mm in 0,5mm steps for steel drilling. Wood drills usually in 1mm steps, except the really expensive ones.
For screws and bolts it is in 0,5mm steps up to 4mm, and 2mm steps above the 5mm size.

For sets I did it that way: I bought the cheapest sets that I could find, just to have a base to start from. And after the drills I use fail I replace that single one with a really good one (and two for spare). Nothing worse than having to rush to the store for a single drilll or other small bit.
 

JDM-oldschool

Plastic
Joined
Jun 2, 2022
Oh you are right, there is a small difference I guess, maybe a bit surreal for me (almost like the imperial system). I have at least three shops with high quality tools in walking distance and another five where I can get cheap stuff...

On the opposite side, small machine shops are almost nonexistend here anymore. Some switched to high quality cnc stuff and the rest is almost gone.
 

boslab

Titanium
Joined
Jan 6, 2007
Location
wales.uk
I have 2, a 0.5 mm increments and a fine 0.1 mm increments set , rough and ready and bit exacting as it were, though I wish there was a long series 0.1 in an index but I can’t find one
Mark
 

JDM-oldschool

Plastic
Joined
Jun 2, 2022
Lovely! Where ARE you in . Verzeihung... Wo bist du in Österreich?

Yah. We buy from the Chinese. You lot buy from the Anatolian Turks?

Had a client ages ago in Schweiz claiming "100% Swiss made".
Then telling customers the shipping delays were because a ship with their product had sunk in a storm.

On what? The Bodensee?
No. Agean.

The "100% Swiss" parts went down enroute from a precison die-caster in Turkey!

I am from Graz, and work at Magna there, former Puchwerke. Great stuff has been engineered here in the past!

A good part of the suppliers I work with get their injection cast molds from China in the meantime.
In one case they had to make two sets of tools, one for the european plant and one for the Chinese plant.
Highly accurate high gloss polished headlamp reflector tools.
The one for Europe was made in Portugal and it took 4 loops to get the reflectors in tolerance.
The chinese one was made there and was within tolerances from the beginning.

If you have a tight quality control then you can get really good stuff from them.

But everytime I see something that is branded "made in Germany" that is clearly not how it looks, i say that there must be a town in china that is called Germany :)
 

NewGunPlumber

Aluminum
Joined
Dec 18, 2019
Standard set would be 1 to 13mm in .5mm increments. I have a couple nice sets of Dorma drills that are .1mm increments up to 10mm.
 

Georgineer

Hot Rolled
Joined
Dec 27, 2008
Location
Portsmouth, England
It used to be said that they renamed a place in Japan as Scotland, so they could label their whisky "Bottled in Scotland". I've never discovered if it's true.

Back to the drills, in the UK most sets are in 0.5 mm increments, but if you go to a proper tool shop you can get them in 0.1 mm increments. I believe they are available in 0.05 mm increments, but I guess you would pay extra for that. My commercial drill stand (1.0 to 6.0 mm) has places for 1.25, 1.75 etc as well as the regular steps.

George
 

L Vanice

Diamond
Joined
Feb 8, 2006
Location
Fort Wayne, IN
... But every time I see something that is branded "made in Germany" that is clearly not how it looks, i say that there must be a town in china that is called Germany :)

Perhaps that explains where this fancy Leinen-style bench vise came from. I never did figure out how to get that right hand bench mounting bolt into it's hole. (Can't get the jaw clamping screw out of the way.)

Larry

MFV5 vise 1.JPG Vise base
MFV5 vise 2.JPG Cast into the base
MFV5 vise 3.JPG The shipping box
 

Bill D

Diamond
Joined
Apr 1, 2004
Location
Modesto, CA USA
Lots of informative answers. Thanks for all the info. it makes me feel better to know there are several standard jump increments and they change around as the bits get too big or too small.
EPA great explanation about resistors and the drills as well. I knew there was a method to their madness.
I have never realy used metric except for the few times I needed to drill a clearance hole. I have used a tap to clean out threaded holes I do not think I have ever tapped a blank hole into metric threads.
My understanding is they invented the drills first then figured out the shank size for a nice close fit into the hole.They called that diameter the correct major diameter for that bolt size. Hence it is a m10 bolt not a 10mm bolt. It is a diameter that is a nice slip fit into a 10mm hole.
Bill D
 

Benta

Hot Rolled
Joined
Mar 24, 2005
Location
Germany
Sure they do. They are tap drill sizes for metric threads.
Which threads, please? The 1.25 mm doesn't fit any metric size, neither coarse nor fine. 1.75 mm fits M2 fine, which is an unusual size.
I live in "metric-land" and am not hampered by numbers, fractions or letters for drills.
 

Bill D

Diamond
Joined
Apr 1, 2004
Location
Modesto, CA USA
I have noticed in the big box stores they sell carded taps and a tap drill to match. Often the tap drill is not correct it is just the closest fraction size drill. I have never seen a letter or number drill substituted for a fraction one in such a set. Not that I have really looked very hard.
Bill D
 

eKretz

Diamond; Mod Squad
Joined
Mar 27, 2005
Location
Northwest Indiana, USA
Which threads, please? The 1.25 mm doesn't fit any metric size, neither coarse nor fine. 1.75 mm fits M2 fine, which is an unusual size.
I live in "metric-land" and am not hampered by numbers, fractions or letters for drills.

1.25mm is the recommend tap drill for M1.6×.35 - unusual or not, it is needed when it's needed. I generally substitute a close size from my inch set when I can get away with it.
 

NewGunPlumber

Aluminum
Joined
Dec 18, 2019
Lots of informative answers. Thanks for all the info. it makes me feel better to know there are several standard jump increments and they change around as the bits get too big or too small.
EPA great explanation about resistors and the drills as well. I knew there was a method to their madness.
I have never realy used metric except for the few times I needed to drill a clearance hole. I have used a tap to clean out threaded holes I do not think I have ever tapped a blank hole into metric threads.
My understanding is they invented the drills first then figured out the shank size for a nice close fit into the hole.They called that diameter the correct major diameter for that bolt size. Hence it is a m10 bolt not a 10mm bolt. It is a diameter that is a nice slip fit into a 10mm hole.
Bill D
Waaaaattttt? A 10mm bolt is 10mm major diameter. Just like a 1" bolt is 1"

Somewhat difference is metric can be simple. 10mm bolt has a 1.5mm pitch so you use a 8.5mm tapping drill. Etc etc etc


Metric is just like imperial but uses decimals instead of fractions.
 








 
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