Clueless on drill bit sizes

[Scott Hemsley]

Ok, I'll admit it, but when it comes to determining drill bit sizes for a pin vise without having a selection of bits & the part to be drilled in front of me ... I'm lost.  So when it comes to ordering said bits, online, I'm totally in the dark.  Therefore, I'm asking the community at large & specifically those who have an unbuilt Airfix Dakota in their stash, the following question: 

 

I've got a set of Res-Kit wheels for the Dakota, but I have to enlarge the hole for the 'axle' to fit into.  Can anyone tell me the number of the drill bit I would need when measured (held?) against the kit wheel.  The largest bit in the set I currently have available is noticeably smaller than required.

 

Scott

[Tbolt]

Checking my kit a 1.5mm drill bit fits in the kit wheels nicely, though when drilling a hole they tend to end up a little bit larger so it's always best to use a slightly smaller drill to start with anyway and then go up if needed. The axle measures out at 1.43mm so I would start with a 1.3mm drill then go up from there. It's best to get a set with a good range of bits, one of the common ones go from 0.3mm to 1.6mm and a few larger drills as well are handy as well.

[fishplanebeer]

If you invest in a set of modeler's drill bits, not excessively expensive given that you will use them for years to come, then it's just a simple case of trial and error, and as Tbolt says, start off with one that is perhaps a wee bit too small and go from there. You can always make things bigger but it is 'difficult' to make things smaller.

 

If you fiddle around with a bit that is too small it is quite easy to enlarge the hole a wee bit and this is always the method I use to get parts to fit correctly and much safer than going up a size.

 

Regards

Colin.

Edited June 17, 2022 by fishplanebeer

[Scott Hemsley]

Thanks guys.  At least I now know what I'm looking for if I have to buy an individual drill bit,  At the wife's suggestion (since I probably won't get to a LHS for a while), ordering a 2nd, but more complete drill set may be the way to go. There's a few nice sets on Amazon.ca ...

 

Scott

[dnl42]

Can you measure the kit's axle diameter? There are many sites showing drill bit sizes, but this is one Google found for me.

 

HTH

-- 

dnl

[Tail-Dragon]

37 minutes ago, dnl42 said:

Can you measure the kit's axle diameter? There are many sites showing drill bit sizes, but this is one Google found for me.

 

HTH

-- 

dnl

That's an excellent drill sizing chart that dn142 posted above. I would suggest downloading the PDF version, printing it out, pasting on your modelling wall, and investing in an inexpensive digital caliper. (Amazon.ca has them for as low as  $13 delivered!)

Digital calipers

I use them for many, many things. 

 

Colin

Edited June 19, 2022 by Tail-Dragon

[Jochen Barett]

18 hours ago, dnl42 said:

Can you measure the kit's axle diameter? There are many sites showing drill bit sizes, but this is one Google found for me.

 

HTH

-- 

dnl

Great!

 

I wonder who invented the "number size", how he/she came up with it, what made the person do it and if the person died in the mental asylum or was cured some day.

[FinnAndersen]

37 minutes ago, Jochen Barett said:

Great!

 

I wonder who invented the "number size", how he/she came up with it, what made the person do it and if the person died in the mental asylum or was cured some day.

Well, I was equally clueless about the OP's question until the conversion table was mentioned. Then I just shook my head and wondered who on earth could come up with such an incredibly stupid idea. 

 

/Finn

[bjohns5]

56 minutes ago, Jochen Barett said:

Great!

 

I wonder who invented the "number size", how he/she came up with it, what made the person do it and if the person died in the mental asylum or was cured some day.

The number size drill bits correspond to the American Wire Gauge (AWG) sizing chart for wire diameters. That's why you often see them referred to as "wire gauge" bits.
https://en.wikipedia.org/wiki/American_wire_gauge

Edited June 19, 2022 by bjohns5

[Scott Hemsley]

Quote

dnl42 said: Can you measure the kit's axle diameter? There are many sites showing drill bit sizes, but this is one Google found for me.

Unfortunately, measuring anything at this time to the accuracy that determining the size of drill bits demands, is not possible.  However, I have downloaded that chart you linked ... thanks for providing that.

 

Quote

Tail-Dragon said:  would suggest downloading the PDF version, printing it out, pasting on your modelling wall, and investing in an inexpensive digital caliper. (Amazon.ca has them for as low as  $13 delivered!)

 

That's something worth considering.  Thanks for pointing it out to me.  

 

Thanks again, guys.  Just proves you always learn something on BM.

 

Scott

[Jochen Barett]

2 hours ago, bjohns5 said:

The number size drill bits correspond to the American Wire Gauge (AWG) sizing chart for wire diameters. That's why you often see them referred to as "wire gauge" bits.
https://en.wikipedia.org/wiki/American_wire_gauge

 

Yes, and I love it for the sake of simplicity and the absence of natural beauty in the system!

 

"By definition, Nr. 36 AWG is 0.005 inches in diameter, and Nr. 0000 is 0.46 inches in diameter, or nearly half-an-inch. The ratio of these diameters is 1:92, and there are 40  gauge sizes from the smallest Nr. 36 AWG to the largest Nr. 0000AWG , or 39 steps. Each successive gauge number decreases the wire diameter by a constant factor. Any two neighboring gauges (e.g., AWG A and AWG B ) have diameters whose ratio (dia. B ÷ dia. A) is 92 39 ≈ 1.12293 , {\displaystyle {\sqrt[{39}]{92}}\approx 1.12293\;,} while for gauges two steps apart (e.g., AWG A, AWG B, and AWG C), the ratio of the C to A is about (1.12293)² ≈ 1.26098 .

The diameter of an AWG wire is determined according to the following formula:

d n = 0.005 inch × 92 ( 36 − n ) / 39 = 0.127 mm × 92 ( 36 − n ) / 39   . {\displaystyle d_{n}=0.005\;{\text{inch}}\times 92^{(36-n)/39}=0.127\;{\text{mm}}\times 92^{(36-n)/39}~.}

(where n is the AWG size for gauges from 36 to 0, n = −1 for Nr. 00, n = −2 for AWG 000, and n = −3 for AWG 0000. See rule below.[a])

or equivalently:

d n =   e ( − 1.12436 − 0.11594 n ) inch =   e ( 2.1104 − 0.11594 n ) mm =   ( 0.324860  inches  ) ( 0.8905287 ) n   =   ( 8.25154  mm  ) ( 0.8905287 ) n   . {\displaystyle {\begin{aligned}d_{n}&=~e^{(-1.12436-0.11594n)}\,{\text{inch}}&&=~e^{(2.1104-0.11594n)}\,{\text{mm}}\\&=~\left(0.324860{\text{ inches }}\right)\,\left(0.8905287\right)^{n}~&&=~\left(8.25154{\text{ mm }}\right)\,\left(0.8905287\right)^{n}~.\end{aligned}}}

The gauge number can be calculated from the diameter using the following formulas:[c]

Step 1

Calculate the ratio R {\displaystyle \,{\mathcal {R}}\,} of the wire's diameter d {\displaystyle \,d\,} to the standard gauge (AWG #36 )

R = d  [inch]  0.005  inch  = d  [mm]  0.127  mm  {\displaystyle {\mathcal {R}}={\frac {\;d_{\text{ [inch] }}\;}{0.005\,{\text{ inch }}}}={\frac {d_{\text{ [mm] }}}{\;0.127\,{\text{ mm }}\;}}}

where the middle expression with d [inch] {\displaystyle \,d_{\text{[inch]}}\,} is used if d {\displaystyle \,d\,} is measured in inches, and the right-hand expression with d [ m m ] {\displaystyle \,d_{\mathrm {[mm]} }\,} when d {\displaystyle \,d\,} is measured in millimeters.[d]

 

Step 2

Calculate the American wire gauge number n using any convenient logarithm; pick any one of the following expressions in the last two columns of formulas to calculate n; notice that they differ in the choice of base of the logarithm, but otherwise are identical:

n = − 39 log 92 ⁡ ( R ) + 36 = − 39 log 10 ⁡ ( R ) log 10 ⁡ ( 92 ) + 36 = − 39 ln ⁡ ( R ) ln ⁡ ( 92 ) + 36 = − 39 log e ⁡ ( R ) log e ⁡ ( 92 ) + 36 = − 39 log 2 ⁡ ( R ) log 2 ⁡ ( 92 ) + 36 = − 39   l o g B ( R ) log B ⁡ ( 92 ) + 36   , {\displaystyle {\begin{aligned}n=\;-39\log _{92}({\mathcal {R}})+36\;&=\;-39{\frac {\log _{10}({\mathcal {R}})}{\;\log _{10}(92)\;}}\,+36\;&&=\;-39{\frac {\ln({\mathcal {R}})}{\;\ln(92)\;}}\;\;\,+36\;\\\\&=\;-39{\frac {\log _{e}({\mathcal {R}})}{\;\log _{e}(92)\;}}\;+36\;&&=\;-39{\frac {\log _{2}({\mathcal {R}})}{\;\log _{2}(92)\;}}+36\;\\\\&=\;-39{\frac {\ log_{B}({\mathcal {R}})}{\;\log _{B}(92)\;}}+36~,\\\end{aligned}}}

In general, the calculation can be done using any base B strictly greater than zero.[e]

and the cross-section area is

A n = π 4 d n 2 ≈ ( 0.000019635  inch  ) 2 × 92 ( 36 − n ) / 19.5 ≈ ( 0.012668  mm  ) 2 × 92 ( 36 − n ) / 19.5 . {\displaystyle A_{n}={\frac {\pi }{4}}d_{n}^{2}\approx \left(\,0.000019635{\text{ inch }}\,\right)^{2}\times 92^{(36-n)/19.5}\approx \left(\,0.012668{\text{ mm }}\,\right)^{2}\times 92^{(36-n)/19.5}\;.}

The standard ASTM B258-02 defines the ratio between successive sizes to be the 39th root of 92, or approximately 1.1229322.[3] ASTM B258-02 also dictates that wire diameters should be tabulated with no more than 4 significant figures, with a resolution of no more than 0.0001 inches (0.1 mils) for wires larger than Nr. 44 AWG, and 0.00001 inches (0.01 mils) for wires Nr. 45 AWG and smaller.

Very fat wires have gauge` sizes denoted by multiple zeros – 0, 00, 000, and 0000 – the more zeros, the larger the wire, starting with AWG 0. The two notations overlap when the 2 step formula for n , above, produces zero. In that case the gauge number n is zero, it's taken as-is. If n is a negative number, the gauge number is notated by multiple zeros, up to just under a half-inch; beyond that point, the “wire” may instead considered a copper bar or rod.[a] The gauge can be denoted either using the long form with several zeros or the short form z "/0" called gauge "number of zeros/0" notation. For example 4/0 is short for AWG 0000. For an z /0 AWGwire, use the number of zeros z = − n + 1    for    n < 0 , {\displaystyle \;z=-n+1~{\mathsf {\text{ for }}}~n<0\;,}   and similarly   n = − z + 1    for    z > 0   . {\displaystyle \;n=-z+1~{\mathsf {\text{ for }}}~z>0~.} in the above formulas. For instance, for AWG 0000 or 4/0, use n = − 4 + 1 = − 3   . {\displaystyle \,n=-4+1=-3~.}"

and

"Rules of thumb

The sixth power of 39√92 is very close to 2,[4] which leads to the following rules of thumb:

When the cross-sectional area of a wire is doubled, the AWG will decrease by 3 . (E.g. two AWG Nr. 14 wires have about the same cross-sectional area as a single AWG nr. 11 wire.) This doubles the conductance."

 

It is so much easier than the metric system, but there is next to no reference to the magical number 12 in the system and it would have been so much nicer to have a system corrseponding to shot guns https://en.wikipedia.org/wiki/Gauge_(firearms)

 

Something like 12 x 12 divided by the number of 1 inch long drill bits needed to weigh as much as a lead ball that fits into a 1/2 inch (outer diameter) pipe ...

 

[FinnAndersen]

6 hours ago, Jochen Barett said:

"By definition, Nr. 36 AWG is 0.005 inches in diameter, and Nr. 0000 is 0.46 inches in diameter, or nearly half-an-inch. The ratio of these diameters is 1:92, and there are 40  gauge sizes from the smallest Nr. 36 AWG to the largest Nr. 0000AWG , or 39 steps. Each successive gauge number decreases the wire diameter by a constant factor. Any two neighboring gauges (e.g., AWG A and AWG B ) have diameters whose ratio (dia. B ÷ dia. A) is 92 39 ≈ 1.12293 , {\displaystyle {\sqrt[{39}]{92}}\approx 1.12293\;,} while for gauges two steps apart (e.g., AWG A, AWG B, and AWG C), the ratio of the C to A is about (1.12293)² ≈ 1.26098 .

Let me see: With the metric system, you eyeball the diameter of the axle and get the drill bit you believe fits. If it does not fit you take the next larger or smaller bit until you have a match and can start drilling. Of course it's easier to measure the axle with a caliper and instantly get the right bit, but that's almost cheating, so a no-go. The same goes for the american system, until you want to measure, because then you need the chart, unless of course you have cheated by memorising the entire chart. Hey, wait a bit, why dont we invent a digital caliper that has the chart built into it? That way we have a tool that is foolproof and can be used for absolutely nothing else.

 

I was trained as a shipbuilding engineer and thankful that I did not have to deal with such convoluted thinking. It's complicated enough as it is (or was until computers), building ships and other stuff. 

 

/Finn

 

 

[Jochen Barett]

For "engineering" the imperial system seems to be a nightmare or a special delight for masochistic people ( https://www.mindbodygreen.com/0-22868/10-ways-to-spot-a-masochist.html ).

 

On the other hand for coach building and wood working it seems to be extremely well suited (maybe even better than metric!). Check this man's work: https://www.youtube.com/c/EngelsCoachShop1/videos

 

(still waiting for that caliper with a large alphanumeric display "just shy of three sixteenth of an Inch" and for an explanation "How many RCHs are there to the inch?")

[bjohns5]

For situations where you are trying to figure out what size hole to drill to fit an existing axle or pin, the best bet is to get a screw/wire sizing template like these two. Or you can just drill a variety of different size holes yourself in a piece of scrap plastic and do the same thing. The 61-80 one comes in very handy when you don't put your drill bits back in the holder each time you take them out and you end up with a pile of tiny bits that you can't tell which size is which.
https://www.micromark.com/Micro-Drill-Bit-Gauge-61-80
https://www.micromark.com/Gauge-for-Drill-Bits-and-Screws

Edited June 20, 2022 by bjohns5

[FinnAndersen]

40 minutes ago, bjohns5 said:

For situations where you are trying to figure out what size hole to drill to fit an existing axle or pin, the best bet is to get a screw/wire sizing template like these two. Or you can just drill a variety of different size holes yourself in a piece of scrap plastic and do the same thing. The 61-80 one comes in very handy when you don't put your drill bits back in the holder each time you take them out and you end up with a pile of tiny bits that you can't tell which size is which.
https://www.micromark.com/Micro-Drill-Bit-Gauge-61-80
https://www.micromark.com/Gauge-for-Drill-Bits-and-Screws

I was tempted to post a cool reply, but realise that there's other ways to go about modelling and engineering than what is taught in the metric world. Just shows how adaptive humans are. 

 

/Finn

[Chuck1945]

It’s only in the last 3-4 years that I have bought two sets of metric drill bits ranging 0.01-2.0mm. Before that for 40+ years it was a loose assortment of various AWG sized bits kept in an old 35mm film container. Just sort through them to find the size needed 😎

[Tail-Dragon]

The small drill indexes (AWG #60-#80, and metric 0.3mm - 1.6mm) can be found online at many hobby sites, tool sales, or Amazon.

The large drill index (AWG #1 - #60) was found on Amazon for around $30 plus the cost of the index case (purchased separately - the drills (cobalt) came in a plastic case).

The digital caliper was under $20.

 Ranges from 0.228" down to 0.013",  roughly 1/4" down to a fat hair!

Covers pretty much anything you will ever have to measure or drill in our hobby!

 

 

[fishplanebeer]

I have the Microbox set in mm's and it caters for all my needs.

 

The moldings of kits is not so precise as to worry about such micro differences as they approximate as best they can to a particular hole size, so to be honest I wouldn't get too hung up about all this stuff. Just go with a bit that is a wee bit too small and then carefully work your way out until you have a hole that fits - simples!

 

Regards

Colin.

[Ngantek]

Yeesh I hate awg.

 

I feel a little bit like 'get a caliper, measure the shaft, pick the corresponding bit' pretty much solves this problem with little room for confusion. Depending upon scale, a relatively inexpensive set in the .5 to 2mm range will do you for most small scale modelling, and should be easy to find in most modelling shops.

 

If you must work with corresponding awg bit sizes or whatever other arcane 'fortnight BTU ft/s per calorie' scale, the addition of a lookup table should solve it, or indeed just measuring bits from the box with the calipers.

[Peter2]

For about €8 in Aldi I bought a box of 40 small drillbits in 20 sizes from 0.6 to 2.5 mm, two of each. They are described as Left Cylindrical and Right Cylindrical, which will mean something to many of you (not me, unless it's the direction of the spiral?). A slight snag with my tiny drillbits is they try and slide around the box - because I sometimes put them back in the wrong "slots" in the box. 🚿

[fatalbert]

I can recomend a set of smoothing broaches.These are tapered reamers where you can enlarge a hole from .4 mm up to 1.4 mm.You can get a set from ebay for £11.49.There are also other sets that goes from .6mm up to 2mm and .7mm to 3mm.I find them very handy.

Edited June 23, 2022 by fatalbert