Metricification of Imperial measurements.

[dr4g0nfly]

I'm of an age where I am quite happy working in just about any measurement. From Miles through Barleycorns (1/3") to 'thou's of an inch, and from Kilometres to Millimetres and fractions thereof.

So a simple question. When should we not convert between them?

This question is raised by this months Woodturning magazine article on making a pocket pipe. In it the instructions say drill a hole 3.81mm diameter (Do What!). Now I'm quite lucky in having closed several workshops and 'acquired' many twist drill bits, including several 3.8mm, but what is a 3.81mm?

So I set to working it out, nope not 16ths, nope not 32nds and not 64ths, I even tried 128ths, a drill size I've never even heard of (and it wasn't one of them either).

So I worked it backwards 25.4mm / 3.81mm = 6.66667, ah, It's a 1/6 of an inch. Now that is probably a drill bit size but I can't find one. It's bigger than a (Old English) size 'V' at 3.77mm and smaller than the size 'W' at 3.86mm. And I can't see one listed in any Drill Chart either! Drill Size Conversion Table (http://www.csgnetwork.com/drillsizeconvert.html) Anyone seen or got one?

So the instructions are telling us to use a metric equivalent of an unobtainable English size :C

Are there times when we should not convert from one measurement system to another, or an I just being grumpy :~ ?

[Vernonv]

Maybe it was a misprint and should have been 3.18mm i.e. 1/8" ????

[dai sensei]

Here's the one I use, but again, no 3.81mm. I have a metric drill set that goes up in 0.1mm increments, so can get 3.8mm, close enough I reckon.

[Drillit]

Hello Dragonfly4,
The answer is a Wiggle (not sure what colour) or the Twist (Chubby Checker).
So use the 3.8 and either wiggle or twist and that should be 3.81, me thinks.
PS. I thought after great debate about this that the Woodturner decided to
stay with both forms of measurement as their UK readers went ape...t over
metrication. Drillit.

[swk]

This won't help though...



Dragonfly your maths is a bit out, you done it upside down (numerator and denominator swapped).

6.66666 isn't one sixth and the actual proportion is 0.15 (inches, exact) which is 3/20". Still no drills of that size.

I reckon it's supposed to be 1/8th and they've got the decimals the wrong way round.

In any case, as others have said a 3.8mm drill should be close enough for 3.81!


SWK

[hughie]

I'm of an age where I am quite happy working in just about any measurement. From Miles through Barleycorns (1/3") to 'thou's of an inch, and from Kilometres to Millimetres and fractions thereof.

So a simple question. When should we not convert between them?

This question is raised by this months Woodturning magazine article on making a pocket pipe. In it the instructions say drill a hole 3.81mm diameter (Do What!). Now I'm quite lucky in having closed several workshops and 'acquired' many twist drill bits, including several 3.8mm, but what is a 3.81mm?

So I set to working it out, nope not 16ths, nope not 32nds and not 64ths, I even tried 128ths, a drill size I've never even heard of (and it wasn't one of them either).

So I worked it backwards 25.4mm / 3.81mm = 6.66667, ah, It's a 1/6 of an inch. Now that is probably a drill bit size but I can't find one. It's bigger than a (Old English) size 'V' at 3.77mm and smaller than the size 'W' at 3.86mm. And I can't see one listed in any Drill Chart either! Drill Size Conversion Table (http://www.csgnetwork.com/drillsizeconvert.html) Anyone seen or got one?

So the instructions are telling us to use a metric equivalent of an unobtainable English size :C

Are there times when we should not convert from one measurement system to another, or an I just being grumpy :~ ?


Some charts will convert to a ridiculous number. I worked with a large drafting office many years ago and they had conversion chart the was meaningless for us. Sometimes they request a hole dimension to three decimal places ??? When queried Oh its just for a bolt hole.

Generally these sort of number come from people with little technical background and they just don't know, so ignore and go ahead with what is logical and practical

[dr4g0nfly]

SKW, thanks for pointing out my mathematical error, hopefully you can't see my blushes from Aus!.

I must admit I wondered if the numbers of the Drill size had been transposed but it quotes that size 3 times in an engineering drawing and twice in the text, one error I could have lived with, but...!

I agree that if I were to make the pipe I'd use the nearest sizes I have (I used to smoke a pipe so it would have been a wonderful thing) but getting hold of Mediterranean Briar (Erica Arborea) is not the easiest thing here in the UK.