Thread: Metricification of Imperial measurements.

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

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.

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.

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

Originally Posted by 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 16^ths, nope not 32^nds and not 64^ths, I even tried 128^ths, 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 Anyone seen or got one?

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

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

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.