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Re: Bluebird & Other Scale Models

Posted: Mon Jul 24, 2017 10:30 am
by conistoncollie
Or, put another way, trying to perfectly mate the underside of a 12 foot fabrication to a 6 foot wedge machined from a solid billet to within 1/100mm... twice!
1/100mm? Thought we weren't keen on base-ten flummery.
0.0003 inch, or 4 tenths, much more imperial. Pretty tight tolerance on a 1/2 in ground shaft let alone over 6ft. Can imagine temperature variations caused that 6ft lump to expand and contract well beyond that.

Talking of thous, I once had to show a young apprentice lad what a thou was, so I set up the anvils of a mike to 0.001, held it up to the daylight and said "thats one thou, how many of those do you think there are in an inch?" After pondering the question for a while he replied with "there must be millions"

Re: Bluebird & Other Scale Models

Posted: Mon Jul 24, 2017 12:16 pm
by Renegadenemo
1/100mm? Thought we weren't keen on base-ten flummery.
0.0003 inch, or 4 tenths, much more imperial. Pretty tight tolerance on a 1/2 in ground shaft let alone over 6ft.
MKW always quoted their planing wedge to be inside 1/100mm end to end so I never bothered to translate it into English as most people can only count to ten.
Our steering shaft was an interesting one. it was centreless-ground from three lengths of cold-drawn seamless hydraulic pipe to 0.9980" The man would only give me two thou clearance on the bearings and two of those were actually 0.998 themselves and had to be lapped before the shafting would slide but the tolerance on those shafts over about 18 ft was very impressive. Green & Preece grinding did it for us.

http://www.green-preece-grinding.co.uk/

Re: Bluebird & Other Scale Models

Posted: Mon Jul 24, 2017 1:45 pm
by rob565uk
Speaking of numbers and bases, two amusing stories spring to mind:

A friend of mine, blessed with a sharp mind, and even sharper sense of humour, was asked his opinion of who was right and wrong in a dispute between two people at work.
His reply was "Well , I think its 6 to the base 10 of one and 10 to the base 6 of the other...

Back in the 1970s in the early days of the dreaded decimalisation in the UK, I went to buy an eight foot length of timber, to be told that it was only sold by the metre. So I enquired how much it would cost and was advised " 15 pence a foot Mate" 😕

Re: Bluebird & Other Scale Models

Posted: Mon Jul 24, 2017 3:06 pm
by conistoncollie
Had the same once trying to buy some 1/4 ply. Sorry mate, only available in 6mm,
OK, can I have a 2 metre x 1 metre sheet?
Sorry mate it comes in 6 foot sheets.

Once I specified a size on a drawing 1.985 in. Client asked for it to be 2.000, thinking it would be easier to machine.

And finally, had a drawing once where the hole was specified M 1/4. Good luck with finding a tap for that.

Re: Bluebird & Other Scale Models

Posted: Mon Jul 24, 2017 3:26 pm
by midlife
We ordered 2 x 1/2" taps & received 1 x 2 1/2" tap, it's been used as a trophy for years


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Re: Bluebird & Other Scale Models

Posted: Mon Jul 24, 2017 4:54 pm
by conistoncollie
midlife wrote:
Mon Jul 24, 2017 3:26 pm
We ordered 2 x 1/2" taps & received 1 x 2 1/2" tap, it's been used as a trophy for years


.
Perhaps try cutting it into five.

Once asked a trainee to cut a 3 inch diameter steel bar in half.
He was gone for hours so I went to check. He had it standing up in the vice, dripping with sweat, cutting it in half .... lengthwise.

Re: Bluebird & Other Scale Models

Posted: Mon Jul 24, 2017 5:13 pm
by Renegadenemo
My least favourite metric/imperial gotcha was the top skin for the air intakes. It would come out of a 8x4' sheet but in no way were we going to get it out of a 2x1m sheet. You'll never see it but that skin had to have a 4" strip welded on all the way across the front edge before we could begin wheeling it in.

Here John and me are dressing the weld.

Extending panel.jpg

It wheeled in perfectly after that.

Wheeling intake skin.jpg

Re: Bluebird & Other Scale Models

Posted: Mon Jul 24, 2017 10:58 pm
by sbt
Small Arms are fun measurement-wise. I think the best one is the FN FAL, of which there are two groups, Metric and Imperial (of which the British Armies SLR was one). Both groups fire the same ammunition, 7.62 NATO, a modification of the .300 Savage cartridge, also known as the .308 Winchester. The M16 and SA80 both fire a .22 inch round, the 5.56 NATO. Then there was the .280 British, originally termed a 0.270 in round, accepted into UK service as the 7mm Mk1Z which was actually, and always was, 0.284 in / 7.2 mm in diameter. A very few Metric FN FALs were built to shoot .280 British...

Re: Bluebird & Other Scale Models

Posted: Tue Jul 25, 2017 10:33 am
by Piston Broke
The only places still operating imperial system
imperial.png
Why are our kids are forced to learn the times table up to 12 when we have been on a base 10 system since the 70's

Still remember father in law telling me he used to confuse his apprentices by asking them to measure 6 foot 30mm of cable

Re: Bluebird & Other Scale Models

Posted: Tue Jul 25, 2017 12:30 pm
by conistoncollie
Out of interest, anyone know what threads are used on the latest US F35 jets?
For years they had their own imperial standards, and strange US Gallons.
Presume there is now some uniformity.