|
Post by A'van on Jan 15, 2021 11:41:32 GMT 10
TVs are still available in inches.
A fitter i once knew, recon a Thou ( Thousands of an inch) Was an easier or better measurement than the same in metric, i don't know, i have neve worked with so fine measurements.
|
|
|
Post by GerryP on Jan 15, 2021 12:06:06 GMT 10
It's now quite common to also use microns or micrometers, which is one millionth of a meter. So 1 thou (1/1000") is equal to 25.4 microns.
My lad programs and uses computer controlled machinery to make medical laser equipment which is machined to micron tolerances. Quite a feat seeing a human hair is around 70 microns and the human eye, unaided, cannot see much below about 40.
|
|
|
Post by Old Techo on Jan 15, 2021 12:23:19 GMT 10
Hans,
Not heard that comparison made before but I see some merit.
It is perhaps similar to my point about 1 foot being a very useful quantity that is not available in metric.
One thou is commonly used in simple engineering like say vehicles. Five to 10 thou may describe max drum-brake runout. Piston to bore gap may be a couple of thou. Crankshaft bearing clearance may be 0.5 to 1.5 thou. So a range of half a thou to 10 thou may cover many common specs.
In tighter tolerances the tenth of a thou is used. I used it in a recent post about machining (linishing) on my lathe. I was removing metal by the tenth of a thou.
In metric the only equivalent I can think of is the Micron and that is much smaller. 25.4 Microns = 1 thou.
So all of those thou numbers become bigger x 25.4 times. It is a bit like the wheel size argument. The numbers get much bigger.
Microns are handy re fuel injection where tolerances may get down to 1 Micron. That's a bit more awkward in thou. 1/25 of a thou or 0.00004
Edit: BUGGA !!! didn't see your post Gerry. My wife interrupted my typing with a pesky question
|
|
|
Post by notathome on Jan 15, 2021 12:26:37 GMT 10
When doing my Toolmaking apprenticeship we used to regularly work in 1/10 ths of thous with tolerances of + or - 1/10th of a thou.
You soon learnt how to use a micrometer correctly.
The other thing that we had to do was make our own Johansson blocks which, when made correctly, would “ring” together due to their almost perfect flatness. ... Look them up they are an interesting measurement aid.
I really didn’t get fully into metric machining as all the equipment we used was in imperial, so a lot of actual real number conversions took place.
|
|
|
Post by A'van on Jan 15, 2021 14:27:43 GMT 10
I have never heard of Johansson blocks, thanks for bringing them up i learnt something new today.
|
|
|
Post by notathome on Jan 15, 2021 15:39:49 GMT 10
Avan They are commonly called Jo Blocks and can be used for instrument testing among other things
|
|
|
Post by nsgnomad on Jan 16, 2021 0:53:43 GMT 10
... Time for a cuppa. Don't you mean ...time for a 250 ml-a.
|
|
|
Post by nsgnomad on Jan 16, 2021 1:06:59 GMT 10
I have never heard of Johansson blocks, thanks for bringing them up i learnt something new today. X2. In the Wikipedia article, it mentioned 'wringing ' as a means of joining the blocks together. OT you would appreciate this as it sounds like the action to hold up 'shrimpboats'. 😁
|
|
ken
Avid poster
Posts: 246
Tow/Motorhome: Ford Territory AWD
Caravan: Coromal Element 612
|
Post by ken on Jan 16, 2021 11:27:00 GMT 10
Interesting discussion. Sometimes, when considering "systems", like weights and measures it is interesting to ask yourself, "if I was starting out again and had to design a system of weights and measures, would I come up with factors such as 8,12,14,16,20,36,640, 1760, 5280, 63360 etc or would I simply just use a factor of 10?". I think I know what most people would chose. The preference of some people to use feet and thousandths of an inch, I suggest, is just one of familiarity. Not one engineer, surveyor, designer or architect in Germany, France, Italy or anywhere else in Europe would ever consider the foot or thou as being essential or even preferential as a method of measurement. And then with reference to the "quarter acre block". We've all heard this but it doesn't really tell us what it actually looks like, unlike a hectare being 100 metres x 100 metres, which everyone can visualise. When I bought my first house in 1966, is was thought of as being on a typical quarter acre block, but was it? It measured 150 ft x 50 ft. Now, to work out what a quarter acre is, we need to multiply 5280 by itself, divide by 640, then by 4 and compare it to my block of 150 x 50. Easy eh? It turns out my block was 7500 sq ft but a quarter acre is 10890 sq ft so I was way short. Bugger, I feel a bit ripped of but on the positive side, it meant less grass to cut.
|
|
|
Post by Old Techo on Jan 16, 2021 12:16:17 GMT 10
OT you would appreciate this as it sounds like the action to hold up 'shrimpboats'. 😁 Yes Roger
I wonder though how you know about them?
Have I missed some aviation link to your good self?
|
|
|
Post by Frank and Brenda on Jan 16, 2021 12:26:06 GMT 10
I'm lucky in that I can easily visualize either 15 feet pur 5 meters Being born in Belgium I was brought up with the metric system, then in 67 at 12yo we came to Australia where I had to learn to use inches and feet for the next 10 or so years So working with either is easy, the one thing about the metric system we use is that we don't use the deci (desi) and daca (deka) measures, as I used in Europe A decimeter is 1 10th of a meter eg 10cm and a decameter is 10 meters
|
|
|
Post by Old Techo on Jan 16, 2021 12:50:18 GMT 10
Frank,
The lack of the deci is what I'm calling the missing link and leaves that big gap ratio of 100 between cm and Metres.
Now how about being a good lad and setting a fine example to your friends (both of them ) and spelling it properly? METRES
We have toooo many imported Yankee bad habits aready
|
|
|
Post by ancientmariner on Jan 16, 2021 15:26:23 GMT 10
Bit harsh there OT, you will soon be giving Frank a complex.
|
|
|
Post by nsgnomad on Jan 16, 2021 16:50:54 GMT 10
OT you would appreciate this as it sounds like the action to hold up 'shrimpboats'. 😁 Yes Roger
I wonder though how you know about them?
Have I missed some aviation link to your good self?
Oh, OT, your radar is not working too well then. I thought over the years that I had given enough hints to my 25+ years with DCA and it's subsequent names including 23 years with ATS. I still have one of the shrimpboats at home. Surplus after they brought in labelled displays. I remember working one day after they had done some maintenance on the screen. They had forgotten to put the special film on the glass and it was a devil of a job to get the shrimpboats to stick.
|
|
|
Post by Old Techo on Jan 16, 2021 17:04:58 GMT 10
Bit harsh there OT, you will soon be giving Frank a complex. No chance Graham,
I can't compete with Mick
|
|