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Measurements of race bodies?


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#1 Pablo

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Posted 26 April 2023 - 08:58 PM

Kind of a trivia question. Why is it some guys refer to a body as "7 thou" and others call it "7 mil". 

 

1.0 is one inch

Every time the decimal point is moved to the right one time, this is what happens:

0.1 is a tenth of an inch

0.01 is a hundredth of an inch

0.001 is a thousandth of an inch (one thousand times 0.001 is one)

Am I wrong?

 

I call a .007 body a "seven thou". Some guys call it "7 mil". 

 

:crazy:


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#2 Jay Guard

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Posted 26 April 2023 - 09:09 PM

I believe that mil is an abbreviation of the Latin word milli which means thousand. So mil and thou are the same. Milimeter is different as it is one thousandth of a meter or approximately .03937 inch.
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#3 team burrito

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Posted 26 April 2023 - 09:50 PM

it's an engineer's thing.


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#4 Bill Seitz

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Posted 27 April 2023 - 07:48 AM

It does require some discretion, however. I've heard "mil" used with a metric connotation which is quite a different result that thousandths. There's also the "mil" used with plastic sheeting which isn't thousandths as I've discovered. "7 mil" and .007" are not interchangeable unless the parties using such understand what each other mean. In conversation where I wish to abbreviate, I prefer to use "7 thou" (for 7 thousandths) rather than "mil", but all parties better know we're talking inches and not metric.


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#5 Larry Horner

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Posted 27 April 2023 - 11:30 AM

Pablo, when Martin did the machining for the spur gear of my mini-can sidewinder, we had this exact same discussion!


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#6 Pablo

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Posted 27 April 2023 - 12:20 PM

:)  Yup. I think Jay Guard nailed it. Cheater and I discussed this years ago as well.

I reckon the main thing is to avoid communication glitches.

 

In Spanish, un mil means one thousand and un milion means one million.

 

The King's English is the best language in the world. That's why international airline pilots and ship captains are required to speak it.


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#7 Dave Crevie

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Posted 27 April 2023 - 03:40 PM

Ok. Maybe this will help;

 

millionths.JPG

 

It takes ten tenths to make one thousandth.

 

It takes ten, ten millionths to make a tenth, or 100 ten millionths to make one thousandth. ( We don't call it a ten millionth. If we have 5 ten

                                                                                                                                                millionths we say 50 millionths. )

 

Generally, in the tool room we work in tenths. In the laboratory we will work in millionths on occasion. The environment for that fine a measurement must be closely controlled. You can prove this if you have a very good digital micrometer that reads tenths and a steel dowel pin at least 1/2 inch in diameter. Measure the pin, and let's say it checks .5000 on the money. Now breath on it for a few minutes. Measure it again and chances are it will check .5001 or .5002. A lot of disputes have been created between machinists and the quality control guys by this. In most cases, room temperature is dictated, and the personnel handle the items being measured as little as possible. 

 

Just for everyone's convieniance I have added the conversion chart for fractions to decimals that is accepted by both the US Dept of Weights and Measures and the ASTM. I suspect that, just like a butt, everyone has one. But it might be more accesable here.

 

 

fractchrt.JPG

fractchrt1.JPG


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#8 Brian Czeiner

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Posted 27 April 2023 - 11:44 PM

I have on several occasions measured the plastic we get in just to be sure we got what we ordered. Though being ordered in mills, it still measures out to be the same thousandths of an inch give or take a few hundred thousandths. My vinyl/mask is another story. Mills seem to be a much thinner definition.


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#9 team burrito

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Posted 28 April 2023 - 11:29 AM

i got this from wikipedia: A thousandth of an inch is a derived unit of length in a system of units using inches. Equal to 11000 of an inch, a thousandth is commonly called a thou /ˈθ/ (used for both singular and plural) or particularly in North America a mil (plural mils).


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#10 Dave Crevie

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Posted 28 April 2023 - 02:49 PM

I wouldn't take anything from Wikipedia about manufacturing or measuring as gospel. What I clipped is from an industry publication devoted to geometric dimensioning and tolerancing. There are lots of books on this if you want to follow up;

 

Geometric Dimensioning and Tolerancing; American Society of Manufacturing Engineers. By James Meadows. (ASME digital collection avail. as download)

 

Chapt 16: Measurement and Gaging; Society of Manufacturing Engineers. (part of the SME "big book". Avail. as download)

 

And for you Brian; You probably have this stuff, but in case you don't;

 

plasticguagecon.JPG

 

And because the world won't convert to English;

 

met inch.JPG                      met inch2.JPG

met inch1.JPG                       met inch3.JPG


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#11 Gene/ZR1

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Posted 28 April 2023 - 06:22 PM

The Angstrom or Light Band has to fit in somewhere.

If you start out with 0.007 sheet, depending on the mold size x-y, what do you end up with. 


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#12 Dave Crevie

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Posted 29 April 2023 - 04:02 PM

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