Thou

R

reallylongnickname

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Why do machinists call everything a "thou?" 0.1
0.01
0.001 are all called a thou. I never hear, "Take off a tenth," or "Take off a hundredth"
 
"Take off a tenth" means remove .0001"
Anything larger than tenths is expressed in thousandths. It is our basic unit of measurement in the same way that the inch is to a carpenter.
 
reallylongnickname said:
0.1
0.01
0.001 are all called a thou
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Not here in England and I doubt in the US either.

A thou is a thousandth of an inch, i.e. 0.001".

A tenth, when people are talking about machining, generally means a ten thousandth of an inch, i.e. 0.0001"

When talking about dimensions in machining (where imperial measurements are being used), one thousandth of an inch tends to be considered the coarsest 'resolution' for reasonable precision.

If precision doesn't really matter, people do talk in coarser resolutions ("Oh it was about half an inch" or "Yeah, if you give it a diameter of 7/16, that'll be fine") but often, machining tends to require precision of at least a few thou, so that's how people talk.

In the rest of the world (i.e. not the US and the UK; although model engineers in the UK are increasingly changing to metric too), machinists (hobby or professional) talk in millimetres or decimal fractions thereof or if the required precision is really tight, microns (one millionth of a millimetre metre, thank you @WobblyHand :oops::))
 
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SouthernChap said:
Not here in England and I doubt in the US either.

A thou is a thousandth of an inch, i.e. 0.001".

A tenth, when people are talking about machining, generally means a ten thousandth of an inch, i.e. 0.0001"

When talking about dimensions in machining (where imperial measurements are being used), one thousandth of an inch tends to be considered the coarsest 'resolution' for reasonable precision.

If precision doesn't really matter, people do talk in coarser resolutions ("Oh it was about half an inch" or "Yeah, if you give it a diameter of 7/16, that'll be fine") but often, machining tends to require precision of at least a few thou, so that's how people talk.

In the rest of the world (i.e. not the US and the UK; although model engineers in the UK are increasingly changing to metric too), machinists (hobby or professional) talk in millimetres or decimal fractions thereof or if the required precision is really tight, microns (one millionth of a millimetre).
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I'm sure it was a slip of your fingers, but a micron is one millionth of a meter and a thousandth of a millimeter.

micron /mī′krŏn″/

noun​

  1. A unit of length equal to one thousandth (10−3) of a millimeter or one millionth (10−6) of a meter.
  2. A measure of length; the thousandth part of one millimeter; the millionth part of a meter.
  3. A unit of length; the thousandth part of one millimeter; the millionth part of a meter.
 
WobblyHand said:
I'm sure it was a slip of your fingers, but a micron is one millionth of a meter and a thousandth of a millimeter.

micron /mī′krŏn″/

noun​

  1. A unit of length equal to one thousandth (10−3) of a millimeter or one millionth (10−6) of a meter.
  2. A measure of length; the thousandth part of one millimeter; the millionth part of a meter.
  3. A unit of length; the thousandth part of one millimeter; the millionth part of a meter.
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Eh a slip of the brain more like :oops::grin:.

Good catch, thank you for being my editor (I'll edit as appropriate). :) :encourage:
 
I was on a tour where a group of small woodland owners were being shown the Oregon Saw Chain plant. The maintenance foreman was explaining how they formed and ground the teeth of the saw chain from flat stock, and said that the measurements were in "tenths." I told him I was a machinist and understood what he was saying, but the rest of the crowd wasn't likely to appreciate just how precision his work was. He then explained that he was talking about holding tolerances to "one ten thousands of an inch, which is 1 one hundredth of a human hair." That got the point across.

In the job shop 50+ years ago, we thought a "half thou" was absolute precision. A "thou or two" was good enough for logging equipment, and "ten thou" was more like farm repairs.
 
Speaking of thou's . Been watching all the NHRA races on FT1 channel lately . 11,000 horsepower , 330 MPH and lose by a thou of a second and have to go home empty handed . No Wally . o_O
 
mmcmdl said:
Speaking of thou's . Been watching all the NHRA races on FT1 channel lately . 11,000 horsepower , 330 MPH and lose by a thou of a second and have to go home empty handed . No Wally . o_O
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I used to make and sell timers for equestrian events, primarily rodeo/gymkhana type. I used a photoelectric eye to start and stop the timer. I designed the timers to time to 1/1000 sec. Now, in 1/1000 sec, a horse moving at 40 mph will move about 3/4" so just stretching its neck or head up or down will easily move that distance.

Although the timer was significantly better than a line judge with a stopwatch, it was foolish to think that the run time was accurate to 1/1000 sec. I viewed it as a tie breaker, much like tossing a coin. As such, it worked well, eliminating sometimes bitter arguments over who won. Nevertheless, it was surprising as to how many times, runs were equal to 1/1000 sec.

As to the NHRA races, those cars are traveling 5" in 1/1000 sec.
 
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