Thousandth of an Inch

https://en.wikipedia.org/wiki/Thousandth_of_an_inch

by userbinator • 3 years ago

35 65 3 years ago

en.wikipedia.org

csours• 3 years ago

Aaaargh, why do people do such stupid things?? Because they started doing it a long time ago when it wasn't stupid.

phinnaeus• 3 years ago

I've been regularly watching various machinists on YouTube for a few years now, so this feels very normal to me even though I have no actual experience in machining.

hprotagonist• 3 years ago

i know a few machinists who can think in thous.

serf• 3 years ago

my dad's a machinist; I am from exposure. Every time I express anything technical to him there is a translation that has to take where we stumble around until we convert what i'm saying (metric) into thou.

i've been doing it for years and i'm still shite at it.

swighton• 3 years ago

What I find amazing is that one thousandth of an inch is not particularly precise when it comes to machining. You can easily make parts to that accuracy with common mills and lathes.

Also surprisingly (to me) is if you have a pin that goes into a hole that is 1-2 thousandths of an inch larger than the pin, it feels like a sloppy loose fit. If you want the pin to feel like a really nice smooth fit you need more like a couple TEN THOUSANDTHS of an inch clearance.

taneq4• 3 years ago

You can do it on common equipment but I dunno if I’d call it “easy.” There’s a reason that +/- 0.05mm costs a lot less than 0.02mm.

metaphor• 3 years ago

This.

For the unindoctrinated, this concise Typical Tolerances of Manufacturing Processes reference[1] may be useful towards establishing pragmatic expectations for manual processes.

[1] https://mae.ufl.edu/designlab/Lab%20Assignments/EML2322L-Tol...

aaronblohowiak• 3 years ago

Or as a machinist might say, a few tenths.

nickpinkston3• 3 years ago

Yea, I'm always blown away by the old master machinists I've worked with when they talk about getting to "50 millionths" (ie half a tenth of a thou) on manual lathe and measurable with a bench micrometer [1].

Also the auto body guys whose hands are like profilometers [2] and can just feel various surface quality [3]. This is actually where precision originally came from with the 3 plate lap where you're just using fingers and candle soot to create crazy high surface flatness [4].

[1] https://willrich.com/product/starrett-direct-reading-bench-m...

[2] https://en.wikipedia.org/wiki/Profilometer

[3] https://en.wikipedia.org/wiki/Surface_roughness

[4] https://ericweinhoffer.com/blog/2017/7/30/the-whitworth-thre...

samstave• 3 years ago

You should watch the documentary on the most famous Card Mechanic (Card Magician, but they like to go by 'mechanic') - Richard Turner.

He fan feel thousands of inches and can note the individual thickness of each card he touches.

He is also 100% blind, and he talks about how sensitive his touch is.

He is unbelievably remarkable

https://en.wikipedia.org/wiki/Richard_Turner_(magician)

the documentary he is in is called "Dealt"

https://www.imdb.com/title/tt3127902/

kotenshu• 3 years ago

Which is why a more common unit in imperial machining is the "tenth", which is one ten thousandth of an inch.

akgoel• 3 years ago

Like the article says, we machine parts with tolerances in thousandths of an inch, but certain specifications like paint thickness are specified in “mils” which is also thousandths of an inch.

rootusrootus2• 3 years ago

Another really common one is plastic sheeting. That's probably the item I most often personally come into contact with that is measured in mils. (that is, things I need to know the thickness of, which excludes the paint all around me)

Cerium• 3 years ago

Disposable gloves are also measured in mils. When I bought a micrometer one of the first things I measured was a disposable glove and I was concerned that the measurement was really wrong. Then I searched online and found that the specified thickness is only on the finger pad area of the glove. Measuring there was dead on.

taneq4• 3 years ago

I think it was all over once America started using ounces to measure volume.

klodolph8• 3 years ago

Ounce / fluid ounce is roughly the same as gram / milliliter. A fluid ounce of water weighs about one ounce (1.04 oz/fl oz or something), like a milliliter of water weighs about one gram (0.997 g/mL or something).

The US customary units are pretty logical, they're just not powers of 10.

analog31• 3 years ago

More fun with units, a "tenth" is a tenth of a mil.

synack2• 3 years ago

When doing PCB layout, you're basically forced to think in thousandths, but work in millimeters... You end up memorizing multiples of 2.54mm (0.100in)

seniorsassycat2• 3 years ago

Why is that? Common components use thous but tooling moved to mils?

synack2• 3 years ago

Essentially, yes. Older components tend to have imperial footprints, newer ones metric.

klodolph8• 3 years ago

There's something even worse... 0201, 0402, 0603 are all codes for SMT component sizes... and they mean something different depending on whether they are metric or imperial. 0201 imperial is 0603 metric.

Most parts were imperial IIRC until at some point they started selling parts that were too small (smaller than 0201) and switched to metric. I can understand wanting to switch to metric, but reusing the same goddamn size codes is too chaotic for my taste. Come up with different numbers.

You'll still use metric, but you'll just end up seeing lots of 2.54 or 0.254 everywhere.

0_____02• 3 years ago

My sophisticated wild-ass guess: Film and sheet thicknesses are often specified in mils, and PCBs are essentially fancy sheets of stuff laminated together.

My unsophisticated wild-ass guess about why they persevere: Like Fahrenheit, it so happens that mils as a scale intuitively correspond to sizes of trace we care about. A 5 mil trace is pretty run of the mill for signals. 20 mils for most IC supply traces. 3 mils is small and expensive to make (last I checked! capabilities have changed rapidly in my decade of experience)

russdill• 3 years ago

A lot of tooling and tolerances still uses thousands of an inch as well, complicating the use of a metric grid.

seniorsassycat2• 3 years ago

Curious why we jump from 16ths or 32ths to thous rather than 64ths, 128ths, 256ths, 512ths and 1024ths

I guess they are a mouthful without good abbreviations and there was a tech jump between woodworking and machining so in betweens aren't used

nickpinkston3• 3 years ago

I had an old machinist ruler that actually did have 64ths - barely could read it haha - time to get out the calipers!

One reason these whole even numbers are used is because it's easier to inspect with basic tools - ie just fold/layer it a few times and measure the thickness - like using a rule to measure 64 sheets of 1/64" stock and hoping to get 1". The evenness is about doubling/dividing to achieve this effect.

They also had very primitive measures for bore size that worked the same - ie "gauge" for shotguns was the number of how many balls of the barrel's size added up to 1 pound of lead, so you could have a basic scale and infer everything from there.

bittercynic• 3 years ago

I don't think it's usual to make that jump, but to use fractions in some contexts, and thou in others. Around a machine shop the measuring devices go by decimals, and in wood shops they use fractional measures.

rtkwe• 3 years ago

It mostly stops around 32nds to at most 64ths at best in woodworking where it gets hard to measure accurately using a tape and the Mark 1 Human Eye. Then in machining there's usually digital or dial readouts for things so it's easier to work in a round number like 1000s.

tedunangst• 3 years ago

"instead of our engineers and machinists thinking in eighths, sixteenths and thirty-seconds of an inch, it is desirable that they should think and speak in tenths, hundredths, and thousandths"

Jedd2• 3 years ago

Yeah, it's a bit of weird disjoint. Almost a tacit admission, in fact.

I've heard that in some crazy parts of the world - say 95% of the planet - it's base-10 all the way down.

Makes you wonder if they're on to something with that kind of whacky scheme. Hopefully it works out for them.

BeFlatXIII• 3 years ago

How do they measure out ⅓ and 1/6 and 1/12 using only base 10?

kazinator3• 3 years ago

No, it's because the mil works with decimal fractions.

If a measurement is 3.125 inches, you know that it's 3 inches and 125 mils.

You don't need support for fractional syntax in order to have an input field for inches that goes down to mil precision: just a regular decimal numeric input.

You cannot dismiss the advantage of decimal fractions as casually as you can reject the metric system.

kazinator3• 3 years ago

Mils are awesome for wire thicknesses, trace widths, pin spacings on circuit boards, fine drill bit sizes for through holes ...

Guitar strings are, e.g. 9 to 46: .009" high E, .046" low E.

Classic DIP (dual in-line package) integrated circuits and headers have 100 mil spacing: ten pins per inch. IIRC, you drill a 25 mil hole for the pins. This is international.

The metric system doesn't have a nice mil-like unit for those scales; the millimeter is way too crude, and micrometers are too fine.

The mil is just right for all sorts of miniature things that are still large enough to be worked on by human hands and eyes.

Jedd2• 3 years ago

The metric system doesn't have a nice mil-like unit for those scales; the millimetre is way too crude, and micrometres are too fine.

This kind of absurd claim would be more compelling if you hadn't just used 3 decimal places and a quotation mark to define a distance in a format used by at most ~5% of all the people working in such scales:

... 0.046"

My point - metric can also use decimals. More adroitly, too, I'd argue, because of the consistency.

guenthert• 3 years ago

Classic DIP (dual in-line package) integrated circuits and headers have 100 mil spacing: ten pins per inch. IIRC, you drill a 25 mil hole for the pins. This is international.

But that's just a historic accident.

Related, the metric system was forced upon trade in Germany not before the early seventies. Only few units previously used survived, e.g. the 'Pfund' (pound, now redefined as 'half kg'). My father continued to use 'Zoll' (inch) and lamented American made machinery using threads on nuts which differed from those used in Germany (and everywhere else). Even I know the folding carpenter's ruler only as 'Zollstock' (no one says 'Gliedermaßstab').

And while I used to be very opinionated about the imperial- vs. metric system, after twenty years in California, I feel comfortable at 75°Fahrenheit and am exhausted, if I have to walk more than a few miles. I even caught myself recently referring to a width as 'about a yard'...

ranger207• 3 years ago

My guess would be that fractions with a powers-of-2 denominator were used in pre- and early-industrial contexts and remain in use today by long tradition, but thousandths started to be used only later in industrialization when the benefits of a base 10 system were more clear

stephen_g2• 3 years ago

The most annoying thing about the thousandth of an inch is while it’s often called a ‘thou’, it’s also called a ‘mil’ which sounds exactly as the common slang for millimetre (mill) here in Australia at least (used more often in construction, but it’s still common so makes it confusing).

Luckily we don’t really do PCB design in imperial anymore at any of the companies I’ve worked with (I hear even US companies are moving away from it since so much of the manufacturing is offshore)

sitzkrieg• 3 years ago

guess who didnt read the link :-) but agree, i did pcb design w a few old hands who said mills and got me a few times

TheSpiceIsLife• 3 years ago

You're not going to say 20 mil and the context not be clear if you mean 0.508mm or 20mm, are you?

SlickNixon• 3 years ago

A machined feature could be either.

deathanatos• 3 years ago

Now's where one needs the Wikipedia article titled something like "Engineering Failures Caused By American/Metric Confusion".

There's at least https://en.wikipedia.org/wiki/Mars_Climate_Orbiter and TBH I was hoping there'd be a link to such a list on that one.

I seriously hope I'm Poe's Law-ing your post too, and there's an implied /s on there, because if you could see the level of communication effort I see at work … yeah, I'd absolutely believe that someone would use it in a confusable context.

harikb• 3 years ago

The units are considerably different: a millimetre is approximately 39 mils.

Thousandth of an Inch

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