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)
Why is that? Common components use thous but tooling moved to mils?
Thousandth of an Inch
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Re: Thousandth of an Inch
#12Like 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.
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)
Re: Thousandth of an Inch
#13When 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)
Why is that? Common components use thous but tooling moved to mils?
Essentially, yes. Older components tend to have imperial footprints, newer ones metric.
Re: Thousandth of an Inch
#14What 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…
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.
Re: Thousandth of an Inch
#15What 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…
Or as a machinist might say, a few tenths.
Re: Thousandth of an Inch
#16When 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)
Why is that? Common components use thous but tooling moved to mils?
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.
Re: Thousandth of an Inch
#17Like 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.
I think it was all over once America started using ounces to measure volume.
Re: Thousandth of an Inch
#18Curious 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
Re: Thousandth of an Inch
#19What 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…
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...
Re: Thousandth of an Inch
#20[deleted]