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Measured in Inches...

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MonMotha:
Decimal inches are VERY common in machining and engineering work.  I have several rulers with both decimal and fractional inches on one side then metric (decimal only, of course) on the other.

It turns out that the mil (one one-thousandth of an inch) is a rather handy unit when working on typical "miniature" things like small machined assemblies, circuit boards, etc.  You'll typically deal with a few mils to a few hundred or thousand mils with tolerances of maybe 1/10th mil (so one decimal place), whereas the mm is too big to not require partial millimeters (to maybe 2, 3, or even 4 decimal places occasionally) while the micron (micrometer) is so small that anything less than several hundred of them is often a uselessly small quantity.

Of course, what units you end up using are more likely to be dictated by what the controlling dimension on the overall project is.  If the project is controlled in inches, you'll probably be using decimal inches.  If it's controlled in metric, millimeters or microns.  Fractional inches suck in either case, though, since you'd end up needing things like 1/512 in to get the necessary tolerance, and that's a pain to convert to, well, anything.

Also, FWIW, I remember getting a hearty laugh out of a group of engineering students sitting in the ham radio shack back in school when I used the term "metric fuckton".  Obviously, that's larger than a standard short fuckton.

danny_galaga:

What a mess  :o  Fer Chrissakes guys, let go of the past and embrace metric!

Howard_Casto:
My take:  All measurments are different but equally useful if used in the fields they came out of.

Imperical is a combination of measurments used by tailors and carpenters.  The markings were derived from the typical lengths they had to cut.  The size of the inch has actually fluctuated over the centuries, but it's ticks are usually derived from a common materials thickness.

Metric was created by scientists because they use a lot of math and base-10 fractions are a lot easier to deal with. Also because they typically deal with small quantities, the size of 1 unit was reduced.

Imperical with metric fractions as MonMotha explains, the newly emerged computer aided machining industry came up with the system. Basically they needed easily maniplulated fractions like the metric system, but it's units had been made too tiny, and thus they used the size of an imperical inch as the base. 

So:

Scientists should use the metric sytem, machinists should use imperical metric.... you and me should use straight Imperical. ;)

danny_galaga:

--- Quote from: Howard_Casto on March 31, 2012, 06:27:13 am ---My take:  All measurments are different but equally useful if used in the fields they came out of.

Imperical is a combination of measurments used by tailors and carpenters.  The markings were derived from the typical lengths they had to cut.  The size of the inch has actually fluctuated over the centuries, but it's ticks are usually derived from a common materials thickness.

Metric was created by scientists because they use a lot of math and base-10 fractions are a lot easier to deal with. Also because they typically deal with small quantities, the size of 1 unit was reduced.

Imperical with metric fractions as MonMotha explains, the newly emerged computer aided machining industry came up with the system. Basically they needed easily maniplulated fractions like the metric system, but it's units had been made too tiny, and thus they used the size of an imperical inch as the base. 

So:

Scientists should use the metric sytem, machinists should use imperical metric.... you and me should use straight Imperical. ;)

--- End quote ---

I think the term is Imperial. Also, the machinists theory is suspect, since a whole bunch of industrialised countries use metric in their machinery. As, I believe does the US armed forces (could be wrong on that, let me know).

Question: What measurements do they use on a Honda or Toyota made in the US?

MonMotha:
The US DOD has converted to metric for all their new designs, but they still support a LOT of old designs.

It's not necessarily a computer aided thing; machining in the US has long used decimal inches going back to before metric was particularly popular or even known amongst the general population, here.  It's relatively easy to convert a fractional inch into decimal inches, and the utility of fractional values really starts to diminish when you get to teeny tiny quantities where "being able to easily divide it by several common factors" is no longer an issue.

Essentially all cars, both designed in the US and overseas are fully metric these days (with some weird exceptions for things like tires, which have F'd up sizing globally).  It kinda pissed off all the mechanics, since they had to go buy new tools, but that would have happened anyway since you're going to have to work on "imports" these days whether you want to or not.

There are also a lot of old standards defined in inches.  One thing that really irks me is when something was clearly designed in inches but is specified using metric measures as "authoritative".  I've even seen some (really bad) datasheets that would take a part designed on a 1/10" grid, convert it to mm, round 2.54mm off to 2.5mm, then call that measure the "authoritative" measure, giving the 0.1" dimension "for reference only", even though it was actually the correct one.

In general, I frequently use both systems of measurement.  My CAD software will happily let me pick what I'm using.  I can freely intermix e.g. a metric snap grid with an imperial database/display.  Some parts are designed in inches and work well on an inch based grid, while other parts are designed in metric and work better on a mm grid.  I've also found occasional use for 1/4mm spacing, which would itself be something of a "hybrid" oddity.  I do tend to create my production artwork measured in inches, but I give 'em 5 decimal places, so it doesn't really matter.  My fabricator will happily accept files in either format, but I know inches are far more popular (I've asked their CAM people).

I prefer to pick one system and stick with it as the "authoritative" system on a project.  What I pick mostly revolves around what I have to work with in terms of outside materials and interface.  I do use inches for circuit boards usually since I find the mil a very convenient unit for that purpose, but I often get grumbles from people for spec'ing M2.5 screws (until I tell them that a #4 is about the same size and will also work if they prefer) because I like metric screws better.

Most of the younger engineers, scientists, and, to a somewhat lesser extent, technicians I know and have worked with can easily work in either system of measurement and can handle both on a single project.  It's mostly the older "technical guys" hard-set in their ways that denounce metric.  The average American also is opposed to it, but this opposition is essentially non-present in technical fields.  FWIW, it is required by most major accrediting agencies for technical college degrees (engineering, science, etc.) that students be given problems in both systems of units in the US.  Most coursework will even mix units in the definition to make you deal with that.

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