Last edited by Curt Harms; 07-13-2020 at 8:55 AM.
I have not "switched" to metric, although I use it when the occasion requires. But I generally convert metric to inches. For carpentry and other not critical tasks, I work in "Imperial" fractional units. But for machining and other precision tasks, I prefer to work in decimal inches (i.e. 0.001", 0.0001", etc.). Much like Kph, I find Mph easier to understand, since that is what I grew up with.
David
It really doesn't matter which system you choose. You can work in either and I'm not one that personally believes one is qualitatively "better" than the other. The best advice I received on the topic was choose a system and stick with it and buy all your tools with the appropriate scale. For example, if you choose metric, then when you buy a set of chisels, buy metric. I echo the advice from Roger to avoid a mixed shop at all costs.
This is a VERY subjective thing. There are folks who waive silver crosses at the idea of using metric and there are those like myself that have dived into it as fully as possible. I started using metric in my shop two years ago and that's my personal "standard" for all projects that do not require using Imperial (some client projects) or are more practical using Imperial, such as some home improvement tasks. I find it far easier to work in MM. And yes, I not only wish I would have done it sooner, but I also wish the US would have followed through with making it "the public standard" decades ago. Most industry switched a long time ago; many materials we buy are actually metric but re-"branded" to inches/feet and with little exception, the rest of the world generally uses metric. So we in the US sit here "monkey in the middle" with both systems and mixing them can be "fun"...just ask NASA about that.
As to accuracy, it does not matter what measuring system you use relative to accuracy. Accuracy is on you, not the measuring system.
Most of my measuring devices are duel-scale so I can operate in metric while still using Imperial where I need to without having completely separate measuring tools.
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The most expensive tool is the one you buy "cheaply" and often...
The thing is...a lot of what we buy in materials are metric underneath, but remarked in inches for the convenience of the retail trade. Plywood is a very good example. It's been metric for a very long time. Screws and bolts in much of the products we buy are metric. Etc. As I noted above...we're sitting in the middle with both systems currently overlaying each other.
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The most expensive tool is the one you buy "cheaply" and often...
I switch to fully metric about a year ago and it was a painless transition. I like it much better than working in Imperial.
Precision and accuracy are independent of measuring system.
Precision is how repeatable your measurement (think how tight of a grouping is on a target).
Accuracy is how close you are to the "actual" value (think how close you are to the bullseye on a target).
You can be highly precise and accurate with a story stick with no units at all.
The inch is actually defined in terms of the metric units. The original inch was defined as three well dried barley corns from the center laid end to end, but is now defined at 25.4 mm exactly. Actually, all the US standard lengths have been based upon metric standards since the middle of the 1800s
National Bureau of Standards (now NIST) Weights and Measures Standards of the United States- A brief history
https://www.govinfo.gov/content/pkg/...b586b60735.pdf
John
It's a bit of a pain either way you go for the Americans in the group. I use imperial, but my Euro tools all have metric scales. I have a conversion table hanging in the shop, but you eventually memorize the MM equivalents for common fractions. Also, if you know 25.4mm to an inch, then you know 1/2" is right in the 12.75-13mm range, and 1/4" is around 6mm etc. I cant think of a time where i ever measured something in metric over 100mm. I like the metric system, but i dont like having to relearn 32 years of using imperial, about $1000+ in squares, rules etc, and then having to tell my lumber yard i need two cubic metres of 50mm walnut that is atleast 275cm long. This lumberyard is in the part of Pennsyltucky where a fella could get shot for saying something like that.
Unfortunately, I stick to imperial, because the overwhelming current flows in that direction. If you want to work in metric, good on ya, but you wont be working strictly in metric. Unless you saw and dry your own lumber, the second you go to buy lumber, you will order in Board Feet, specify thickness in quarters of an inch, and specify length in feet.
The "three quarter inch" plywood I get is pretty consistently .72" thick. That's 18.3mm. I'd say it is unclear whether it is metric or imperial. (My guess is that it is 3/4", with all the tolerance taken to the shy side.) And the "quarter inch" plywood now runs .21" or so. That's 5.3mm. Again, not obvious what the underlying system is.
Folks who think that our supplies etc come in English units are the ones who are confused when their "3/4"" plywood doesn't fit in the slot cut by their 3/4" router bit.
Decimal inches would be great if there were 10 decimal inches in a foot, but as far as I know there are not, or at least I've never seen such a ruler.
The size of the underlying unit is not important for woodworking purposes, though it is very convenient that a milliliter is cubic centimeter of water, which at 4 deg weighs one gram (and is close enough at other temperatures to make no practical difference for most things). I find it way easier to do the multiplication to make up a small amount of shellac knowing for a 2 lb cut I want 240 mg/ml (or 24 g/100 ml) than converting gallons to quarts, cups, or ounces and pounds to (confusingly also, but different) ounces.
We stubborn U.S. folks have failed a few attempts to move to metric, some with significant expenditures of our tax dollars. I wish we had. Fortunately I picked up enough to be fairly functional during the 60's and 70's when the public schools I went to survived the attempts to move the masses to this more sensible measurement system. Kitchen-n-Bath stuff has been metric for years. A lot of folks have moved that way or even started there.
I worked I.T. for nearly 40 years and after practically dreaming in binary, octal and hex for decades I find imperial very relaxing. Maybe it triggers a different part of my brain but knowing that the next step in 64th's up from 17/64 is 9/32 and then 19/64 seems quite normal to me. The computer keyboard or guitar neck look senseless to those who do not use them but, to those who do, they read like a book. Imperial measurements are no different. Maybe its a child-o-the-50's kinda thing ;-)
Last edited by glenn bradley; 07-13-2020 at 12:05 PM.
"A hen is only an egg's way of making another egg".
– Samuel Butler
I use both for a couple of reasons. Some of my tools have imperial scales, some have metric, some have both. For projects like making cabinets, metric is helpful given if using the 32mm systems. I have measuring tools in both systems.
A few things I have learned:
When using metric, just use millimeters (mm), not centimeters. Mixing them leads to errors, avoid measuring tools that aren't mm.
Doing arithmetic with imperial fractions is challenging, I have found that programs like excel will do calculations using fractions quite well.
Except for when using 32mm hardware and/or fitting drawer slides, most of the time, it's more important to make cuts repeatable than an exact number.