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I keep using this example: In the wood shop, I'm going to cut a bridle joint. Requires cutting boards into thirds of their thickness. Metric lumber is often milled to 19mm thick. What's a third of 19mm? You want to show me which line means 6.3333mm on a metric tape measure? US Customary lumber is milled to 3/4" thick. What's a third of 3/4"? You want to show me which line means 1/4" on an inch tape measure? Now let's cut a half-lap joint in that same lumber. In metric that works out to 9.5mm, there's also no line on a typical metric tape measure for that. But there is a line for 3/8".
I'd much rather build furniture in inches than millimeters because in the wood shop I have to divide or multiply by powers of 2, 3 and 4 way more often than powers of 10. It is in this context that the inch standard which is subdivided by powers of two rather than ten arose, and it still works very well.
Metric users often correctly accuse Imperial or US Customary (though the two share names of units they are not identical) users of making excuses or relying on workarounds, in the context of woodworking joinery I find it's the reverse. "Of course we don't use 6.3333mm, you just know to cut the cheeks 6mm and the tongue 7mm. 6+6+7 is 19."
I'll grant you, doing stoichiometry in ounces and pounds would be a fucking nightmare. But woodworking joinery? Nah I'm doing that in fractional inches.
While neat, I believe your lumber example is misleading in the context of metric vs imperial. Woodworking is extremely imprecise compared to many other types of engineering and using that system for those problems may be ideal.
Deliberately using 1/3rd of 19mm to get 6.33333mm is not as a complex problem as it may look at first glance. 6.333mm IS 1/3rd of 19mm just with more precision. The nature of woodworking requires fairly large tolerances and .3333mm is likely within any tolerance range you would work with. Hell, even +/-3.333mm (10x) is probably within spec in many cases.
Your example conversion from 1/4in to 9.5mm is irrelevant unless you are working a project that is deliberately converting imperial to metric. If a project is designed in metric the measurements and reference points are going to be rounded to metric. The same goes for designs that are in imperial. While it's possible to design identical pieces in each measuring system, it's not ideal. Tolerance can compensate for most small differences and you will get two extremely similar pieces.
From your standpoint, everything has been imperial and you make design choices around how imperial works. It just makes sense to you. Design conversions from imperial to metric won't make any sense and the "natural math" of each system is lost. If you were raised on metric, the same situation would apply I suppose.
You explained the biggest complaint of imperial as a positive: fractions. Pure math is just easier then fractions when working up and down ranges of precision. Divide 10cm by 2? 5mm. 5mm by 4? 1.25mm, etc.. Problems like 19mm/3 are irrelevant because of allowable tolerance. Every exact measurement is not abstracted by a 16th or 8th or 32nd or 64th....
Admittedly, I am no woodworker. However, I am curious if someone from the EU could chime in on this problem from their perspective.
I didn't convert a quarter inch to 9.5mm. First of all a quarter inch is somewhere around 6.5mm. I divided 19mm by 2. Just like I divided 3/4" by two to get 3/8".
I'm talking woodworking here, not carpentry. .3333mm is ~1/64", which is the maximum error I would allow in making a joint. I usually work well within that. Missing by 3.3333mm on a feature specified to be 6.3333mm is an abject failure. That's an error of over 50%.
PVA wood glue contracts as it dries, so it doesn't fill gaps well. The looser the fit, the weaker the joint. I aim for a friction fit. Most of the time with glue on the mating surfaces the joint must be tapped together with a mallet.
Your reading comprehension is what I've come to expect from Lemmy. I repeat myself for the slow kids at the back: because I often have to divide my work into halves, thirds or quarters and rarely into tenths, fractional inches in powers of two are more convenient in this application.
Remember folks, in metric, 5/2=2.5, 5/3=doesn't matter because "tolerances." That's one of those excuses I was talking about.
Do keep trying to lecture me about something you don't even slightly understand. It's adorable.
Chill. We both wrote walls of text and there are going to be misunderstood details. If we want to talk about details, I called out my ignorance of woodworking and why imperial is likely good for what you are talking about.
My overall points, and I'll summarize this time, is that:
Wood working (carpentry? Whatever.) is not exact.
Dividing 19mm by 3 is a weird example. Your example did a better job of highlighting a math peculiarity, TBH. (My first thought is that the cut was was going to account for any minor errors.)
Fractions suck. You are comfortable with them, but I see them as a useless layer of an outdated measuring system. We made our points, for and against. Cool.
A key point that I didn't call out specifically is that imperial does not work in high degrees of precision easily without eliminating fractions. It's possible, and vocalized, but not generally written. 1/1000" as a good example.
While I was awaiting your reply, I also thought of the abuse the imperial system has suffered over the years. A 2x4 is not a 2x4. In reloading (another hobby of mine), .300 actually means .308. .223 could mean .222, .223 or even .224. However, .222 always means .222. I am forced into imperial for safety and consistency reasons. (Don't even get me started on 'grains', wherever the fuck that came from.) For some reason, the metric system is now mixed up in that field as well and it's a mess.
The word "misleading" was chosen with purpose and doesn't mean that you writing with malice. It seemed, true or not, that conversions got mixed up in this which would even confuse an MIT graduate.
Woodworking is the trade of building furniture and cabinetry, carpentry is the trade of building structures. A woodworker built your dining room table, a carpenter built your dining room. The two trades have some overlap in skills and knowledge but they are different skill sets. As for exactness...let me put it this way. A lot of woodworkers balk at using pencils to mark their cuts because the width of a 0.5mm mechanical pencil lead is considered too great a margin for error. A single bevel marking knife is used to apply a score mark with a perfectly sharp edge to the wood.
It is typical for metric woodworkers to mill boards to a finished thickness of 19mm. It's also a common thickness for plywood in metric land. I think it was chosen because it is close to 3/4". Many common woodworking joints such as mortise and tenons, bridle joints, etc. require dividing the board into thirds; a typical mortise for example is a rectangular hole or slot in a board 1/3rd the board's thickness. So working in metric with 19mm stock, you either have to cope with measuring, marking, and cutting 6.3333mm, or having to "just know" to cut a 7mm mortise with 6mm of wood on either side.
Meanwhile working in US Customary (which is not the same as Imperial) using wood milled to 3/4" stock, a third of 3/4" is 1/4".
19mm/3 isn't a weird example, I didn't pull that number out of thin air.
DIFFERENT SCENARIO: Now I'm going to make a half-lap joint which requires cutting the stock in half. Cutting a metric 19mm board in half gets you 9.5mm. Cutting a US Customary 3/4" thick board in half gets you 3/8".
For this application, fractions genuinely don't suck. There are advantages to using fractions in work like this, namely that you can do integer math on the numerator or demoninator rather than floating point arithmetic. Plus, measuring and marking tools being marked in powers of two rather than ten is more convenient in a field where most of what you're doing is halving and quartering dimensions.
Sure, precision metalwork is done in thousandths of an inch or even ten-thousandths of an inch, and I personally prefer machining in metric.
Yes it is, for awhile at least. The board is rough sawn out of the log at 2" by 4" and dried at that dimension. Rough sawing doesn't produce a perfect board, and the board will shrink and warp a little during drying, so the dried board is then further flattened, straightened and squared via a milling process which takes about a quarter inch from each face, resulting in a finished dimension of 1 1/2" by 3 1/2". Lumber is priced by their rough cut dimensions because that's how much of the tree the sawyer had to use to make that board.
Back in the day it was common for lumber yards to sell construction lumber in a rough cut state at a true 2" by 4", and the carpenter would mill it himself. Then the railroads happened, and lumber was being shipped from the forests of the West coast back east. Railroads charged for cargo by the ton, and lumber mills could save a mint on shipping by milling the boards to finished size before shipping. This saved carpenters the work of milling the boards themselves. They still called the boards "2x4s" because they were still used for the same purpose. An thus the modern commodity retail 2x4 was born.
Similarly, that 3/4" lumber I keep saying I use: I buy that from my local sawyer rough sawn to 1" thick. I then plane it flat and straight, which takes about an eighth of an inch from each face. So I wind up with a finished board 3/4" thick, which as previously discussed is a convenient size for woodworking.
I have to admit: That sounds pretty nice. Next time I build something with wood I will try to use inches. Thanks!
There's a method to the madness. I'm pretty sure woodworking joinery is why inch fractions are the way they are. Lots of stuff I'd rather do in metric, machining for example, but specifically woodworking works very well in fractional inches.
I mean, you can make the exact same argument the other way round.
My bed is made with boards of 27mm thickness. One third of that would be 9mm. Easy.
Also if you need precision, calipers go down to 50um (micrometer), 1/20th of a mm.
What's half of 27mm?
We can keep doing that dance, it's possible to find similar inconveniences in the fractional inch system, like "what's a third of a whole inch?" but I find that within each system's conventions (like using 19 and 27mm stock versus 3/4" or 1 1/2" stock) you're less likely to run into them working in fractional inches. I think because the wood shop is just a fractional kind of place, I divide by two and three out there a lot.
The machine shop isn't so much, which is why we tend to work in either thousandths of an inch or increasingly in metric. Most CNC machines will gladly accept both.
As for calipers: In the wood shop, I frequently use a set of dial calipers calibrated in 64ths of an inch. Especially with my thickness planer on which one full turn of the handwheel moves the cutter head 1/16", so the major, medium and minor marks on the caliper dial work out to a full, half and quarter turn on the handwheel. The analog display makes the relationship between the calipers and the tool very intuitive in a way that improves accuracy and repeatability largely by decreasing error.
I don't really need precision beyond 1/64", but I do need to be able to tell if it's a thin 64th or a fat 64th or a dead nuts 64th.
This is why I think the metric system should be redone in base 12. Or maybe base 36.
Base 10 in general is a mistake.