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The explanation of dimensional sizing isn't quite correct. The lumber is indeed cut at the mill to its nominal size (like 2x4), but it's rough from the saw. (Th
by jccooper 6y ago
The explanation of dimensional sizing isn't quite correct. The lumber is indeed cut at the mill to its nominal size (like 2x4), but it's rough from the saw. (They use big, fast saws that tear up the wood.) Rough-sawn used to be sold, and you'll sometimes see nominal-size lumber in old houses. You may even be able to find it at some lumber yards, but it's rare.
To neaten up the board, the mill usually then surfaces it on all four sides, shaving off the rough cut to leave a nice smooth surface. This takes off around a quarter inch per side. Thus a 2x4 ends up as 1.5" x 3.5".
It's a little strange, but makes sense historically and per manufacturing practice. Kinda like a "quarter pounder". But what's really inexcusable is that plywood is no longer sticking to its nominal size. A 3/4" thick ply is actually 23/32” thick. For a full table see: https://www.inchcalculator.com/actual-plywood-thickness-size/ https://www.inchcalculator.com/actual-plywood-thickness-size...
- coronadisaster 6y ago"The lumber is indeed cut at the mill to its nominal size (like 2x4)" That is still true today?
- beervirus 6y agoYeah I’m not sure about that still being the case. I’ve always read that these numbers are just a historical artifact.
- DrPhish 6y agoI do industrial IT for a Candian wood products manufacturer (dimension lumber, studs, veneer, plywood, OSB and previously Kraft paper) and I can say for certain that it is still sawed to a 2" by 4" shape in the sawmill and (after being kiln-dried) planed down in, well, the planermill. The 2x4 is "nominal" and doesn't represent the final dimensions of the finished product. And yes, rough 2x4 lumber is still sold, and it is in fact 2" x 4". Wood products manufacturing is fascinating, and I could go on about various minutiae all day. AMA I guess?
- TwoBit 6y agoWell any interesting facts would be useful.
- coronadisaster 6y agoIs the metric system on the horizon?
- DrPhish 6y agoThere is a mix of metric and non-metric products, with panel products having more than lumber. Occasionally you even run into other weird measuring systems such as in traditional Japanese beams. North America seems very stuck in imperial measures when it comes to lumber specifically, likely due to entrenched skills and thinking in carpentry. Even PET (precision end trimmed) products designed for cookie-cutter construction are in inches (eg 140 and 5/8"). There is even resistance by old guys against metric threading on machines since all the old tooling and warehouse stock is imperial!
- oh_sigh 6y agoIf mills can cut closer to actual vs nominal sizes and finish equally, then they will choose that, because every cut turns $(wood) into trash(sawdust).