Lumber - actual vs nominal sizing

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Small Cabin Forum / Cabin Construction / Lumber - actual vs nominal sizing


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KinAlberta Member	# Posted: 2 Aug 2019 11:00am - Edited by: KinAlberta Reply One of the earliest things I learned about lumber is you can buy either rough boards or finished boards. Therefore most 2x4s arenâ€™t 2x4s but instead they are just 1 1/2â€ x 3 1/2â€. At that point I assumed that planing rough lumber took 1/2â€ off the board. So I was later surprised to learn that larger nominal dimension boards are often not 1/2â€ on the two sides but even less on one side. So a 2x8 is 1 1/2â€ x just 7 1/4â€. Since then Iâ€™ve encountered lumber in old buildings that didnâ€™t follow any of these rules. And actually I have new finished/planed 2X6, that is 1 1/2â€ x a full 6â€. Anyway, this article below explains a lot but like the quote below it can be misleading as I just mentioned that a 2x8 isnâ€™t 1/2â€ less on both sides. Then it seems thereâ€™s a couple more ways hardwoods are sized. Note that last one of the Wikipedia excerpts below looks to be an unfinished reviewed Wikipedia edit (a rough cut). Lumber â€œ... Lumber's nominal dimensions are larger than the actual standard dimensions of finished lumber. Historically, the nominal dimensions were the size of the green (not dried), rough (unfinished) boards that eventually became smaller finished lumber through drying and planing (to smooth the wood). Today, the standards specify the final finished dimensions and the mill cuts the logs to whatever size it needs to achieve those final dimensions. Typically, that rough cut is smaller than the nominal dimensions because...â€ â€œAs previously noted, less wood is needed to produce a given finished size than when standards called for the green lumber to be full nominal dimension. However, even the dimensions for finished lumber of a given nominal size have changed over time. In 1910, a typical finished 1-inch (25 mm) board was 13â„16 in (21 mm). In 1928, that was reduced by 4%, and yet again by 4% in 1956. In 1961, at a meeting in Scottsdale, Arizona, the Committee on Grade Simplification and Standardization agreed to what is now the current U.S. standard: in part, the dressed size of a 1-inch (nominal) board was fixed at â€‹3â„4 inch; while the dressed size of 2 inch (nominal) lumber was reduced from â€‹1 5â„8 inch to the current â€‹1 1â„2 inch.[11] â€œThe following paragraph is exactly backwards from North American cultural practices where finished retail and rough lumber share the same terminology, as is discussed in the paragraph after about 'architects, designers, and builders': In rough sawn lumber it immediately clarifies that the lumber is not yet milled, avoiding confusion with milled dimension lumber which is measured as actual thickness after machining. Examples â€“ 3/4", 19mm, or 1x. In recent years architects, designers, and builders have begun to use the "quarter" system in specifications as a vogue of insider knowledge, though the materials being specified are finished lumber, thus conflating the separate systems and causing confusion. Hardwoods cut for furniture are cut in the fall and winter, after ...â€ https://en.m.wikipedia.org/wiki/Lumber History of Yard Lumber Size Standards SEPTEMBER 1964 https://www.fpl.fs.fed.us/documnts/misc/miscpub_6409.pdf

paulz Member	# Posted: 2 Aug 2019 10:33pm Reply Interesting. I am a nominal 6'1" but the Committee on Aging and Osteoporosis has gradually reduced my finished size to a current 5'11".

KinAlberta Member	# Posted: 6 Aug 2019 11:35pm - Edited by: KinAlberta Reply At least thatâ€™s still a vertical measure. Plus think of the future savings on pine boards. Youâ€™ll only need 6â€™ long boards. Less waste too.

KinAlberta Member	# Posted: 7 Jun 2020 09:35pm - Edited by: KinAlberta Reply What I don't understand is why the loss in width, from nominal to actual, increases from 1/2â€ to 3/4â€ on wider boards. (The change is always between nominal 2â€-6â€ widths at 1/2â€ loss vs 8â€+ widths at 3/4â€ loss) A 2x6 is 1 1/2â€ x 5 1/2â€ = 1/2 less A 2x8 is 1 1/2â€ x 7 1/4â€ = 3/4 less Gauge of metal is even more confusing to me with a specific gauge being different thicknesses depending on the type of metal.

ICC Member	# Posted: 7 Jun 2020 10:55pm - Edited by: ICC Reply Shrinkage. Trees are felled and sent to the sawmill where they are cut to the rough dimensions. Then kiln dried. Then surfaced or planed to the finish size; 1.5 x 3.5 for a 2x4 for example. Wider lumber shrinks more across the width so a piece that is rough sawn to 8" wide or wider, is taken to the next lowest full inch plus 1/4" You get a variance between the finish sizes as once the lumber is sawn, dried and surfaced it sometimes shrinks a little more and sometimes expands a little if there is much change in moisture content as the lumber is stored, shipped, etc. Metal is nuts because of the different histories of different metals and because the US has refused to change to the metric system of standards the rest of the world uses. Steel uses gauge numbers that are from an archaic system. Galvanized steel is actually thicker than the same gauge of raw steel as the galvanizing adds thickness. Aluminum gauge is derived from a decimal relationship. Copper is completely different as it is measured in ounces per square foot and assigned gauge numbers. The metric countries measure metal thicknesses in millimeters. So one metal thickness is the same as all the others. ASTM is the materials standards association. Started in the US it is now international. They state, "The use of gauge number is discouraged as being an archaic term of limited usefulness not having general agreement on meaning." But US industry doesn't want to listen.

NorthRick Member	# Posted: 8 Jun 2020 05:12pm Reply Ha! I remember back in school in the 70's, we were all going to go metric. I remember them even installing speed limit signs in KPH and MPH. Well, here we are in 2020 and, outside of the scientific world, we are still using miles, ounces, pounds, ounces, and gallons. Oh, except for foot races, because 10 kilometers just sounds farther than 6.2 miles.