huangyhg

the birth of nominal wood sizes
when was the birth of nominal wood sizes?
what is the origin of nominal wood sizes?
just curious ...
wood sizes are as they are because they once related to actual wood member dimensions. a 2x4 100+ years ago was very very close to actually being 2"x4"; but it was undressed lumber. when dressed lumber began to come into use, it was produced from sections which were already cut to 2"x4" undressed, which were then dressed, bringing them very close to what we are now familiar with. this is another case of a standard evolving naturally in the market to leave us with an unintuitive result, but a reality we need to deal with as engineers. and don't let anyone tell you that metric countries are any better: their timber sizes may be called rational things like 200x50 (mm), but they relate again to strange actual dimensions like 190x45 (mm). they changed the system and adopted one no more rational than the old imperial one. if anyone knows of a metric country with truly rational sizes, i would be very interested in hearing about it!
if you look into older engineering manuals (ketchum's fantastic work from the 20s comes to mind immediately), you will find that the actual dimensions for several sizes are listed as being slightly larger (having 5/8" of an inch rather than 1/2" between sizes). i'm not sure when this changed, but the most recent tables i have seen that list these 5/8" sized
some of the australian sizes are the actual dimensions specified- normally the seasoned ones.
but just to be confusing some others are reduced as you say.

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