I built a spreadsheet that will calculate the board feet needed for new
projects by putting in each piece and its dimensions. I have built it with a
"waste factor" for jointing sites, kerfs, exact widths I need not available
when selecting my wood. Since I am a newbie, and don't have enough
experience yet to know, I was wondering if anyone has a % they use to add
for waste when you do your own calculations.
Cave Creek AZ
====Firsts and Seconds (FAS) is supposed to yield 83% clear cuttings, so add 20%
to account for defects. Select and Better (S&B) yields 92%, so add 9%. #1
Common (1COM) yields 67 to 75%, so add 50 to 33%. (Yeah, I know, the numbers
sound weird, but consider an example: you need 10 BF net, you're buying 1COM,
add 50% to get 15 BF. 67% of 15 is 10.)
Amount of wood needed
=================Suppose you're making one widget, and you need 20 board feet, net, after
cutting out defects and subtracting waste due to odd sizes. You might need to
buy 25 or 30 board feet to get the 20 you need. But if you're making twenty of
the same widget, you can probably get the 400 BF net you require from 450 BF
What you're making
==============Cabinet face frames rarely require anything wider than 2" net. 1COM often
yields 90% or better when it's cut into short, narrow strips. Kitchen tables,
OTOH, need long, wide, clear boards. You might have to buy six 8' FAS boards
to get six clear 4' cuttings.
As a general rule, to take into account both defects in the wood and waste due
to odd sizes, I add 20% for S&B, 25 to 30% for FAS, and 50% for 1COM. I
usually wind up with a bit of extra, but that's better than running out.
Doug Miller (alphageek-at-milmac-dot-com)
Yes, the numbers sound wierd. It took me a long time to realize that
these were not just random gibberish percentages, but fractions of
usable lumber in 12ths.
92% = 11/12
83% = 10/12
75% = 9/12
67% = 8/12
Once you realize that, it's not quite so mysterious.
As a hobbyist I used to figure about 100% waste, but my wife caught on pretty
quickly. Now I can only get away with about 30%.
Buffalo, NY - USA
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