Percent Waste used in calculating board feet

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.
Thanks Craig Orput Cave Creek AZ
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Grade ====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 gross.
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.
-- Regards, Doug Miller (alphageek-at-milmac-dot-com)
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spam snipped-for-privacy@milmac.com (Doug Miller) wrote:

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.
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Exactly.
-- Regards, Doug Miller (alphageek-at-milmac-dot-com)
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Now, of course, you realize that the "clear cuttings" are of various dimensions?
Bid with +25%, keep the excess, you'll need it to fill in where you screw up on the next job.

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As a quick rule of thumb if I were to actually figure it out it would be 20% Some jobs require more some less But the 20 % keeps me out of trouble

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You can get close by figuring around 20%, providing you've done the project before and the methods are familiar to you. If your new to the methods required, 30% may not be out of line.
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Last update: 9/21/03
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Pops wrote:

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%.
-- Jack Novak Buffalo, NY - USA (Remove "SPAM" from email address to reply)
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