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Double check my math (board feet question)

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Forum topic by rut posted 03-09-2012 01:07 PM 1853 views 0 times favorited 13 replies Add to Favorites Watch
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rut

81 posts in 1844 days


03-09-2012 01:07 PM

So I’m trying to determine how much lumber I need for a kitchen cabinet project I’m starting. This is what I’ve done.

1. Took the total linear footage of the cabinets and multiplied by height to get sq ft

Base: 20’ x 3’ = 60 sq ft.
Upper: 23’ x 2.5’ = 57.5 sq ft.

total: 117.5 sq ft.

My lumber yard states to expect about 83% or better usable wood (from select grade).
So to get to 100% I multiply

117.5×117% = 137.48

Add in 10% waste and I’m up to

137.48×110% = 151.25 sq. ft.

So is this the same as the amount of board ft that I need or is there more calculations involved?

Also, only 83% yield does seem low but I guess they know better.

Thanks,
Rut


13 replies so far

View jmos's profile

jmos

736 posts in 1832 days


#1 posted 03-09-2012 01:17 PM

Rut, I have to say I’m confused by your calculation; are you just replacing the doors? Your calculation only covers one flat plane, no sides or back included.

If its the whole box, I would do the math per cabinet. If its just the faces I’d calculate what you need for each door (rails, stiles, and panels) and what you need for the face frames (assuming your using them.)

Give us some more information.

-- John

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rut

81 posts in 1844 days


#2 posted 03-09-2012 01:21 PM

Yes. This is just for the cabinet faces (face frame and door/drawer). The sides will be veneered plywood. I didn’t separate out the face frame from the doors/drawer fronts, instead trying to get a ballpark estimate of the whole amount of wood needed to ‘cover’ a cabinet (knowing I’d need a bit more)>

View CharlieM1958's profile

CharlieM1958

16242 posts in 3680 days


#3 posted 03-09-2012 01:27 PM

I’m not sure about how much to allow for waste, etc., but your basic math looks correct, assuming you’re taking about 4/4 stock.

-- Charlie M. "Woodworking - patience = firewood"

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jmos

736 posts in 1832 days


#4 posted 03-09-2012 01:32 PM

What style doors? Are you doing European style with no face frames, a door fully inset into the face frame, or a more traditional face frame with a overlay door? Each would take progressively more lumber.

As for your math, for the 83% yield, divide by .83 instead of multiply by 117; small difference, but 83% of 137.8 is 114.125, not 117.5. You can also multiply by 1/.83, or 1.205 to get the correct number (which would be 141.6)

The waste calc really depends on the how picky you are about the boards, and how closely the board width matches what you need, and how much gluing up of smaller boards your willing to do. I usually allow about 25%

-- John

View BinghamtonEd's profile

BinghamtonEd

2281 posts in 1832 days


#5 posted 03-09-2012 01:32 PM

Since the title is about double-checking math, I will add the following. This doesn’t have a dramatic impact on your project since the BF is low, but on a bigger project, just to be safe :

You multiplied 117.5×117%, which is incorrect. That’s adding on 17% of 117.5 (83 % of 137.48 is around 114). You need to be saying 117.5 is 83% of your total, so you need to do 117.5/.83 to get the correct total, which is 141.57.

117.5 = x * .83

Maybe this will save you an extra trip to the yard sometime

Edit : jmos beat me to it :)

-- - The mightiest oak in the forest is just a little nut that held its ground.

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BobLang

124 posts in 2862 days


#6 posted 03-09-2012 01:33 PM

I would buy 200-250 BF of material. Hardwood is sold in random widths and lengths, and that has a large impact on your yield. When you get the lumber, go through the stack and pick out the widest nicest pieces for drawer fronts and door panels. You should be able to get the frame material out of what remains. You’ll always be able to find a use for leftover lumber, but if you need to stop in the middle of the project to go buy one more board it will be costly.

There is an article on this topic in the April 2012 issue of Popular Woodworking Magazine

Bob Lang
readwatchdo.com

-- Bob Lang, http://readwatchdo.com

View rut's profile

rut

81 posts in 1844 days


#7 posted 03-09-2012 01:42 PM

Thanks for the correction guys.

View rut's profile

rut

81 posts in 1844 days


#8 posted 03-09-2012 08:28 PM

One followup, will 200 board ft fit in the back of a p/u (dumb question I know)?

View DS's profile

DS

2151 posts in 1882 days


#9 posted 03-09-2012 08:57 PM

10% waste in solid wood is very optimistic. For face frames and frame-n-panel doors 25% to 35% waste is more realistic.

I can get 10% waste on sheet goods with grain, as low as 4% waste on sheet goods without grain, but that is with a very sophisticated cnc optimizer program and nested routing.

What’s the worst that can happen if you buy too much? Cutting boards for Christmas! heheheh! :-D
What really sucks is making a return trip to the lumber yard for one more stick. Yowsa!

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

View RogerM's profile

RogerM

759 posts in 1861 days


#10 posted 03-09-2012 10:24 PM

200 board feet would be a piece of wood (or several pieces of wood) that is 5 feet long by 4 feet wide by 10 inches thick. Pretty good load I would guess but most P/U’s ought to handle it.

-- Roger M, Aiken, SC

View WDHLT15's profile

WDHLT15

1572 posts in 1938 days


#11 posted 03-11-2012 01:00 PM

The 83% comes from the definition of select grade. Select is FAS on the best face and #1 common on the worst. To be FAS, there must be 83% of the square footage of the board in clear (defect free) cuttings. Minimum cutting size is 3” x 7’ or 4” x 6’. Each board size must have a specified minimum number of cuttings.

So, the 83% is a grade factor and may not be your cabinet yield. I, too, would figure the total BF needed and add 25% for waste.

-- Danny Located in Perry, GA. Forester. Wood-Mizer LT40HD35 Sawmill. Nyle L53 Dehumidification Kiln. hamsleyhardwood.com

View Lee Barker's profile

Lee Barker

2170 posts in 2312 days


#12 posted 03-11-2012 02:46 PM

Interesting discussion.

This practice can become pretty intuitive. Not perhaps to the state of being able to look at the kitchen and come up with an estimate, but rather knowing which way to fudge the numbers at the end because of the nature of the species or the particular complexities of the project.

At the heart of the numerical part is the percentage, and some valid ones have been suggested.

My number is 35%. I would do exactly what you did—calculate the acreage of the field—and then multiply by 1.35: 118×135% = 160BF.

The next part of the process is going to the yard and pulling out what I think I need for the job—not calculating BF as I go. Just a pile o’ boards, and I’m getting an intuitive feel for the yield. At some point I’ll stop and add it up, compare with the 160, and hunch it one direction or the other.

At the heart of this is whether you can accommodate an overage of 3 boards at the most, or whether you’re comfortable stashing the surplus no matter how much.

It is much more gratifying to me to be able to choose the last piece from a few remaining boards than it would be to be cutting the last board for the last pieces. I always want to be able to choose.

Kindly,

Lee

-- "...in his brain, which is as dry as the remainder biscuit after a voyage, he hath strange places cramm'd with observation, the which he vents in mangled forms." --Shakespeare, "As You Like It"

View ELCfinefurniture's profile

ELCfinefurniture

112 posts in 1782 days


#13 posted 03-11-2012 03:55 PM

Google “densemores handy lumber table”

-- {Current North Bennet street school student}

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