How to calculate odd shaped slabs?

[Ludo]

Hello All-

  I have some 10/4" Black Walnut slabs that start at the butt end around 22" then grow slowly to 26" at 9' and finish at 38" in a crotch.  The entire slab is highly figured and I would like to sell them based on bdft.  Besides drawing it to scale on graph paper and "counting boxes", is there another way of calculating the bdft of the slab?  I remember watching someone calculate the square inches of animal hides pretty accurately but I don't remember how it was done.  Any help would be greatly appreciated. 

[Southside]

Just go in 1' increments, then add them up, that would be pretty close I would think. 

[Jim_Rogers]

I thought that I read somewhere that the industry standard for measuring round edge or live edge slabs was to first measure the total length. In your example 9'. then at one third that distance from the narrow end on the narrow face you measure the width. Lets say at (9' x12" = 108" /3 = 36" or 3') 36" from the narrow end of the slab (usually the end towards the top of the tree) it measures 30" wide. And your slab is 2" thick. I would scale that as 2" x 30" x 9' or 45 bdft. Now you have to add your value per bdft to get what you want for the figure of the grain.

I believe they say that the loss of the narrow end of the piece is offset by the wide end of the piece.

Jim Rogers
(others will probably have other methods, but this is the method I use)



 

[terrifictimbersllc]

I use area of a regular trapezoid.  I do it in a minute or so when I cut slabs, as I charge by area of saw cuts  in my slabbing work.  Not selling lumber by bf but it would be an accurate measure of same.   Measure the width at each end of the slab between two lines on each side. Each line is that which has as much wood outside the line as voids inside the line. The average of the widths at each end is the average width of the slab.

(W1 +W2)/2 = avg witdth W .   W in sq ft x inches in thickness = board feet.

In more detail hook a string  (chalk line although you're not making chalk lines, just using the string's straightness and its position at each end of the slab) to a corner of the slab right inside the bark on one end.  Take the string down to the other end and hold it tight such that the bumps of wood outside the line match the voids inside the line, a judgment call yes but it ought to be pretty good.  Now note where the line is either inside the edge of the wood by x inches or outside the edge of the wood by x inches .  Now move the hook to the other side of the slab right to the opposite edge of the wood from  where it was and do the same thing with the line again at the other end.

Measure the two ends widths you just defined.  W1 is the width of the wood between the two positions where you had the hook,  and W2 is the width between the positions of the taut line at the other end which you noted above.

This can be done very quickly 30 secs tops with a string and a tape measure.

If you don't get my description I can draw and append a picture.    I am not saying whether this method meets any conventions or not, just that it can be used to get  a very accurate measure of an irregular wood area.   And note, the method presumes the ends of the slab are parallel to each other, i.e. "square".

[Kcwoodbutcher]

You can try and figure BF in slabs but in reality a good guess is good enough. BF measure implies that all of the wood is useable for lumber, which is not the case in slabs.Take a guesstimate, set a bf price and go from there. The figure in the wood has a tremendous bearing on the price of the slab, as does the shape. Slabs that will make a good table top or bench command a better price than very odd shaped pieces. The price also increases dramatically if they are dried. If you dry them then you take the risk of splitting and warping not them. I'd say dry slabs should fetch 2 to 3 times the price over green.

[WV Sawmiller]

I agree with KC. I don't see where BF has anything to do with this case. I'd think you could use weight & moisture content for a close estimate but why?  Sounds like you are selling to a niche market who don't have anything similar/comparable to compare against anyway. Good luck.

[logboy]

Its not hard. Take your average width and multiply it by your length and thickness.  So if you have a tapered slab that is 30" on one end, 36 on the other, and 8 feet long and 8/4 thick, then your average width is 33" and there are 44 Bdft in it. Dont get too carried away, as your BF price is really just a reference or a starting point. Then go from there to add or subtract value based on character, figure, etc. Slabs are not lumber. Do not go excluding certain aspects of a slab from your board foot total just because you wouldnt include them in lumber. If you cut it, stacked it, and dried it, then it has value. I have yet to see any sort of industry standard when it comes to slabs. Everyone I know has their own way of doing things. Some price off of figure alone. Some go off strictly board footage. I do a mixture of both.  Numerous parties have told me large walnut "table top grade" logs are being exported to Asia for $15 a board foot.  In my area of the midwest, walnut slab prices start at $10 and go to $15.

[Ludo]

Thanks guys-

    These are pretty spectacular slabs that Den Socling dried for me in his vacuum kiln.  I have never seen figure like this before (in my own walnut) and I have an offer for all of them at a bdft price.  Thanks for the suggestions and methods, Ill try them and see how they work for these particular slabs.  I need to be accurate and have a method that I can explain to the buyer so it is fair for both of us. Usually for live edge I just measure both ends, take an average and look it up on the tables but because these are oddly shaped and super nice I need to have patience and do it right.

[Remle]

My, how times have changed, 45 years ago you could have used a drafting tool called a "planimeter " .  Today you can down load free planimeter software for your computer. With it you can trace the shape to your computer to figure the area and have record of each slab size and shape to share with prospective buyers. You might want to check an option such as this out..

[beenthere]

Agree with Remle that the planimeter would work.
But with the explanation just given by Ludo that the buyer has offered a bdft price, then seems prudent to find out how the buyer is going to measure the bdft in a slab. 
If the buyer just squares up the center area like one might with an unedged board, then other methods (i.e. by the surface are in 1" increments) is for naught.

[Peter Drouin]

I just square it up for the BF and sell for enough to make the $$$$ I want. :D

[Chuck White]

I just square it up for the BF and sell for enough to make the $$$$ I want. :D

X2   ;)

[ozarkgem]

I figure they can't buy it anywhere else. I set a price I am happy with. How hard is it to replace the slab you sold? That makes it worth more in my book. I must be too cheap, I keep upping the price and they still buy them.