Gang-Ripped Lumber Yields

      A discussion of the ways lumber is lost during ripping operations, and of what is a reasonable yield from the job. October 15, 2010

Question
I purchased 1800bf of 4/4 #1 common wood ripped into 3.125", 2.0625" and 1". The result was 1182 before cutting into any product. Is this the normal yield when purchasing gang ripped material?

Forum Responses
(Sawing and Drying Forum)
From contributor J:
How many lin ft of each rip size did you get?



From contributor G:
This is a pretty bad yield. I'm assuming the 1182 is a net footage and the 1800 is a gross, which is a 70% rip yield. Considering you have 3 rip widths (even though they do not complement each other all that well), you should be able to do better depending on a few factors. Was it your lumber to start with? What length was it? How wide were the boards on average? Were there specifications to rip off all wane, or was it just the product of the 1c? I'm guessing this was on a fixed width 12" arbor.

If you are buying the product in the future, buy it on the lineal and make sure you are comfy with the price on each. Otherwise you are taking on the risk of the ripper's yield, and some of the variables are completely out of your control.

Even if he did yield 80%, it wouldn't matter if they were not widths that you wanted, right?



From Professor Gene Wengert, forum technical advisor:
It would not be unusual to find the average width of No.1 Common to be 5.5". I assume that the ripping person would be able to rip into one 3.125 and two 1.00" pieces on the average, or two 2.06 and one 1.00, if the gang rip saws were set up that way. Assume a kerf of 0.125, plus at least 1/4" for edging on each side. With two kerfs and two edgings, that is 0.75 out of 5.5 or 15% loss already. Also assume that the saws and kerfs do not work out exactly to 5.5", but there is perhaps a half inch strip that is discarded (10%). Then add a bit of side bend. Then add a bit of loss because the saws are not fully adjustable to always achieve the optimum yield. All this means that 70% gang rip yield is reasonable. If you want higher yield, use a straight line rip, but then labor would be higher.

With No.1 Common gang rip strips, you will likely lose another 15% when defecting them, depending on the definition of a defect and the lengths you need.



From contributor G:
Gene, I'd agree with you that 70% can be the right number, and the edge rips you describe may be a reasonable yield on a gang rip, but not with 8-10' well manufactured material from a vendor that you will want to continue purchasing from. Depending on length, and if we are using a system that has a scanning optimization with user override for proper wood placement, you can definitely work your zero line edge rip down well below 1/4 inch.

To the questioner: Always best to confirm your cost of conversion, projected waste and actual waste. No shock here, but longer lengths will generally lead to slightly wider boards. Unfortunately they will also lead to more edging waste due to sidebend. There is likely a sweet spot for the products you produce. You mentioned previously that you generally cross cut first and then rip. If this is the case, you will do better with a wider (longer) product.

It might be worth a conversation with your lumber supplier on a width sorted product. If you are able to determine which pieces will jump up the yield on the pieces you are really looking for, you may find a vendor willing to pull those pieces at a premium that works for both of you.



From Professor Gene Wengert, forum technical advisor:
Contributor G and I agree - a computerized ripping system will achieve much higher yields indeed. Further, if you look at yield versus the width of lumber, some widths may have only 40% yield while others 90%. So, using certain widths for ripping certain sizes (widths) of cuttings can be a real big benefit, enough to easily cover the labor involved in sorting.

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