Sawing and Drying Sweet Gum
My problem is the extremely high losses during drying. Checking and splitting resulted in a loss of ~25%. Bowed boards accounted for another ~20% and made it difficult to joint a straight edge. Cupping is minimal, so the loss is mainly across the width of the boards. I quartersawed/plain-sawed the logs using a Lucas mill.
I would hate to relegate sweet gum to a hobby wood, since it is abundant, easy to work and beautiful. Any help with this bowing problem?
From Professor Gene Wengert, forum technical advisor:
The excessive warp with gum is why it is not a commonly used wood. You can try 12" sticker spacing and also very fast drying. The splitting you mention is commonly seen in red gum (the heartwood), but also is a problem in sapwood (sap gum).
Overall, the wood shrinks about 15% in drying, which is much higher than most other hardwoods. It also has interlocked grain that causes this warping and splitting. Gum also moves considerably after drying when the RH changes; that is, it is not known to be especially stable. For best color, the wood is, and has been for decades, often steamed prior to drying.
In short, your experiences are normal for this wood.
From contributor T:
I have processed a fair amount of it for a small operator, especially this and last year, and you simply have to accept the fact that it is going to move more than most species no matter what you do. But I *do* believe I have found ways to noticeably minimize it.
In gum, it seems the amount of tension in the log is exacerbated by the interlocking grain, and these logs will move more. I remember milling a fresh-felled gum log that had a good amount of lean when it grew and some of those boards just arched skyward as I milled down the log. So avoid taking gum trees with a lot of lean or that are limb-heavy on one side. Look for the absolute straightest trunks with the least crotch wood; a tree can appear to have balanced weight distribution in the crown, but there's no way to know how the tree has responded to that stress.
I now fall sweet gum in early winter and let the logs lay sealed, in the shade, a couple of feet off the ground for several months. Not into fall, but late winter. Saw and sticker and weight as heavy as possible. I haven't decided if I have any less loss by air drying down to 20% before putting in the DH kiln or going right into the kiln. I have done it both ways and couldn't see much difference in the amount of loss to movement. I did, however, notice a difference overall simply by letting the logs lay in the winter; I believe the logs lose enough tension that it makes a noticeable difference once milled.
The worst movement I deal with in gum is twist. I hate twist and there is no way to avoid it in this species. Maybe I just notice the twist more because I dislike that defect the most of all (as far as warp goes). It will bow, crook, cup, and twist and all you can do is try to minimize. Some say you cannot minimize movement in this species, but I believe I have seen a noticeable difference following the routine I described.
Just accept the fact that it takes more work and you'll have higher loss, or leave them in the forest. You stated you would hate to relegate it to hobby wood, but that's where it already is, and it's doubtful you'll ever get it out of that category unless you can find a market that will pay the 20%+ more for it to make up for the inherent losses that other species suitable to their needs simply don't have. Yes, I hear furniture makers used to use it, but I don't know how it ever competed with other more suitable species if that's the case.
I think Koppers takes sweetgum and the tie market is pretty strong right now.
From contributor R:
I built a log smokehouse several years ago with sweet gum. Reason for using this wood was the abundance of it. Milled the logs, stacked, and secured them in a couple of days on a concrete slab. It has really helped with turning out beautiful smoked hams and sausage. The structure is as sturdy as the day it was built.
From contributor W:
I cut some with beautiful heartwood figure - red, gray, blue, yellow, etc. About 80% of it air-dried relatively flat. The other 20% bowed and warped/twisted. I got relatively minimal checking because I used Anchorseal immediately after felling the logs.
I find the interlocked grain woods like sycamore and sweet gum do okay as long as they are not glued up in wide panels. Gluing them up in wide panels is asking for heartbreak.
I have used sycamore successfully as secondary wood like drawer sides. I believe sweetgum would work very well as paneling where each board is free to move unconstrained. That is what I intend to do with the beautiful sweet gum that I have. Either that or make small boxes. I will never try to use it in tables and furniture where flatness is important.
From contributor Y:
The coolest figure I've ever seen was in some spalted sweet gum logs I got here on the west coast. If you can force the stuff to spalt, it's worth it, even with a 50% loss. Sure enough, it is a tough one to dry with lots of wiggling around.
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