Techniques for Heavy Glue-Ups
Tips for successfully accomplishing a monster glue-up (14 inches thick, 30 wide, and 144 long). February 1, 2011
Question
We just been tasked with a huge glue-up. 14" thick x 30" wide x 144" long. We will be using 8/4 material to glue this up. Do the grain rings matter as much in the stack as they do when gluing up doors? We just purchased some 7x7 turnings and the rings seem to be just whatever came out of the pile. There is no up/down alternating. Also, is it better to glue up the width first, then the thickness or vise-versa?
Forum Responses
(Architectural Woodworking Forum)
From contributor F:
Definitely glue to width then thickness. Try for 1 3/4 thickness of each slab. Wide belt them to achieve nice flat panels then glue the eight or nine panels to obtain the final thickness. What is this massive glue up for and what sort of hardwood are you using? Basswood for a huge carving?
From Gene Wengert, forum technical advisor:
Make panels first and then laminate, as already mentioned. When sanding the panels smooth, it is possible to have some issues with the surface fibers (damaged and loose) that are inherent after sanding. Knife planing is so much better. In any case, check surface flatness and laminate within minutes to insure a premium joint. Obviously, the MC must be correct, or when the piece changes MC, it will create a lot of stress on the joint, creating end checks. Grain orientation is not an issue.
From contributor M:
Gene makes a great point regarding gluing off a sanded finish. One world renowned piano manufacturer did some testing and determined that a glue joint off a sanded surface is 25-27% weaker than a knife planed surface. Piano rims are glued off a planed surface.
From the original questioner:
It is basswood for a carving blank. To all: do the radial rings matter as they do for standard panel glue-ups? If they do, how do you alternate the thickness - every other like the width? We don't have a 30" wide planer, so we are going to have to go with the widebelt with a 60g belt.
From contributor C:
Maybe try a wide scraper as soon as it comes out of the sander to remove the loose stuff you get from the sander. If you have a couple of guys it should go fast. Then again, the older I get, the more often I'm wrong.
From contributor R:
Better talk to the carver. I would think that he wants the grain basically running out in the same direction. If his is hand carving, changing grain directions in the wood may force him to switch directions when he gets in another layer. He may also want to spec the glue since something like resorcinol will dull his tools.
From contributor M:
You could also go with 10/4 or 12/4 and have fewer layers. Another option would be to edge glue 10/4 or thicker 14-1/2 to 15" wide and then plane and face glue to make the width. When you get to 15" wide, plane to 14-1/4" and glue two pieces 14-1/4 x 15 to make the 14-1/4 x 30". Then clean up the one glue line and sand to final thickness. The face will have a butcherblock look.
From contributor K:
If you get to choose the wood before buying, I would avoid any lumber that has a small arc in the annual rings, which would mean it was cut near the pith of the tree. Then as I edge glued each layer, I would try to plan to lay out each panel maybe started with the heart up, then down, then up, and be consistent as much as you can. If you are then going to glue sanded panels together, I would go with thickened epoxy for that. It will have plenty of open time, and likes to have that textured tooth to grab onto. I would vacuum bag that part. I would get thirty tons of pressure which is more than that would need. Do you have a large press, or how did you plan to clamp this up?
From Gene Wengert, forum technical advisor:
Make sure that the species you are using can easily be dried at 10/4 or thicker sizes. For example, the time to dry 10/4 or thicker oak is so long that it is more practical and economical to dry thinner and then laminate with more layers.
Epoxy will make a great joint if you do not squeeze it too hard. Epoxy joints need to be thicker than most other adhesives in order to be strong; thin is poor. On the other hand, would carvers like epoxy joints? Probably not, as the dried adhesive is so hard and difficult to cut.
Regarding sanded surfaces, not all produce weak joints; that is, a properly operated sander (not too much stock removal and a reasonable feed speed will do ok. Glue spread may have to be increased due to the rougher surface. Shear strength will increase but tension may not. (For example, if paper is dull or sanding pressure is too high, tension will fall). 690 grit is ok, but watch the feed rate for sure. Also, scraping (as mentioned) is a good idea. Grain angle of the individual strips really does not matter. Many other factors, such as MC and sharp (= fresh) sandpaper are much more important. Grain orientation is only important when using low grade cut from near the center of the tree (sharp curve of the rings).
