cross grain gluing

[chuck vernon]

In previous post I described my method of gluing up a board of strips of various woods, planing it smooth, cutting it in two, rotating the pieces 90 deg. and gluing the piecesytogether to make a bowl blank. A reply stated that they would not have rotated the pieces, as this could make it unstable. My theory was that it would make it stronger, kind of like plywood. Could someone explain how crossing grains causes instability. I am not gluing end grain in this process. Thanks.....

[John Keeton]

Chuck, when wood takes on moisture, or releases it, depending on ambient conditions, it will move (expand/contract) perpendicular to the direction of the grain - across the board for lack of a more technical term. Movement is dependent on many factors - species, ambient conditions, temperature, etc., but having boards glued together with the cross grain at 90* means one board will move at 90* to the adjoining board and could easily cause a glue joint failure - or, at the least, a palpable joint (not smooth.)

If you would like to email me, I will send you a document that explains in significant detail the shrinkage characteristics of wood, including various tables for most species.

[David Reed]

What John said... I was thinking if you rotated each succeeding board by perhaps 10-30 degrees, more or less. This would still stress the face joints some, although somewhat less, improve the resistance to cracking like you are looking to do and even provide some visual interest perhaps. This plus using available tables of wood expansion, choose those which are more stable. Vertical grain typically moves less than flat sawn boards as well.
Just a work around which may still work.

[Robert McGowen]

At least I know you read my reply! :) One additional fact, for me anyway, is that you would end up with a blank that is end grain,side grain,end grain,side grain, etc. It seems like tear out and sanding would be kind of unpleasant, plus the look of the alternating grain would not be the best, in my opinion. Good luck with you project though, however you choose to do it.

[Tom Wilson66]

The stability of plywood comes from having an odd number of layers, with the volume of the layers in each direction being about the same. That is one reason why the ourside layers are generally thinner than the inside layers. This "balances" the forces from expansion and contraction to keep the assembly stable. What you described would have two layers, each in a different direction. The affect of this would be the same as heating a bimetal strip, and it would warp like crazy. One piece I saw was a countertop a man had made by glueing a maple strip top to a plywood substrate. This resulted in an even number of layers, and the first time he put it in an area of differant relative humidity, it did a major cup. He had to competely remove the top and replace it. Since he didn't glue it together, and allowed room for movement, it worked just fine after that. Hope this helps explain the issues with the situation you were wanting to do.

[Richard Coers]

Veneer and solid wood don't act the same. When you get the wood thin in veneer, cross grain construction makes it very stable since the movement can be controlled. Solid wood will still move, and cross grain construction will not control that much power.

[John Beaver]

Wood movement behavior in turning is different from flat work. When you take the center away, the wood loses a lot of the support that a flat piece of wood has. A one inch thick donut of wood is a lot weaker and more prone to movement then a solid piece of wood the same diameter. The solid wood has the support of the rest of the piece to hold it's shape, where the donut has nothing to help hold it's form.

Picture what happens when you turn a wet log and the way it warps when it dries. Now what happens if you take another bowl and put it perpendicular to the first bowl. Because the wood moves across the grain, the two bowls will warp in different directions. Now imagine if you had sliced layers of those bowls and stacked them together. Eventually that contrasting movement will weaken those joints.

There is one more element in this that is often overlooked. If you take two pieces of wood and look at the end grain you will see that the growth rings create a pattern, I call these smiles or frowns. It is important to keep the smiles or frowns going the same direction. (I even try to match similar arcs of the growth rings in the two pieces). This not only helps in the future movement of the wood but is aesthetically more pleasing.

Robert also makes a valid point about dealing with turning a piece where the layers of end grain and side grain are adjoined. Turning and sanding would be much more difficult, and would tend to make a bumpy surface as the side grain will sand down more then the end grain.

[Reed Gray]

Well, if the pieces are small/thin enough, you might get away with it as the glue may be stronger than the wood movement, but it will be at war with itself forever.

robo hippy

[Thom Sturgill]

Well, if the pieces are small/thin enough, you might get away with it as the glue may be stronger than the wood movement, but it will be at war with itself forever.

robo hippy

I remember seeing an article where they were testing the strength of various joints and were surprised that cross-grain lap joints had wood failure just like straight grain joints, which is to say that the glue connection was stronger than the wood.

Most movement occurs in the drying stages. If the wood is kiln dried and kept in a relatively controlled area (ie in an air-conditioned house but not used in a kitchen, just displayed or used at the door to hold keys, on a desk as a candy jar, etc) then the movement should be very minimal and probably not a problem.

[John Beaver]

Most movement occurs in the drying stages. If the wood is kiln dried and kept in a relatively controlled area (ie in an air-conditioned house but not used in a kitchen, just displayed or used at the door to hold keys, on a desk as a candy jar, etc) then the movement should be very minimal and probably not a problem.

Wood movement is something that never stops !!! Wood absorbs and dissipates moisture with the changes in humidity, creating constant expansion and shrinkage. Even if the joint holds, the wood itself can crack. Even if it all works, it's likely you will be able feel the joint more as time goes by. It is possible that a piece with cross grain will hold up forever, but I think it's prudent to work with the potential movement and minimize the risk.

[John Keeton]

I agree with John - the movement is ongoing and is why one never fully captures a panel in a frame. And, why one always completely finishes the panel prior to placing it in the frame. It will contract and expand with the seasons.

However, on the stands I build for urns, the rings are created with two pieces of kiln dried maple laminated at 90*. To avoid problems, I always place the joint in a detail such that it cannot be felt in the event of movement. These rings are approximately 5" in diameter, and 5/8" both in height and thickness. I have had no failures, but much of that is also attributed to the wood being completely sealed on all surfaces, all wood being from the same board, and I use Titebond III for flexibility and strength to accommodate the minor movement that may occur.

[chuck vernon]

Thanks: You guys have been very informative.. I guess time will tell how the bowls hold up. Meanwhile I am having a lot of fun. Just bought some paduak and brazilian ebony today. Do not yet know what I am going to do with it.

[Nathan Clark]

I have had some bowls like you describe in oak and cherry for 20 years with no shifting or warping. Alternating grain looks much better than matching grain when stacking boards for bowls. I've lived in arid environments my who life and your mileage may vary. I can pictures if anyone is interested.

[chuck vernon]

Thanks: This gives me some hope for my bowls.

[Steve Peterson]

There is one more element in this that is often overlooked. If you take two pieces of wood and look at the end grain you will see that the growth rings create a pattern, I call these smiles or frowns. It is important to keep the smiles or frowns going the same direction. (I even try to match similar arcs of the growth rings in the two pieces). This not only helps in the future movement of the wood but is aesthetically more pleasing.

John, Can you clarify what you mean by keeping the smiles or frowns going in the same direction? Does this mean line them up as all smiles? Or alternate smiles and frowns so the growth rings form continuous wavy lines?

Steve

[John Beaver]

To avoid the wood cupping in different directions and causing more stress on the joint, the smiles or frowns should be going the same direction. This might be counter intuitive to flat workers, but wood turnings move differently from flat work. Solid wood bowls have movement and the goal with laminated bowls is to work with the natural movement so everything moves together. Trying to counter the natural movement is what causes joints to weaken or fail.

Nathan: I am glad you have had success with your pieces, I would love to see them. This is a discussion often had in the segmented community, where one person has had success and others failure. Where I see failures I want to avoid that situation.

I always wondered how those large salad bowls built with alternating grain could work. And while I'm sure they've had many succeed, I saw one the other day that had completely failed - way beyond the point of any repair. To me, even one failure is not acceptable.

[Robert McGowen]

I sell about 95% of what I make and it is usually shipped by UPS to a place with an entirely different climate than where it was made. Like John said, just one failure would not be acceptable. If I wanted to risk it on my own coffee table, that is fine, but I try to use the best technique available when it is sitting on someone else's table.