Glue ups and expansion/contraction

[Chris Skoglund]

Hello everyone. New to all this. Where can I turn to get information on understanding wood expansion and contraction and how that affects gluing wood together? For example, can you glue faces of the same wood together? Can I glue the broadside of maple lengths together? Can I glue the narrow edge to the broad edge? Can I glue hardwood or softwood to plywood? From the little bit of google reading I've done it seems like a complicated subject. I'm looking for a good reference site. Thanks in advance!

[Art Mann]

Here is a calculator I have used in the past to estimate expansion/contraction. I don't know how accurate it is.

http://www.woodbin.com/calcs/shrinkulator.htm

I don't normally glue different species together and certainly not hardwood to softwood because of the different expansion coefficients and moisture uptake/release characteristics. I have made cutting boards of mixed hardwood species with good results. I have never had any problems gluing narrow edge to broad edge and I have glued up 1 inch thick material to make 2 inch thick material many times. The critical thing is to use perfectly jointed and flattened material to get the greatest possible wood to wood contact. A crack you squeeze away with clamping pressure will eventually reappear. The problem of wood expansion and contraction is indeed complex and you must always be aware of its potential problems, especially on long pieces.

[Jamie Buxton]

There is an excellent book about the physics of wood: Understanding Wood by Bruce Hoadley. It has been a basic reference bible of mine for thirty years.

[Marvin Wilson]

Here's a chart that gives typical expansion and contraction rates for a variety of species http://workshoppages.com/WS/Articles/Wood-Movement-Charts.pdf. It's a little simpler than Hoadley's epic work but still quite helpful. And I want to include a link to one of my favorite wood sites for your enjoyment, if you love wood you will enjoy this. http://www.hobbithouseinc.com/personal/woodpics/#letterA
It's a database with thousands of images of different varieties from around the world.

[Jim Matthews]

Glue joints are strongest long grain to long grain.
You're right on the money about Seasonal expansion breaking glue joints.

That's where mechanical joints have their place, to bolster the strength of the glue bond.
It's my growing belief that laminations are much stronger than the average maker's mechanical joint
and have a place in building quality furniture.

The catch is that you must be very careful about the surface you "show" on the outside of these constructions;
and getting veneer right has proven trickier than I anticipated.

*****

Here's how I manage laminations, like the one you describe.

If I'm gluing face to face as you describe, I rip the board down the middle and flip one piece 180 degrees on the short axis.
This puts the grain in opposition and makes a very strong assembly (http://www.woodworkersinstitute.com/page.asp?p=1663).

Gluing any wood to a plywood substrate will require either an extremely thick base piece, or a veneer of matching thickness on the opposite side.
Recent experiments with shop made veneers have left me with heavily warped 1/2" plywood panels with 1/4" thick shop veneers.

The exposed surface of your veneer will absorb moisture and change shape with tremendous force.

Follow this link (http://www.joewoodworker.com/veneering/backer-veneer.htm) for a concise explanation of the problem and some solutions.

******

I'm a newbie at this, less than 4 years trying to do things so they'll last.
I believe that the traditional mechanical joints will last the longest, as they're the ones we can still find in ancient buildings and furniture.

That said, laminations offer tremendous flexibility in making furniture and if properly applied, can be much stronger than solid wood.
I recommend further reading on the subject, including a search of Gary Knox Bennett from Oakland, CA.

I don't know if he's the first to apply these laminating methods to fine furniture, but he's the first I saw do it, and I copy much from his playbook.

A recent post here from Paul Miller showed a Sketchup drawing of a trestle leg design (for a workbench) that exemplifies the technique.
The idea is that in using laminates of quality plywood, you can build a void in any given part by leaving out material, rather than
using tool to remove wood to make a pocket, groove or hole - it requires planning, but the results are compelling.

At the end, you can apply the veneer of your choosing as a "show" face.

Having seen furniture made with plywood of the highest quality, I can say I was completely fooled into believing was solid wood construction.
Inset feet in the hollows of the legs, face frames around the drawers and heavy banding were all used to cunning effect on wear surfaces.

I'm now migrating to plywood for any uninterrupted panel larger than a drawer bottom, with shop veneers applied.
Hardwoods for joinery and moving surfaces, plywood for the "flat and straight" parts.

******

If there's a community college nearby, or a woodworking school that offers weekend instruction - a few hour's tuition will save you months of struggle.

[Chris Skoglund]

Thanks a lot everyone. I just ordered Understanding Wood.

[Chris Fournier]

Thanks a lot everyone. I just ordered Understanding Wood.

Jamie's advice was excellent and you will not be dissappointed. This is a must have book for any woodworker and a great investment for you. Enjoy!

[Wade Lippman]

One thing you have to remember is that today houses are airconditioned in the summer and humidified in the winter. Stuff that would have been disastrous 50 years ago is fine today. 6 years ago I put some tight fitting curly maple drawer fronts on 90* to the correct orientation because they looked much better; figuring I would rebuild it if they stuck in the summer. Doesn't stick in the summer or leave a gap in the winter. Really doesn't seem to move at all.

And modern glues give plenty strong joints on end grain; I have several end/long grain joints that are fine after many years.

Doing it right is always better when practical, but climate controlled houses excuse doing it wrong.

[Richard Coers]

One thing you have to remember is that today houses are airconditioned in the summer and humidified in the winter. Stuff that would have been disastrous 50 years ago is fine today. 6 years ago I put some tight fitting curly maple drawer fronts on 90* to the correct orientation because they looked much better; figuring I would rebuild it if they stuck in the summer. Doesn't stick in the summer or leave a gap in the winter. Really doesn't seem to move at all.

And modern glues give plenty strong joints on end grain; I have several end/long grain joints that are fine after many years.

Doing it right is always better when practical, but climate controlled houses excuse doing it wrong.

You make no reference the the cut of hardwood that does not move for you. Suggesting that you can ignore expansion and contraction because houses are climate controlled, is dangerous advice to a new woodworker. With your advice, he can go ahead and glue any solid wood to one side of plywood because wood never moves in upstate NY. I suggest your advice could not be worse. Never ignore the most basic rule of woodworking, all flat sawn wood expands and contracts in it's width, no matter where you live. ALWAYS! Quartersawn moves a lot less in it's width, but more it's height. Even then, I would not ignore wood movement, never!

[Mel Fulks]

There IS a difference between movement of kiln dry and air dry . I think movement of kiln dried is often exaggerated .

[Wade Lippman]

You make no reference the the cut of hardwood that does not move for you. Suggesting that you can ignore expansion and contraction because houses are climate controlled, is dangerous advice to a new woodworker. With your advice, he can go ahead and glue any solid wood to one side of plywood because wood never moves in upstate NY. I suggest your advice could not be worse. Never ignore the most basic rule of woodworking, all flat sawn wood expands and contracts in it's width, no matter where you live. ALWAYS! Quartersawn moves a lot less in it's width, but more it's height. Even then, I would not ignore wood movement, never!

Isn't all curly maple flatsawn?
Anyhow, I didn't say he should ignore it; in fact I said exactly the opposite, that it was better to do it right.
I merely explained it wasn't as important as traditionally if the environment was conditioned; and if you feel that couldn't be worse advice please ignore it.

As a matter of fact, my first WW project was a trunk with cherry glued to plywood. It is the same (abeit darker) as the day I made it 10 years ago. I followed commercial plans and the author correctly didn't have a problem with that. Okay, it was effectively quartersawn, but still....

[Howard Acheson]

>>>> Where can I turn to get information on understanding wood expansion and contraction and how that affects gluing wood together?

The best source is Bruce Hoadley's Understanding Wood. Amazon will have it.

>>>> can you glue faces of the same wood together?

Yes...


>>>> Can I glue the broadside of maple lengths together?

Yes....

>>>> Can I glue the narrow edge to the broad edge?

Yes....

>>>>Can I glue hardwood or softwood to plywood?

Yes and No.. but only the edges, not the face. Plywood and other composition materials (hardboard, MDF, chipboard) have virtually no movement due to changes in moisture content. Whatever little movement they have can be ignored Solid woods have quite a bit of crossgrain movement and it varies by species.

[Cody Colston]

Regarding wood movement, I recommend reading in Hoadley's book, the opening paragraph of chapter 6. Wood and Water.