Wood Expansion

[tomscanio]

In veneering it seems that you can apply a veneer to, say, MDF. The two must have different expansion rates, but apparently that's not a problem. I've never done veneering. This is what I read.

However, if you take, say, 3/4 inch wood and edge join it to make a table top, you're not supposed to put it on plywood or MDF because the differing expansion rates can cause the top to buckle.

If both of these are correct, where is the magic point in wood thickness where one technique is OK and the other isn't?

Thanks for the help.

Tom Scanio

[rollo]

Good question, Tom (this relates to my post on the finished projects, probably better to have started a new thread). I looked on the internet for "thickest veneer" and couldn't find much. I'm going to try to glue a 1/2" thick piece of walnut (about 9x18") to 3/4" thick baltic birch ply. I'm not sure what will happen, but it would be great if someone who's done this before would weigh in. I really don't want to have the walnut or BB box crack after glue up.

[Russianwolf]

It seems like I have seen David Marks use vaneers about 1/4 inch thick, but I could be wrong.

But I can say that the thickness that would work will be VERY dependent on the wood. Some types of wood, Padouk for example, move very little. So a thicker piece won't have an effect in cases like this.

[Tom Miller]

I think the issue is the total force that the veneer can apply when moisture variation is compelling it to expand or contract. If the veneer is thin enough, the total force is not enough to measurably affect a 3/4" piece of mdf. The mdf will keep the veneer from expanding in that plane, though it may expand in a perpendicular direction.

If the veneer is thicker, the total force is greater, and will either cause the mdf to bow, or the glue interface may fail. Same is true when the mdf is replaced with "real" wood; now there are competing forces.

The preceding isn't based on firsthand knowledge through woodworking, just idle speculation.

Regards,
Tom

[JimD]

I have not tried veneer more than 1/8 thick but I am pretty sure 1/2 inch is too thick, expecially since it is not tiny. What will happen is the glue will not be able to withstand the force and the pieces will separate. When I can, I prefer to install veneer over lower grade wood of the same species. If you are putting wood on top of something that will not move, you need to be thinking of something a lot thinner than 1/2 inch IMHO. Size makes a difference too, I suspect and 9x18 is pretty small assuming that 9 inches is across the grain. I still don't think it will hold together.

Another variable is your climate. The humidity swings are different in different parts of the country and world. This is more like to work in Phoenix than were I live in South Carolina.

Jim

[leehljp]

This is something I have thought about for years. Did my first veneering job in the late 60's with walnut over plywood. Did OK for a first timer, had a little help from an experienced uncle.

I would not attempt veneering over 1/8. 1/16 is more suitable. I haven't talked with anyone but just plain observation of veneer on furniture a hundred years old to more recent - there is something about the wood that when it is thin in the veneer form - it does not expand and contract like thicker pieces do. I think it has to do with the oil, varnish, lacquer, or poly finish that manages to make its way into the cells all the way through on the thinner veneer, filling or driving the moisture out so that the wood does not move like the thicker wood does.

Look at fine veneer furniture a half a century old or older, it does not move, and it is usually around 1/16 or less thick

[rollo]

so how are the salk speakers done?:
http://www.salksound.com/gallery-avail.html
Screwed with expansion slots? I wouldn't think this would be acceptable to a high end speaker mfg due to the rattling that could be heard between the cabinet and the baffle. Glued with caulking or rubber cement?

[drumpriest]

When veneering, it's very important to veneer both sides with a similar material, so that you don't cup or bow. Most commercial veneers are about 1/32" thick. David Marks typically uses 1/16" veneers, he cuts them at about 3/32" and drum sands them down to final size.

[tomscanio]

Thanks

Thanks for all the input. I really do appreciate it.

Tom Scanio