veneer problem - warping

[Jim Delucas]

This is my first post and, unfortunately, I need help.
I tried my hand at making a chessboard out of maple and mahogany veneers over a substrate of MDF. I used The backing was also maple. I used Tetebond II as mu adhesive. After 3 hours I released the vacuum from my vacuum press and pulled out the cauls with the work in between. What I got was a big disappointment but a lesson learned if I can figure out what happened. The mahogany squares came out flat and looking good. The maple, on the other hand, almost every maple square and part of the maple backing came out of the press warped.
Help!!! I'd like to try again.

[Tim Martin]

Hi, can you take any pics to help describe your problem a little better?

[Mike Henderson]

I would recommend that you do some test gluing with the maple only and try to find out why it's warping. Usually, when you glue a piece of veneer in a press, it comes out flat. If the glue was not good (maybe not enough or not cured) it will warp after it's out for a short while, especially if you put water on the veneer to remove the veneer tape.

The test I'd do is to glue up some of the maple to some MDF and do the following when you take it out (this assumes the veneer is flat when you take it out of clamps):

1. Try to peel it off as soon as you take it out of clamps (take a chisel and try to pry it apart). If it peels, the glue has not cured and you need to find out why. Maybe the glue's bad or you didn't leave it in clamps long enough.

2. If it passes the first test, spritz it with water and set it aside. After about 10 minutes take a look at it. If it's warped, the problem is not enough glue. The glue is holding in places but not in others. You need to use more glue. With some veneers excess glue is a problem because the glue will come through the veneer and ruin the finished work. However, maple is not usually a porous veneer. Try some more sample pieces with more glue and see if the glue comes through.

If your problem is warped veneer right out of the press, I don't know what to suggest - I've never seen that. The only thing I can think of is that you're not getting a proper press. That is, the caul is not pressing flat against the veneer which allows it to warp.

When you mix two types of veneer, it's possible that one will be thicker than the other so the thinner veneer really doesn't get pressed. The way you deal with that is to put a piece of plastic on top of the veneer (to keep the glue off the rest of the stack), then a piece of duck (or canvas) cloth to accomodate the different thicknesses of veneer, then your MDF caul.

That's about all I can think of.

Mike

[Mitchell Andrus]

I'd recommend a glue that's made for pressing veneers. More solids, bigger solid particulate and lower moisture content. All of this helps control seepage, creep and warping. Also, leave the glued panel open for a few minutes to release some moisture before placing the veneer down. When vac pressing with H2O based adhesive, I place a few paper towels on the surface to wick surface seepage.

You might also try a solvent based adhesive. I've been tinkering with 1/2 and 1 hour clear epoxies. By the gallon and given that you use less per application, not too expensive. Peels off the inside of the bag too.

JW below has a great pre-catalized veneer adhesive, Ultra-Cat.

http://www.joewoodworker.com/catalog/default.php?cPath=40&osCsid=7aba19b16106fd2789a26125df41e593