Recently I took a job that is going to use crotch mahogany veneer. I do not have a press of any sort and am wondering what the best way to get it flat is when I glue it up. I have already started this project and have waves or bumps in the back panel. I have the doors and the top left to do. The doors should not be an issue, but the top is 18" deep by 56" long. I will lay out one long piece. The veneer is almost 1/16" thick.
From contributor F:
Naturally, a press is the best way to bond veneer to a substrate. However, there are other methods.
Always use a platen on both faces as you clamp or otherwise apply pressure. In your case, a good platen would be flat 3/4" thick particleboard cut to the same dimensions as the part you want to apply veneer to. The platen's purpose is to spread the clamping pressure beyond the footprint of the clamping device. You can make clamping cauls from some beefy and stiff solid wood material of your choice. Should be somewhere in the neighborhood of say a full 2" by 4". These cauls should be made slightly convex on the edge that will be placed against the platens. I usually make them with a 1/4" maximum bow. The purpose of the bow is so that pressure will be applied to the center of the pressing as well as the edges where the clamps will be applied. The cauls are used in pairs on the outside of the platens, one on each face, and in line with one another. Use your common sense to determine how many pairs of cauls it will take to apply enough pressure to the size of the part you are veneering.
The process is:
Apply your adhesive to one side of your substrate and place your oversized veneer on the glue. Apply adhesive to the second face and put its veneer in place. Align the two 3/4" platens on each side of the veneered part. Place this sandwich on top of a set of cauls which rest on a table at the correct spacing. Place the mating cauls on the top of the sandwich in alignment with the ones on the bottom. Apply clamps to the outside faces of the caul ends and apply light pressure until you have all of the required clamps in place. Gradually bring the clamps to full torque and breathe a sigh of relief.
1. Either wax the cauls (contributor F calls them platens - the sheet goods you're pressing between) or put waxed paper between them and the veneer. Otherwise, you're likely to find your veneer glued to them.
2. Consider doubling up the thickness of the cauls to at least 1".
3. Get as many heavy-duty clamps on this thing as you can fit.
4. Plan for the weight of this whole apparatus so that it is well-supported and you don't accidentally end up making a curved panel.
5. Apply your glue with a roller to get a thin, even glue line.
6. Very often crotch veneer needs to be treated and pre-flattened. Search the Knowledge Base here for recipes and sources of flattening solution.
Crotch is one of the most difficult veneers to work with; I strongly recommend trying this method with another veneer first and deciding whether it's for you. At the end of the day, an 18" x 56" crotch mahogany panel is really a job for a press. Can you not find someone near you to press it for you?
1. Don't use a yellow or PVA glue unless you want checks and splits in the crotch. Use a urea resin glue; this also has the benefit of a longer working time. A 2 ply lay-up would be even better.
2. If you decide you have to do this yourself, make absolutely sure that every square inch of the veneer surface has adequate pressure to hold the veneer flat until the glue sets. It would be time well spent to do a practice piece first.