I am searching for a plywood substrate commonly referred to as calibrated or platform, in a 3/4" x 4' x 10' panel, for laying up wood veneer on both faces. The substrate grain must run the 4' direction. My local distributor reps Columbia products and cannot get it at this time. Who else manufactures this? If I have to freight if from anywhere in the USA, I will consider that. Will also consider a combicore type product. I prefer not to build my cabinetry from MDF.
From contributor C:
That's hard stuff to find these days, and the all ply platforms are not very stable. We can make a crossbanded, basswood strip core which you can press to. It is stable, lightweight. We could also make blanks or sheets with face and back veneers for a 5-ply product. We usually do a cut to size format for furniture and higher end cabinets.
My experience with these platforms was, to put it mildly, a pain in the butt. I had two guys filling voids and holes fulltime just to get it ready for calibration. Another problem I had was with the thickness consistency of the plies - all over the place, in some cases up to .040" in thickness difference from one side to the other. By the time I was finished calibrating, I was a good bit into the next ply. About 75% of the platforms I worked with were in terrible shape prior to me doing anything. I usually wound up having to crossband the core after I was able to get some kind of uniform thickness across the board. My suggestion is to stay away from this type of substrate, if it's even available.
You brought up the idea of sanding off the veneer face of one side of a plywood substrate and replacing it with something else. Here's the problem with that - once a plywood substrate is calibrated, pressed with a veneer face and back, preferably with the same species or a face and back with the same density and allowed to stabilize, it develops a kind of memory that is unique to that specific board. It sounds strange, but the substrate accepts the covering veneer and the covering veneer accepts the substrate, therefore creating stability. It's a very touchy process that requires the right formula to work.
Now don't get me wrong, I have done exactly what you suggest and have had both success and failure. If you have the machinery and the means to modify a plywood substrate to suit your needs, i.e. a good sander and a decent press, I would suggest lightly sanding both sides with an 80-100 grit belt and applying a face and a back to the board. If possible, cold press the board - this will limit any warp. Sanding off one face will open up the plywood to the elements, therefore creating the possibility for warp. You're messing with the critical part of any piece of wood - its balance. By building up - or should I say, applying equal face construction to both sides of the board - you're maintaining some kind of balance. Now most would argue that you shouldn't add plies of veneer going in the same direction - that you should crossband and recalibrate, then add your plies, and I agree, but if done properly you could get by with the method I suggested. For cabinet parts, okay. Wall panels, cab doors, no. Bite the bullet and just go with veneered MDF or particleboard. Why go through the hassle?