Mold makers often use of this technique when making castings patterns. Layers of wood are temporarily glued together in a way to be easily pulled apart after the carving or milling work is done. After a casting pattern is made, it is often separated into two or more parts for making a sand mold for casting. This is a useful trick when needing multiple identical parts in wood – say two identical halves of an item, etc. Of course you can use it for making more than two pieces too, within practical limitations.
The idea is to glue two or more layers together so the layered assembly may then be cut or milled to profile in one operation, then separated. The glued layers end up all being cut to the same identical profile. You can do this by nailing or screwing layers together of course, but must then worry about the nail or screw holes showing up in the finished product, not to mention the fastenings are a hazard to your saw blades and tools. Glueing everything together is one good alternative.
How are the layers separated after being cut or milled to profile? The mold maker’s method makes this very easy and simple. The individual layers are separated by paper, placed between each piece as the pieces are glued up. The individual layers are pried apart after the work is done, with the separation occurring within the paper layer itself. You end up with each layer being coated with a thin film of glue and paper, since the paper splits within itself. This glue/paper film is then scraped or sanded off. (Note: Glue should be applied to BOTH sides of the paper.)
Using a slick paper seems to work best for me – like glossy newspaper advertising inserts. Regular newsprint or notepaper works too, but the slick stuff seems to part more uniformly with a thinner film of paper stuck to the pieces because the glue does not soak all the way through. Then, there is the glue. Normal white or yellow glue like Titebond™ works, but thinning the glue down helps considerably for making for a far easier separation and clean-up afterwards. A one-to-one ratio of glue to water works just fine, can be applied with a brush and is quite strong enough to hold most things together for the milling part.
Another helpful bit is to leave a piece of extra stock on one end of the glued together pieces as it is milled to profile. This is so you can insert a chisel or screwdriver to separate the pieces without damaging the main portion of the part. This extra bit is then trimmed off after things are separated. Also, a small undercut or nick in this extra bit helps as a point to introduce your chisel. See the sketches which should be self-explanatory.
I have successfully used this method for lathe stock too – when needed for making multiple pieces like wheels or rollers. As a safety measure when glueing up parts for the lathe, drill a hole on the centers and run a waxed dowel the same size as the drilled holes through the centers as the parts are glued up. The wax keeps the glue from sticking to the dowel. A thin wax coat can be put on the dowel by slightly heating it with a propane torch or heat gun while rubbing a stick of paraffin wax over it. I have also seen sprayed-on wax used but don’t trust the idea much myself. To make it easy to separate the parts after the lathe work is done, use a parting tool while still on the lathe to slightly nick the edges of the pieces at the paper separators. Then a light tap with a chisel at those points will separate the pieces without marring them. The dowel may be tapped out with a slightly smaller round rod or punch.
Here’s a corollary, earlier post which expands on the idea a little: http://lumberjocks.com/GnarlyErik/blog/35605
I hope these little tricks are of help to someone!
-- "Never let your dogma get run over by your karma!"