I made the single-curve nightstands in the photos above, but the same steps I've used here, including many rules of thumb and limitations I discovered along the way, could easily be applied to a wide range of bent ply pieces and parts. Once you've made the molds the nightstands are easy, so this is a great project for designs with lots of self-similar parts, too.
You can check out more and larger images of the finished product on my website. http://www.phil-seaton.com/ Click "NightStand" once you get there.
Step 1: Tools and Materials
In addition to some everyday items, such as a paint roller & tray, quart-size mixing container, sandpaper, etc, a few special items are needed:
Glue: I recommend DAP Weldwood Plastic Resin Glue. It comes in a powder form and mixes easily with water; it cures chemically to an ultra-hard brittle glue with absolutely no give. This is important, as the layers must not be allowed to flex next to each other to maintain the curves. Also, the chemical cure helps to make sure the glue in the middle, far from any air, still cures completely.
Particle Board / MDF: Your mold will need to be made solid, so be sure to purchase enough for both sides of your mold, including at least 2-3" beyond your actual piece. I highly recommend assuming that the two halves of the mold will come out of a rectangular area, as the parallel outside edges will need to be clamped to each other. For this project, I used exactly a full sheet of 3/4" Particle Board.
Veneers: There are several factors to consider when choosing veneer for your project. 1) The look you want on your final piece 2) The tightest curve you're planning to bend (I recommend bending a small piece around the tightest curve in your mold to make sure it doesn't snap) 3) The number of layers you'll need given the veneer's thickness and 4) The type and thickness of your interior veneers (which aren't as visible as the surface veneers).
Veneer Tape & Roller (+ a spare sponge): Veneer tape is special stuff that shrinks as it dries, closing gaps that may have been present in your veneers before taping the edges together. Chances are very slim you'll have veneers the right size & shape for your project, so you'll need this to make large enough continuous sheets. You apply water to one side (like a stamp), and then roll it on with a hard wood roller.
Dowels & matching drill bit: You'll need these to align the slices of the mold as they're cut, and also to stack them all once they're done. You'll need at least 3 dowels per side of your mold, and it helps if they're all in once piece. So if your piece is 2' wide and you can only get 3' dowels, I'd recommend buying at least six. Get a spade bit to match; 3/4" or 7/8" for dowels and spade.
Flush-trim Bit: Once you've got one slice of your mold perfect, you'll be using a flush-trim router bit to make the others exactly the same. Get a good beefy one, but make sure it fits your router. I found a bottom-bearing bit to be easiest for the setup, but you should be able to make it work with a top-bearing bit also if that's all you can find.
2x4's (qty 2 or 3) for clamping cauls (if you make these curved cauls they can save you some clamps, but they're not totally necessary)
Stop and reconsider if you don't have, or don't want to buy, the following tools which can be found in most well-equipped shops:
- Table saw. A nice heavy one is always best, but even a contractor's saw should do for this
- Band Saw. For rough-cutting mold slices
- Router. For flush-trimming mold slices
- Heavy clamps (you'll always need more than you think. Make sure you have some long enough to go around the longest end of your mold.
- Drill press (it's critical that the holes you drill for registration of mold slices be drilled straight!
Step 2: Design Your Profile
As you explore the design, try to come up with ways to employ the special properties of bent ply. In this design, the uniform strength in all directions throughout the curve prevents the design from having weak "break points" which would require much thicker wood if separate pieces or solid wood were used.
Step 3: Iterate & Select Final Design
It's helpful to do simple studies in CAD software. I use Rhino, but almost any software package would help to explore these sorts of implications.
Step 4: Build the Molds
Once you've cut one carefully on the bandsaw, sand down using a (1" belt sander if available) to the exact edge of your profile curve.
Step 5: Cutting Mold Parts / Mold Assembly
Mark these first two pieces as your template. To use the template to generate an identical slice:
1) Drill the registration holes through first.
2) Drive short dowel segments through the template and the new slice
3) Rough cut the new slice on the bandsaw. Make sure not to gouge the template, as it will affect all future slices!
4) Clamp the template piece and new slice to the workbench, and use the router flush-trim bit to cut both pieces identically.
5) Remove the new slice and repeat until you've built up the full thickness of the mold. Apply wood glue between each layer as you stack them together on the longer dowel sections. When they're all in, Clamp the mold together while the glue dries.
6) Scrape any excess glue from the mold surface. It must be completely smooth!
Step 6: Verify That the Mold Halves Fit
In this image, you can see the positions of all the dowels, and the measurements I've used on my night stands.
Step 7: Prepare Your Veneers
2) Cut the veneer edges straight if necessary, and tape strips together using the veneer tape and roller into full rectangular sheets. For the outermost layers, put the veneer tape on the outside (it can be sanded off at the end).
3) Alternate grain directions with each layer (the crossgraining is very important for strength). You can likely use thicker veneers for the cross-grain sheets, as the wood will be much more flexible in that direction.
4) Make sure to use an ODD NUMBER of veneers.
5) Make sure your stack is symmetrical around the center! You shouldn't have different wood on the different faces, or a different pattern of veneers going out from the center one.
Step 8: Glue Up
1) Use a paint roller to coat BOTH SIDES of each veneer sheet in glue. DO NOT coat the outside faces of course! MOVE FAST. You need to make sure you cover everything, but by coating both sides you should be saved from any quick work missed spots.
2) Place a layer of wax paper on each side of the stack to keep it from gluing to the mold with any excess glue.
3) Insert veneer stack into the mold
4) Apply clamps
1) If you're doing this in your living room, as I was unfortunate enough to do, don't tell your landlord about the project!.
2) Be careful not to breathe the dust form of the glue. It's nasty stuff. Mix it outside. Once mixed, it's mostly odorless and can be used indoors.
3) Don't be shy about how much glue you mix. If you have a little extra, that's fine. If you run out, it's game over for the project, and you've just ruined a whole bunch of expensive veneer.
Step 9: Wait
Step 10: Pull the Nightstand Out of the Mold
Don't be disappointed if the piece is very rough looking around the edges. It'll clean right up!
Step 11: Clean Up the Final Piece
If everything has gone to plan, you'll see the beautiful edges of a new bent-ply piece of furniture! Congratulations!