Question
I am in year three of joinery/cabinetry school and have been assigned a weekend project. What are the steps to build a curved 17" X 22" X 3/4" thick solid wood door with a radius of 60"?
The door can not be made from plywood and can not be veneered. So when it's done it will have a continuous solid plank appearance. End grain showing on top and bottom. I'm allowed to ask around because he wants to see what we all come up with.
So how would you build this door? If I was to cut some 8/4 stock down and glue up a board (say with 10 or so pieces), would this, when steamed, still bend over a form? Or because of all the glue joints, would it be too stiff to bend?
Forum Responses
(Architectural Woodworking Forum)
From contributor S:
The technique you are looking for is coopering. Google the term. Trying to seam bend the curve the way you describe is not going to work. The glue joints would fail and the long grain would split.
Your stave pieces could be six straight pieces (2.83") with their edges beveled. These will lie over a radius form and simply be edge-glued together to form the arc. Your arc is not that great, so you should be able to progressively glue and clamp them together starting with the middle two pieces. After it's dry you just scrape and sand it round. You could increase the number of stave pieces if you want to form a more perfect arc, but the method is the same.
Draw it out full size to determine the best thickness, width and bevel angle. These kinds of curved door panels are almost always veneered and with end-grain caps, but your assignment seems focused on finding a suitable construction method.
Anyway, no steam bending here and no internal fastenings or hardware required. This is probably the quickest method and the one most often employed in the past (before plywood and vacuum bags).
Another approach might be the kerf cut method. Glue up your full 3/4" panel flat and then kerf the inside (concave side). Use a dado saw and remove 1/2" of material every inch or so to enable the panel to bend. Clamp or glue it down into a concave form and glue solid filler strips into each dado. These strips must be cut perfectly to fill the now dovetailed dado slots.
This method has the advantage of presenting a solid curved panel with a smooth convex face of your choice. A bookmatched face might be the best choice here.
Now make a curved blank out of 3/4" MDF. It should have an outside radius of 61" and an inside radius of 59". Next, resaw this guide strip into two pieces (this saves time and ensures that they're identical).
Take your blank and attach the MDF strips to either end. Be sure to attach them in alignment with one another or you'll wind up with a twisted door. When attaching the second side of the second guide strip, place the whole assembly on top of the table saw table (convex side down). All four corners should be making contact.
Make up some kind of adjustable fence for you new router table, and starting with it close to the bit, guide the piece over it and you'll get a perfect cut. Move the fence 1/4" over and repeat till done.
The reason for making the router table as narrow as possible? To be able to make tighter radius doors. This will work not only for true radius doors, but for irregular shapes as well. Just make sure the guide strips are the same and in alignment.
The only one I can’t quite wrap my head around is your idea, contributor M. After you plunge the router bit 1” up through the fence, how is it being used to cut the solid wood panel? If I move the fence after the first cut over 1/4", it will cut through the fence I plunged though. Or are you saying that I’m moving my second custom fence forward and back? And if I have two curved MDF guides in the radius I want, how am I attaching them to a straight panel? Or is my blank a big block at this point? Say 18” wide by 24” tall by 3” thick? And I’m cutting all the material out into a curve, on your router table idea?
If you add a second board to the first, you can cover up the kerfs in the back simply by laying the kerfed sides facing one another. Insert glue on the back sides and bend to the radius you wish. Hold in place with tape on a curved caul, let the glue cure for a day, and presto - a bent panel for your door.
True solid door panels would be shaped/carved using solid stock. Cut a solid wood block slightly larger then the door panel. Lay out the arc on top and bottom. Set table saw depth and fence appropriately to cut to the layout marks. Move fence and saw height and repeat until each side is scarfed continuously about 1/4" apart on both sides. Remove excess with slick and sand smooth.
Set your tablesaw to 1 or 1.5 degrees off true, then rip 1" wide x 13/16" stock on both sides. Do a few pieces, lay them together to see how they sit, adjust the angle as needed (by eye). When 5 or 6 of these small parts look good, get to work. I'd say that you need 23 pieces. Use a good blade. Once cut and fitted, cover the forms with saran wrap, apply Titebond type 2 extend wood glue. It'll give you enough open pot time to glue up the staves. Make sure that your assembly is at least 1/2" longer and wider than finished size. After it's glued up, secure the two forms around it with strap clamps. If you don't have them, use a few angled blocks and clamp it up.
Once cured, use a scraper to remove the bulk of the glue, then sand it to where you want it to be. Or use a good scraper (curved) to bring it to true. Then you'll probably need to hand sand to finish. Tape your fingers for this part - trust me. This is inexpensive.
For gluing up, I like epoxy, because there's plenty of open time, and you need very little clamp pressure. For clamping, I like a form with the arc for the outside of the curve, leaving a tab at one end of each form to clamp against. Then a hole drilled somewhere underneath, along a tangent to the other edge, allows the clamps to push all of the staves into the form, for one easy glue-up.
Use a right angle disk grinder with 24 grit for hollowing the inside, to start out.
The blank should be glued up from 5/4 or 6/4 staves about 2" to 5" wide based on the necessary desired radius, if a slab construction is desired. The blank should be slightly oversize in length, thickness, and width. Pay attention to the thickness in and out of the desired radius. A simple jig would be made to the convex outside radius of the door and a sled made to carry the router over the face and route away. The inside of the door can be left segmented if a secondary interior. Or a jig and a sled made for the router to run the concave interior side. The bottom and top rail can be bandsawn, then finished on the same jig. The vertical stiles are straight then sanded in to radius. A bit involved, but predictable at about 12 1/2 man hours for a nice one off door.
Comment from contributor E:
Contributor M described a milling table for your router. Once you have the coopered or staved blank drawn up, it is a great way to mill it precisely to shape. Start out with the idea and see if you can follow his description: You make matching templates for the ends of the panel and attach them, being very sure they are perfectly aligned. They need to be larger than the panel all the way around - say an inch larger, for conversation's sake. Then you roll this form over a router with a bit that projects the same amount, in this case 1" exactly.
If you were just doing a convex form, this would be enough. However, since there's a concave side you need either a narrow or a shaped table to pull it off.
Here's a tip for gluing up the staves: after you rip and joint them to the right width and angle, use clamps this way to glue them up: Put two pipe or bar clamps on your bench and arrange the glued strips between them, making an arc. Place caul blocks at each end, curved to the radius you want for the outside. Clamp the caul blocks down into the slats while you (and a friend) adjust the bench clamps to the proper width. You get clamping action by pulling the arched staves down into clamps set at the precise width of the finished panel. It's much stronger than a band clamp because of the mechanical advantage.
