I suggest after making a paper template, that you use a straight edge to bisect the oval, and mark the exact center. Then turning the straight edge at angles and across the exact center, mark an angle or two. Use a protractor to measure the angle of the new line, and set the straight edge to the same angle relative to the center line and mark the new line. That will give you the angles you need to cut on the straight pieces in order to form the oval. It will also tell you how long the pieces need to be (outside circumference of the oval).
Use a compas to trace the template outline about 3/8ths in from the outline to allow for the rabbet. Then use the same method to mark another line to the outside of the template's mirror size, out to the width you want the frame to be, and draw a second line. With the bisecting lines marked, you can then work out the width of the material you'll need to cut and assemble in order to cut out your final frame. It will be much wider than the frame width. You may find you need to add additional segments in order to use available material.
You will find that you need carefully milled material. Warps, twists, bowing will make it impossible to make a decent frame, so start with strong, straight grain material--you'll likely pay a premium, and the wider the stock, the more you'll pay and the harder it will be to find acceptable stock.
Cut the pieces a little over sized on length, then mark the angles as precisely on each piece. Be very careful to lay the pieces out and mark their locations, and the back so you don't mess up your cut. Personally, I'd produce two long pieces extra because being human, I WILL mess at least one cut up.
Cutting exact angles is always a challenge, particularly since they will vary around the circumference. I'd bet the pink slip on my car that you will have to use a block plane to perfect the angles and fit to make it form a closed oval.
I would cut slots and use splines to connect each part, cutting the slots face down on the router table. This will assure that your face will be relatively even. Since you cutting slots into the end of the long train, your spline can be long grain as well (whew, that's easier). There are all kinds of joints you could use for this, but splines are simpler and less likely to be messed up.
Once all this is done, you can cut the paper template to the exact width of the final frame, and trace the shape onto the assembled and glued up blank you've constructed. I'd put green painter's tape on first and trace the line onto that. The tape will reduce tearout.
Cut the shape out very carefully with a jig saw. Cut a little proud of the line, and plan on sanding like mad to smooth the inside and outside shapes. A spindle sander will make this go faster, if you cut a pattern into 1/4-1/2 mdf, you could use a trim bit to really make it perfect, but you will want to pre cut about 1/8th or so proud with the jig saw.
Theoretically, you could rough assemble the straight pieces, using double stick tape to hold them down, then use a band saw to cut each piece first. I'd do this after fitting and cutting the slots. But frames are really tricky and you will have to make sure the joints are really tight when you mark them up.
Cut the rabbit into the assembled and glued up frame. Roundover the edges and if you're going to shape the front, you can do it now. It may be tempting to do any shaping on the unassembled straight parts, but the shape won't follow the curve, although after cutting the oval parts, you could shape them individually. Either way, plan on more sanding time, then double it.
You will then need to finish the frame, and add a backing to protect the mirror. Personaly, I'd cut a piece the same size as the morror and use brads or clips to hold that in. Use a lot of them.
To allow for shaping and the rabbit and backer, I'd start with 4/4 stock.
That is if you want a nice wood finish on the frame.
Now, if it were just going to be painted, I might consider simply cutting the frame out of a couple of sheets of MDF glued together, all in one piece. Cut two rabbits, one about 3/8ths inch for the mirror, one nearly the full width of the frame, for a 1/4 inch plywood backer, which will add strength to the frame. Why a wide rabbit? So the ply doesn't show at the edge. You could pre drill and use screws to hold the ply in place, or just glue it in place. Of course this will be far more fragile, but relatively quick to make
Hope you don't mind the novella. I'm sure folks will come along and add or suggest alternatives. I make frames for my wife's paintings. They are always a challenge, extremely exacting as to cutting angles so they fit. A tiny error in cutting angles multiplies as you add sides or parts, so that will be your challenge.
The more I do, the less I accomplish.
Last edited by DesertRatTom; 01-28-2017 at 11:13 AM.