More than 12 years ago, my father-in-law, Lloyd Wells, stripped and re-stained a set of oak chairs. Unfortunately, on 1 chair, he lost the 2 curved pieces that attach the chair back to the seat.
I was asked to make 2 replacement curved pieces to repair this chair. I could use another curved piece from one of the other chairs as a pattern.
The originals were probably steam bent to the 90 degree angle. I have tried steam bending, but found it very difficult to steam bend any wood over 1/4" in thickness. There must be some tricks, like bending green wood, that I am not aware of.
But I have fabricated curved pieces using the lamination method of gluing thin strips together. I decided to try the lamination approach to this project.
Designing the Clamp Fixture
I scanned the sample piece in my scanner and imported it into Google Sketchup.
I included the ruler in the scan, so I knew how much to scale it to in Sketchup.
From basic geometry, if you know 3 points on a curve, you can draw and calculate the radius. I used Sketchup to do this.......
Once I knew what the radius was, I could design a fixture to clamp up the strips.
I made the fixture from 3/4" thick plywood, which is how tall the glued up lamination needs to be.
Cutting Thin Strips of Red Oak
A couple years ago, I bought a table-saw jig that allows you to safely saw thin strips of wood. Once you set the jig, you move the fence each time you saw a new piece.
1st glue and clamp-up
On the 1st clamp up, I clamped about 1/2 of the 3/4" thickness needed. It would be too difficult to clamp up all the pieces needed for the 3/4" thickness.
After the first clamping dried, I then attached the rest of the stack.
The Saran wrap under the pieces is to keep the glue from attaching the bent pieces to the fixture board below.
Below is the laminated piece after it dried and I removed it from the jig. You get no "spring back" with the lamination method when you release it from the fixture, like you get with steam bending. With steam bending, you have to do trial and error and actually bend the piece with a smaller radius than the end result, because of spring back.
I took the laminated piece to my stationary belt sander, and smoothed up the top and bottom of the stack.
Then to the router table, where I used a 3/8" radius round-over bit, to yield a round 3/4" diameter piece. I took about 3 passes on the router table versus 1 just to be on the safe side.
Having the extra length on both ends is really nice, because it gives you a place to hold the piece while you are routing it.
I test fit the pieces prior to 1 coat of stain and varnish.
I used about 3 parts Golden Oak and 1 part Spanish Oak stain to get the best match to the existing old chair.
One trick I have used to speed up finishing of small parts, is to bake them in the oven at 120F for 10 minutes. This dries stain, and also polyurethane. You can't leave them in much longer, or the varnish will start to bubble.
I used this trick on this project, once for the stain, and once for the polyurethane.
Panic Button Hit
After the 2 pieces were out of the oven, I screwed the 1st one in fine. When I went to screw the 2nd one, the screw holes did not line up with the chair holes I had put it on the dry run !!x&*%F^#&
I took the piece back to the bending fixture, and it had un-wound, or the curve opened up!!!!!! Now 1 piece had been dried for several days from gluing, and the other only about 48 hours. I used yellow Tite-bond glue. Maybe the 48 hour piece was not fully cured, and it opened up?
So, I clamped the bad piece back in the bending fixture, and put it back in the oven for 15 minutes, then the freezer for 10 minutes. Thank goodness, it went back to close to the right curvature, and I was able to install it. Lesson Learned here with respect to using the oven on bent laminated parts!!
Closing Thoughts on this Project
The lamination method worked well on this project. I used the Dremel with sanding drum to make the ends pointed like the originals.
One Lesson Learned was not to use the oven to speed up stain or varnish drying with bent laminated parts, unless the glue has been dry for a week!