It seems like the arched form needs to be lifted off the table by some amount. I’m not sure by how much. My technique in situations like this is choose from a range. Start with too little and keep adding until it seems like too much. Somehwere in between “too little” and “too much” there should be a “just right” or at least a “close enough”!
In this case I start adding spacers underneath each end. Here is the range of heights.
The wife and I talked it over and we felt like the third one from the left was close enough. That was just under 3/4”. I had done some sketches earlier and we had settled on a truncated pyramid shape for the support. I pulled a couple pieces of MDF out of the scrap bucket to play with. Since my chop saw has a stop at 15 degrees, I started there. I found a support that was as long as it was wide did not look right. The arch lifted up too much. I ended up with a block that was about 3” wide and about 2” along the length of the arch.
I found a couple pieces of lacewood that I wanted to use for the support. They were about 1/8” thick so I trimmed 1/4” off the width and length of the MDF block.
I thought I could rip these down the length and have enough to cover all 4 sides. No good, the lacewood was too narrow to cover the block. The pieces were not long enough to cover all 4 sides. However, the length WAS sufficient to cover one long and two short sides. I ripped the lacewood at about 2/3rds width. I then cut the narrow piece in half to make a piece that could cover the second long side. I hope that makes sense ;) The next picture shows the glue up to get a piece to cover the 4th side.
While the glue dried I worked on figuring the compound angles to miter the ends of the lacewood. I have never had good luck with this if I try to figure out the angles ahead of time. I get better results by testing the angles with a piece of scrap. It took about 4 tries to get a miter that looked good.
I then cut the compound miters. I had to be very careful as I had no extra material to spare. [Warning: these are small pieces. Make sure you have a means of cutting that keeps you safe. I am not going to share what I did here. Anyone cutting small pieces needs to do so in a way that is safe for them.] Anyway here are the 4 sides ready to glue up. Can you tell which one was glued up from 2 pieces?
After the lacewood was glued on, I sanded the edges flush with the top and bottom of the MDF. I had a thin (about 1/16”) piece of walnut that looked like a good way to trim out the bottom. I decided that I wanted a little inset between the support and the arch. I had a piece of thin mahogany that was just wide enough to cover the MDF on the top. I set the length to just cover the MDF as well. I now have all 6 faces of the MDF covered. When I went to test fit the arch on top, I found that the arch was not flush with the top.
I angled the top face with the disc sander until it matched the arch. Here is the final support.
All that’s left is sanding, assembly and finishing. I’ll sand the pieces using this progression of grits: 80, 100, 120, 150, 180, 220, 320 and 400. Not sure about finish yet. Stay tuned for the project posting…
-- Steve - Impatience is Expensive