Elliptical Jamb Extensions
However, just a few weeks ago I decided that we should try a single seam full circle jamb. It was only about 16" in diameter by 8" deep, so seemed like a good one to try this on. Like you, we use a combination of solid wood and bending ply. On this jamb one edge was buried while the other was fully exposed. So, we only used a single 1/16" layer of mahogany on the inside of the jamb and the rest of the layers were bending ply. We capped the exposed edge with 1/8" thick segmented sections of mahogany glued to the edge and then flushed on the shaper.
We made a full round form and then carefully test fit an inner 1/16" mahogany layer to make a good tight single seam. That was put on the form with only one outer layer of bending ply glued to it. The bending ply was about 1/4" short of completing the circle, which allowed for it to be pulled really tight with strap clamps. A strip of plastic packing tape on the form where the 1/16" inner layer ends met kept glue squeeze out from sticking the mahogany to the form.
Then we added a second layer of bending ply after inserting a strip to fill the first layer of bending ply gap, again leaving the length short of completing the circle. When this dried we did the same with a final layer, making for a 3/4" thick jamb. Leaving the bending ply layers short is key to pulling the whole thing tight. We had almost no gapping between layers because of this.
The whole thing worked like a charm... albeit a bit time consuming. The only problem was that I forgot to take a photo before the pair of them got shipped out!
From the original questioner:
Thanks for the reply. It's funny, I slept on it and came to the two halves solution, then read your post. As to a seamless oval, your idea of leaving a gap and filling it later is something I hadn't thought of.
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