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  Form-Bent Radius Jambs  
  By Ed Williams (Great American Carpentry Company, Dallas, Texas) with Peter Krause & Louis Statman  
This is a pretty simple process for making radius jamb heads. To ensure perfect accuracy, we made plywood form plates using a router and trammel arm. The skeleton is made from the MDO fall off, though any plywood will do. The ribs are on 3 in. centers.
For the finished jamb, we laminated two layers of 3/8-in. bending plywood and one layer of 1/8-in. birch plywood, (bending plywood is too rough for finish paint!)so we allowed a 7/8-in. space between the outer form radius and the inner form radius (plus room for skinning both forms).
We stapled on bending plywood for both the inner & the outer forms...   ...so the ribs wouldn't telegraph through to the finished product.
Then we covered both forms with wax paper...   ...so the glue wouldn't adhere to the forms.
Once the three pieces were cut to size, we coated both sides of the middle layer with Plastic Resin glue, and sandwiched all three pieces at one time in the form. I prefer using the Plastic Resin glue because it dries harder, holds the shape better than yellow glue, and it reduces spring back. It takes about four people to place the three pieces in the form and get the clamps on. I've done it alone, but it's a ten-round fight.
We made the radius heads wider than the net size needed, so we could trim them to size on a table saw. This method is great for any raidus or ellipse, and irregular shapes, too.
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