We make a lot of radius casings, but every time a radius jamb is ordered with it, it seems to slow us down. Right now we use two pieces 3/8 bendable Luan and spray adhesive. First we lay the template cut from the CNC and using L shaped plywood piece, screw them down to the table in that given radius. Second, we lay the first sprayed 3/8 bendable Luan against the stops that have been screwed to the table. Third, we very carefully start applying the second piece of Luan while pushing up against the stops. Fourth, we trim one side of the jamb to even it up, then set the table saw to exactly desired width and rip again.
This works for most applications unless the circumference of the radius is more than 8 feet. I’ve seen various window manufacturers’ jambs that are 4-8 layers laminated up and it seems that there has to be a more productive way for us to do a similar type construction method. The advantage for the window manufacturer is that he can set up jigs for his given radius, but it would take me too much time to make a separate jig for every one.
A company here in NC called "Curvemakers" has patented a machine they made which is simply remarkable. It uses high frequency and an anvil roller to laminate to a template. They have an awesome system. I would like to see how some of these guys make them in an infinite radius and productive. I have some ideas that relate to a table and some pneumatic clamps using the offset of the casing radius to form all this. I have tried the US Concepts arch clamp for jambs and sent it back.
(Architectural Woodworking Forum)
From contributor A:
Have your CNC cut the negative forms. Prepare your stock by kerf cutting, and then trim 3/4" off the total width. This cleans up what your R.A.S. did, and prepares you for the 3/8" thick "edgebanding" that you'll glueup later. Bend the stock via clamp and caul, around the CNC'd forms which you've transformed into a perfect jig. Edgeband both sides with 3/8 material and flush trim. Next, completely fill in the kerfs with Duraglas/Tigerhair/Stranded body filler. Make a packing clamp to hold the radius jamb to proper radius once you release the clamp and caul array. Do not release this packing clamp until you slide the jamb into its opening for final install. I also use a pair of custom made cleats tensioned with bailing wire once the packing clamp is in place and the product is broken off the form. This allows you to temporarily remove the packing clamp and belt sand the snot out of the fiberglass work. It also really helps with installation.
I hope my process didn't get lost in translation, as some of the complicated procedures we all use are sometimes hard to explain by typing on a computer. And I don't have any radius jamb tasks which I could photograph, for about 3 more weeks. If my words are blurry, just ask and I'll try to reiterate.