I'm trying to make a 4" casing to go around this arch which has a 37-3/4 radius. It has to be solid oak. The only thing I can come up with is a ton of laminations. Also, there is only going to be a profile on the inside and outside edge. Anyone have any other ideas?
(Architectural Woodworking Forum)
From contributor H:
It can be done in segments cut from wider stock. 12-14 " 3 segments. Mould them long and cut back to tangents for length.
You could also, since it is a casing and will be fastened to the wall, bricklay your lumber, so you have a basic arc shape, and then cut the arc. Although you have an easy time matching grain, it sits horizontal, which may or may not be a good thing.
Alternatively (and even more complex, but fewer laminations): Make the arc out of MDF, subtracting enough from the inside and outside for the profiles. Use this arc as the form. Oak veneer on the MDF. Glue/clamp your laminations directly to the arc – you could probably do the inside and the outside at the same time, since you've only got to build up an inch or so (?). Fair the curve(s), flush the top, rout the profiles. You still have the problem with grain, but it looks more like a solid nosing on a table or countertop, which is not foreign to most. Way more complex, but another way to skin it, if you don’t like a ton of laminations.
If you don’t have a lot of experience with curves and laminations, I say go for it! This is a good basic project which will serve as a foundation for more complex work in the future.
You only need to make one form. The form will be convex, or the inside rad. Two sheets of 3/4 ply glued together with the inside rad or the casing. Cover this edge with masking tape to keep the laminations from sticking to the form.
Pre-plan where all your clamps will be and how you plan on holding everything together. I do it with the form vertically. The trick to getting a tight join is having one or several caul strips to help distribute the clamp load. These can be extra lams that are not glued, or, as I prefer, something a little stiffer. You could get away with Titebond, but a plastic resin would be better if it is light in color. Unibond 800 is good. After 24 hours, pull it out of the clamps. Joint one face, run the other side through the planer to size.
It sounds as if you are going to just use a router to run the profile. This is fine. Remember, the outer radius lams edges are under tension, and they will want to tear out very easily.