Roundover router bit to get a large radius molding

Question

I'm looking for a router bit (preferrably from named brands like CMT, WPW, Dimar etc) to get a profile of an arc of a large radius, something like 55-60mm and of a chord length equal to something about 30-40mm. This profile (or the one that looks very close to this) is often used on a picture frames you can find in the local stores.

Here is the sketch of the profile I'm trying to get after milling one plane of the rectangular piece of wood with a router:

I have found many bits with a profile that is very close to this one - CMT 954.509.11 (details here - http://www.cmtutensili.it/show_items.asp?pars=RB~7/8/954~2~2~1), but the largest radius I can get from a bit like this is about 19mm.

So, my question is - does anyone know the particular bit that fits my needs described above? Or, alternatively, is there another way to get this profile?

Answer 1

Rough out shape using multiple rips on a table saw, then either

1) Sand. Create a set of concave sanding blocks by feeding a length of 2x4, on the flat, across a table saw at an angle. Choose an approximately appropriate blade diameter. Recess will be closest to circular the closer you feed to 90 degrees, and will be an ellipse otherwise. Cut high quality sanding belts of various grits in half and glue them into the concave recess.

2) Router. Buy a large high speed steel router bit of any profile and grind it to shape on bench grinder.

I've done both of those.

3) Shaper. Use router like a shaper, making two passes, assuming you can find a wing bit that would cut 1/2 half the profile.

4) Lathe. Turn square stock on a lathe to your diameter, then rip the flats on a table saw. You could get at least two lengths per turning depending on the measurements.