Machining Small Radius Molding

The problem: holding a small, curved piece of brittle wood fixed while machining a small moulding profile into it. Here, pros offer various solutions. December 20, 2005

Question
I'm a professional millworker who specializes in radius work. Ive made many complicated pieces of trim, but this time I've hit the wall. I have to make a small radius overlay moulding, 3/4 x 1 1/4, profiled on 3 sides with a 3/8 x 7/8 rabbet on the back side. There is no room for fasteners to hold it to a template. The radius is about 22", and the piece is 30" long. The piece is made of Jatoba, and is very hard and brittle. I spent most of a day with various templates trying to hold it from the backside, with the rabbet registering the part to the template and a screw at each end to hold the blank. That was dangerous though.

Has anyone had much luck using hot glue to hold such small parts to templates for profiling? Laminating the billet to be machined is an option as there is too much cross-grain at the ends of each piece, and its very explosive. Any advice would be greatly appreciated.

Forum Responses
(Architectural Woodworking Forum)
From contributor F:
I recently made some faux bamboo moulding and one lathe turned blank yields two pieces of moulding so instead of turning one piece blanks and then sawing them in half, I made "half blanks" and used some good quality double sided tape in between the two halves. If you put clamp pressure on two sided tape it develops a strong reversible bond. Two side tape plus your end screws might work.



From contributor D:
Almost any molding has a flat surface on one of the four sides. We make this flat side fat - bigger - so we have a handle to support the cutting pressure and to hold onto (hands, templates, clamps, etc).

We do curve parts all the time where the outside or inside is left wide, while profiling goes onto the opposite edge, and/or top or bottom. With little curve moldings - 11/16 x 11/16, we make the part double thick or thicker - 2-1/2 x 11/16, profile, then saw apart on the band saw or even the table saw.

Often, a part is made in two or three pieces to complete the arch to avoid that attention getting end grain. A one piece 180 will have a lot of cross grain movement, and will likely split if nailed- even with pre-drilling. Even if we could get a 180 degree arch, 6" radius, in one piece of wide stock, we'd still break it into two pieces at 90 degrees plus for shaping/safety.



From contributor H:
Contributor D is right. Segmented construction is often required. The widest board we'll work with is about 8", and we prefer to stay at 2" to 3" wider then the final moulding. Jointing tiny mouldings can be difficult, but some method can usually be devised.


Click here for full size image



From contributor G:
Similar to Contributor Fs method you might try gluing the Jatoba to the template with paper between the two pieces. It usually splits apart easily when its done.


From contributor F:
Contributor G is correct that my "clamped double sided tape" method is a substitute for the "paper joint" method. I decided to try the two sided tape because the thought of scraping of mucho lineal feet of paper and glue was not very appealing.


From contributor H:
When we need to do these as suggested with extra thickness, rather then glue or tape on extra material we just run them out of thicker wood. Then they can be sent through the Timesaver with 60 grit to remove the excess thickness after profiling.


From contributor B:
Here's something I've done a few times - maybe you can get stock that's more "user friendly" by doing the moulding in two (or more) pieces. Also, like Contributor D suggested - leave them big if need be and cut to size last.


From contributor J:
To contributor H: Is that a dime on that moulding?


From contributor H:
Yes, it's a dime. The mouldings were cut with custom router bits on the CNC. It was segmented construction if I remember correctly.


From the original questioner:
I ended up using double sided tape, seating it well with a rubber mallet right before running it.