Springback and Accuracy with Radius Glue-Ups

Advice on making glued-up radius pieces conform to a precise, accurate curve ó and stay that way. May 11, 2011

Iím trying to glue up radius doors in my vacuum press but when I take them out the doors spring a little throwing off the radius. My question is, do they make a glue that will prevent the springing from happening? If not how else can this be done?

Forum Responses
(Adhesive Forum)
From Jeff Pitcher, forum technical advisor:
You should use a thermo-set adhesive such as Urea Formaldehyde Resin. This will prevent any springback but will take much longer to cure at room temperature.

From contributor D:
I assume you're talking about radius jambs, built up with veneers. We do make dozens of these daily. Unfortunately it's more of an educated guess than a science. We overcompensate the radius in anticipation of springback, which is more with stiffer veneers, less the more veneers you are using, and progressively more the smaller the radius is. We get it right most of the time, but if not we are using an rf bending machine so the part can be remade in five minutes if we're off. Probably not what you wanted to hear, but in 12 years of doing this I've never seen any glue as the magic bullet.

From the original questioner:
We are making cabinet doors, the doors need to finish on the same plane as the counter top which is why I need to be dead on. I had a feeling a lot of people would say make a tighter radius but with me doing it in a bag it is tough to guess and check. Iíll give the new glue a try.

From contributor A:
The glue has very little if anything to do with spring back. The wood is causing the springback. The glue simply holds the fibers together. Experience and an educated guess will help you to anticipate the spring back. Wood species plus laminate thickness plus number of layers equals springback. 1" thick curve comprised of (4) 1/4" layers will springback more than (8) 1/8" layers.

From Jeff Pitcher, forum technical advisor:
You're mistaken. Thermoset resins are commonly used in the industry for bent laminations such as stair rails and window casings. Their use considerably lessens springback.

From contributor D:
You don't have to remake the part every time. You can add a couple more veneers, increasing your part size. If it is off less than the thickness of a veneer, just cut to the proper radius after it cures. Unless you have lots of different radii, you should be able to adjust your jig for the very next glue-up and be fine for the rest of the project. Even if you do happen to cut through a veneer when cutting to that proper radius, just bag it up again with another veneer applied to your now perfect stock.