spring back on bent laminations

[joec]

I am building a table with a curved rail on the front. I wonder how to account for any springback. Anyone with experience in this please chime in. The rail will be in two parts, each 18" long by 3 1/2" tall. It may be short enough to not have to worry about it.

 

[Mike Davis]

In my experience any springback will occur in laminations of four strips or less. Once you get around five pieces glued the lamination tends to cling to the form. Of course this can vary with thickness of the strips, species of lumber, tightness of arc, and maybe other unforeseen factors.

 

[Rwe2156]

The key is fairly thin strips, and a hard setting glue. Do not use yellow glue.

Epoxy or plastic resin glue work best. I've used both and think I get better results with plastic resin, but it sure can be a mess!!

If you're bending to a specific shape, you should always overbend a little regardless of what glue you use, you're always going to get a little spring back.

 

[JohnnyR]

If you make the rails first, design the table to it and it won't make a difference. While using one form for both rails will probably result in equal spring back, it's safer to make one rail 7" wide (plus waste) and rip it in two.

 

[mlzettl]

I have never had an appreciable problem with spring back in a bent lamination. DrBob's recommendation of thin strips and plastic resin or epoxy is spot on. I generally use plastic resin, but have used epoxy on occasion. Leave everything clamped up until the glue is fully cured. A while back I did two 48" diameter semicircular dining table aprons in mahogany. I used seven 1/8" strips and plastic resin glue. There was virtually no spring back. Certain woods bend better than others as Mike Davis mentioned, so some research ahead of time is worthwhile. Cracking or fracturing can occur with certain woods, and I had a problem with purpleheart once, and concluded that it just wasn't a good wood to try to bend, at least in the application that I was trying. I think if you err on the side of making the strips thinner rather than thicker, you will be OK. It may be more work, but in the end the effort will pay off. For tight curves, you can always pre bend the pieces by steaming first, then doing the glue up. Most of the work is actually in making up the form, and planning the clamping. I suggest a dry run before you use the glue.

Hope this helps.

Matt

 

[tvrgeek]

Glue. Glue, Glue. Learned this recently doing a curved dashboard for my Triumph. Powered resin glue. And of course, the thinner the better. For my dash, I used super thin ply cores, sanded down to 2 layers so many of the inner layers were side grain so more flexible. Harder of a narrow band.

 

[Rwe2156]

Matt is right if you don’t need a certain shape don’t worry about it. When I built this bow front table, I did the lamination first and based the full size drawing and joinery off of it.

 

[joec]

I am altering the plan already, so I can make the top fit the curve. Thanks for the responses.