Thread: Slowly, slowly.......

Originally Posted by Rocker

Major,

I am not sure whether the fact that you got some springback can necessarily be blamed on the glue; perhaps it was due to the plies being a bit too thick at 5 mm. Admittedly, I use 6 mm plies for the laminations of my rockers, but I get some springback, which doesn't really matter to me.......With plies only about 2 mm thick, springback is unlikely to be a problem.
Rocker

You will always get some springback. The formula is: LAMINATING SPRINGBACK =<!--[endif]--><o =""></o> 100 ( 1/n²- 1 ) % where n = number of plies
<!--[if !supportEmptyParas]--> <o =""></o>SO:
n = 2 springback = 33%
n = 3 springback = 12%
n = 4 springback = 6%
n = 5 springback = 4%
I found this formula some years ago and it's proved pretty reliable
Graeme

Thanks Graeme,

I'll add that formula to my list of usefull information

Graeme .

Does the length come into the formula ?I recently laminated "vic ash" strips ( 2 ply) 60mm x 8mm with a camber of 12 mm to make slats for a bed I was making and the springback was 2.5mm which is 21% . The battens turned out to be a bit too stiff but that's another storey .

Just a related note. I have recently been working on a project involving some rather radical 90 deg bends at 150 mm radius, two plies. Each lam is 5mm thick by 50 mm wide. This is all basically irellevant as my real issue was that the project was on hold for some months (higher, paid for, priorities) and i felt that my precut laminations of woolybut had probably dried out a bit much. So I sprayed them with water, wrapped in a wet towel and then plastic for about two weeks. I have now done 5 bends in a row that are undoubdedly the easiest and the best of the 16 bend series. I have never been sure of the relationship in bending ease between temperature and "wetness", but it seems to me that if the timber has a relatively high water content (>15%)then the steam can much more readily penetrate and soften the lignins. Comments anyone (especially you Major P)
Jacko

Yo Jacko,

I helped a mate try to steam bend some Purple Hart with a MC of about 9-10%........ what a disaster. :eek: We steamed for about an hour & wacked it quickly on the form & as we clamped it up *PING* several major failures happened at once. We gave up for a couple of weeks while the mate did some research.
He ended up talking to a retired marine cabinet maker who said just what you are advocating. Increase the MC to somewhere approaching 20% & then steam the piece. Then it needs to be left in the form with a compression strap for 48-72 hours depending on the relitave humidity.
He said you can cheat and put it in an air conditioned romm for 48 hrs & the MC will return to about 8-10%
Anyway, in the end, the 5/8th steamed pieces worked out really well without any twisting at all