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Lamination Question

2K views 22 replies 11 participants last post by  TroutGuy 
#1 · (Edited by Moderator)
How many layers of 1/8" thick oak can be cold bend laminated into a 15" radius curve in one gluing? I am planning on laminating 12 layers to get to 1.5". Should I do this all in one go? Or should I glue and clamp a few layers and wait for it to dry before adding more until I get to all 12 layers?
 
#2 ·
With the right slow setting adhesive, it can be done at one time. Got plenty of clamps? One for every 4-5 inches?
 
#3 ·
Get the slowset and do it all at once. For making your radius, you will "ALWAYS" get glue on the outside of your pieces, that will require clean-up to go to the next round of layers.
 
#4 ·
I agree with both above; do it all at once, and don't get stingy with the clamps. I have a friend that does bending for a living and he has at least 300 clamps (the big, blocky wood type) that he freely uses. Lots of glue, paper under it all to catch the mess and lots of clamps starting from the center and moving outward.
 
#5 ·
Thank you guys, any recommendation on glue? I was thinking titebond, but that says 10 minute open assembly time, and 25 minutes total assembly time. I read that as needing to have the boards in place in 10 minutes, which might be cutting it close. Unless I am misunderstanding the 25 minutes total assembly time thing.
 
#6 ·
I have done 8-10 lamintations to acheive a similar thickness. The key as most have stated, a slow set and a longer open time (I used Titebond III). I built an MDF jig with plenty of areas for clamp holds (one ever 3-5 inches, the closer the better). It works best to have everything ready to go, I covered the form in wax paper, clamps pre-positioned, a good roller to spead the glue, laminations a little oversized (to allow for triming as nothing stays perfect) and the laminations layed out and ready. Once you start you really cant stop, I did not worry about run out as i trimed that off later. Glue them all on one side, stack them all up, place them in the form and begin clamping from the center out. Once it has dried trim it to width and length and you are good to go… i have done this on 3 differnent pieces w/ great success.
Hope this helps.
 
#8 ·
I would only recommend using a Urea glue or West Systems epoxy. PVA glues do not work well for laminating. They will not hold the curved shape. Too much spring back. Urea and and Epoxy glues are the industry standards for good reason. They work.
 
#9 ·
TopamaxSurvivor - once I started applying the glue it took about 20 mins total (10 mins to glue and stack and about 10 to get it all clamped)... based on the specs for the glue (Open assembly time10 minutes (70°F./50%RH) Total assembly time20-25minutes (70°F./50%RH)) it has held up well.

John - I would agree those are better options - especially if it is unsupported, i should have also stated that I did fasten mine to a piece of lumber with corresponding radius of curve as i did encounter some spring back in what I glued up….
 
#13 ·
When we did this with Michael Fortune, we only put glue on one side of the lamination.
You lay all of your stips side by side (tightly) I use a little blue tape at the ends then pour the glue into a puddle and use a 1/16th metal notched mastic spreader to get everything covered within about 30 seconds.

You have more working time with the clamping part of the lay-up. This is because once you have put the sandwich together, you have dramatically slowed the amount of oxygen hitting the glue surface….like worrying about your glue drying out in the bottle.
This doesn't mean you have hours, but IS where you get the 25 minute working time.
 
#16 ·
An example of Urea glue would be Unibond 800 : http://www.vacupress.com/veneerglue.htm

I think Joe Woodworker sells another type of Urea glue. These are resin glues. There are a few manufacturers of Urea glues.

White glue is a PVA glue and not very suitable for bent lamination. Some people use yellow PVA glue when working with certain techniques of veneering but it not a glue for laminating wood. It is a flexible glue. It also will expand and contract when used for normal edge gluing of boards. You will notice when, for example, a table top that is made of a few boards edge glued will have a slight ridge at the joints after some time. This is the glue flexing and slightly squeezing out of the joint.
 
#18 ·
You're about right at 1/8 inch and can do it all at once. The thing to watch is the glue one uses for this. The PVA glues introduce too much water into the wood and will cause springback as it dries out, and the tension remaining will cause further widening or the radius due to glue creep. a BETTER CHOICE WOULD BE UNIBOND 800. It's alcohol based, the set time can be adjusted by altering the mix ratio, and it has a long open time.

Asteve
 
#19 ·
Damn….I wish I would have known 22 years ago that Yellow PVA was a poor choice for bent lamination…now I'm worried that all the thousands of Circular Stairs and curved railings we've built are gonna fall apart!!
KIDDING!! LOL!! Sorry….just being a smartass…

Seriously….nothing wrong with using Yellow PVA for MOST bent lamination, providing it's a good quality glue. PVA is the industry standard in the curved stair and railing business for most applications.
John is correct though as far as 'spring back' with PVA….although it can be controlled to a certain degree by adjusting the # of lamination's, adjusting radius etc.
There are applications where Urea's and Epoxies should be used though. Typically on tight bends, bends that exceed 120-130 degree's…especially a combination of the two.
 
#20 ·
So, I have started looking up unibond 800, and every where I read says that this glue needs a vacuum to set up. Since I don't have a vacuum pump or vacuum bags, I am wondering if the vacuum is really needed? Will clamps be good enough? Or am I losing quite a bit by not vacuum bagging?
 
#21 ·
I think you might be misunderstanding the need for a vacuum bag with Unibond 800. Bent lamination does not necessarily demand the use of vacuum bagging. Clamps, straps, rubber bands, etc can be used. It mainly depends on the size of the project. Vacuum bagging is used to make veneering or bent lamination easier and quicker. A standard veneer press can also be used with Unibond 800. The important thing is to make sure pressure is applied evenly.
 
#23 ·
Nomad 62 is right on about this one. Check out Radiuswoodguy's stuff - http://lumberjocks.com/Radiuswoodguy/projects. All of his bent lams are done with a PVA glue (NOT Titebond), and there have been no problems that I'm aware of.

Nomad62 is wrong on one 'count' though. Radiuswoodguy's clamp collection is WAY over 300. We had ~500 on the floor one night, and there were still more in the racks. See for yourself - http://www.youtube.com/user/radiuswoodguy.

If you're really concerned about spring-back, you can do a couple of things. 1) thinner lams, and 2) do your glue-up in a couple of 'stages'. You do need to be careful about glue on the outside lam, but it is manageable. Use as many clamps as you can squeeze in there. Perhaps most important is to use cover sheets (1/8" MDF works fine). One sheet on the inside of your form and two on the outside. This will help spread out the clamping pressure, as well as eliminate clamp marks (waves), which are nearly impossible to sand out.
 
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