Bent Lamination-Form outside the bag

[Doug Mason]

I am in the planning phases of making a queen sized windsor bed based on Jeff Miller plans. The tough part of this project is making the Headboard and footbard arches (I'll be using an ellipse layout jig). Each arch is 1 3/4 inch thick, 2 1/4 wide and roughly 10 feet long.

For each arche I will cut about 20 stips--each strip being 2 1/4 inch wide and a little more than 1/16 inch thick. The most obvious way to laminate these is building a form and cauls (it will be big!)--which is how it is done per the Jeff Miller plans.

But here is my question. I have a vacume press--so could I not build a form and put the lamination in a bag and then clamp the bag over the form (eliminating most clamping)? Of course this is the opposite of having the form in the bag. I have seen this done on video's--but I have no experience in doing it this way. I could make a long bag from 30 mil vinly I get from Tap plastics.

So what do you think? Would 20 cherry laminates (totaling 1 3/4 thickness by 2 1/4 wide) in a bag clamped to the outside of a form work per this scenario? Or am I asking for more grief than just using a form, cauls and a boatload of clamps?

[David DeCristoforo]

You can do it that way but you still have to make sure that the glue-up conforms precisely to the form. Also, you would need to incorporate some kind of mesh (http://www.veneersupplies.com/product_info.php?cPath=60_67&products_id=2301) or flexible platen to allow the air to draw.

If you have the form why not just put it in the bag?

[Doug Mason]

Thx for your input David.

I wouldn't put it is a bag because the Headboard arch alone is 43 inches high by 60 inches wide--thus it would have to be a huge bag (unless I'm missing something?) I'm trying to do this whatever way is simpest/easiest--which is what got me thing of using a form outside the bag.

[David DeCristoforo]

I would make the bag. The materials are not that expensive and they are pretty easy to make. I have bags up to 4'X8' plus tons of odd shaped ones that were made for special projects or to fit specific molds like your headboard rail. Making a bag to fit your mold is really not going to be any harder than making one to hold just the lamination and if you can stick the whole thing in the bag, it will be easier to handle.

[Jamie Buxton]

Yes, I've done bent lamination with the form outside the bag. The vacuum just squeezes the laminates, while the form established the curve. It works. In fact, for some things, it works better than putting the form inside the bag. For instance, for your arch, you can establish the curve with just three points: the middle and the two ends. The "form" can be something as simple as three chunks of 2x4 clamped to your workbench. You bend the wood around those three points, squeeze it with the bag, and you're done. When I do something like this, I make the curved part first, so I know what it came out to be. Then I make parts which connect to it.

The coolest version of this technique I've seen is the construction of the railing for a big spiral staircase. The guy slid his railing laminates inside a bag which was 6" diameter by 30 feet long or so. He clamped it to the stair structure to bend it exactly to the spiral he needed, sucked vacuum, and a few hours later had a railing. I'm pretty sure the guy was Richard Wolf, who often posts on SMC, but I think the pics may have been on some other forum.

[Doug Mason]

Thx for your thoughts David and Jamie. Geez, both of you guys are just down the street from me!!

What got me to thinking of using a form outside the bag was, as Jamie pionted out, and what I forgot to mention, is the fact that the form doesn't need to be that strong (easier to make)--hence it might be easier (at least in theory!!!).

[Jamie Buxton]

Here's a thread by Richard Wolf. He's using a vacuum bag with the form outside to make the stringer for a spiral staircase. Unfortunately, there's no pics of the bagging itself. But you can see that putting the form inside the bag would have been more difficult. http://www.sawmillcreek.org/showthread.php?t=32267&highlight=vacuum

[Steve Jenkins]

I would add that if your final width is 2-1/4" I would make my plys about 2-1/2 to 2-3/4 then trim them to size after glue up

[David DeCristoforo]

"...putting the form inside the bag would have been more difficult"

Putting a stairwell sized form inside a vacuum bag would indeed have been "more difficult". The OP is looking at a somewhat more manageable size form.

[Jay Jolliffe]

Anyone have a picture of doing it this way? Better yet how about a book showing it.