|
||
Steam bending and lamination
Question
Therefore, I have decided to try steam bending. On one of my coffee tables, I use a 1" glulam 48" radius as a leg. However, instead of steaming 1" material, I was wondering if it would be feasible to steam two 1/2" boards, gluing them together over a form. Has anyone tried steaming boards and then gluing them over a form right after they come out of the steam box? Forum Responses
What glue would you use to glue soaking wet wood? How would you clamp to avoid crushing/distorting the steam-softened wet wood? I'm not sure I can see how letting the pieces dry properly would add to your labor/time. From contributor B: Steam bending of kiln dried wood doesn't make it all that wet. I've had no noticeable problems gluing with Titebond after several hours. The wood certainly is not any softer than before going into the steam box. I don't need to steam bend green wood which I've always been told bends more easily (makes sense since it has a higher water content). There would certainly be gluing and clamping issues there.
For shallow bends (that is, bends that are not very severe), often heat is all that is required to get the wood soft. Wood MCs can be around 16%. As the bend gets more severe, steam is used to soften the wood. The wood also must be between 22% to 28% MC. Such softening will allow radii of 12" or so without much problem. But the wood must be wet and hot when bending. Then the wood is held in a bent form while being dried and before gluing. The surfaces to be glued, after drying, must be smoothed and made to fit the adjacent piece. I hope this explains the divergence of comments noted above. Gene Wengert, forum technical advisor
From the original questioner: How long would you leave the clamps on when steam-gluing two 1/2" thick pieces? From contributor B: For steam bending and then laminating I usually will over-bend the pieces about 50% so that the springback after releasing from clamping will bring the pieces to approximate radius. Since I'm not trying to lock the piece to the form radius I can remove it in 3 to 4 hours without problems. Until the glue is dry and the wood MC has reached the desired level... 6 to 7% MC typically. Gene Wengert, forum technical advisor
From the original questioner: So you steam the two pieces, let them dry, then glue them? At first I thought you steam them, quickly smear glue on the two pieces, and clamp the two pieces to a form at Godspeed. From contributor B: No, sorry, I should have been more clear. Steam bend at ~50% tighter radius and leave on the forms 3 to 4 hours. Remove from forms, glue layers together on form. Leave clamped up for recommended clamp time of glue.
I've never actually done steam and lamination together, but I've done them separately quite a bit. I'd be worried about moisture problems unless, like some have mentioned, you allow the wood to dry out before glue up. Failing this, you could try urethane glue. You might want to do some testing. From contributor D: Have any of you heard of or used Compwood or compressed wood? It's this process out of Europe that steams wood and compresses it lengthwise in a horizontal press. It compresses the wood to something like 80 percent of its original length, which destroys most of the lignin cell connections (or something?). Afterwards, as long as the wood is stored properly (out of sun and wrapped in saran wrap), it stays in a plastic state for like 6 months. When you want to use it you bend it and leave it in form for a day or so and voila. Just curious if this technology is used much in the USA. From contributor B: I spoke with a company out of Maine, I believe, who has purchased the system. If I remember correctly the system costs in the 100's of thousands of dollars to purchase so you'd have to have a major production need. From contributor D: I think you can also buy small amounts from them retail if that is all you need. I spoke to the manufacturer of the machine and played with the wood at an AWFS show in Anaheim. A really neat product, but as said, the machine is about half a million dollars. The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment). Comment from contributor C:
The second thing I do is "strap" my pieces with stainless steel bands bent on each end to fit end to end over the wood, which I also put in the steamer to get hot, so when I put them on my material and quickly put them on the forms, they help to retain the heat. As I clamp the pieces to the form, I start at the area of least bend to hold the stainless and as I proceed, the stainless acts as a "compression band" which doesn't allow blowout and also puts an end to end compression on the wood, which helps greatly. I put some rather healthy bends in some very figured wood using this method. Just remember - the stainless must be kept tight. And if you don't know to use heavy leather gloves, you will quickly figure it out. But the key is to steam it well - a tea kettle in a 12x12 48 long box won't make it. A turkey frier (5gal) over a box (well supported) with a hole in the bottom works good, just don't let it cook dry and trash the pot (lesson learned).
Would you like to add information to this article? Interested in writing or submitting an article? Have a question about this article? Have you reviewed the related Knowledge Base areas below? 
|
