How to bend wood like this - Outdoor furniture project

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Originally Posted by Alan Lightstone

How do you insulate the box? It's 3/4" exterior plywood. I'm using the Rockler steam generator.

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Whether insulation is worth the trouble depends on where and how you're going to use the box. I don't insulate mine at all, but I mostly use it to steam relatively thin wood (as your project demands), so I don't need terribly long times in the box . If you're going to bend 1.5" wood, you'll need at least an hour in the box as Bradley says, but 10 minutes in live steam will completely "melt" a 1/8" lam strip. Takes somewhat longer if you load a big box up with many such strips, but still, you're talking less than 30 minutes.

Also, understand that if you insulate a plywood steam box well on the outside, you are going to break down the plywood over multiple heating cycles. You're basically guaranteeing that the plywood will be reaching steam temperature almost as quickly as your bending wood does, and that it's going through extreme moisture content cycles. Even exterior grade off the shelf plywoood is not designed for repeated cycles of 200^oF temperature cycles.

My advice - do a test run on one or two strips of wood of the thickness your target material is. Bring the box up to temperature, put your wood in, and check after 15 minutes, then again after 20+. You'll likely find strips of the sort you're doing are in great shape to bend.

If you do find yourself in cycles where the Earlex is running low, keep a thermos of very hot (boiling when poured) water at hand. You can top off the Earlex when it gets low, and recovery time for steam will be very low. If you feel some insulation would be of help, you can probably find a cheap thermal blanket at a used household good store, or pickup up a thinsulate camping blanket you can wrap around your box.

Making 85" thin resaw cuts from 8/4 white oak is not the easiest thing in the world to say the lease. Spending lots of time moving and readjusting the roller thingies to support the wood before and after the bandsaw, jointer, wide-belt sander.

I haven't bent any wood yet, but getting ready to. Building the hardware portion of the jig now.

I have seen a number of people (including Marc Spagnuolo) soaking the wood beforehand overnight to help with the bending process. I have no idea what I can use to soak 6" wide by 85" long blanks. Not going to build a trough. And don't see any PVC pipe that large (can't imagine what that would weigh). Is the soaking helpful? Necessary? Again, this will be kiln-dried white oak, so I'm behind the eight-ball there to start.

I just got the thermometer to measure the temperature in the steam box. That will show me if I need one or two of the Rockler (Earlex) steam generators.

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How do you insulate the box?

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I tried blue foam insulation first but it can't take the heat - rigid fiberglass worked fine. You may be able to overcome the heat loss with 2 steam generators, and you are bending a lot thinner stock than me. for 1" stock to soften, I need the insulation. That, and a steel backing strap for the bend made it all work for me. Your thermometer will tell a lot - you really need 210-215 F and insulation will help you get there. Start timing when you reach that point. I have been using the same ext. ply insulated box for about 5 years and the plywood is still OK. I'm sure I will need a new box at some point but replacing that is less of a problem for me than having a higher failure rate, as nice straight grained walnut and cherry are more dear than ext. ply.

Hopefully the second steam generator can overcome the heat loss. I'll be able to check it in a couple of days.

I'm kicking myself for giving away the blowup kiddy pool we had for our granddaughter. That would have fit the wood for soaking. But does soaking help? People mention it with fabric softener added.

Soaking helps. It can lead to discoloration. I have various pipes with end caps for soaking, including a piece of a plastic culvert. Watlow heaters are also very helpful. Very flat grained plain sawn lumber is easiest to bend. I made a few parts that only worked when green, plain sawn wood was used. Here is a snip about Watlow heaters.

Watlow silicone rubber heaters are rugged, yet thin, lightweight and flexible. Use of these heaters is limited only by the imagination. Heat can be put where it is needed. These silicone heaters improve heat transfer, speed warm ups, and decrease wattage requirements. Fiberglass-reinforced silicone rubber gives the heater dimensional stability without sacrificing flexibility. Because very little material separates the element from the part, heat transfer is rapid and efficient. The silicone rubber heaters are constructed with a wire-wound element or an etched foil element. The heater construction creates a very thin heater allowing it to fit applications where space is limited.
Silicone Rubber Heaters | Watlow

My game plan is to do whatever I can to make it possible to bend thicker laminations. No way I'll be able to bend 1.5" kiln-dried white oak, but also not looking forward to the prospect of having to laminate 24 strips of 1/16" either. 1/4" would be great. 1/2" (not-likely I think) would be awesome. So if soaking can get me to 1/4", that's real progress.

1/4 inch should be very doable. Banjo rims are done with 1/4" and 5/16" and are bent around a 9 1/2 inch diameter. I agree with the others that the furniture in the first image must be made from veneers.

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Originally Posted by Alan Lightstone

My game plan is to do whatever I can to make it possible to bend thicker laminations. No way I'll be able to bend 1.5" kiln-dried white oak, but also not looking forward to the prospect of having to laminate 24 strips of 1/16" either. 1/4" would be great. 1/2" (not-likely I think) would be awesome. So if soaking can get me to 1/4", that's real progress.

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You could do it without any steam if you were cutting the lams down to 1/16" - simply bending them around the forms with a backstrap to control them would work. 1/8" with kiln dried, you likely need the steam for the curves you're after - but it's just as much to make sure that the lams set in something approximating their final shape. Beyond 1/8" with quarter sawn white oak, you're going to want them steamed up to temp and to use a backstrap as Bradley says, to prevent tearing on the outer radii (but also note, that since you're laminating them with glue, other than needing one really nice one for the outer bit, a small bit of tearing in the tight bends isn't going to compromise your build in any way, structurally or visually.

For a clue as to how tight you can bend steamed 1/8" lams, look at the narrow end of this basket. This is, to be sure, air dried red elm, so not as prone to breakage as your kiln dried oak, but then, that's a tight bend, too.
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(Just to brag on my beloved, since I'm here - the yarn in the basket is all hand spun, hand dyed with natural dyes, wool from our flock, and the hanks of fiber are stricts of unspun linen she processed from flax that she raised).

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Originally Posted by Alan Lightstone

Wood arrived yesterday. Busy making the forms now. Using 3/4"MDF. OMG the weight of 8 of these on top of each other to accommodate the 5-1/2" wide wood that needs to be bent will require help, to say the lease.

I made the curved portion of the form out of 1/2" MDF using a Carter Accuright circle cutting jig that I had on my bandsaw. What a PIA. Shoulda just made a trammel with my router. Probably would have come out a little smoother too, though mine will work. Killing me the waste of MDF when I'm done. Not that I ever use MDF, but still taking a ton to make the bending form.

I couldn't lift or transport 4x8 MDF sheets, so I'm going to make this out of 2x4 MDF sheets and domino them together.

Now I need to build a larger steaming box than I have, and probably get a larger steam generator. Lots and lots of work to do. Any good suggestions for steam generators. Somewhere I read that wallpaper steamers, whatever they are, are good.

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You can steam wood in a bag instead of a box and fold it up after use. https://www.youtube.com/watch?v=50uXPPt8-VI I have used a couple of Earlex steam generators and a 30 gallon bag successfully, you might get by with one and a blanket for heat retention. For larger quantities of steam the propane burner and gas can shown in the video are pretty common.

Have you done a test bend with dry strips to ascertain the thickness needed for lamination w/o steaming? The whole process you are planning is very laborious compared to straight lamination or segmenting the curve. I have never done that, and no doubt it will work but I wonder how flat across the laminations will be after steaming/drying and how tight your finished gluelines will be. Seems like some testing would be a good idea before slicing up all that material.

A small furniture shop near here has done a fair amount of steambending for thick chair parts using a ratchet winch and bending straps with endstops, milling the parts to final size/shape after bending. That would be my preference on aesthetic grounds.

Well, the verdict is in on using a single Earlex steamer. The highest temperature it could get to was 174 degrees F after one hour. So I installed a second Earlex which I had, and that gets up to 212 degrees F in about 30 minutes.

Several areas of the box are leaking some water. Can caulk stand up to that heat, or is there something else I can use to seal it from the outside without taking things apart?

I may definitely wind up just using dry bent lamination, but was hoping that by steaming the laminations first and pre-bending them, then later putting them back on the form for a more normal bent lamination I could use thicker laminations. Clearly much, much more work this way. May not be worth it, but well, well down the path.

No question in retrospect that segmenting the curve would have been far easier, though I really don't know if I could produce identical pieces/curves that way. No CNC machine here.

Steamboxes always leak water. If you want to control the leaks, I would assemble the box with a temperature rated caulk or roofing compound in the joints (and, I predict, it'll still leak some), set the box at a slight angle so the water all runs to one end, and make the water come out through a leak (hole) of your choosing on the downhill end.

Your plan to steam bend, then glue up in a second step is absolutely sound. I've done it many times.and there is no reason for you not to succeed. You should have no difficulty getting 1/4" laminations to work this way, although my personal preference is to use slightly thinner lams than that - usually 5/16" or 1/8" - just because they soften up so much faster in the steam bath. On the other hand, they also cool very quickly, so you need to be quick and efficient in getting them from steamer to form. 1/4" will give you noticeably more leeway in that regard.

My boxes have a drain hole.

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Originally Posted by Bradley Gray

My boxes have a drain hole.

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Mine does too, as well as a hole on the door side to allow steam to escape. It's the wood joints along its length that have some areas that are leaking.

That being said, I really will need for this to move outside to use. I don't think it's a great idea to be releasing steam in my workshop, rusting all my machines.

I was impressed by the bag technique shown in the video. He had some serious BTUs under his steam generators.

So lots of progress, but a few more questions and a perplexing situation.

I finished building the form, and attached a winch. That took a few extra tries as the wood is so long that I needed more space than I had to allow the cable from the winch to reach the wood pre-bending, yet still be able to tighten down on the form. It turns out that wasn't so easy.
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So I wanted to make a few packers to sit outside the white oak laminate strips per the online suggestions. I grabbed a piece of spalted maple that I had sitting around for years collecting dust, resawed it to about .15 inches and steamed it for an hour. It's unbelievable how fast those Earlex steam generators go through water. And filling them when hot is no great task either. I wore gloves when taking the board out but chose poorly. Got a small 1st degree burn on one finger. New gloves ordered, lesson learned.

It bent quite easily in the mold (although this is totally a two person job), and I left it in the mold for about 8 hours.

I took it out this evening, and this is what it looked like:
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I really don't know what to make of this. The board does not appear to have any cracks, but sprung back massively. Is this just the wood I chose for that? I really didn't want to waste white oak on these packers if not necessary.

Really, really wondering if just making more bent laminations instead of steam bending would be far easier. But I'm seriously down the rabbit hole now, so I'll work on this for a bit.