Adventures in wood bending

My original title for this post was "How NOT to build a steam box". Still not sure I went with the right one, but whevs, as the kids are saying. (I think it needs more ... spelling. Like, maybe "whyevfs". Or maybe less? "wfs"? Meh.)

Anyway, I'm currently working on some bookcases for a friend, and like EVERY project, I just had to go and make them complicated. The "client" needed a bookcase to go behind her couch, and really wanted a curve involved somehow. And, long story short, I needed to come up with a way to bend the edge banding to go on the faces (and backs) of the case.

I'll have a post about the project as a whole when I'm done, but wanted to vent (ha! Vent! Get it? Oh, no, wait. I should have saved that pun for the end. Sorry.) about this particular part. Mostly because I've been posting pictures to Facebook and there are a LOT of very confused people out there.

So the concept of bending wood is pretty straightforward: put the wood you want to bend in some kind of container, fill the container with nice hot steam, and wait for a couple hours or so. Then you take the wood out, clamp it in the shape you want it to stay and let it dry. Presto bendo!

I watched a couple of YouTube videos and took note of the ones that seemed to work, and then set out to bend some wood.

My first challenge was to come up with some kind of heat source. Fortunately, our barbecue has a side burner (which we've used exactly twice). If I could set up a steam box in the back yard, I could boil a big ass pot of water on the barbecue and wouldn't have to worry about running out fuel, thanks to the natural gas line.

The next part was to come up with a steam box. I saw quite a few people build theirs out of plywood, but I watched one enterprising fellow build his out of a length of heavy plastic pipe. I figured that was faster and slightly cheaper than the plywood option, and hied off to the plumbing supply store. I got a 10' length of heavy-duty PVC drainage pipe (I cut a couple feet off just to make it slightly less unwieldy) and a couple of end caps to help seal the steam inside. I drilled pairs of holes every eight inches or so, just slightly below center, and ran dowels through to give me something to rest the wood on. I even grabbed a cheap temperature gauge and attached it near the venting end of the pipe so I could have an idea of the temperature inside the pipe without having to open the cap all the time. (And I remembered to drill some drain holes at the low points to make sure the condensation build-up had a way to get out, and that the pipe wouldn't get too pressurized. Yes, I was that deluded - pressure! Ha!)

With that taken care of, I needed to find a vessel in which to boil the water for to be making with the steam hot. Finding a steel bucket proved to be a lot harder than I thought it would be, but my Crazy Neighbour came through as he usually does, and found a metal bucket that wasn't rusted too badly. I fashioned a top for the bucket out of a piece of plywood and some little c-clamps, and figured that would hold well enough for a proof of concept.

It's worth pointing out that I was still labouring under the impression that all of this was going to work on the first try. Faithful readers, you already know I was wrong.

So I had a heat source, a vessel, and a steam chamber. The next problem was getting the steam from the bucket into the pipe. After casting around a bit and checking out the usual suspects, I found a deal on a replacement shop vac hose. I figured it was probably a little bit long, but my main YouTube inspiration (he of the plastic pipe steam chamber) had a great jeezly long feed pipe and his set-up seemed to work out just fine.

I attached one end of the shop vac hose to the plywood bucket lid, ran the other end in through the end cap of the PVC pipe, and threw together a couple of quick stand-offs to support the pipe on the sawhorses beside the barbecue. And I had myself a steam box!

It took a little while, but the water in the bucket eventually started boiling, and steam began making its way into the shop vac hose which, catastrophically weakened by the boiling hot vapour inside, promptly collapsed upon itself and started to melt.

Back to the drawing board!

(The good news is that the shop vac hose is the same size as the one on our shop vac and, after a minimum of careful trimming, we now have a back up hose should ours ever get run over by the car. Again. But that's another story.)

For take two, I abandoned the frailty of the plastic shop vac hose and went to something that was a little more purpose-built for moving hot air: dryer vent!

A quick re-jiggering of the bucket lid and a little hollowing out of the end cap, and Take Two was up and running later that day.

Man, that dryer vent got hot! Whew!

Unfortunately, the inside of the PVC pipe did not. Time to reconsider.

I did a little more research and thinking, and came to the conclusion that the steam just wasn't getting into the pipe fast enough. The dryer vent was so big, and so poorly insulated, that the steam was cooling off about halfway through, and nothing of any significant temperature was reaching the chamber.

I decided I needed two things: a narrower gauge transfer pipe between the bucket and the steam chamber, and a way to get the steam into the transfer pipe faster. It took some online shopping and perseverance (and mutilation of the most beautiful gas can I'd ever seen), but I managed to accomplish both.

The gas can works better because the steam has nowhere to go except through the narrow opening. With a vigorous enough boil, the steam is forced into the transfer pipe (a piece of flexible exhaust pipe for a motorcycle) quite quickly. I also moved the entry point for the steam into the middle of the steam chamber so that both ends would heat evenly, and the heat would be concentrated in the center of the wood, which is where I needed it to bend.

Yep, all in all, a much better set up than my first two attempts. In the end, it wasn't any more successful, though. The side burner on the barbecue just wasn't powerful enough to get the water really boiling. It only reached a gentle simmer, not the high rolling boil that I needed. No boil, no steam:

I was pretty much at the end of my rope at this point, and ready to just cut the bends out of a plank on the bandsaw, but I was convinced to give it one more go. Mostly because we're going to have to do some wood bending if we're going to restore our canoe, but partly because I wasn't going down without a fight on this one.

So I ordered a turkey fryer propane burner and reassembled the entire monstrosity in the front driveway.

(The neighbours were.... well, "intrigued" might be under-selling it. Let's go with "concerned".)

But damn me! It worked! We got steam!

The set up required some further tinkering, of course. After about 45 minutes or so, the transfer pipe started making a weird kind of chuffing noise. I poked around a bit, and figured out that the lower bend was full of condensate. I drilled a small hole right at the low point and once it finished draining, the noise stopped and full steam resumed.

Oh, hey! I bet you didn't know that PVC pipe will start to lose structural integrity right about 250 degrees F!

Yeah, I was getting some serious droopage. I hauled out a few extra sawhorses and roller stands to shore it up as best I could, but I was starting to think that I wasn't going to get a second shot at it out of this particular rig.

But I had a pipe full of steam, the wood was getting nice and toasty and I was going to give it a serious go. I set up my bending jig in the workshop and made sure I had a clear path between it and the steam chamber.

After almost two hours, I decided I'd see if the wood was at least close to bending. It was not.

I probably could have left it in longer, but really, I wasn't getting that curve out of it without the wood being 90% moisture, and I was worried I was going to run out of propane as it was. I had probably also failed to plan for how much the wood was going to twist as I was bending it. I would have had to have kept it in the jig for hours and I only had one jig - and four pieces that needed bending.

So, yeah. After all that, I had nothing to show for it except a badly misshapen length of PVC pipe and some slightly damp pieces of sapele.

The next time, I'm just making the box out of plywood, damn it.