Problems Steam Bending Thin Wood

[John Goodin]

I have been trying to steam bend into a half hourglass shape 1/10" X 2" strips of sapele with little success. The Earlex steam bender is attached to a steam bending box made of cedar fence pickets. The box is not too large as to require a second steamer. The strips have been steamed from 12 to 30 minutes with the same result of a very slight curve. It is kiln dried lumber which sets the lignin but understand it is still doable with a longer steam time. One thing I have wondered about is if the cedar the box is made of is absorbing a lot of the moisture from the steamer since the sapele comes out of the box hot but dry. The box is well sealed but some condensation does drip out the bottom. This has been one of my more frustrating woodworking experiences and any advice would be appreciated.

[Bradley Gray]

I would recommend getting a thermometer and making sure your box gets to 210F. I had to insulate mine for this to happen.
Another big cause of failure is bending without a steel strap to keep the wood in compression.

[Nelson Howe]

I'd go with a hot pipe and a bit of aluminum flashing to back up the wood. A cheap Harbor freight heat gun blowing into some pipe does a good job.

Nelson

[Mike King]

What is the moisture content of the sapele before steaming? Is it air dried or kiln dried stock? It is much more difficult to bend kiln dried stock.

Do you have a thermometer? At your elevation, you should be able to get the steam box to 200-210 degrees. If your stock is quite dry, try presoaking it in a water bath for quite a while (say a day) before steaming. You may also need to steam the stock for a longer period of time .

Or, go for a laminated glue bend. It is more predictable.

[Zachary Hoyt]

I use a copper pipe with a propane torch inside to bend anything up to 1/8". It's a different technique but not too hard to learn.

[Julie Moriarty]

If all else fails, John, try ammonia. I ran across this method when trying to bend thin strips of quilted maple for guitar binding. I was having serious problems bending it on the heating iron. No matter what I did, it kept cracking. So I went searching for help. That's when I learned about ammonia.

What I did was take a 36" long piece of 3/4" PVC, glue a cap on one end and a slip-to-thread coupling on the other. Next was to fill the tube with ammonia, insert the maple strips and cap it. I let it set for 30 minutes. When I removed the strips of wood, they were almost as pliable as wet spaghetti. I wrapped them in aluminum foil, so as not to wet the form, and clamped them in the form. No heat.



I let it sit overnight, because the aluminum foil retained the moisture. I had to tear openings in the foil while the wood was clamped in the form to let out the moisture. The next day I had this



Yeah, it's a bit stinky but I'd use it again on difficult woods.

If you give this a try, test it first. I noticed it made fumed mahogany (the dark strips off to the left in the picture above) bleed out. The ammonia turned noticeably darker. Even the quilted maple darkened the ammonia. But it didn't darken the wood after it dried.

[roger wiegand]

I'd use a bending iron rather than steam (though I agree with the assessments above that you're probably just not getting hot enough). Either a hot pipe, or if you need to do it a lot a guitar side iron like this:

Bending_Iron.jpg

I've used a heavy iron pipe with a blowtorch for heat, you can get closer or farther from the heat source to fine tune the heat. It's kludgy compared to the thermostatted iron, but works for one-off jobs. I've never used steel backing for such thin wood, just bend it over the iron a little farther than where you want it to end up. A bit of trial and error, but pretty much every luthier bends instrument sides that way.

[John Goodin]

I was able to get the steam box up to 210 degrees and most likely the wood is kiln dried. There are plans for a heat pipe made with a metal fence post and a electric charcoal lighter I may try.

[Jim Mackell]

If you fill the Earlex up to the marked line, you'll get about an hour and 45 minutes of steam. That should completely and totally saturate the wood and make it easier to bend. Works on mahogany and cherry.

[Mike Cutler]

You shouldn't be having this much trouble with 0.100 thick wood. You could almost do a cold bent lamination with it.
I suspect that your steam box is taking up too much of your energy to reach temperature, and that the pieces you are actually trying to bend are not getting a long enough steam environment.
My bending box is a single sheet of aluminum backed, foam board insulation. It is about 6' long and 12" square, or whatever a single sheet of the insulation will yield.
I use an old turkey fryer and pressure cooker to develop the steam. The box is not air tight, and you don't want it to be. It needs to "leak" a little steam to create a saturated environment.
I've done a fair amount of steam bending for boat trim, and curved work, and the minimum steam time for me is an hour, regardless of thickness. Usually when bending strips there are multiples of them in the steamer, so I take the equivalent thickness of all of them together, and use that for time. It's an energy calc' in the end.
I've never bent Sapele, and bending already kiln dried wood is more difficult. You also need to mill the wood for the bend, so that you're not bending short, or runout grain.
There is a definite learning curve to steam bending wood. You may want to try on some green softwood strips first to get your technique, and bending forms down.

[Bradley Gray]

I just finished bending some AD 3/16" cherry to a 1" radius with a strap after 1 hour at 210 F. Insulated steam box, Earlex generator - 6 out of 6 bent perfectly.

[John Goodin]

Thanks for all the advice and I like your guitar body Julie. I am not there yet and will probably never develop your skill. Anyway after tiring of the lack of progress I spent a little less than 40 bucks and built bending iron from a 2 3/8" fence post and a electric charcoal grill starter. The charcoal starter had to be put in a vise to decrease the diameter enough to fit into the pipe. The metal brackets in the image are used to connect 2X4 stringers to the fence posts. After polishing a little and adding a dimmer to control the amount of heat it works like a charm.


IMG_4521.jpg

[Bradley Gray]

Awesome job!

[roger wiegand]

Very slick-- I may steal your design!

[Al Launier]

Very creative. Well done indeed!