Steam Bending Questions?

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Going through odd shop woods I came across a couple (test?) pieces of steam bent wood. Years ago I picked up a derelict canoe from an aging-out canoe club elder. He gave me a lengthy tour of his collection, including an impressive paddling library. And before I left he gave me a few things; the never put together halves of a glass slalom kayak and four 18+’ lengths of ash gunwale.

And a couple oddities. A length of 7/8” square ash, steam bent with a long, gentle curve in the middle, almost at a 90 degree angle. And a length of 3/4” x 1” wood steam bent 180 degrees, into a U.

P1030014 by Mike McCrea, on Flickr

The U bent piece is eight 1/8” thick strips laminated together.

P1030017 by Mike McCrea, on Flickr

I know bupkis about steam bending, and assume these were test or demonstration pieces he had made. But now I’m curious. How tight a curve can be steam bent? I’m thinking the inside curve compression and outside curve elongation both have limits.

And what wood species allow for bending sharper curves?

Is laminating separate pieces a better solution for forming tight curves? And if so, how the hell is that accomplished – one strip at a time and laminated when/how?

Inquiring minds that will never-say-never steam bend wood want to know.
 
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I have limited experience with steam bending but I believe the general strategy for laminating strips is to first have a form cut out to form the correct shape. The form should allow the strips to be clamped to it (you see this with stripper builders bending their stems). The strips are steamed and then clamped into place to cool and dry. Marks are made on the side of the clamped up piece (diagonal line) so that the pieces can be removed and put back in the same position

Once mostly dried off the clamps are removed and the strips mostly retain their shape. Glue/epoxy is slathered on the mating surfaces of each piece and then they're clamped back to the form again until the glue dries.

How tight of a radius you can make I don't know. Thinner pieces obviously means a tighter radius. Straight grained wood can obviously bend better than knotty wood or pieces with runout. Wood like ash, which seems to have more "give" or shock resistance, generally bends better than stiffer wood, like oak. Wet wood bends better than dry wood. You wouldn't believe what you can do with a thin strip of wood when it comes off the sawmill from a fresh log.

How much moisture you can put into a piece of already dry wood will depend on the species, how thick it is, and how long you steam it.

Alan
 
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I’ve seen green 1/4” ash steam bent into a knot. Green wood is preferable, but not necessary. I (and many others) back up bending a small radius rib with a leather strap. I have had good success bending spruce, white cedar, ash, and white oak. I’ve also had them all crack on me. As Alan said, having straight grain with little to no run out is key. Some pre soak and there is a such thing as over steaming- not good. 20 min per 1/4” will get you close. I have done a couple lamination bends, but prefer a solid piece if possible. I am no expert, but I have done a fair amount and enjoy it.

Bob
 
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As C&B said, thinner strips can be bent tighter, larger because the difference between inner/outter is less, when you bend, if you support both the inside and outside surfaces, it largely eliminates fracturing (assuming you have the right grain pattern).

So some sort of 2 sided form for clamping performs better

Green wood is best, air dried next and kiln dried is not recommended, but it can work (just not as well).

One thing I learned about thinner pieces, wetting before heating seems to make the bending much easier/better ... I believe this is because the water holds the heat from the steam better and the wood is more pliable because it stays hotter longer ...

Brian
 
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I wasn't going to jump in on this thread yet but if I can get some good weather days I plan on a big, for me, steam bending project on my Bell Rob Roy. What caught my attention was Cruiser's mention of a 2 sided form for clamping which is what I built in anticipation of bending the wood in one piece. Here's my write up so far, still waiting on some good weather days to try to pull this off, probably should have waited until spring but what the hell:

 
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I wasn't going to jump in on this thread yet but if I can get some good weather days I plan on a big, for me, steam bending project on my Bell Rob Roy. What caught my attention was Cruiser's mention of a 2 sided form for clamping which is what I built in anticipation of bending the wood in one piece. Here's my write up so far, still waiting on some good weather days to try to pull this off, probably should have waited until spring but what the hell:

I posted using 2 sided form/clamp making the deck blanks on my last build.

It looks like you made tight fitting forms, but remember you need to allow for the thickness of whatever it is you are bending. If you mate the forms with nothing in them, they won't be fair when you load them with material. For example, if the inside curve is primary, then the outside curve is drawn from the primary using the width of the intended material ..... this is to keep the lines parallel at the clamping distance.

If you take a matched fit like your picture and separate them by an inch, the curve lines of the 2 pieces will not be parallel , meaning they can't close evenly with the desired piece.
For that tight a curve, you will likely want to use thinner stock and laminate up the final piece (e.g. try 1/8" strips, enough for the thickness wanted).
Your clamping solution needs to be worked out in advance, you will get 30-40 seconds of real bend time and that needs to be gradual (material dictates), it only bends so fast and if you push it too fast it breaks .... so you need to get it into the form and bending as fast as you can. Soaking the wood first is a good idea, the absorbed water increases the amount of heat absorbed and gives a bit more bend time.

If you look at he build part for bending the stems, you will see I used a passive clamp arrangement, to allow me to slip the pieces to be bent into position and start bending immediately, I think this may be of benefit to your needs
here at post#34 https://www.canoetripping.net/threads/light-weight-solo-tripper-build.105054/page-2

Then you can finish with the clamp solution for a final press fit.


Brian
 
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Cruiser, Thanks for the feedback. I'll have to re-think the "press". My attempt at steam bending involved using a bag. Look at this video:

It worked great on the first attempt on the Rob Roy. By keeping the wood on the boat while steaming made it much easier and I didn't have to worry about moving it from a box to the boat in a hurry.
 
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I’ve moved on from the propane burner and gas can steamer (that could have been my photo, I had the same setup). I now use a wallpaper steamer. $35-50 so much easier and cheaper overall, especially with the price of propane these days. I even used it to remove wallpaper in our new old house when I renovated the one bedroom.
Jim
 
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I used this small steamer recently, it pumped out enough steam to bend some cedar ribs, which I steamed one at a time.
I bought my bag material at Walmart, Food saving bags come in an 8” x 20’roll, it held up well, no issues.

IMG_3148.MOV.jpg36DD3DB6-1503-4C1C-844E-AE0795433154.jpeg
 
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I steamed kiln dried Douglas fir for the chine logs on my skiff build.

First, I soaked the lumber, and needed a 16 foot long soaking chamber. I didn't want to immerse the boards in the creek, thinking that my lumber might be lost in a flood.

There's a drain at the foot of the front walk that goes under the driveway and emerges from a bank. I put the boards in the drain pipe and plugged it....

20210620_184927.jpg
drain plug resized.jpg

...and filled the drain with water.

hose in drain resized.jpg

After soaking for a week I steamed the chine logs in place, as shown in a couple other posts above.

A gas can on a Coleman stove -- what could possibly go wrong?

steaming 01 resized.jpg
 
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