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Old 25-07-2015, 05:39   #1
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Steam bending

Hi All. This is my first post and I hope it is in the right place.

I am trying to steam bend 10' lengths of 2-1/2" wide by 3/4" thick sapele for our toe rail. We built an insulated steam box with a 6" diameter stovepipe in the middle of it. We steamed the wood at what appeared to be 212 degrees F for about 1-1/2 hours. When we pulled it out of the steam box it was still very stiff but we managed to clamp it up to the hull to deck joint and let it sit overnight. The next day when we pulled the clamps off the wood sprang about half way back to its original straightness and by the next day it was damn near all the way straight.

Does anyone have any experience with steam bending that can give me some advice? The videos that I have seen on YouTube do a very good job of explaining how to Build the box but not much in the way of the guidelines for how to tweek the times and temperatures and clamp-up time. etc. Thanks in advance.

shipster
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Old 25-07-2015, 05:55   #2
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Re: Steam bending

I have found that instead of clamping it in place I would hang it over something, a saw horse maybe and place weights on the ends to get it to about the correct bend, maybe even a bit more then required. After it drys then clamp in place and attach. Only has to be close to the correct shape before clamping it in place. I have even just soaked the wood in water overnight, place over something with weights on each end and stops so it doesn't go to far and got them really close before attaching.
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Old 25-07-2015, 06:21   #3
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Re: Steam bending

We steam for about an hour per inch of thickness, a bit longer as thickness increases. Springback is always going to happen, on planking we often use the "job" to act as the form just as you have but will add some spacer blocks to accentuate the curve, will also add some wedges at the ends to " over twist", both help in slightly over bending, Usually if the timber has taken the bend it will go back, but always good to leave bent like overnight, work & fit the piece in reasonable time, as I2ridehd mentioned shape can be held around any similar form, some extra especially at the ends is good.
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Old 25-07-2015, 07:04   #4
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Re: Steam bending

I have steam bent wood like hickory and ash but never sapele so can't say specifically about it but agree with comments above.

Springback happens so need to compensate with your forming jig or get the work fastened properly to hold it in place and make sure it holds it's shape.

Also agree about the ends. Keep in mind you have no leverage at the ends so they will be straight.

The way around this is to start with pieces too long and cut them down to the proper length after bending.

Hope it's not too late for that, otherwise accept you will have flat spots and not fair curves. Good luck.
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Old 25-07-2015, 07:20   #5
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Re: Steam bending

I don't think woods like sepele, ocumi, mahogany are amenable to steaming. You need big cell woods. Oak, Hickory, fir. Laminating is generally how the others are bent to form.
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Old 25-07-2015, 07:25   #6
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Re: Steam bending

^^^what he said^^^
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Old 25-07-2015, 08:29   #7
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Re: Steam bending

Thanks for the replies.

I know and understand the issue at the ends so I have an extra foot or so added in. Thanks. I also have been finding out the difference between open cell woods like oak and ash vs. closed cell woods like the $300 worth of stinking' sapele that I have spent umpteen hours milling and sanding and everything else so I am reluctant to drop back and punt. Call me stupid if that what I need.

We're gonna try a second piece today however because we are essentially bending a 2-1/2" board, i.e. the Hard way, we are gonna keep it in the steamer for at least 3 hours. That factors in the 1 hour per inch of thickness. We're also gonna keep it clamped for 48 hours or so. I'll let you know in a couple of days if that works.

Delancey, you're killing' me with the rock.

Again, thanks all.
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Old 25-07-2015, 08:47   #8
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Re: Steam bending

Best of luck. Let us know how it works out.
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Old 25-07-2015, 11:30   #9
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Re: Steam bending

Laminate, laminate, laminate. Google west system epoxy. They have great how to articles and will talk as long as you want over phone on techniques.

Good luck

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Old 27-07-2015, 05:02   #10
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Re: Steam bending

Complete failure...

After we steamed the wood for 4 hours or so we pulled it out and it seemed bone dry and stiff as a board, so to speak. As I have been talking and learning from people in the know I have found out that 1) sapele don't bend and 2) kiln dried wood prevents plasticizing of the lignum. I guess I didn't do enough homework here. I wish this forum would let you cuss like a sailor.
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Old 30-07-2015, 08:16   #11
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Re: Steam bending

second (third?) the laminate route. You' re gonna want to epoxy coat all sides anyway, so....
Going the flat-ways? Impossible. Perhaps long, diagonal cuts with necessary degrees of material removed? (scarf joints?) Naturally, you,d need to start with a wider board and shave edge to shape...
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Old 30-07-2015, 08:35   #12
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Re: Steam bending

I think you can still salvage the wood. Saw it into strips and laminate it together. If you use a thin blade in your table saw you will lose less than a 1/2" and maybe less than a 1/4". You will need lots of clamps.

And don't put it all back together the same way. Spin every other lam 180 so the grain is opposed. Wood wants to springback to it's original shape and this fools it a little. It doesn't know what to do.
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Old 30-07-2015, 08:39   #13
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Re: Steam bending

Quote:
Originally Posted by shipster View Post
Complete failure...

After we steamed the wood for 4 hours or so we pulled it out and it seemed bone dry and stiff as a board, so to speak. As I have been talking and learning from people in the know I have found out that 1) sapele don't bend and 2) kiln dried wood prevents plasticizing of the lignum. I guess I didn't do enough homework here. I wish this forum would let you cuss like a sailor.
Sorry to hear that. Learning the hard way sucks. The other way to do a cap rail, which is what I would call what you're making, would be to cut curved pieces out of wider width boards which unfortunately means a lot of waste. I think this is the most common approach.

Regarding epoxy, great stuff. Way too over specified in my mind. Resorcinol works great and would be an appropriate adhesive for this application, only downside is that it requires a tighter fit and greater clamping.

https://en.wikipedia.org/wiki/Resorcinol_glue

I would never recommend epoxy coating a cap rail unless it was going to be painted, or unless you intended to stay on top of your varnish maintenance.
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