Steaming wood


Hi, I need to make some porthole liners for a barge and I was thinking of steaming some wood strips. Size is approx 1.15m long - it is a 0.381m diameter porthole - 60mm wide and 6 - 8 mm thick. I was thinking of using mahogany or similar dark hard wood.
Can I bend steamed mahogany to this radius?? - or any other suggestions??
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Laminate. Thin, dry sections. Wood that's green, or air dry is always a better bet for steaming than something that's been through the kiln.
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snipped-for-privacy@hotmail.com wrote:

My understanding, is that steam bending works best on *green* wood.
You might have better luck doing bend lamination with matching scarf joints to build up the desired thickness. Issue here would be that the circumference would change upon each lamination application, so you'd have to cut laminations longer than needed and test fit them to get the appropriate lengths.
~Mark.
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As others have suggested, I too would use a bent lamination technique to make the porthole liners. If for no other reason, they will be very stable in a barge environment.
Basic bent lamination technique: Slice the wood into thin strips 1/16" -1/8" (1.5mm-3mm) Glue and wrap the strips around a form, (use a slow setting glue) Clamp in place. Unclamp and machine to finished size, sand and apply finish.
Dave
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I would recommend this method too. Stagger the joints around the circle and use a scarf joint. They will be almost invisible and the staggering will make it very strong.
Jim

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Steaming is a big and technical subject. Curved work in general and boatbuilding are even vaster, so nobody will be able to tell you how to do this or even run through the options in a quick ng reply.
Mahogany is not a wood for steam bending. Bending requires a strait grain and mahog has too much cross grain. Further to that i do not know how you would intend to make a complete ring of timber. Are you steaming pieces and then scarfing them together? If you laminate you might be advised to buy structural veneers rather than trying to cut them.
Tim w
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After attending a recent seminar at Lee Valley Tools conducted by Michael Fortune and watching him bend wood, I'm convinced almost any radius within reason can be obtained. I'm not that sure Mahogany is the best wood since straight grained wood is the best for steam bending, but you should be able to find something suitable. My first suggestion is that you read up a bit on bending wood. http://www.leevalley.com/wood/page.aspx?c=1&pD588&cat=1,45866,45867
There's also another route you might consider for these portholes. Bendable Lauan also known as Bendable Plywood or "Wiggle Board", (information also courtesy of Mr. Fortune) might meet your needs. You could laminate several layers together to obtain your desired thickness. I've provided one sample picture of it in the link below. It does come in longer lengths (at least 96") than listed on the website.
http://www.vandykes.com/product/02007822 /
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I'm guessing that mahogany veneer would need to be 1/16" at most to agree to an 8" radius. Experimentation is needed. As an alternative, turn the veneer such that the bend is cross-grain and laminate. A couple of laminations of light glass cloth can supply cross-grain strength.

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snipped-for-privacy@hotmail.com wrote:

Try this: http://www.wcha.org/tidbits/steamfaq.html
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On 9 Jun 2006 12:18:42 -0700, snipped-for-privacy@hotmail.com wrote:

Yes it is possible to steam mahogany to this radius. Steaming is somewhat of an art. After bending wood there might be compression failure or other defects. Use straight grain wood, free from knots or other defects. Green wood bends much easier than dried wood, so if you can get some green (not dried) mahogany you're good to go. Making the form and strap is probably the most time consuming part. You want the form made such that your clamps hook into it quickly/easily. Steam the strips for about 1 hour, use thick leather gloves, BBQ tongs, and have everything carefully setup in advance. Planning is very important. After removing the steamed strips you have a very short time (30 seconds or so) to get them into the form. Make sure you will have enough water and heat to last 1 hour. If there is any interruption in the heat/steam your wood will probably be ruined. Woods that are particularly good for bending are as follows:
ash, elm, beech, birch, hickory, oak, and walnut
I'd probably use 1/8" thick strips. After curing in the form, then laminate (glue) them together. Your liners will be very strong.
Warning: It is very easy to get steam burns--be careful!
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snipped-for-privacy@hotmail.com wrote:

Mahogany is not a good wood to bend. It's almost impossible to steam bend anything close to that radius. The rig you would have to make would be dangerous. According to my Fine Woodworking Bending Wood book the best radius you would see for 1" thick mahogany is 32" to 36".
Even bent laminations are tricky with mahogany. If you want to attemp this keep the strips really thin 3/32" to 1/16". Cut lots of extras, you'll need them. Bend SLOWLY. Have both an inside and outside form. My guess is 1/2 to 3/4 of them will break. Use epoxy if you do this. I prefer a nice slow setting gel type.
The other choice is cutting a circle. This would be the most wasteful, but might be your best bet.
The advantage to bending wood over cutting curved forms is tensile strength. Grain orientation (and therefor tensile strength) is inconsistent on a curved cut form, where a bent form will have fairly consistent grain orientation. IMO A pothole liner would not need need the tensile strength a bent piece of wood would give. It would be supported on all sides, unless I'm missing something.
The other best bet option. Choose a contrasting wood that does bend well like Ash, White Oak, or Red Oak. Walnut and Cherry will also bend well.
Christian
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Christian Brink wrote:

I'd avoid ash or red oak on a boat--you can pretty much count on everything being wet even on a barge so decay resistance is an issue--white oak or walnut would be much better bets IMO. Cherry I'm not sure about, I'd have to look up the decay resistance figures.
--
--John
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J. Clarke wrote:

I do use Ask and Red Oak for bent lam fishing nets (which I try to keep in the water as often as I can :) ), I have never had a problem, if they have been finished properly. I assume these are going to be above water line.
Christian
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You might consider some variant of a mast hoop. See http://www-personal.umich.edu/~mrwizard/wkshps/shpnotes/hoops01.pdf
In my very limited experience with laminating curved wooden pieces, I found that if you pulled the wood around the form, it would probably break. If you kept the piece in compression, it probably wouldn't. Push it into/onto the form.
Roger snipped-for-privacy@NOSPAMinsightbbNOSPAM.com http://home.insightbb.com/~derbyrm
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snipped-for-privacy@hotmail.com wrote:

So, that's about 12" dia. porthole?
I have been thinking about puting a porthole forward in the doubly curved cabin front, mine would be possibly 6 inches diameter.
I think a piece of sewer pipe cut and sanded to match the curves, inserted into a hole cut in the bulkhead and epoxied in might be the easiest.
I would try to find a plastic pipe close enough to accept the portlight I have, or build up an epoxy and glass form on a piece of pipe for a mould. It would seem to be a lot easier, and paint would disguise it's heritage.
Terry K
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On 9 Jun 2006 12:18:42 -0700, snipped-for-privacy@hotmail.com wrote:

Barge....mahogany?
Anyway, I'd go with Marine grade plywood. It is hard to find the stuff below 1/4" but if the bend is too much you can make multiple scores on the back side with a C-Saw set to a bit less than an 1/8". You can find it in mahogany veneer as well.
J
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On 9 Jun 2006 12:18:42 -0700, snipped-for-privacy@hotmail.com wrote:

Might be possible to soften laminations in a dishwasher (!)
Also 'pre bend' them on a former, so once dried they can be glued with minimal further bending.
Also... make them over long then cut through both layers with a slightly extended snap-off knife to get a decent butt joint on each.
cheers, Pete.
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