bending ply...any ideas?

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yourmomm

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hi-in the process of STILL repairing the damage from my wooden boat fire-ive got to bend sections of ply around a very sharp curve to make a new seat for the cabin-i cant make a supporting frame as i dont have the width available for such a frame on the inside of the seat (where my fridge is!)-i have made up a jig around which to bend the ply though. the previous (now very burnt) seat was made up of two laminated 6mm sections of ply bent around a sharp curve and these were then faced with 5mm mahogany. in trying to recreate this process, i have snapped about £60 worth of 6mm ply and have come to the conclusion that this curve is impossible without extra help...

is it possible to steam wbp or marine-ply? i would have thought the steam would wreck the glue...i am in the process of trying to soak the ply in warm water to see if that helps as i write this-failing that, i intend to kerf-cut the ply to see if it bends any easier, but i have a feeling this would still result in it snapping. my last resort is to make the curve up from 2 sections (less curved) sections of ply, but i am not keen on this idea, since to my knowledge, ply cannot be scarfed together (..?) and the resulting join would be an area of serious structural weakness in a chair which has to support my lardy frame....

any suggestion from people who have experience in bending ply would be greatly received...

many thanks in advance

ryan
 
It is possible to purchase ply that is designed for bending as it has cuts on one side. However, you will really only be able to bend in one direction. You would also be able to bend 4mm easier than 6mm. 3x4mm = 2x6mm
 
As David Tav has pointed out" bendy ply" will do the job. Another way to go is to cut the ply on the bias, ie so that all layers of ply are 45deg, to the vertical, this will allow you to ge ta tighter curve.
If you are going to Kerf use very small gaps between the cuts.
 
Ply will bend more one way than the other (usually) - it often has a thicker core veneer which helps, and it has an odd number of veneers, so there is more flexibilty in one direction.
In your case, it might be worth using thinner ply - there's no reason why you can't use 1mm to get a really tight radius.
Kerfing is the alternative as you suggest - make sure the kerf cuts are closely spaced. It would still help to laminate from thinner pieces as you can stagger the kerfs when glueing up. Use an epoxy thickened with microfibres and it will be incredibly strong.
I think there is a ply available (called architectural ply ???) that will bend around a tight radius, but I have never used it. Try Robbins Timber, Bristol.
And yes, you can scarf plywood. I built a clinker epoxy-ply 14' boat with every plank scarfed and bonded with epoxy prior to bending them into place with no problem at all. From memory the scarfs were 1 in 12, and I made a simple jig to cut them with a smoothing plane - just a flat board with two wedges fixed 6" apart with the ply strip clamped between them.
I wouldn't want to do this sort of job without epoxy (West or SP) and microfibres.
I've never tried steaming ply - I'm sure that the cheaper non-WBP stuff will fall apart (which might help as you can then stick it back together in the shape you want!). Marine ply might stay stuck together, but someone else who has actually tried it might know.
 
"is it possible to steam wbp or marine-ply?"

Yes - 'wbp' stands for Water Boil Proof. Use good quality wbp don't use marine ply inside - too expensive.

do as Boatbuilder says, cut on the bias, use the right glue..

and good luck with the 5mm mahogany !
 
wow-thanks for all the advice-once again a job seems so much easier when you know how...

having wasted a whole day in frustration and expensive mistakes, the above advice gives me new impetus to get the job done!

thanks once again...
 
Thank you - I didn't know that.

Being a bit of pedant myself I am happily corrected !

Years ago , believing (or not) that WBP stood for boil proof I boiled a small piece to see if it was what it said, after about an hour it delaminated , maybe I was just lucky with the sample.......
 
Yes you can steam wbp or marine ply (I think WBP originally stood for "Water and Boil Proof but that may be a myth) and marine ply would not be much use if the glue weren't water resistant.

However as others have said, bending anything more than 3-4mm is very hard work. Much better to laminate up thinner sheets.
 
As others have said. "Bendy ply". However the usual boatyard method is to laminate very curved pieces. You can buy faced ply from specialist suppliers down to about 1/16". The easiest amateur way is to make a couple of formers for the internal shape by cutting a radius in (say) 1" ply then screwing layers of ply of anything from 1/8" to 1/4" to that, depending on the radius, from the outside using a good woodglue between them. (Cascamite will do if its below decks, Epoxy if outside) Then remove it from the frame by removing the screws (Don't laminate over them!) It will then hold that shape and its a relatively easy job to glue your thin facing ply to that. If you make it oversize and then cut it to shape you can have most of your screws outside the part. Another surprisingly easy way is to strap the pieces down with lengths of old car inner tube. Trust me it works!.
 
Why do you think that WBP doesn't stand for Weather and Boil Proof? I always understood that it does and a quick google search reveals that lots of suppliers do as well and the Scottish Timber Trade Association also thinks so. You might be right, but where do you get that info from?
 
I bent marine ply around a fairly tight radius by cutting a series of grooves in the back at the point it was going to curve. I did it with a bench saw set to whip off a couple of plies, but a hand circular saw would do it just as well.
As others say 6mm is perhaps a bit thick although the backrest pads around the cockpit coaming on my little motorboat were even thicker and done using the same grooving method.
 
I have always understood WBP to mean Weather and Boil Proof. I should be interested if it is proven to mean anything else.

Certainly the glues used in BS 1088 ply should be resistant to steaming but they are also likely to resist transfer of the moisture to the inner plies so the effect could be limited.

Robbins do a bending plywood in 5mm & 8mm but it is not WBP bonded. That Stagflex stuff in David's post looks interesting. Don't know how good it is in a marine environment.
 
Actually you are perfectly correct WBP stands for Water and Boil Proof. My apologies, I thought the previous post was right when he said differently.
HOWEVER it only applies to the glue which is usually high temperature phenolic. It doesn't mean that you can boil or steam the ply. In practice you might well be able to with good quality ply but I never have. Even BS1088 Marine grade ply can be made out of a variety of woods and numbers of laminations. In practice the best quality was always thought to be "Bryanzeel" (I think that's spelt right) But you can get a variety of ply from far eastern countries that complies with BS1088 but is absolute rubbish! If you consider a typical 12mm panel it can be anything from 11 ply with the same hardwood used throughout or 5 ply where only the outer panels are anything like reasonable and the three central cores are soft whitewood. Its all BS1088 WBP though but I can tell you that without good edge sealing the softwood will disintegrate in a wet environment because it rots like hell long before the glue gives way. What the hell would happen if you boiled it I don't know! So apologies WBP is waterproof and boilproof but in a way the other post was right in that it does not apply to the panel it is only the glue.
 
Ahhh, but I didn't write 'a bit pedantic' - I wrote 'a bit of a pedant' and that I surely am.........and modest as well - thank you......
 
Re your seat - would it be possible to laminate it in fibreglass, using a section of Formica (which bends easily) as a mould?
If a varnished finish is desired, then you could perhaps laminate on a very thin (single ply even) sheet of the plywood used for making models (?)
 
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