can you bend plywood with heat gun?

[chuckt]

Im working with 6mm Meranti on my Chris Craft restore and its not very bendy. I've got some decent compound curves near the bow. It occurred to me that I might could bend the plywood with a heat gun? I experimented last night and got a little bend out of them but not much and the springback this morning was significant.

I don't want to steam bend because: (1) I dont have a steamer; and (2) the plywood is getting epoxied and my understanding is you don't try to epoxy damp wood.

I can force the curves without pre-bbending but it requires putting screws all the way through my plywood. I would rather not penetrate all the way through my new hull although if I have to, I can just epoxy the holes with a syringe.

[Mrleft8]

Why don't you get some bending plywood?

[sdowney717]

perhaps cut them less wide or maybe ought to run a different angle.
Screwing thru your planks is fine, your going to be filling em up with epoxy. And then a sheet over top. There will be no future troubles.
But you will see it from inside hull? Isn't that ok?
You could use drywall screws. they are strong wide heads, easy driven and small holes. Take out when epoxy sets.

[chuckt]

Too late left8. Already have all the plywood I need plus some. Like I said--it isn't essential I prebend--I can force it into shape. I am just wondering if this might work or if there is a reason not to do it (other than the fire hazard). I don't want to weaken the glue between the plys or somethign like that

Your'e right sdwoney. The very small holes filled with epoxy should be no problem. And they will be covered with a layer of epoxy and xynole.

[sdowney717]

yeah, if you heat plywood so the glue bond weakens it might be cause future delamination troubles.
You know the boat in a seaway is going to be stressed and twist some due to forces on a hull, so plywood will be perhaps be trying to move a tiny bit.

In fiberglass hull it is called pancaking and flexing and can destroy a hull

[wizbang 13]

[wizbang 13]

this boat (above) is 6mm meranti, surely your bend is not more?

[chuckt]

No, its not more than that--and stop calling me Shirley (sorry--couldn't resist). Look at that twisty curve amidships! This was done without heating? Was the plywood cut to strips? Surely thats not a single piece.

[wizbang 13]

Sir Lee, pre -scarphed,stitch n glue. No mold, no frames ,no stringers. Yes ,it has a twisty bit, cuz it's "tortured" (compound curve). I did that for strength/weight , but bending it was no problem! No heating or H2O.

[chuckt]

I guess I will just "torture" it as Wiz suggests--I like the sound of that. I'll start with calling it mean names and taunting it. Then I will question its parentage and imply it isn't very good plywood. Maybe mock its country of origin.

[spirit]

Okoume would have bent more easily... but your 6 mm meranti should do very well.
Don't pre-coat it with epoxy, since that would diminish bending.
Good luck!

[switters]

I guess I will just "torture" it as Wiz suggests--I like the sound of that. I'll start with calling it mean names and taunting it. Then I will question its parentage and imply it isn't very good plywood. Maybe mock its country of origin.

That is very witty, the reality is that tortured plywood is a bit of syntax error. It should be understood that tortured plywood is is actually plywood, torturing. The plywood in this case being the torturer, and the boat builder the tortured.

Just note who is doing the most cussing and screaming when the plywood is almost but not quite in place.

pre-bending for several days and letting it "sit there and think about it" works great if you have the time.

[chuckt]

Maybe a little water (wait for it) . . . boarding.

[Chipito]

I've had good luck bending 6mm ply with a heat lamp and heat gun. Just be careful not to overdo it. Never used moisture, just even heat.
Jeff

[Tom Lathrop]

You can bend wood very well with heat. The process is about the same as when steam is used. Moisture contained within the wood heats up and makes the fibers more pliable. Doesn't work well in very dry climates since there is little internal moisture to work with. In may ways it works better than steam because almost immediately after the heat is removed, the wood holds the new shape. Luthiers use this method in making the severe bends on musical instruments. The Chinese lay big teak timbers in a fire and then bend them in place on junks.

Plywood is another animal. The cross grained plies make bending much less effective and the glue effectively prevents moisture migration. Still, it can work, if less effective than solid wood. I have bent 3mm and 4mm ply for models with heat guns but it takes patience to avoid scorching the wood. I think 6mm meranti might be asking a lot if the bend is severe. Some moisture on the surfaces will help a bit. To prevent rupture of bent and twisted plywood panels on a boat, I temporarily attach a strip of wood along the edge to distribute the force over the panel and prevent rupture from point stress loads. Panels can be tortured much further without breakage using this method.

[AJZimm]

I bent and twisted 9mm okoume ply for garboard and next-to-garboard lap planks for my 18' Alaska. Used towels wrapped around the plank sections I wanted to bend, boiled up kettles of water and poured it over the towels for half an hour, with plastic sheeting to contain the water and keep the heat in. The ply moved into place easily and I clamped it in place until it was cool. It retained the shape I bent it to with almost no springback. I let it dry for quite some time (weeks) while I planked up the remainder of the hull before epoxying.

I reasoned that the glue is boil proof and I wasn't going to get it that hot with the hot water, so that it was the lignin in the wood that was softening and allowing the bend. I also found a reference to a similar method for bending plywood in a furniture building reference, somewhere on the web, though I've since lost the link.

It's holding up fine so far, and the boat is into it's 3rd summer, with some significant pounding for hours on end on some trips I've taken.

[chuckt]

This is what it took to torture it into position:



Not very pretty I know. I started dry fitting the other side and experminented with steeper angles. THe steeper angles make it easier because there is less compound curve.

[wizbang 13]

Might be able to shoot a bunch of staples through stiff webbing. When glue dries, tug webbing for fast staple removal. Or maybe working 100 miles an hour is not called for, for a one off repair.

[chuckt]

Looks a little better now. I swear it took all those blocks to make sure I had good contact everyhwere. Only some of those screws go all the way through the hull. Anybody reading this, I would use the Okoume for similar work. I think 6mm Meranti is a bit stiff. But it did go on there so . . . And it does seem to be going better on the port side with a steeper angle -- maybe about 75 degrees to the keel. Boy, three layers of this 6mm Meranti seems immensely strong. She will have a much stronger bottom now than what she was born with.

[wizbang 13]

Chuck, when it's finished, you may be happy to have the hardwood on there , in case you hit a coconut or something at 20 knots! Your flying along now, how do you have time to duck around on the computer? New bottom is strong, the frames and floor work won't even get loaded.

[chuckt]

Thanks Wiz. The trick for me is that I do 2-3 hours almost every night and 4-6 on Saturday and Sunday. Epoxy bottom construction is forgiving too so I don't have to be quite as painstaking as I would with traditonal planking. I don't know how you guys do it--getting all those planks in place with no gaps. If I have a little gap--hey, no problems-shluck a little goo in there. What gap?