Roof Problems

[TD_Dodger]

hey guys sorry about this question but im having a big problem.

ive gone through two pieces of luan ply for the roof. once i get it to curve i leave it over night for it to just bend on its own. once i start to curve it more and more it cracks right at the curve line. its happend twice.

what can i do to prevent the crack?

should i cut it just at the curve where you wont see the line from the inside?


please help.....


ill post pictures of what i mean this evening

[Miriam C.]

Three things you can do.
1. Get thinner ply and make two layers.
2. Really hot water or steam the ply, then hold it on with
straps as it slowly bends.
3. Cut Kerfs along the curve. Careful to not cut it too much.

Have fun!

[alffink]

TD_Dodger

How thick is the Luan, that your using?
1/8" usually bends pretty easily

I'm only a few miles away from ya and it's been somewhat cool and damp at night, higher temps would help, but it's not cold.

What is the radius your trying to bend? if it's too tight may have to find a different technique

[whitefishpoint]

Something to check.

I had some luan where there was a gap in the core material about 1/8" wide. You could see the gap if you looked at the edge. The wood would snap right there where the core gap was. I had to find a piece that had no core gaps then it bent ok.

[TD_Dodger]

hey guys sorry about this question but im having a big problem.

ive gone through two pieces of luan ply for the roof. once i get it to curve i leave it over night for it to just bend on its own. once i start to curve it more and more it cracks right at the curve line. its happend twice.

what can i do to prevent the crack?

should i cut it just at the curve where you wont see the line from the inside?


please help.....


ill post pictures of what i mean this evening

Thanks for the response guys the wood is 2.7 mm thick atleast thats what it says.

here is the link to the pictures of what i got going on.


http://tnttt.com/album_ ... er_id=7242

[TD_Dodger]

TD_Dodger

How thick is the Luan, that your using?
1/8" usually bends pretty easily

I'm only a few miles away from ya and it's been somewhat cool and damp at night, higher temps would help, but it's not cold.

What is the radius your trying to bend? if it's too tight may have to find a different technique

Funny you are actually in the same town as my parents rialto. its so frustrating im so close to finishing and stuff like this happends grrrrrr

[planovet]

That's not that severe of an angle except right at the top.

Try finding a better piece of luan as mentioned or go to a higer quality ply like baltic birch. I bent my 1/8 birch over a more severe angle with no cracks. I did wet it with some towels and very hot water. You could also try easing the curve a little right at the top.

Good luck!

[TD_Dodger]

Three things you can do.
1. Get thinner ply and make two layers.
2. Really hot water or steam the ply, then hold it on with
straps as it slowly bends.
3. Cut Kerfs along the curve. Careful to not cut it too much.

Have fun!

sorry but im fairly new at all this, but what are kurfs? lol

[planovet]

Kerfs are grooves cut into the back of the ply. They go from side to side and about 1/2 the thickness of the ply. How close together you put them depends on the severity of the curve but usually 1". They can be cut with a table saw or a circular saw. If using a circular saw, use a straight edge guide to cut the kerfs. Support the piece you are cutting (rigid board material under the entire length of the piece) prevent it from breaking at the kerfs. Try a couple of test cuts on some scrap before trying it out on the final material. This is more for saw cut depth than anything else.

Here is a picture of some kerfs Endo put into the ply of his inside ply:

[Playtym]

Hello TD_Dodger,

Sorry to hear that you are having problems. If my metric tape measure isn't lying to me, 2.7mm is close to 1/8". Cutting Kerfs into that thin a panel would be challenging and might not leave enough material to achieve any real strength.

It appears in your photograph that the grain is running the long direction of the sheet. I think if you were to turn the sheet 90 degrees from the way you are trying to install it, it will bend easier. If you do turn the panel, make sure your joints fall on flat surfaces and at a distance far enough from the radius that the is no ongoing stress in the joint(s). You may still need to use moisture or steam to achieve this radius.

On my build, the front radius is 20" and I used two layers of 1/8" Bender-board plywood. This material can be purchased at most better lumber yards and is available with the grain running either the long or short direction of the sheet, depending on your bending needs.

I know how frustrating these things can be. Somewhere in the replies you receive, you'll find a direction that makes sense for you.

Good Luck, Buff

[Miriam C.]

I guess I didn't pay attention the the mm.....boiling water will bend it easy unless it is flawed.

[Lou Park]

It sounds like your trying to bend it too much without something backing up the outside. I'm not sure if I can explain this right but, from your pictures you are doing two things wrong for bending plywood with the grain in that direction.
1.. Your nails are few and far between, on the curve (and just before and after) you need to nail every couple of inches, not every 8".
2.. No straps, get a couple or a few straps that can be tightened as you nail. this will support the outside of the ply. You see, you have the sides supporting the inside while it bends, but nothing from keeping it from kicking out so it's going to break.
Once you do this, leave it for a few days to take the shape.
Lou

[Ageless]

DO NOT APPLY WATER TO LUAN!!

It's tag says 'water resistant' ( another name for BS)

[Gage]

Try laying it cross wise. It'll bend much easier and not crack if you buy quality plywood. That means not from a 'Big Box Store'.




There is nothing hidden in the above message.

[TD_Dodger]

Try laying it cross wise. It'll bend much easier and not crack if you buy quality plywood. That means not from a 'Big Box Store'.




There is nothing hidden in the above message.

hey there you are. havent seen you since you came to my house, still intrested in that propane tank?