Warping

[RumrationParticipant @rumration]

Hi,

Just got a sheet of 3 mm lite ply out of my stock, and it is warped along its length. (1200mm) Is there realistic method for reducing, or even better, removing said warp?

[RumrationParticipant @rumration]

3mm ply

[Bob Abell 2Participant @bobabell2]

Hello Captain Rumm

If you can live with the ply being twice as thick……Just glue bow to bow = Dead flat ply

I always do this for keels and formers

Bob

[Ray Wood 3Participant @raywood3]

Hi Rum

I guess its too late as you have the Lite Ply but I think is horrible stuff, ok for aeroplanes where weight is an issue ! but give me birch ply any day for boat building.

Regards Ray

[RumrationParticipant @rumration]

Hi Bob,

Do you mean back to back I.e. face join two pieces together with opposing warps? For a moment i deciphered as in bow/stern! I am interested in making bulkheads and formers. I think that the warp might be useful if I was constructing the hull.

Ray, yep too late. And yes, the wood is from my model aircraft stock, so going to use it. I’ll certainly go for birch when I replenish stuff.

As an experiment I have supported the sheet between a couple of chairs, dampened it, and placed weights on it so it is very slightly bowed in the opposite direction. See what happens.

Thanks.

[Ray Wood 3Participant @raywood3]

Hi Rum

Did you know SLEC do crossgrain sheets of 1/8" birch ply for around £2.60 for 4' X 1' brilliant for bulkheads and cheaper than chips in Kent these days

Regards Ray

[RumrationParticipant @rumration]

No I didn’t. I’ll look at it.

Chips only £1:50 here!

[RumrationParticipant @rumration]

Thinking now. What is crossgrain ply? I understood that each laminate layer had 90’ rotated grain in ply sheets.

[Dave MilbournParticipant @davemilbourn48782]

Glyn
Ray means sheets whose surface grain runs across the width rather than along the length.

Ray
"One man's meat" – I've been using liteply in my boat and aircraft designs for about 40 years – ever heard of Precedent Kits? In the right place it's far more suitable for models than birch ply; it's all a question of application. Slots and tabs, appropriately positioned, will automatically flatten a bent piece once it's fitted, and you can add a lot of strength and "straightness" with a cunningly-placed strip of bass or balsa. Like Bobbable says, laminated parts should be done with opposing curves and weighted down flat while the glue sets. None of this is particularly clever stuff.

Birch ply is good where its strength is needed and it is waterproof, but it's twice the weight of liteply and really needs power tools to work it if it's more than about 0.8mm thick. The liteply cuts and bends easily so it will bend back easily from being 'warped'. I use it for most of my {quite small} models and have no issue if it's slightly bent, but I do store it either flat down or upright on end along with a lot of other sheets. If you are that worried then be careful how damp you get it, because it's made with a PVA adhesive and therefore may de-laminate if too wet.

Dave M

[Ray Wood 3Participant @raywood3]

Hi Dave

Yes I've built some Avionics/Precedent kits in the past I think the 46" Huntsman 31 back in 1970 was an open grain ply, but I don't think they called it lite, anyway bring back Aerokits good old birch ply bulkheads with 1/16" skins that didn't want to bend to the bow !! Yes the bandsaw is the most useful bit of kit in the workshop with a coping saw to cut out the centres.

Happy Days Ray

[Dave MilbournParticipant @davemilbourn48782]

The Model Avionics Huntsman kits (1972) were WBP plywood, cut on a band saw. I personally did more than a few of them! They didn't discover Liteply for a good few years, when the original Hiboy came out. The less said about the liteply boat kits the better…..
Aerokits were designed to absorb the thump of a diesel or glowplug motor. These days brushless electric motors are more powerful and don't vibrate at all – unless you've fitted a horrible coupling, bent shaft or unbalanced prop. Liteply would substitute for most of the parts formerly done in WBP birch ply. Lighter boats go faster and use less battery capacity. You heard it here.

Onwards and upwards!

Dave M

[RumrationParticipant @rumration]

Thanks guys, Good info and explanations as always. I’m going with my lite ply. Warped or not I’ll make it do hopefully! Not started build, just got the ply out to to test run getting the plan parts onto the wood. Tried to previously suggested methods both worked ok.

Got all the bits except a prop. Will do a blog when I start for your entertainment! That will be a new experience as well.

[Paul TParticipant @pault84577]

Rum

You can remove the warp by damping it in your bath and then placing it on a firm, flat surface under a thick, flat board and plenty of weight (bricks) on top, leave the ply there for a few days and the warp will disappear.

If you are not using the ply straight away you should store it on a firm, flat shelf sandwiched between thicker and heavier boards.

Hope this helps

Paul

[Dave MilbournParticipant @davemilbourn48782]

Much as I hate to take issue with Paul (well, in public anyway…) but I'd not soak Liteply in the bath. There's a real danger of it getting wet as opposed to just damp and de-laminating i.e. the layers come unglued. My method, before I stopped bothering, was to wet a tea-towel and wring it out well, then place the ply face down on it and turn the rest of the towel back over it. Now weight it down with a thick flat board and bricks, the dog, the car, the mother-in-law, whatever and leave it for a couple of days.
A steam iron will fix a warp in a matter of minutes, I'm told, but if Liz caught me with the iron in my hand then I'd live a miserable life from that day on.
Note – all of this applies only to Liteply. Birch ply is a different material altogether.

DM

Edited By Dave Milbourn on 19/11/2017 14:17:35

[Paul TParticipant @pault84577]

Dave

There is nothing better than an alternative point of view especially when we both have wide experience in the same subject.

You are of course absolutely correct in pointing out that excessive wetting can cause greater damage and I was remiss in not being clear about the length of time that the ply should be immersed.

It just goes to show that familiarity with a subject can make you blase when discussing it with others and I stand corrected.

Paul

[CookieParticipant @cookie15923]

I have used a steam iron in the past with a towel in between with good results .

Dave

[Colin BishopModerator @colinbishop34627]

Just offer to iron Liz's best dresses Dave – problem solved.

Colin

[Paul TParticipant @pault84577]

Don't forget to check on the line of the grain

[Author]

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