Straightening thin plywood

[Quarryscapes]

I have just begun assembly of a Laser Cut plywood kit, but a few of the larger panels have got a noticeable curl to them. What would be the best method of straightening them out prior to assembly?

[009 micro modeller]

Not very high tech, but could you just weigh them down on a flat surface for a while?

[Quarryscapes]

Not very high tech, but could you just weigh them down on a flat surface for a while?

 

I have been doing for the past 2 days but it does't seem to be having any effect. 

[chris p bacon]

There isn't a lot you can do to actually straighten them, when you assemble the kit it would need to be done on a flat surface and you can use some parts to act against others. 

 

Does it just form a simple grid or do they make up a box beam ?

[DCB]

You could try steaming them and maybe introducing a curve the opposite way so they end up flat?   Putting them between book covers under a pile of books, as in a 4ft high pile of books for a month might work.   Otherwise you may have to accept that they are scrap

[009 micro modeller]

I tend to find with these sort of things that they are OK once assembled with the other parts helping to straighten things out.

[yelrow]

I dampen wood, then support it either side, while it dries. Results are varied, by works more times than not. john

[N15class]

As above but only dampen the concave side as it dries it should pull straight, or paint the concave side that should also pull it straight. Do remember when painting that you need to paint both sides to begin with or it may well bow again.

[AlunKimber]

I found similar with thin plywood - not sure if it's the the same size you are talking about though. I got reasonable results by dampening them with warm water and pressing them overnight – it improved things quite a bit. See here.

Cheers

Alun

[Il Grifone]

I was going to suggest dampening and weighing down, but I've been beaten to it.

 

Unfortunately ply is prone to warping. Brace it well, treat it to waterproofing and hope for the best!

[Bernard Lamb]

You could try steaming them and maybe introducing a curve the opposite way so they end up flat?   Putting them between book covers under a pile of books, as in a 4ft high pile of books for a month might work.   Otherwise you may have to accept that they are scrap

 

That is how I curve wood in model ship building.

I suppose it would work trying to do the opposite as you suggest.

I steam the wood over a candle flame, taking care not to set every thing alight or even just to avoid scorching.

Bernard

[Quarryscapes]

That is how I curve wood in model ship building.

I suppose it would work trying to do the opposite as you suggest.

I steam the wood over a candle flame, taking care not to set every thing alight or even just to avoid scorching.

Bernard

 

I'm guessing you wet the wood first? 

 

This is all 1/16" 3 ply, one bit has been cut along the grain and is incredibly flexible, the others seem to have gone diagonal across it so they are very rigid...but still warped! I've found so far that wetting it and leaving it made it curl up like an old leaf, wetting it and weighting it returned it to it's original state of curvature.

 

I found some oak 12x6mm strips, think I'll use them to make a frame work like a barn door to stick the ply to. 

[timbowilts]

If the kit is not fit-for-purpose do yuo not have a case for returning itfor a refund?

 

Presumably this could be a manufacturing fault and as long as purchasers do not complain the manufacturer will continue to make such stuff.

 

Tim T

[Mallard60022]

Some ideas here?

https://www.google.co.uk/search?q=how+to+straighten+out+warped+plywood&oq=How+to+straighten+out+warped+plywood&aqs=chrome.0.0.25344j0j7&sourceid=chrome&ie=UTF-8

 

I too would dampen the wood on the concave side with a very fine spray or just a lightly damp sponge and then weigh heavily on a dead flat surface with a couple of layers of newspaper to absorb moisture. Good luck.

Phil 

Edited May 7, 2018 by Mallard60022

[N15class]

I'm guessing you wet the wood first? 

 

This is all 1/16" 3 ply, one bit has been cut along the grain and is incredibly flexible, the others seem to have gone diagonal across it so they are very rigid...but still warped! I've found so far that wetting it and leaving it made it curl up like an old leaf, wetting it and weighting it returned it to it's original state of curvature.

 

I found some oak 12x6mm strips, think I'll use them to make a frame work like a barn door to stick the ply to. 

Only wet concave side or it will do nothing. With any thin wood product you need always to do the same to both ides to keep it flat. If bowed doing something to the concave side adds tension so will help straighten. When we used to do shopfitting even 3/4" ply would bow if one side was only painted. When you add a laminate to one side as per worktop they use paper as a balance on other side. That's why plywood is always odd number of layers.

[Mallard60022]

Little anecdote. I was using some 1.5mm Bass Wood the other day, thinking it would be better than the very thin ply I have used in the past and I know it would be stronger than Balsa for making Platform 'tops'. Lovely wood, beautifully smooth and nicely 'firm' for the thickness. However, when I experimented with a small piece on an end ramp surface and used a strengthening piece (same wood) on the middle 3/4s, glued (PVU) to the ramp piece, it began to warp before my very eyes. 

I think I should have varnished both sides or at least used some sort of spray paint? 

Cured it by adding some more PVU  glue and immediately weighing it flat with loads of lead flashing scraps.

Phil

[Bernard Lamb]

I'm guessing you wet the wood first? 

 

 

 

If you do not wet it then you will not generate much steam.

It is a bit of a trial and error game.

Or at least it is for me.

Fortunately I have only built models that are to be painted and any scorch marks can be hidden under the finish.

Bernard