Panels bending

[krismusic]

Hi guys. This is an ongoing problem that has reared it's head once again. From time to time, over the last 30 yrs I have had the job of knocking up quantities of panels for exhibition stands. 2x1 frames . Used to cover them in 6mm ply but now use fire resistant MDF, 6mm. The problem is that from time to time the panels bend once assembled. The nearest I can describe is that it is a similar effect to what happens if you do not use a balancer when using laminate. It doesn't happen every time and I thought I had solved the problem by not glueing the boards and relying on 40mm air staples. The batch I am producing currently has curved. Any ideas what may be causing this? Sorry for the long post.

 

[jasonB]

Are you covering one or both sides of the frame?

Jason

 

[krismusic]

Are you covering one or both sides of the frame?

Jason

No, one side. Covering both would probably solve the problem but is not practical, unfortunately.

 

[bjm]

Are you using shrink-wrap packs of 2x1 straight from one of the sheds? It sounds like it could be due to the timbers distorting once they are in a warmer environment rather than anything to do with the mdf.

Brian

 

[jasonB]

Doing one side is likely to be the problem, as the timber & wood will move at different rates you are likely to get warping. This will not be helped if only the front of the panel is decorated. As you say you are making an unbalanced structure.

Jason

 

[hpl]

Hi krismusic.

I also produce panels for exhibition stands from time to time, only for the past 10 years, but we often have the same problem. If the client is prepared to pay for a better job we have found ways of getting over it.
The best panels we ever made were cutting strips of 18mm far eastern ply 70 wide and using these instead of the 2x1. We then sealed the panel with a good quality varnish on the back and edges. The fronts were laminated with formica. They went out to Singapore and then when they returned to the damp UK they were stored in an old chicken hut that got very damp at times. These lasted very well and were reused a few times as the original client ceased trading. We have never tried it but I think just using the ply instead over the 2x1 would probably be enough.
Other things we have done is to seal all the timber/ply both sides, often with paint, and this seems to work pretty well. Also part covering the backs with a reasonable width strip down both sides seems to balance it.

Most of these things don't seem to get done most of the time as the designer that we work with in these things is always cutting corners and wants to spend as little as possible, and often they are only scrap at the end of the show and it always takes a few weeks for them to bend, but where we can we will work with a balanced panel, or a balancer down each side.

Hope this helps,

Johnny B

 

[krismusic]

Hi krismusic.

I also produce panels for exhibition stands from time to time, only for the past 10 years, but we often have the same problem. If the client is prepared to pay for a better job we have found ways of getting over it.
The best panels we ever made were cutting strips of 18mm far eastern ply 70 wide and using these instead of the 2x1. We then sealed the panel with a good quality varnish on the back and edges. The fronts were laminated with formica. They went out to Singapore and then when they returned to the damp UK they were stored in an old chicken hut that got very damp at times. These lasted very well and were reused a few times as the original client ceased trading. We have never tried it but I think just using the ply instead over the 2x1 would probably be enough.
Other things we have done is to seal all the timber/ply both sides, often with paint, and this seems to work pretty well. Also part covering the backs with a reasonable width strip down both sides seems to balance it.

Most of these things don't seem to get done most of the time as the designer that we work with in these things is always cutting corners and wants to spend as little as possible, and often they are only scrap at the end of the show and it always takes a few weeks for them to bend, but where we can we will work with a balanced panel, or a balancer down each side.

Hope this helps,

Johnny B

Nice one Johnny. These b*ggers are going within 10mins of being assembled! In your experience, do warped flats have a disastrous effect on the end result once assembled into a wall? Or can I hope that it will all come out in the wash? I wonder if pinning a strip the thickness of the 2x1 onto the back of the uprights would have any effect? Anything wider would interfere with screwing the flats together. I will definiteley consider ply battens next time. 8) ( Thanks to other forum members for the replies BTW)

 

[hpl]

I never go on site so not sure on what they look like then but I don't remember any complaints on that front on new panels, and nobody seems very fussy on exhibition panels. Only remember them being a problem when we want to reuse them a few months later.
On the ply on the back it doesn't have to be right up to the edge of the panel. You could leave a gap to get the screws in on one side (I'm assuming that you are screwing the panels to each other on site) and then add the strip. If you then have the other edge with balancer right up to edge this will stay straight and then when you screw the two panels together you can use the straight panel to help straighten any bend in the other panel that exists. Hope that makes sense. :lol:

Johnny B

 

[hpl]

Just re-read your OP and realised that you are using MDF. Always have more problems with the mdf because it takes on moisture so much easier. We use 4mm FR ply most of the time, although I guess 6 mm would be better as we struggle with the staples pulling through the 4mm, but it is all cost related :?
Last ones we had a problem with were ceiling panels, 4mm ply one side only, for an on going stand. When it can to re-use we had to cut the 2x1 in several places to allow the panel to straighten and then re fix the 2x1. These don't seem to have moved again.

 

[krismusic]

Just re-read your OP and realised that you are using MDF. Always have more problems with the mdf because it takes on moisture so much easier. We use 4mm FR ply most of the time, although I guess 6 mm would be better as we struggle with the staples pulling through the 4mm, but it is all cost related :?
Last ones we had a problem with were ceiling panels, 4mm ply one side only, for an on going stand. When it can to re-use we had to cut the 2x1 in several places to allow the panel to straighten and then re fix the 2x1. These don't seem to have moved again.

Hi Johnny, thanks very much for the reply. Always best to learn from experience, preferably someone else's. A lot less painful! :lol:
I did a test stapling a 20mm strip of FRMDF onto the back of the 2x1. It hadn't gone when I left the workshop. I'll see in the morning. Sorry, must be being dense, I read what you said about the balancer several times and still don't understand. Are you suggesting a full sheet on the back? Cost would be a factor. I agree ply would probably have been better but the surface of FRply is shocking! All the best, Kris

 

[hpl]

Hi Kris,
Probably my explanation on the balancer. You mentioned that putting a full sheet on the back would interfere with screwing them together. The guy we make them for just fixes the panels together with screws through the 2x1, so guessing that you are saying with a full strip on the back this isn't possible. To add a balancing strip either side on the back gives the same problem with the fixing, so if you added a balancing strip to one edge and put the other one away from the edge then you can still have space to get in with a screw. This may help, plan view.

The balancer that is right on the edge will keep that edge straight, the balancer that is set in will help keep the panel straight, and if it still isn't straight enough then when you fix it to the next panel, with the one straight edge this will help pull the other edges straight. I usually use off-cuts as the balancer, preferably 100mm wide or more.

Hope that makes more sense.

Are you also saying that the panels are bending nearly as soon as you make them? I've never had that problem. It is always after they have been sitting around for a while. I would be interested if the narrow strip of MDF does the job, I've never tried that, I would think it is too narrow, but maybe not. I guess that even at 40mm wide you could still get a screw it there.
I also agree on the surface of the FR ply being terrible quality, but most that I do are either emulsion paint or covered entirely, and strangely enough the emulsion paint is good enough for most clients on a tight budget. If they want quality then we usually laminate, but that is obviously at a much greater cost, but looks soooo much better. We just avoid mdf now because of the problems we get with the movement. It is only OK when we do both sides, but even then it doesn't last like the ply panels do.

Johnny B.

 

[krismusic]

Hi Johnny, it is very good of you to go to so much bother to explain. I understand exactly now! :roll: Your solution still would not be ideal as we usually clamp the panels together before screwing. Also extra time and expense. Adding the minimal (20mm) strip seemed to help a little but did not solve the problem completely, so I decided it wasn't worth the effort. I knocked up 10 panels today and they have stayed nice and straight! This leads me to think that maybe the boards needed to condition before assembly. God knows what will happen when they get into a nice damp exhibition hall! :lol: This time I think I will change the way we brace the walls and use vertical braces to try and pull the panels straight. Another time I will definitely stay away from MDF. A mate suggested lining paper to improve the surface of the FR Ply. Another job I would not welcome but may be a way to go. Anyway, thanks for all your advice, exactly what I hoped for when I posted. 8)