How to cure warp in MDF doors?

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Just wondering whether there are any clever tips from people on this forum for fixing warp on MDF doors? These were probably warped even before painting, but they are inset into the cabinet (living room) and therefore any slight twist is very visible and I now really need to fix it. Because of their size (1600mm x 800mm) I had to make them in 15mm MDF (to try to keep weight down) ... so this thinness obviously won't have helped. The warp is just in one corner in most cases, but is out by 20mm or so!

Options I have considered:

1) Take them down and try to flatten them under weight. If so how long does this take do you think?
2) Brace them by inserting metal plate or similar
3) Use steam etc.?

Thanks for any help - much appreciated!
 
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Depends why they are warping.

It may be the self weight, in which case 'unwarping' them by re-bending them will be temproary.

If it is a bit of warp, then a metal strap/frame will definatey help.
 
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Thanks Aron ... but don't quite understand the concept of 'self-weight'? These are traditional, vertically hung cabinet doors, with 3 concealed cabinet hinges in each.

I think the warp was always there, or it might have come about while the MDF sheets were waiting to be cut (eg. I think I might have stupidly leant them up against a wall etc.)

Any tips on metal straps anyone? I imagine I might rout out 2 perpendicular recesses for 4mm thick strips of metal, and then while the MDF was being weighed down perfectly flat I would screw the strips in before covering & repainting etc. ... but this is just a guess!
 
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if you were going to go to that degree, might it not just be better to replace the doors?
 
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Good point cjard! Hadn't thought of that. But ... have put my table saw away and seriously can't be bothered to re-erect it! Plus avoids cost of new MDF etc. ... not to mention time to paint inside & out, and difficulty in drilling hinges to precisely match where existing ones are etc.
 
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This is just an idea.
What about putting something like this
http://e-magnetsuk.com/magnet_products/neodymium_magnets/rectangular_magnets.aspx
(They do round ones as well by the look of it)
Into the stops in two or three places, with a corresponding magnet in the door. Glued in.
Would it be strong enough to hold the warp? Would it make the door awkward to open?
I don't know. Seems less trouble than frames and so on though. One stuff klike MDF is warped it seems to have a "memory"
 
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Thanks Dave ... no ... don't think that will work as have used push to open catches, and there is no door stop etc. Not sure they would have been strong enough anyway - it takes quite a bit of force to get them flush.

Think I'll give the recessed metal strips a go ... am pretty sure it should work and not take too long.

Shall report back ...
 
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are you sure its the doors and not the frames ??
have you got a picture??
2 push latches and a door stop where the bow in is
 
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If they're 1600 tall, I'm not really surprised they have warped, particularly if there are no stops, and in this case the material is quite thin. In my experience most doors will get some movement if they're not back against a stop. That's the snag with inset doors. They show every bit of movement. I'm not a fan of push to open catches either really.
Good luck with the metal strips. It might work, as long as (as BA says) it is the doors and not the frames that are warped.
The thing is that you might end up with almost a metal framed door with mdf covering to get them flat, if you see what I mean.
 
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Thanks big-all. Picture below. Pretty sure it's not the frames ... all the other doors fit quite well, it's only these big ones and the warps aren't always in the same plane / direction.

I think 2 x push latches will be difficult, because you have to have some movement in the door to allow them to work ...ie. I think once you fit 2, neither willl work (or at least, work well). I'd prefer to sort it so that only one latch is necessary.

 
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15mm is just too thin to avoid warping, even if you could correct them they will warp again, they would need laminating all round to keep them from warping at those dimensions.
 
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I think you'd be wasting your time with 4mm metal strip as its too thin. Better maybe to fit catches so the door pulls flat despite warp then hopefully over time they will settle flat or flatter. Another thing - are they finished ie painted on the outer face only? were they still as warped pre painting? finishing one side only will tend to curve a panel plus outer face is exposed to central heating etc so natural tendancy is for outer face to shrink and cup also aggravated further if cupboard is on a damp wall as the reverse face will expand.
 
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take a strait edge diagonally from corner to corner on the face off the door then the opposite corners
if the strait edge remains in full contact along its edge the door is flat and the frame is out
 
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Thanks Aron ... but don't quite understand the concept of 'self-weight'? These are traditional, vertically hung cabinet doors, with 3 concealed cabinet hinges in each.

They are big and heavy looking at the pics, if you held them flat on one edge, they would bend downwards from their own weight.

Obviously hanging them vertically the effect is small, but gravity will be pulling them down and this can result in a bit of warp.

MDF is not prone to warp itself as it has no 'grain', it will only warp due to moisture content differences between faces, which shouldn't really happen in your application.

Either way, a frame or locking mechanisms will help to fix the problem.
 
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Thanks big-all - good idea re: straight edge ... will try it out and see. These doors are painted all around, inside & out ... so pretty sure that paint isn't the issue here ...
 
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