Advice needed re unstable doors.

[simon45089]

Hello , I am struggling with an issue on some recently completed cabinets I have just installed and thought I would seek advice on this excellent forum.

I recently made a large media unit- lots of cabinets with various shelves all constructed from MR mdf for a client. The client wanted all of the faces of the doors-( lie on type), to be grooved with a narrow spacing of 30mm to give a reeded effect.
I did as requested and all looked good in the workshop- an unheated barn. The doors are made of 18mm MRmdf. They measure approx 970mmx 750mm each and have 24 grooves running vertically on each face. The depth of each groove is about 8mm deep.(necessary due to the router cutter moulding requested).
There was slight bowing of the doors after a short time, but nothing a magnetic catch could not straighten out once fitted in the workshop.
However...... once fitted at the clients home, and with central heating beating out overnight, the bowing has greatly increased and the doors wont shut.
I assume this is because the balance of the two hardened sides of the mdf has been seriously compromised due to the number of grooves, and heat has exacerbated the problem. I am happy to remake the doors- this was not a cheap job, but what material to use ?
Will birch ply/ marine ply do the job and not bow like the mdf ? The doors will be painted so I can use any material as long as it remains stable. Anyone have any idea or experience re this issue ? I assume cnc users remove loads of surface material so how is this issue avoided?

Any advice/ experience greatly appreciated as I really want to get this sorted.
All the best,

Simon.

 

[Myfordman]

Experiment with two layers of 9 mm laminated. One to take the reeding and the other to keep it stable perhaps?

 

[Phil Pascoe]

Are they painted?

 

[simon45089]

They are currently unpainted but ultimately will be. Thanks also for the laminated idea, thats another one I have been considering. maybe 12mm ply backer and 9mm grooved mdf on top ?

 

[Inspector]

I would be tempted to take the old doors and cut similar grooves in the backs offsetting them by half the groove on the front. That should relieve the stress and maybe flatten them. If the design allows you could also add some battens to the backs to help keep them flat.
Pete

 

[Adam9453]

My advice would be as above, the panels need to be balanced so I’d groove the backs to balance them. You might also want to consider adding solid timber lippings to all four edges of each door. If you could post a photo then it would be easier to advise what steps might be best to avoid the same problem occurring again on the remake. P.s. I’d also be tempted to make the doors thicker and make them from a sandwich of 9mm mr mdf, 12mm birch plywood, 9mm mr mdf. This should be stiffer and the extra thickness allows you to put the grooves in the same place on both sides to maintain balance.

 

[Jacob]

"Kerfing" is a trad way of making something bendy. You'd expect it to bend and it has.
Maybe find another way of achieving the reeded effect? Best would be something off the shelf ready made and stable. You used to be able to buy reeded hardboard but that was years ago.
Or stick something on to an already stable base
PS still available! https://www.diydata.com/materials/manma ... _board.php
my old dad fitted out our kitchen with it in about 1959!

 

[simon45089]

Jacob, thank you for that reference re hardboard. That was what I originally sought and failed to find during numerous internet searches. As your reference states, this is now difficult to find- the reeded effect shown in the second picture. If anyone can point me in the direction of a supplier of this product I will send a reward to the finder- or charity of choice.
Unfortunately due to the design of the unit I cant really go over 20mm re thickness, so a 30mm sandwich isnt going to work. Grooving at the back also wont work as I am already 8mm deep into an 18mm panel. I did experiment with letting in a 14mm x 5mm metal bar into the rear of the panel, top and bottom. It didnt work.I truly appreciate the thought and advice given to date.

All the best,
Simon.

 

[Jacob]

I'd try phoning any hard-board supplier and they may be able to direct you if they don't have it themselves. Reps like being helpful as a rule. Best of luck!

 

[simon45089]

Picture as requested. (Upside down .) Just click on it and it miraculously rights itself !

 

[Inspector]

Grooving at the back also wont work as I am already 8mm deep into an 18mm panel.

Simon when I said to groove the back I said to offset it from the front. That would mean the groove on the back would fall between the grooves on the front in the thick area. Not in line with each other. Like my high tech drawing below. :wink: Picture the triangles as open

∇ ∇ ∇ ∇ ∇ ∇
∆ ∆ ∆ ∆ ∆

Pete

The forum software shifts the lower row to the left rendering the illustration useless. #-o

 

[simon45089]

Thanks Pete. I think that will make the doors just too bendy as they are quite broad. Food for thought though,
Simon.

 

[Chrispy]

I would be tempted to do nothing just yet anyway , leave the doors open and let it aclimatise to its new home see what happens then paint if it flattens out.

 

[tsb]

Could you try using 12mm mdf then strips of 9mm glued to the front

 

[simon45089]

Thanks for the advice guys. I am going to make a a test door and try the two part lamination approach suggested and see how I get on.
cheers.
Simon.

 

[Silfi]

If reeded hardboard is unavailable would beaded mdf panels be suitable eg--
https://www.wickes.co.uk/Wickes-MDF-Pri ... m/p/133809
Perhaps an 18mm sandwich with that on either side should be stable.
The grooves are at 100mm centres.

 

[simon45089]

Thanks but not the profile required. Spacing of reeds is 30mm- hence the issue. I have made loads of fake t and G in mdf with wider spacings over the years and never had a problem with bowing, which is why I tried- and failed with this method for the reeding the customer wanted.