Cupping of MDF Doors

Depending on the nature of the particular MDF stock, machining one side may relieve surface stress and cause the finished piece to deform. December 27, 2008

We made some MDF one-piece raised panel doors this week. During finishing we're noticing cupping of the doors in both directions on the front side. Is this typical, or is it maybe due to unbalanced coats of finish front to back?

Forum Responses
(CNC Forum)
From contributor J:
Could be due to the rigidity of the machine.

From contributor M:
I have made many MDF one-piece raised panel doors. The problem is very likely due to the type of MDF you use. The density of different brands and types of MDF boards varies throughout its thickness. Relieve material on one side and you create stress imbalance in the board, which causes the warp. The best way to avoid this is to use a type of MDF that is more consistent in density throughout its depth.

Panfiber Elite (not to be confused with regular Panfiber) works well. Medex works best of all of the types I have tried so far. These panels are a bit more expensive, but in addition to reducing warp, you will save a ton of time in the sanding and finishing area with either of these boards. It will far outweigh the added cost of the MDF.

Try a good high solids primer for profiled pieces, like ML Campbell Clawlock. It is a catalyzed primer, but sands very easily. Also well worth the small added expense when sanding time is taken into account.

From the original questioner:

Thanks. Contributor J, the doors were flat after machining. Contributor M, we do use MLC Clawlock. We'll try another set with the MDF you suggested.