My mdf top lifed up.

[knight_toolworks]

it must have been doing it for the last few dasy but I thought it was me. I noticed the corners have come unglued.
I used 3/4" mdf as the base layer I sealed the edges and underside and flattened the top. then used yellow glue to glue the 3/4" mdf spiolboard on. well I lifted it off tonight and a little bit of the spillboard was left behind but that was about it.
I was going to seal the edges but kept forgetting. the boards have been in my shop for 2 months before I built the shopbot table. my shop is in the basement of this old building and htere are nto usually any large humidity swings or temp swings. any ideas?

[myxpykalix]

You just didn't use enough glue in the first place. MDF sucks the glue up. That happened to me. I took a veterinary hypodermic and slightly pryed up the edge that was loose squirted the glue in as far as i could, clamped it down for a day and that took care of it.

[knight_toolworks]

I poped it off last night and used a bunch of silicone adhisive and some poly glue. but what caused it to warp in the first place? the stuff sat flat when I put it on.

[davidp]

Steve

Mdf is an extruded material and as such as it reamins flat because the tensions on each side are in equalibrium. As soon as you machine one side you will realease the tension from one side and so the board will cup, warp bend whatever. The easiest way is to surface both sides that way the tensions will be equalised. You will need to occassionally turn your spoilboard over when you notice that it no longer remains flat.

If you veneer solid timber on one side only, you will see the same effect.

for what it is worth.

regards,

David

[davidp]

Steve

Mdf is an extruded material and as such as it remains flat because the tensions on each side are in equalibrium. As soon as you machine one side you will realease the tension from one side and so the board will cup, warp bend whatever. The easiest way is to surface both sides that way the tensions will be equalised. You will need to occassionally turn your spoilboard over when you notice that it no longer remains flat.

If you veneer solid timber on one side only, you will see the same effect.

for what it is worth.

regards,

David

[knight_toolworks]

that makes since I thought you only did the other side for a vacuum. well now I know (G)