[ger21]

If you are holding parts by vacuum through the MDF, you'll need to surface it regularly to keep it smooth, as you'll be cutting into it when you cut your parts, creating grooves that reduce the holding power due to vacuum leakage.
How often depends on how deep you are cutting into the spoilboard, and how much holding power you need. I sometimes surface our spoilboard several times a day. I try to only remove .002-.005" each time.
And no, moisture will not make it less porous.

[praveenr]

Thanks for the messages. So from the replies I understand that "moisture does not affect porosity of the MDF" from a vacuum point of view.

So: Looks like We need to do resurfacing of MDF for 2 reasons:
R1) To remove the top and bottom coating layer : to ensure POROSITY of MDF.
R2) To make the spoil board flat w.r.to the CNC axis.

Actually we are using the vacuum bed for foam cutting with a oscillating knife.
We keep a sacrificial open cell foam (styrofoam/EPS) on MDF and then my EPE foam on the EPS.
So we will not be making cuts on the MDF. (unlike a CNC router ).
So my MDF flatness is never affected by the cutting.

Does the MDF still needs periodic resurfacing to maintain POROSITY?
Or : periodic resurfacing is only for maintaining FLATNESS ?

[praveenr]

Any thoughts on this ?
Is resurfacing needed to maintain FLATNESS or for POROSITY also ?