Vacume Table

[naijin]

Hi there, I am thinking of building a vacume table for my cnc router, can anyone recommend some suitable non porouse material to built it, and where to obtain such materials, the table will be 800 x 900 mm approx.

Regards
Nick

[malb]

I used to operate a commercial 2400x1800 unit with a vacuum table. The vaccuum table base was a moulded plastic affair, basically flat sheet with V channels moulded in along and accross leaving 'islands' about 80mm sq to support the spoilboard. The base also had a channel moulded around the edge to accept a circular cross section neoprene extrusion gasket as a seal between the base and spoilboard. The whole affair was supported by a T slotted table underneath. I think you could replicate this at your size with 16mm melamine coated MDF board by cutting to size, mounting on the table and cutting the channels with a V bit in the CNC, and the gasket groove with a a core box bit. It would pay to seal the edges of the MDF base with epoxy or similar to prevent vacuum leakage through the edges.
For a spoilboard/diffuser we used full size sheets of 18mm MDF, skimming the skin of both sides to leave the porous core as a diffuser and support for the worksheets. The work surface of the spoilboard was skimmed daily (or more frequently if required) and the surface height reset each skim.
The killer with this system was the two 10HP (8kw) vacuum pumps needed to generate the vacuum. Even scaling down to your size, you would probably need something equivalent to the motor/blower assembly from a 3HP dusty to match the holding power of the commercial unit.

[simops]

I also use MDF, skinned both sides as my bleeder /spoilboard.
unfortunately in Australia you cannot source (well I haven't been able to) ultra light density fibreboard such as available in States and NZ. ULDF is even more porous and ideal for vacuum.....

cheers