I want a vacuum table!

[firetrappe]

I'm also looking at vacuum beds. I only need to hold down sheets of foam rather than MDF, but I thought you might be interested in a bed that a friend of mine made which uses a vacuum cleaner.

His uses an MDF torsion box bed with a matrix of holes and grooves in the top. The vacuum is split between the bed and an extraction hose which keeps some airflow going to the motor.
He uses a sacrificial sheet of foam (depron) with an identical matrix of holes cut into it. The grooves in the bed hold the sacrificial sheet down and the holes provide suction for the sheet being cut.

Surprisingly it works pretty well and prevents the sheet being cut from moving laterally. I doubt very much that this setup would work for MDF, but it might give you some more ideas.

Si.

[Tenson]

Ahh I think I've just had a great idea about how to do this :)

The bed of my machine is currently built from strips of 10mm HDPE with 40mm box section steel below it. Between the strips is 40mm T-slot alu profile. The alu is there obviously to allow easy clamping and the steel just to give strength.

The HDPE is not only screwed into the steel and alu but also bonded with 'green glue' which is an elastic damping glue, seemingly much like silicon sealer.

So my idea is to put end-caps on each of the steel box sections and drill some holes up to the HDPE to suck vacuum. There will of course be leaks in the steel section where there are a few screws. The existing screws up to the HDPE don't matter since it will just help to suck down any work like the open holes I will make. On the under-side of the steel box section there is a nut and bolt at each end and also two directly tapped screws in the middle. The nuts at each end shouldn't leak a lot because they tighten down nicely on the steel and I could smear some silicon around it. The directly tapped screws in the middle might leak and I can only think of inserting them with some teflon tape, but only being two per box section I can't imagine it will allow much air flow.

So, I would then have a vacuum being drawn directly from my existing HDPE bed on which I can route some channels to spread the vacuum and possibly take a gasket.

If this works it would be great because not only do I already have most of the work done, I get the strength of my existing steel and alu supported bed. If I wanted I could still place a sacrificial board on top and pull a vacuum through that if I had a proper vacuum pump. Having watched a few videos I know I'd need to seal the perimeter of the MDF board and skim the top and bottom. I'd need to do each strip separately though or the air would come through the bottom of the board from the T-slots.

I may need to find a way to plug the holes for when I use flood coolant. At the moment the coolant gets channelled into the T-slots which I blocked at the ends and goes down a little drain.

Here is my existing bed.