I want a vacuum table!

[Tenson]

Hi Alex,

Isn't the stock sheet only held in place by the low tac paper adhesive then? If the vacuum pulls through the paper then obviously it will hold the stock but it will also allow air into the vacuum once the stock is cut through. Is it just a case of helping to reduce air leaking?

P.S. Can you link to this paper you mention? Is it cheap enough to use a new sheet each time?

[m.marino]

Depending on the funds you wish to spend there are more then a few options for a vacuum table. One item most folks miss IF not using a vacuum cleaner to generate the vacuum (yes it can be done but requires adapters and still gives a lot of noise) is to not only seal the board if using a wooden structure, but to also put a dust/SWARF trap in between the the vacuum unit and the table. How you place it is up to you. Also IF you set up zones you can decrease the area being used by building a manifold for the table. IF building your own vacuum pump please remember that you REALLY want to have a reserve tank set up and a manifold switch. Otherwise you will burn the motor out way to fast and you will not get a good solid grab as the vacuum is applied via the manifold point.

Those are just points I have learned along the way. Using the design in the video works as long as you SEAL the wood and are able to remove the sacrificial bed once it has been used up (thick means less need to change for loss of depth, thin less loss of depth and more change out). Have fun. -Michael

[Tenson]

I was imagining to have the whole bed active and if I need a smaller area just cover the un-used part with a sheet of plastic. So no need for a manifold?

Reserve tank is a vacuum chamber right? What is a manifold switch, do you mean I need a pressure switch to activate and de-active the pump to (try) and maintain a constant vacuum level?

At the moment I'm planning to build a table like that in the video, and seal it and use a normal vacuum cleaner. If that doesn't seem to hold strong enough I will try a vacuum pump and hope that has enough flow-rate. I'd quite like a vacuum bag press anyway so the pump could be quite useful.

On a side note, why are the bags for vacuum bag presses so expensive? I saw them around £70 each! Any tips where to get at a better price. Those ones for putting clothes in the loft etc are much cheaper, lol.

[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.

[alex wight]

the vacuum doesnt pull the paper into the holes, and after the cut has been made it continues to hold the material perfectly still. Clear / Paper Roll Or A4 Sheet Of Application Transfer Tape Many Sizes App Tape | eBay. Ive not tried this but just sourced it today.

alex

[Tenson]

Oh, I think that is what I'd call masking tape?

[alex wight]

its similar to masking tape, its used for applying to vinyls that are then applied to signs/vehicles ect, then the backing paper is removed, leaving the vinyls in place. I found it a great help.