I want a vacuum table!

[Tenson]

Okay at first I thought it was called a vacuum bed, but if you search google and find the wiki link on that you will know why that is not what I want!

I know roughly how I need to build it having read a few build logs but I do have a few questions.

Firstly I am not sure if I want to use a vacuum cleaner to suck the piece down or a vacuum pump. I will be looking to mainly to hold down 1/4 sheets (1200mm x 600mm) of MDF and ply for routing. When I start cutting hole and parts out though, the vacuum will obviously be broken so I wonder how much flow rate I will need from my suction device. Typically I might be cutting out 8 parts from the 1/4 sheet each about 300mm x 300mm and I could use a 3mm mill to keep the gap around the parts minimal.

Looking at eBay the pumps tend to range from about 50l/min to 120l/min. Would this range be okay for my work or do I need something with far higher flow rate?

Just what sort of flow-rate do vacuum cleaners have anyway? I did a quick google and found one that claimed 42l/min so that seems to have no advantage anyway, unless it was a typo.

I understand the need for a vacuum chamber to give a good suction at the start of clamping while there is not a good seal at first. However what about dust and stuff getting sucked down? If I'm using a pump I presume I need a good filter too. How would this be done? Is it enough to place some open-cell foam over the reservoir inlet or might this just get sucked into the chamber anyway? Maybe fill the chamber itself with wire-wool?

[Jonathan]

I might be wrong, but I thought you can't use a vacuum cleaner for extended periods with virtually no airflow as it relies on the air to cool the motor? Having said that, if the airflow is zero the power drawn will be less, so maybe you'd get away with it.

[EddyCurrent]

One picture shows it used with the small vacuum bed which I think is now discontinued ? no idea about duty cycle though and likely practically useless for Tenson's proposal.

http://www.trend-uk.com/en/AT/produc...tts_230v_.html

[mekanik]

I have a Stihl Industrial cleaner that i use with a homemade vacuum jig for cutting out penetrations in Fermacell board for back boxes, but not sure i would like it running for hours @ at a time, as mentioned no air flow over the motor, can't imagine it would last long without throwing in the towel.
Mike

[Tenson]

Okay well a floor vacuum will tend to move around 3000-4000l/min so certianly a higher flow rate!

As soon as the sheet has some holes cut in it there will be a fair amount of air flow I suppose. It would only take a 3mm wide cut 600mm long to give an open area about the same as the vacuum hose. That's why I worry about using a pump as I think the sort I can afford might not manage without a really good seal. I suppose when the sheet stock is held down perfectly flat I could accurately cut just shy of all the way through helping to keep the suction up. I'd then just cut the perimeter of the piece with a knife. I think I've heard this referred to as 'onion skinning'. Kind of like tagging, but the remaining stock is not strong enough to hold the part, it just keeps the vacuum up.

This is an interesting video anyway:

[alex wight]

Replying reference breaking through the material. I used to use low tac sign making application paper. You applied it to the rear, when the cutter cut the material, it left the paper in place thus keeping the vacuum table sealed. I used off cuts of foamex to blank off the open holes around the material, and the joy with sabre is that you can close off Channel's manually too. Hope this helps.

[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.