I want a vacuum table!

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?

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.

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

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

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:

http://www.youtube.com/watch?v=fOrkvPF0pro

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.

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?

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

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.

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.

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.

http://i608.photobucket.com/albums/t...uk/CNCBed1.jpg

http://i608.photobucket.com/albums/t...uk/CNCBed2.jpg

http://i608.photobucket.com/albums/t...uk/CNCBed3.jpg

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

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

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.

What do you chaps think about this pump? 8.0CFM 5Pa 250W REFRIGERATION AIR CONDITIONING VACUUM PUMP + GST | eBay

It says 8CFM (240L/Min) which is about twice the other pumps I've found on eBay and it's less expensive too. Too good to be true?

Can anyone say from experience if I wanted to cut out these parts below with a 3mm cutter, what sort of flow-rate do I need from a pump to maintain a good 'suck'? If I were cutting soft materials I could leave a very thin skin to keep the vacuum up, but I often work with cast acrylic and I don't imagine I can 'skin' that so cuts would need to be full depth. The advice above of using adhesive backed paper may help me here but I just want to get an idea about flow-rate.

http://s18.postimg.cc/3jsfegg2h/Cut_Out_Example.jpg
free upload

Tenson, even with a good vacuum, there may be a tendency for small parts to move after they are cut out. Leaving a couple of small tags where necessary does work wonders. with some plastics sometimes they try to partially weld themselves back together. I find that "climb milling" will usually ensure that the weld sticks to the scrap rather than the cut item. I am afraid that I can't give you any figures for the vacuum - suck it and see!!! G.

I'm not sure I can really do tags, I need good clean cuts on all parts but acrylic has a tenancy to shatter if cut with clippers for example, which is how I imagine removing the tags then a bit of sanding.

At any rate, is there an easy way to leave tags using Dolphin PartMaster? Drawing all the tags in CAD seems a pain because something like a square cutout becomes 2 or 4 separate cutting paths.

I use a commercial program (Alphacam) and it will allow the tabs to ramp up and then down. This just lifts the Z axis during the the normal X Y travel and does not require any extra cutter paths. If I don't ramp then it does stop at the start and end of the tab and uses additional cutter paths. I keep tab lengths and height to top of tab to the minimum and and can usually remove the tab with a sharp knife. Some sanding is required (not much), but this is far better than losing the part. Carefully placed double sided tape is my own alternative to tabs, but can be difficult to remove. A vacuum bed is really good, but small components are sometimes a problem.

Tenson
I have just hunted out the manual for my Hydrovane compressor, it has a 2.2kw motor and knocks out 9.5CFM @ 100 psi so probably 30psi if sucking would increase the capacity(sure someone on here could do the calcs) but i can't see that e-bay pump knocking out 8CFM and don't forget that's free air delivery once you get it loaded that figure will drop. Hope i am wrong as i just had a look on e-bay & it looks like someone has just bought one.Just my thoughts.
regards Mike

Hi All

I suspect 2.2 KW is only sufficient for a very small Table

I recently visited a factory with a commercial router table with vacuum hold down. The noisiest machine in the factory was the 20HP vacuum pump under the table. Conversation near it was very difficult.

Regards
John

Understanding Vacuum Hold-Down

John really good link there. Also in setting up your zones using a quality manifold and setting up one to two inline reserve tanks that are emptied first before the part is "clamped" to the board will increase the initial clamping force for holding the part. Really good advice in the article I would strongly suggest folks read it. -Michael

Yes I plan to have a vacuum chamber and a number of 'zones'. I got one of the 8CFM pumps from ebay. If it doesn't work for the table I'll use it for vacuum bagging anyway.

I'll let you know how it goes in due course.

Hi,

Can anyone advise about hoses to connect the system together? I designed it expecting 5/8" ID hose. It concerns me though, that once a vacuum is being pulled the hoses could squash shut. Are there special types of hose I need to get? If not, I was thinking to use the engine breather / radiator hose for cars.

Actually I'm curious how any hose soft enough to bend easily can support a vacuum inside without squashing closed?

Quote:

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Originally Posted by Tenson

Actually I'm curious how any hose soft enough to bend easily can support a vacuum inside without squashing closed?

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With a vacuum inside a circular hose you've got inwards pointing radial forces, so a circle is the strongest shape to use. Bending the hose is not the same, as you're applying the force in different directions.

Bear in mind that at best the difference in pressure from your vacuum approaches atmospheric presssure. This is much smaller than for example an air compressor where over 10 times atmospheric pressure is common.

Hmm.. also thinking about it the outside area of the hose will limit the pressure that can be exerted on it by atmosphere.

Alright, I'm off to buy some radiator hose!

Hi Tenson
If you are going to try this with your newly acquired e-bay pump i would just buy some nylon reinforced pipe the same diameter as your pump inlet, i have used mine with 10mm clear(home brew supplies) plastic and not had it flattening when i have been vacuum bagging. coupling to the vacuum bed would be better done with plastic plumbing waste.
regards
Mike

What is nylon re-enforced pipe? You mean the sort with ribs like a vacuum cleaner has?

My pump has 5/8" inlet and so does my bed. Feed to the bed is via steel tubes so I just need to connect those to the vacuum chamber and chamber to the pump. 1m length either side should do.

Something like this:- Clive

Attachment 10854

Hi Tenson
The reinforcement is actually more for strength with internal pressure, 5/8 bore should be OK as long as it's a straight'ish run, too sharp a bend and it might flatten but i would imagine you will have enough leakage to prevent that.
Regards
Mike

Well first trial just now using 5/8" radiator hose from Halfords (£2.99/m). Hose was 5m long 'cos i didn't cut it yet and it didn't flatten.

I connected the pump directly to one of the 4 steel tubes feeding the bed. This has 6 holes in it to the bed. The holes are 16mm each and I have not cut any channels in the bed to distribute the vacuum yet. I put a few bits of MDF on top and they got sucked down pretty strongly! I can slide them around but it takes a far bit of force to pull them directly up. I'm pleased for a first try.

Next I will make channels in the bed to give a much larger vacuum surface area and connect all 4 sections with a vacuum chamber.

Glad to hear it Tenson, continue with the experiments.
Mike

Ahh, now how about your collective thoughts on this - My bed is HDPE so had low friction. Is there a paint or similar I can coat the bed with to give it better grip? How would any paint stick to the HDPE though?! Perhaps just affix a thin rubber sheet with contact adhesive.

Hi Tenson, I presume that you will still be using an mdf sacrificial board on top of your new board, so why not write a program to drill a couple of screw/boltholes and secure the sacrificial board ensuring that you show to fixing position on your table to prevent hitting the fixings. I have arranged a series of clamps along the front of my table which secure both the sacrificial board and my material. these clamps are just outside the cutting area and will hold the work in the event of a vacuum failure (fingers crossed has not happened yet). the vacuum holds the job securely and I get a far better cut as the job is always held tight to the table ensuring that there is no sawdust build-up under the cut. My clamps are simply tightened with wing nuts and take only seconds to secure?release. Glad you are getting there with tour vac bed. G.

Hmm yeah I guess the solution is to clamp / screw down an MDF bed then spray that with a grippy paint. I found something here - PlastiDip - Plasti Dip / Plastic Rubber Paint - Aerosol Can - 400ml Matt Black | eBay

Whatever I go for it should be cheap so I can afford to do it each time I re-surface the board.

Maybe just a coating of bitumin paint.

Hi guys, sorry for such a long time with no feedback. Allow me to update this thread.

I'd say the project was a success. Firstly I'll say the vacuum pump was a waste of time for the vacuum table. It doesn't draw enough air flow so even tiny leaks reduce the pull down force. On the other hand the old vacuum cleaner I have works a charm :)

I think these pictures will mainly explain what I did. but basically I caped each end of the steel supporting tubes under my machine table. I then drilled holes into these from the top. Rather than cut channels into the machine bed directly I place a 24mm sheet of MDF on top with the channels cut into it and this bolts down on the bed at 5 points.

I started cutting that as a 12mm sheet but as I cut the channels 6mm deep it warped. So I glued it to another sheet that kept it flat.

When cutting material that is smaller than the vacuum table I use some decorators dust sheet to cover the unused area and seal it.

Additionally if I'm cutting lots of small parts I throw sheets of paper over them once complete, to keep the suction up.

I try to cut just shy of the material thickness to leave something to keep the vacuum seal but there tend to be little areas where it breaks, hence the above.

Here are my images, sorry I've got to dash out so no time to write lots.

Oh, it also makes a downdraught table for sanding and part cleanup. It doesn't such strongly with only those few holes, but it helps. Good thing about using a vacuum cleaner for suction is I don't need to worry about dust and dirt getting in there. Also it has an adjustable power knob so I can keep it turned down when there are no leaks and stop overheating the motor.

http://i608.photobucket.com/albums/t...e/IMG_0660.jpg

http://i608.photobucket.com/albums/t...e/IMG_0656.jpg

http://i608.photobucket.com/albums/t...e/IMG_0666.jpg

http://i608.photobucket.com/albums/t...e/IMG_0662.jpg

http://i608.photobucket.com/albums/t...e/IMG_0657.jpg

http://i608.photobucket.com/albums/t...e/IMG_0658.jpg

http://i608.photobucket.com/albums/t...e/IMG_0659.jpg

Below you can see were the cut was very nearly through the material, but not quite. Any dust helps to block up small breaks in the seal. I also use a downcut mill, which helps keep the material down and block up gaps in the material skin.
http://i608.photobucket.com/albums/t...e/IMG_0667.jpg

Below are some small parts I cut out, and then covered with paper sheets to help seal. Although there was a thin skin left, it was so thin at some points the vacuum pulled through.

http://i608.photobucket.com/albums/t...e/IMG_0669.jpg

http://i608.photobucket.com/albums/t...e/IMG_0668.jpg

Well done Tenson. The covering of part of the table with an impervious sheet works well. A friend of mine has arranged a polythene "roller blind" which extends from one end of the table - he just pulls it out to whatever length he needs and that works well. To improve your suction you could use a round rubber neoprene gasket seal around the edges of the mdf sacrificial board. I know that you will find having a vac table a big advantage. G.

Thanks Geoffrey. I like the way the very thin dust sheet can wrap around the edges of an unusual shape. Sometimes like in the image above the edge of the sock material is not actually a straight edge. I do also have a silicon seal around the edge of the table. I bought some 6mm dia silicon tube on eBay. I also have some smaller peices that I can use to section off areas of the table. I threaded the holes in the steel tube that feeds the vacuum so I can also put a bolt in any of the 18 holes.

I can also confirm that painting the table with a thin coating of 'liquid rubber' helps reduce parts sliding about. I used Isoflex. I then surfaced the table and haven't put it back on since it is slow to set and very smelly, lol.

I'm moving workshops soon and will need to make the machine quieter not to annoy neighbours, so next will be a big sound-proof box for the whole machine. That's not too hard, but making it easy to access the machine when needed will be more tricky since doors and windows tend to break a sound-proof seal.

Oh and those part drawings I posted earlier in the thread were to be cut from Acrylic. That didn't work well on the vacuum bed directly because it doesn't take well to 'skinning' due to not being easy to remove the final part cleanly with a knife. What I did find worked well, much to my surprise is just putting a flat sheet of MDF on the vacuum table and then sticking the acrylic sheet on there with lots of double sided tape. I keep the protective cover in place on both sides of the acrylic too. I thought that would be far too weak to hold, but it isn't and it's far easier than removing the double sided tape from the acrylic sheet itself.

Quote:

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Originally Posted by Tenson

then sticking the acrylic sheet on there with lots of double sided tape. I keep the protective cover in place on both sides of the acrylic too. I thought that would be far too weak to hold, but it isn't and it's far easier than removing the double sided tape from the acrylic sheet itself.

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Double sided tape is invaluable for thin material, like PCBs. If you're having trouble removing it then I found that WD-40 takes tape off PCB material (SRPB or FR4) very easily, so that might be worth a go assuming it doesn't do anything nasty to the acrylic.

Ahh I tried that too :) Yes it does work, and actually I found soaking the part in white spirit for 15min worked even better. Trouble is even a kitchen tissue will scratch the acrylic slightly. A cotton make-up removing pad works best. Better still to keep the protective sheet in place IME though. How do they stick that stuff on, is it just static? There is no residue from adhesive?

Wouldn't it be nice to have these Vacuum mats Vacuum Work Holding Chucks - YouTube but the mats of throw away. ..Clive