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Thread: The truth about vacuum tables?

  1. #1

    The truth about vacuum tables?

    I don't have any truth to extol but I am looking for some!

    I have decided to replace my CNC for a few reasons, one being that I would like a vacuum table. There are a lot of times a vacuum table would just be easy.

    Now, what about all those times the vacuum table is not so valuable, thats the unknown thing for me. I have seen a lot of videos lately of machines with vacuum tables but people have spoil boards on top and them clamp the workpiece on to that.

    It has me wondering exactly when is a vacuum table of no use? At what size is your work piece too small? Are there ways around it like surrounding your workpiece with something else so the vacuum is more effective?

    Like everyone, I am a bit sick of all the clamping but is the vacuum table the nirvana that a lot of people who don't have one may think it to be?

    Thanks for your responses.

    ps, a lot of companies are offering different pumps like the 'German becker vacuum pump KVT3.140', a dry vacuum pump and a water ring vacuum pump, listed in descending order of price.

    Is there a difference to be had, is one quieter than the other. I don't like the idea of having to vent water vapour out the shop along with a bunch of other stuff. It's only water but it's not another logistical thing I want to bother with.

    ps, a lot of companies are offering pumps like t

  2. #2
    I have a table top cnc router and made a corian vacuum grid. My vacuum "pump" is a venturi style using compressed air. What amazes me, even with this fairly inefficient setup, is how much vacuum pulls through the mdf spoil board. Some of my commercial customers use mdf as riser blocks or pucks to raise their material off of the table some for clearance. The mdf will work best when banded so that the edges are sealed. The commercial vacuum tables can also be zoned so that only the sections used for clamping are live.

    Jerrimy
    I make dirt out of woodworking tools.

  3. #3
    i use mine for sheet goods,, what size is too small? wel this depends on vac amount seal and strategy, most all carvings and non sheet goods are done with clamps and screws,, and i got a big vac setup

  4. #4
    I tried using a vacuum table for a while. However most of my project involve cutting so I still had to clamp. The only time I found it usefull was when doing signs or carvings. Which I might add, I do very little.

  5. #5
    Thanks guys, it looks like it would be worthwhile for me to take a vacuum option which also has ttrack installed.

    For large sheets it sounds nice, put it on and cut even though a single large sheet is usually the easiest to clamp!

    A lot of the time I will have a small 3mm (1/8th) piece of mdf under my 3/4" so that I can go right through and not worry about scruffing up a cheap sheet underneath.

    The vacuum table has me wondering what people do here? The vacuum wont work with a thin sheet underneath the sheet you are cutting so are people not worried about the ongoing damage to the vacuum table.

    I am wondering if there is something I am missing? Is the rubber vacuum table something that you replace often as well and resurface?

    Thanks,
    Jason

  6. #6
    Something to think about is vacuum fixture or fixtures.

    One area I found a vacuum fixture is for PCB routing. You need the stock to lie perfectly flat and the only way to do this is with a vacuum. What I do is to Isolation rout both sides then while I am on the bottom side drill my holes as the last step.

    I have fixtures for various boards and it does not take much of a vacuum to hold them down. Cant use rubber as gaskets though as they keep the board from lying perfectly flat.
    Last edited by Michael Simpson Virgina; 02-09-2012 at 3:58 PM.

  7. #7
    The more I think about it the less I think that it will help me as often as I would want it to be. I didn't try to make that last sentence as confusing as it was

    Still, when paying that much money for a machine it would seem reasonable to pay the extra to have it on hand.

  8. #8
    "vacuum table" can mean different things to different people.
    Our machine has a 5x12 aluminum vacuum table, with a grid of channels every 2" or so. We put a rubber seal around the perimeter, and lay a 5x12 sheet of 3/4" MDF on top. We have two 25HP Becker pumps, drawing through the MDF. You lay your sheets on the MDF, and cut through about .003"-.005". Every 50-75 sheets or so, we surface .01" off the spoilboard to get it smooth again, as you start loosing vacuum as it gets grooves in it, even though they're only .005" deep. Anything smaller than about 2 sq ft needs to get onion skinned to prevent it from moving. This is cutting at about 1000ipm.

    You can cut smaller boards by blocking them in with scrap pieces of board.

    You can use a smaller pump with dedicated pods or fixtures. For smaller parts, you can get away with a low volume high vacuum pump. For larger parts, you may still want something like a 10HP Becker with dedicated fixtures.

    Cant use rubber as gaskets though as they keep the board from lying perfectly flat.
    The proper way to use a rubber seal is to place it in a routed channel. For a 1/4" gasket, you route a 3/16" channel, and the seal will compress 1/16" into the channel, holding your part perfectly flat.
    Gerry

    JointCAM

  9. #9
    OK, Gerry, that answers the question about the spoil. Why do I have the feeling that a machine I am looking at would not be drawing through the MDF. For someone who had not come across this it's mindblowing that a pump will create enough suck through 3/4" MDF - unless the MDF has honeycombs throughout.

    The pump I am looking at with a 2500x1300 table is 7.6kw, or 10hp. I am only 40 short of yours

    One of the machines has sections so that I can block off areas not needed and presumably get better performance over the areas left open. The other machine does not.

  10. #10
    You do need to remove .01 or .02 from each side of the MDF for it to work best. Also seal the edges to minimize leakage.
    Gerry

    JointCAM

  11. #11
    We cut almost exclusively using a vacuum table. It's a piece of 3/4" (20mm) Trupan Ultralight MDF, not the normal MDF. We glue it to our plenum table, as Gerry says, after cutting the skin off it, and then we're good to go. We have 4 "lighthouse" motors and it works fairly well. Not to the level Gerry is using, but for the average guy, it appears to work fine. We cut big and small stuff all the time. No real limit on how small we cut. Depends on the material and the item being cut. If it's too small and looks like it's going to be tricky, we hit the back with some spray adhesive and then we're good to go.

    Like Gerry, when we cut some stuff into it and it's look pretty chewed up, we just skim the top and you have a fresh new surface. You can do that many times before it gets too thin and you start loosing hold down pressure (the thinner it gets, the weaker the vacuum appears to be).

    I'm reasonably happy with it. I've got some improvements I'd make if I had the time and money to do it, but overall, it works fairly well.
    Lasers : Trotec Speedy 300 75W, Trotec Speedy 300 80W, Galvo Fiber Laser 20W
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    Real name Steve but that name was taken on the forum. Used Middle name. Call me Steve or Scott, doesn't matter.

  12. #12
    Join Date
    Oct 2006
    Location
    Bloomington, IL
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    I built my own based on some doc from some shopbot owners that floats around on the net. I used a FPZ regenerative blower as a vacuum pump. I built my own 2" PVC manifold with PVC ball valves. I also installed a pressure relieve valve and Solberg canister filter as recommended by FPZ. Currently I have one 6"X12"X1/4" deep grid/zone I cut in my table now (between T-track) and its plumbed. I have space for 4 more zones on my table plus a vent to atmosphere for changing parts when you do not want to power off the pump. I use it all the time for smaller signs I make. I suck through LDF when I have cut throughs. Once the part is down you cant move it for the most part. I plan to make a couple zones for 24"X48" sheets and another for 12"X24".

    If you have a machine why not make a vac table?
    Glad its my shop I am responsible for - I only have to make me happy.

  13. #13
    Well I am learning something today, I thought you were putting your pieces down straight on to the rubber and using the vacuum created by the gaps.

    So I guess it should work like that for a machine I get, especially if I am blocking off areas to create a better vacuum where I am actually cutting.

  14. #14
    Join Date
    May 2007
    Location
    Atlanta, GA
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    129
    Quote Originally Posted by Gerry Grzadzinski View Post
    You do need to remove .01 or .02 from each side of the MDF for it to work best. Also seal the edges to minimize leakage.
    Gerry, specifically, how are you sealing your spoil board edges?

  15. #15
    Actually, I don't. But, I have 50HP in pumps.

    I've heard of people using edgebanding (PVC or polyester), and others brushing wood glue on them.
    Gerry

    JointCAM

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