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Thread: vacuum table question

  1. #1
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    Talking vacuum table question

    Hi all,

    I'm setting up a new vacuum table and was wondering your opinion(s).

    I have a 5x12 PRT and want to be able to vac-down anything from small parts all the way up to the 5x10 sheets of mdf.

    Are there any drawbacks to having more zones than fewer?

    My idea is to have 25 zones instead of the normal 4 or 8. I would make a bunch of approx. 12"x24" tile-like zones with my smaller CNC and then bolt them down onto the bed of the PRT, and then do a thin surfacing run and go from there.

    alrighty, lemme know what you think!

    -JAMES

  2. #2
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    I've been running 6 years on a 5x8. I have 5 zones, and cannot imagine using/needing more. However, depends on what you will be making.
    For me, furniture parts are done on a non-vac region where solids are clamped/screwed down.
    Cabinetry is typically 4x8 sheets = wide open on primary 4 zones 95% of the time.
    Partial sheets are when the gates get used. If I have a sheet a bit off size, open more zone and use other scraps to mask around the work piece.

    My first vac table attempt was running 80/20 aluminum channel, splitting the table into 6 zones and using pallets in between the aluminum extrusion grids. Sounded and looked like a great idea based on examples shown here. Ultimately, I scrapped the whole thing and ran a solid sheet of ultralight mdf "trupan" with zone division taking place in the manifold underneath. Life got way easier and so did the accuracy of my work.

    I cringe at the thought of 25 zones. A very complex project that I don't mind saying will almost certainly cause more problems than they're worth.
    I'm sure the common response is going to be, what exactly are you planning to produce on this machine, as that really is the ultimate question before the best guidance can be given.

    Jeff

  3. #3
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    it sounds like a nightmare. just imagine how you would plumb it? Plus I don't think suck a small area will hold well sucking through a spoil board. what are you trying to hold in place? there may be better ways to go about this.

  4. #4
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    hi Jeff,

    Thanks for the input. I did have an 8-zone configuration drawn up so what you said makes a lot of sense. The 12x24 grid just matched up nicely with the 5x10 cutting area so I started to get a little carried away with the idea of focusing only on the exact zones I needed. But what you say is true, you can just mask off the areas that you're not needing at the moment.

    In terms of production, I fabricate components for artists and small design companies.. so I'm sort of planning for the most flexibility.

    I appreciate the feedback, I find with a lot of these CNC projects, it's REALLY easy to get out into the weeds.

    Thanks!
    -james

  5. #5
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    hi Knight_toolworks,

    the nightmare would only be when it came down to making the manifold, but I think Jeff (above) was right, in minimizing the number of zones for the most common tasks. Problem with my work is that it's totally random in what people ask me to produce so I just wanted to check with y'all and see what better reasoning there was out there.

    As for the small area 12x24 zone, I made a test panel and hooked it up to my FEIN and was able to lift a half sheet of 3/4 melamine just fine, and took a lot of force to move when i pushed it laterally.

    I haven't yet tested pulling through a skimmed board.

    thanks for the feedback / input!
    ~ james

  6. #6
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    I think for small areas your going to need either a high vac setup or some other method.

  7. #7
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    Wink 8-zones

    Here's a pic of 8-zones ... instead of 25

    Screen Shot 2018-01-25 at 1.44.05 PM.jpg

  8. #8
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    Quote Originally Posted by knight_toolworks View Post
    I think for small areas your going to need either a high vac setup or some other method.
    Yeah this is actually my first foray into vacuum hold-down. I've made a lot of fixtures in the past which worked out great. Still wrapping my head around the vac-system.

    thx again!
    -J

  9. #9
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    Remember a couple rules of thumb...
    What size are your small pieces? Remember there will be little or no vacuum 1 1/4 to 1 1/2 " inches from the edge. Subtract a 1 1/2" borders area from the total area of the part. Apply the rest of the area in square inches times your max vacuum /2 (for psi) and multiply it by .6 (60% for cut slots). If that number is less than 50, it probably wont hold, period. Between 50 and 75, it could hold with special attention. 75 to 100, maybe and over 100 most likely
    Gary Campbell
    GCnC Control
    GCnC411(at)gmail(dot)com
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    http://www.youtube.com/user/Islaww1


    "We can not solve our problems with the same level of thinking that created them"
    Albert Einstein


  10. #10
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    Quote Originally Posted by Gary Campbell View Post
    Remember a couple rules of thumb...
    What size are your small pieces? Remember there will be little or no vacuum 1 1/4 to 1 1/2 " inches from the edge. Subtract a 1 1/2" borders area from the total area of the part. Apply the rest of the area in square inches times your max vacuum /2 (for psi) and multiply it by .6 (60% for cut slots). If that number is less than 50, it probably wont hold, period. Between 50 and 75, it could hold with special attention. 75 to 100, maybe and over 100 most likely
    Hi Gary,

    Can you clarify for me a bit on the math? I've never seen anyone write it out so this is very helpful.

    I made a test vac-waffle and tried it out with my FEIN T2 and it held pretty good.

    For the math problem: The vac-waffle-board is 12.2" x 24.2", offset inwards (as you mentioned) by 1.5" which gives me 9.2" x 21.2" holding area.

    Let's assume the part is the same size as the whole waffle-board. (<-- a highly technical term i just made up! )

    The vacuum pulls 90inch of water or 6.6hg ( which do you use for your calculations?)

    The slots are only 1/8" on this test piece. Do you have a recommended kerf width?

    Is that enough information to finish the math? Am I missing something?


    thanks for your help!!!

    Screen Shot 2018-01-25 at 2.04.02 PM.jpg

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