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IndustryArena Forum > WoodWorking Machines > DIY CNC Router Table Machines > Usage of down cutter tools for part hold down?
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  1. #1
    Join Date
    Dec 2016
    Posts
    10

    Usage of down cutter tools for part hold down?

    Hi there,

    I have a few pockets that I want to cut into MDF Sheet, which need a precise Z depth. It seems like it's nearly impossible for me to push a 4' by 8' sheet flat without a vacuum table, which is quite an expensive solution to what feels a trivial issue.

    If I were to ramp into material with a 1/4" down cutter tool, using the already flat base board as my zero reference, would the tool assist in pushing the MDF board down where it has bowed that couple of millimetres above the surface of the base board, thus giving me the same, precise pocket depths along a slightly bowed sheet of material?

  2. #2
    Join Date
    Mar 2003
    Posts
    35538

    Re: Usage of down cutter tools for part hold down?

    Not likely.
    It'll push it down, but when the feedrate drops for direction changes, the sheet will lift, and the cut will be deeper. You'll end up with very uneven bottoms.
    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

  3. #3
    Join Date
    Apr 2004
    Posts
    5728

    Re: Usage of down cutter tools for part hold down?

    If your sheet is bowed upward from pressure on the edges, everything will be a little off; from the pocket depths to the cutting action. If you know where the pockets are going to be, put some screws in around those areas that secure it to the spoilboard - well clear of them so they don't get cut - to take out the bow. Then secure it at the edges. Of course, if it's bowed from improper storage, you can just flip it over and flatten it out by screwing down the edges.
    Andrew Werby
    Website

  4. #4

    Re: Usage of down cutter tools for part hold down?

    If you paint or coat the bottom side, so that 2-sided tape will stick! Then it can be removed when done and the coating sanded off!

    Widgit
    www.widgitmaster.com
    It's not what you take away, it's what you are left with that counts!

  5. #5
    Join Date
    Apr 2013
    Posts
    1899

    Re: Usage of down cutter tools for part hold down?

    Clean the surfaces (table and work piece) from dust and grease, stick double sided carpet tape along the edges and in the center, stick the work piece to the table, fix the edges as usual with clamps but not too hard. Make sure the carpet tape does NOT overlap anywhere and use it only once. You don't need to paint the MDF at all. Good carpet tapes stick pretty well and will hold for the short time it is used. Removing is MUCH easier if you don't paint the surface. Note that don't overdo the use of carpet tape, if you use too much of it you may not be able to remove the sheet when you are ready or may cause some damage to the artwork.

  6. #6
    Join Date
    Apr 2009
    Posts
    5516

    Re: Usage of down cutter tools for part hold down?

    If you have a spoilboard, just pin it down.

  7. #7
    Join Date
    May 2005
    Posts
    3920

    Re: Usage of down cutter tools for part hold down?

    Depending upon the material and exactly what you are pocketing a vacuum hold down might be easy to accomplish, a shop vac can offer enough vacuum to pull thinner sheets of MDF down. Obviously a shop vac won't last long doing this but if you have only a few pieces to do you can come up with a solution.

    Other solutions already described can work however you need to watch out with the carpet tape method, especially with MDF. If the material left in the Z direction is very thin you may have breakouts when pulling the piece off the table. In other words you need to be careful about tape placement and the resultant strength in the board after you machine it.

    In the end there are many ways to solve this problem but it does depend upon the specifics of the task at hand. For example battens could be used. I know at work I've had to go the batten route when machining thing sheet metal destined to be an upgraded electrical panel. Battens are old fashion but sometimes they are the quick and easy solution to holding something down. Again it depends upon the specifics of what you are trying to accomplish in the MDF and the Z capability in your machine.

    You could always go to the weight room and get a couple of 50 pound bar bell weight and throw on the MDF.

    In any event the question that comes to my mind is this what good will this do if you remove the part from the table and it springs back? All your precision work has gone out the Window. This is a real problem in metal working if you are looking for precision results as clamping something down hard by its nature warps the piece. Un-clamp it and the spring back will throw it out of tolerance. I guess it depends upon what you mean by precision.

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