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  1. #1
    150+ Forum Groupie twisted8's Avatar
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    How to hold pieces down on a CNC machine?

    Hello,
    I haven't had much luck cutting good pieces with my cnc machine. I'm using double sided tape and usually the pieces end up moving anyway and get messed up. Another problem is that sometimes the router gets stock on the double sided tape while is cutting and it makes it skip.

    Any suggestions?

    thanks

  2. #2
    75+ Posting Member Polmer's Avatar
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    Re: How to hold pieces down on a CNC machine?

    I bolted a piece of plywood on the main CNC deck.
    I then screw the piece to be cut into the plywood so it cant move.

    ~Polmer
    ~Polmer
    Level-D 767, Opencockpits+ SIOC+ Lekseecon

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  4. #3
    Have CNC-----will build.
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    Re: How to hold pieces down on a CNC machine?

    I sometimes use a piece of self adhesive shelf paper on the bottom of the piece to be cut, after attaching the shelf paper, I spray it with 3M spray adhesive and attach the material to my sacrificial base piece. This keeps the spray adhesive off my piece and eliminates alot of cleanup.

    Milt

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    Re: How to hold pieces down on a CNC machine?

    Examples:

    http://www.elektor.nl/StreamFile.lyn...s/P1140004.JPG
    http://www.elektor.nl/StreamFile.lyn...s/P1120279.JPG
    http://www.elektor.nl/StreamFile.lyn...s/P1120281.JPG
    http://www.elektor.nl/StreamFile.lyn...s/P1120276.JPG
    http://www.elektor.nl/StreamFile.lyn...s/P1080227.JPG

    The T nut table is not obligatory of course.
    Many people make holes in a thick plate of mdf/plywood where nuts can hammered (right word ?) in.
    These nuts have screw thread inside.
    http://www.elektor.nl/StreamFile.lyn...Posts/7965.png
    In this thread you can screw a bold for holding the clamps.
    Clamps can be milled on your own mill.
    Mills making parts of mills !

    Hope this helps.

    Hessel
    Last edited by Hessel Oosten; 02-22-2011 at 05:47 AM. Reason: addendum
    767 Level-D

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  7. #5
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    Re: How to hold pieces down on a CNC machine?

    Forget the tape. Tape is good only for PCB isolation milling.
    Use T-table (which is expensive) or use these http://radiomodels.com.pl/images/nakretka-klowa-m5.jpg at the bottom side of your MDF or playwood table. Glue them to the table using epoxy glue or something like that.
    These http://www.elektor.nl/StreamFile.lyn...Posts/7965.png are not good enough IMO - could be easily twisted while mounting your object to the table.

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    Re: How to hold pieces down on a CNC machine?

    I have 16mm MDF fixed to my table and I use aluminium 'bridges' with a wood screw. Place some spacer material that is the same thickness next to the work piece then drill a small hole into the sacrificial MDF table between the pieces. The aluminium bridges are 3mm thick with a hole in the centre, the screw down the bridge trapping the work piece and the spacer piece. I also use 'hook' bridges which are L shaped and made for specific thickness materials as seen in this picture -

    This rudder pedal part is being machine from a piece that used to be the side of my console structure - recycling the Boeing!
    Cheers, Gwyn
    Last edited by Westozy; 02-23-2011 at 07:09 PM.

    737NG using Prosim737, Immersive Calibration Pro, Aerosim Solutions motorized TQ & cockpit hardware, CP Flight MCP & FDS SYS1X, SYS2X & SYS4X, FDS PRO FMCs, AFDS units & Glarewings, Matrix Orbital ELEC display, Pokeys Landing & Cruise alt display, Buttkicker Gamers, 3 x BenqMW811ST projectors with a Matrox Th2Go
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  11. #7
    150+ Forum Groupie twisted8's Avatar
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    Re: How to hold pieces down on a CNC machine?

    thanks guys! great suggestions! gotta give this a try.

    How would you hold small pieces tho? for example i'm trying to cut small acrylic blocks for annunciators but they seem to fly away right before the router finish cutting. Maybe I need to use a smaller bit? i'm using 1/8" (3 mm) so it creates a pretty big space between the small piece being cut and the main piece.
    Thanks

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    Re: How to hold pieces down on a CNC machine?

    You could use "bridges", these are for example 4 small bridges of material that the router does not cut away when the part is cut out. The toolpath software normally has the possibility to define "bridges".

    Regards, Wendy

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    Re: How to hold pieces down on a CNC machine?

    Hello twisted8

    For your last "problem" try to not mill all the way through the material - just
    leave a few 1/10 mm. Then you can either break the pieces out or use a knife
    and finish off by filing and sanding.
    A second way is to flip the working piece and mill of from the backside.



    This picture show my MCP Korrys (though in MDF - more or less the same for Acrylic)
    from the top side and as you see my top knob surface is a approx. 1mm lower then
    the top surface of the workpiece so when you flip and mill from the backside
    and the knob / Korry is released it will "fall down" and does not come in conflict
    with the milling tool.
    Some cleanup afterwards is nessasary in any case.

    Happy milling.
    Regards,
    Per-Erik
    www.hoddo.net

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  16. #10
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    Re: How to hold pieces down on a CNC machine?

    Hi Guy my mk one CNC is finished and cutting bits like mad at the moment --mayerial of choice Delrin my machne may not be the Prettiest on the Block but she cuts great and is repeatable - so much so she is making all her own upgrades, and bits for a 2nd machine designed for PCB Routing and smaller precision light cuts parts will post some pics later and take a look at my Youtube clips when i publish the link in my next post...anyways i tend to now place screw holes in Non machined zones an screw tha part down with wood screws to a sacrificial Board, i have had good success with this method. for my CAM i use Vectric 2d for Producing my G code, i have to say bang for bucks im very happy with that piece of software as it allows my to put Holdown tabs around the Job to stop it from flying out when it finishes the last cut .. i know that's all been mentioned already but just so excited that my machine is up and running at last. look forward to contibuting my nutty professor ideas and designs to this forum Cheers Guys and Gals

    http://www.youtube.com/watch?v=0iK1jiyvGho

    Also added Pictures to my album page
    Last edited by wannabeaflyer; 02-25-2011 at 07:30 PM. Reason: add link and photos

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