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  1. #1
    Join Date
    May 2007
    Posts
    61

    gantry design ideas

    Hi everyone,
    I finally have most of the bed built so it's gantry time. These are my gantry ideas as of now I would like to use the shorter (top image it is 12" long) carriage design:





    Any critiques let her have it.

    The material is 4x4x3/16 and 2x4x3/16 steel.

  2. #2
    Join Date
    Jun 2005
    Posts
    176
    The lower picture is better structurally and gives your X axis more rigidity. You have a massive lever on the Z axis though. Are you sure you need all of that Z travel?

  3. #3
    Join Date
    May 2007
    Posts
    61
    Unfortunately yes i do need all that z. I plan on using my machine to make molds for aircraft and fuselage mold halves get pretty deep. If i go with the first gantry style would it limit my speed a lot? or would it just be a lot harder on my linear rail trucks?

  4. #4
    Join Date
    Jun 2005
    Posts
    176
    Gantry structure can, to a certain extent, be based on the likely cutting forces you're going to generate. If you're cutting foam then the cutting forces will be pretty light in that respect. You still need aenough length in the base to cantilever the weight of the Z axis and cutting tool. By that I mean you dnt want any significant weight outside the footprint of the X axis bearings. I still like the lower design better as long as the Z axis and tool are within the footprint, so in your picture, the gantry is back to front with the Z axis and column on the wrong side.

  5. #5
    Join Date
    Apr 2007
    Posts
    8082
    Even more so than a tall but stiff gantry is the problem of finding long enough cutters to reach into the deep molds. Chatter and run-out is a major part of this problem as well.

    Most solutions end up with slicing the mold CAD drawings into manageable layers and use various methods of pinning the layers together to keep them properly aligned while gluing the separately machined layers together to form the complete mold.

    I have used 6" thick molds made of Renshape 440 that were full of chatter damage and had to be reworked with automotive body putty in order to get any use out of them. These were for aircraft wind tunnel models that needed a high degree of accuracy. These molds were cut on a 5' x 10' ShopBot that had a large Colombo spindle on it.

    My point is that the necessity of a very stiff machine is only part of the issue for getting a quality surface finish on the molds. The deeper the mold, the more problems you will encounter.

    CarveOne
    CarveOne
    http://www.carveonecncwoodcraft.com

  6. #6
    Join Date
    May 2007
    Posts
    61
    That is very true and I agree 100%. I Plan on makin it a 5 axis as soon as I have the extra money for the cam program. With that information does it change anything?

  7. #7
    Join Date
    Sep 2011
    Posts
    13
    I agree with what the other Guys are saying. That said, I have been messing around with my CNC Router and the Stiff gantry is Really what makes the difference between a good and bad accuracy of the machine. My first design didn't have that stiff of a gantry and paid a heavy price in accuracy and weight distribution. My newest design makes sure there is no play and the load is more on the center of axis. As for your five axis question, I have been bit by the CNC bug and i always keep getting the urge to make it bigger and better. I am always seeing ways to improve or make it be faster. That being said I would put the money and time in upfront. You will find it will be less of hassle designing something for everything you need rather than trying to adapt it in later. You will save yourself hassles and headaches.

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