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  1. #11
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 9 Hours Ago Has been a member for 9-10 years. Has a total post count of 1,834. Received thanks 192 times, giving thanks to others 5 times.
    My concern with the fixed gantry option was how to protect the x-axis rails from the coolant, but having actually thought about it, it's probably easier.

    I just need to make sure they're spaced up of the drain tray, and have a lip hung down around the table so that any run-off can't run along and under the table.
    Now would you have the rails or the blocks stationary?
    I can think of pros and cons to both methods, but don't think it would make any noticeable difference anyway given the sizes involved.

  2. #12
    Quote Originally Posted by m_c View Post
    Now would you have the rails or the blocks stationary?
    The X axis rails? You have the blocks stationary under the gantry, anything else defeats the whole purpose. You support the bed where it needs supportingt. Am I not understanding?

  3. #13
    Quote Originally Posted by m_c View Post
    Now would you have the rails or the blocks stationary?
    I can think of pros and cons to both methods, but don't think it would make any noticeable difference anyway given the sizes involved.
    I'd have the rails stationary with bearings at the extremes of table but like you say at this size then it's no big deal.

  4. #14
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 9 Hours Ago Has been a member for 9-10 years. Has a total post count of 1,834. Received thanks 192 times, giving thanks to others 5 times.
    I've been thinking about it some more, and just skecthed both options.

    Fixed bearings
    +) Shorter rails. With fixed rails, ideally you need the bearings mounted at the extremes to avoid the working area overhanging the bearings, so you ideally need the rails extending the axis travel past the end of the work area. With fixed bearings, the bearings can be positioned closer together, as the supported area will always remain below the spindle, off course depending on how the table is loaded, it could lead to it bowing.

    Fixed rails
    +) Lighter table. 4 bearing blocks are far lighter than two rails.



    I'm still undecided between fixed v. moving gantry.
    I can see the pros and cons of both, but I'm currently swaying towards moving as it means a relatively constant moving weight (moving table means I'd have to tune for it potentially having a lot of weight mounted on it) and it gives me a bit extra flexibility for table loading (could work with longer length materials with less precutting required). Available space isn't a major concern

  5. #15
    Quote Originally Posted by m_c View Post
    Fixed rails
    (+) Lighter table. 4 bearing blocks are far lighter than two rails.
    Surely a lighter table is a minus. Vibration is the enemy and dead weight dampens vibration.

    Same goes for the gantry, bolting it to a dead weight reduces the rattle.

    Power to move a heavy table/workpiece ceases to be a problem the moment you start using ball screws. You get an enormous push.

  6. #16
    Has anyone used constrained layers to help dampen vibration and resonance in a machine? I'm thinking for the gantry you could use the normal 16mm slabs of alu but also affix an additional 6mm sheet with green-glue. The thinner the layer of green-glue the more friction it generates so the more effective at damping.

  7. #17
    Greenglue is interesting stuff but have you seen the cost involved?!? You have to buy it by the case for a start.

  8. #18
    About 100 for a batch. Not too bad compared with the cost of metal for building a machine. My gantry has about 250 of metal in it, not including ballscrews and bits.

  9. #19
    It's supposed to take 1-2 tubes per drywall sheet so if you're doing up a room then it works out by the case. How much are you planning to use on the machine?

    I've not heard of it being used on metal. That's quite an interesting question to ask.

    I'm not saying it's a bad idea, I'd just find it hard to justify that outlay for (in effect) a single tube of greenglue. Unless you plan to sell off the other tubes or you have other soundproofing projects lined up, of course. If you're selling off the single tubes you could probably find a few buyers without too much hassle. I'd have a tube off you!

  10. #20

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