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  1. #11
    Quote Originally Posted by JAZZCNC View Post
    How do you work that out then.? It's the foundation of the whole machine and what the Fixed Gantry connects too.
    At first glance you might think that, but the foundation of the machine is actually the rectangular gantry.
    Everything refers to the gantry, that is why it is such a rigid design. The overhangs are minimalized.
    Okay, you need something to support it so it doesn't fall over, but a strut? Does that not detract from the beautiful simplicity of the design? That tower in Pisa would get a lot more benefit from a strut than this, but it doesn't mean you should fit one. I mean, how gauche

  2. #12
    Quote Originally Posted by Robin Hewitt View Post
    At first glance you might think that, but the foundation of the machine is actually the rectangular gantry.
    No it's not. Watch this video and you'll see the whole structure.


    The Gantry rectangle is only has strong has it's connection to the base hence the massive plates. It would greatly benifit from more bracing higher up with connection to the lower frame. Yes Maybe not looking has simplistic but what we building here.? machines to do a job good or poser machines.!!


  3. #13
    I didn't see that movie. It doesn't need a strut, it needs the rails fixing to the bottom of the bed and the blocks fitting to the gantry. Dump the overhangs, kill the vibrations. Simples

  4. #14
    Quote Originally Posted by Robin Hewitt View Post
    I didn't see that movie. It doesn't need a strut, it needs the rails fixing to the bottom of the bed and the blocks fitting to the gantry. Dump the overhangs, kill the vibrations. Simples
    Sorry but you'll have to point these overhangs out because I'm struggling to see any.!! Or any that will make a difference anyway.?

    I agree the Bearings on the base and rails on the bed would be a better option but it's not the weak link in the machine. The High gantry frame without support is far more a weak link and source of vibration IMO.

  5. #15
    Hi Robin, Lachlan,

    Maybe this helps explain it. If you remember the days of 'free-body-diagrams' - the bed is part of the system. See picture which shows all the forces acting.

    You can hopefully see how the extra brace can help. This is where myself and Jazz are coming from.

    I think Wal created something like this (although smaller) and grappled with different layouts to make sure the 'tower' was stiff enough.

    Can it work without the brace - of course. Is it much better with it ? - yes, significantly, and for little effort.
    Click image for larger version. 

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    Thanks
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  6. #16
    Why does this chap spend a long time adjusting the rails to be perfectly parallel and then use a lump of pine as the base for cutting? Seems a shame, since pine obviously isn't flat and stable!

  7. #17
    Quote Originally Posted by Tenson View Post
    Why does this chap spend a long time adjusting the rails to be perfectly parallel and then use a lump of pine as the base for cutting? Seems a shame, since pine obviously isn't flat and stable!
    Ye did seem a lot of wasted time and to be honest I don't think he had a clue what he was doing judging on how he went about it.!!

  8. #18
    HI EVERYONE,
    Was surprised and happy to see so many responses. Thankyou! I think the triangular bracing of the gantry is a must for this build it makes sense as a gantry triangulated is so much stronger than a gantry just flapping in the breeze so to speak. I have some 50x50x4 box steel surplus, would that steel cut the mustard for this frame build?

  9. #19
    Quote Originally Posted by routercnc View Post
    See picture which shows all the forces acting.
    But the diagram doesn't show the rails being screwed to the bed and the blocks being screwed to the gantry.

    The nut should be under the gantry and the screw moving with the bed.

    That puts the linear bearings permanently underneath the cutting head.

    Looks a bit odd, but if you draw it you will see enormous benefits.

  10. #20
    Quote Originally Posted by Robin Hewitt View Post
    The nut should be under the gantry and the screw moving with the bed.

    That puts the linear bearings permanently underneath the cutting head.

    Looks a bit odd, but if you draw it you will see enormous benefits.
    Robin I agree the swapping the bearings and rails gives a good benefit because has you say the bearings are always in prime location providing Max support but the screw moving with the bed isn't needed and creates more Mass to move and complexity. Moving the Screw, Bearings/mounts, Motor etc. means the Negatives out weigh the advantages in this case.

    Not being funny or picky here but please stop calling it the gantry it's the base Frame and I'm easily confuddllledd. .

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