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  1. #11
    Quote Originally Posted by qwertyjon View Post
    Can anyone point out any obvious faults before I carry on?
    Yes I can point out a few things. The gantry is a little flimsy with just one piece of 90x90 but worse is the connection to the X axis bearings. Relying just on the bolts in profile won't be enough and it will need much more bracing than that other wise you'll get resonance and chatter at the cutter.
    I would increase the plate thickness on the ballnut mounts and bearing plates.

    Presume those Angle brackets are just for stiffening and your not relying on them to hold profile together, if you are they won't be good enough.

    To be honest I would re-think the gantry single profile piece and beef it up a little.

  2. #12
    A few things pop out for a start.

    1. The gantry is not deep enough, it would be better to have two cross pieces and put the ball screw between them. The reason is that the further apart you can put the rails the better, it helps reduce twisting.
    2. Are the X ball screws that low down for a reason ? it's regarded as advantageous to have them level with the rails, it looks like you could raise them okay.
    3. Most people use 20mm aluminium plate for most of the components.

    This is a good diagram to study.

    Do it yourself CNC router: Design Considerations, the Gantry

    Edit: Dean, I was faffing about with an edit while you posted.
    Last edited by EddyCurrent; 09-03-2014 at 10:05 PM.
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

  3. #13
    Jazzcnc - thanks for your comments, I was planning on using the proper profile jointing bolts with the angle for support. If that makes a difference? I did think that using 12mm plate was a little thin. So I'll redesign with the 20mm that eddiecurrent suggests. I'll have another think for the gantry too.

    Eddiecurrent - thankyou also for your input. I'll have another look at the gantry. The X ballscrews were put there for convenience to attach to the profile. If there are benefits to having them level then I'll definately lift them. Thanks for the site link too.

    Finding this forum has already probably saved me a fortune in redesigns, I appreciate the help im getting.

  4. #14
    Version 2 - 1. Adjusted to use 20mm plate. 2. Raised X ballscrew's, inline with supported rails. 3. Doubled up on gantry crossmembers. 4. Added extra profile on gantry legs. 5. Added plate inside the 'legs', attaching to legs and ballnut mount.
    Click image for larger version. 

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    6. Gantry bf/bk mounts considerably larger, encompassing both crossmembers, and legs.
    Last edited by qwertyjon; 10-03-2014 at 12:10 AM. Reason: Added No.6

  5. #15
    Make sure you have enough room under the gantry, between it and the bed, it looks a bit tight as it is, once you get the spindle hanging off there and some tooling in your not going to have much depth for the stock.
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

  6. #16
    What sort of distance should I expect between spindle and tool tip?

  7. #17
    Not sure exactly what you mean but some people have it so the collet of the spindle, without any tool in it, comes right down to the bed. In my case the largest cutter I'm using is 50mm long so the distance from the end of my collet to the tool tip will be about 70mm. Then I will be using sacrificial boards on top of the bed and in some cases a small vacuum clamp on top of the bed, then my stock might be up to 50mm thick, maybe more, so the spindle has to rise above all that with a 50mm cutter in the collet. Mine is working out to have a 190mm travel on the Z axis.
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

  8. #18
    You did a good job of deciphering my post. Thats exactly what I meant. Thanks

  9. #19
    qwertyjon; If your near Torbay in South Devon, I am wanting to build a machine, the cost MIGHT be reduced if we order the aluminum together? can't do it until the end of the month though!

  10. #20
    Quote Originally Posted by Fozz84 View Post
    qwertyjon; If your near Torbay in South Devon, I am wanting to build a machine, the cost MIGHT be reduced if we order the aluminum together? can't do it until the end of the month though!
    Erm I'm no geological expert but last time I looked Devon and Scotland where several hundred miles apart.!!. . . . Thou with all the floods recently suppose we could have had a land slide. .

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