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  1. #11
    When it comes to the Linear Guideways, what is the differences in performances between a "standard" block and a "flat" block? Could I use standards for the x axis that will be taking the most load and flats for the y?

  2. #12
    This is my first stage design for my router. I will add more photos from different sides soon but if you have any comments or questions then let me know.

    Click image for larger version. 

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    Last edited by Norgmonster; 20-06-2016 at 09:14 PM.

  3. #13
    That's ok for the broad strokes of the design but it's the little details that will bite and you don't show any.! You also need to ask your self if copying someone else's Bad complicated design is worth the trouble.?

    There are easier simpler designs that will work just as well and be stronger. For instance frame with high sides with simple beam gantry sat directly on rails is much stiffer than high gantry sides and far less complicated.

    Word of warning if this is your first machine.? It's common mistake to think that building large machine is just as easy smaller machine. While in essence it appears just matter of scale, which it is to some degree, problems lie in that the obsticles to over come, like rail alignment etc scale upto match so if you've no expereince then expect some serious hair pulling.!!

    Unless you really need large machine I advise to cut your teeth on something smaller.
    Last edited by JAZZCNC; 21-06-2016 at 12:17 AM.

  4. #14
    Thanks for the reply Jazz,

    As the title suggests this is my first go :-)

    My original plan was to make a 2' x 4' bed with the gantry running across the 4' length. That way when the time comes i could just extend the 2' sides to 8' without remaking the hole frame. As you pointed out, this can work in theory but comes with issues to consider.

    When you say high sides do you mean on the x axis?

    In terms of frame materials, is the 80x80 aluminum profile i used sufficient? I originally considers 80x120.

    Should i be using rack and pinion with my plans to extend the frame in the future?

    Let me know your thoughts and I'll go back to the drawing board.:-)

  5. #15
    The high gantry sides introduce a weakness - delete these, raise the longest X axis rails (and supporting aluminium profile beam that it is sitting on) so that they are level with the lowest point on the gantry cross beams. Then re-draw a small gantry end design that links the gantry beams to the X axis rail bearings. This is much stiffer overall as the raised part is now integrated to the bed and can be supported as much as you like.
    This would also mean you could delete the EXTRA lower pair of hiwin rails as there is virtually no moment on the gantry ends anymore. This would save alot of money!

    Gantry beams
    Putting rails on the inside faces of the gantry cross beams makes it difficult to get them aligned/in the same plane. You can't use epoxy leveling for example, and those aluminium beams are not flat. This means you will need to use shims etc. which would be fiddly to get all 4 aligned. Machining them flat to start with might help, but they need to be accurate to prevent binding. These precision guideways do not like much mis-alignment.

    Z axis

    You have not shown details of the 'box Z design'. Be aware you need to allow for head tramming adjustment, Z rail alignment, and Z rail pre-load /adjustment in the way it all goes together. CAD is 100% perfect, but real world is not.

    As per Deans comment if I was starting out I would not go for something quite so complicated.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  6. #16
    Hi All,

    Thanks for the feedback on my last design. I had a feeling that it would not hold up but it was an opportunity to use Fusion 360 for the first time.:-)

    I have taken on your comments and hope that this next one is a step closer.

    For what ever reason, a lot of the components in the design could not be rendered to look like they should be so i hope you can tell what it is you are looking at.

    The size is approximately 2' x 4' with the idea to extend it to 8' x 4' in the future. The z axis trail will be around 20cm.

    I have not done a Z axis yet or properly defined how i plan to mount the stepper motors for the R&P system so beyond that let me know your thoughts.

    Click image for larger version. 

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    Last edited by Norgmonster; 25-06-2016 at 06:10 PM.

  7. #17
    I shore this Rack and Pinion mounting setup and was wondering what any of you guys thought of it?

    Is it worth replicating for my router design?

    Any feedback on my design would be great as well (see photos one posting above).

  8. #18
    Yes the principle of spring loading into rack is ok and how it should be done. But wouldn't copy is weak design for router (he's using Plasma so not so much an issue on the cut). Watch how the mounting flexs @ 0.22s when he puts is hand on it.
    This flex will show in the machine. Maybe not in accuracy but will in resonance and this resonance transfers thru the machine and into the final cut. Is too bad it will cause excess wear in the pinion/rack.
    Last edited by JAZZCNC; 25-06-2016 at 07:03 PM.

  9. #19
    The flex is down to the plate being quite thin (looks to be around 5-10mm). I have also see other spring mounted systems that use a belt between the stepper motor pinion and another pinion that makes contact to the rack. I assume this reduces kickback?

    Could you also have a look at my new designs and let me know what you think (smaller bed, lower gantry and less rails)?

  10. #20
    Ok we are cross purposes here. The Mechanism of being spring loaded is what I thought you was wanting advise on.
    The fact it's direct drive off the stepper shaft is because it's being used for plasma machine which doesn't require the same resolution and torque that router requires.

    This is why you have seen other systems that use belts n pulleys. It's got nothing to do with Kickback. The belts/pulleys are applying ratio to increase resolution and torque.

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