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  1. #1
    BriceO's Avatar
    Lives in Here, Switzerland. Last Activity: 2 Hours Ago Has been a member for 0-1 years. Has a total post count of 20.
    Hi everyone,

    I'm currently building a CNC router of 1.8x1.2 meter to cut wood (and probably test aluminium).
    Click image for larger version. 

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    I use aluminium profile 8 series and 20mm aluminium plate. 4X NEMA 23 with a 48V PSU and a gecko G540. Here is the specs of the motor: (381 oz In. Holding Torque, 2.55V Rated voltage, 3.5 Amps Current Per Phase, 0.73 ohms Resistance, Inductance 2.8 mH).

    I had a proposition to use for the X and Y, 20mm lead, with a max speed of 500 IPM at an acceleration of 0.15G. For the Z, 10mm lead, with a max speed of 300 IPM at the same acceleration. My goal is to have a resolution of 0.01, an accuracy of a least 0.1mm.

    I have several questions:
    1. Is this general design seems to be ok?
    2. Are my max speed and acceleration calculated correctly? Or should I take 20 or 10mm lead?
    3. Is it a correct speed / acceleration for the size?
    4. Do I need to have a ballscrew preload torque?
    5. Is the position of the linear bearing/ballscrew good?
    6. Which space should I have between linear block?


    Thanks for your help.

  2. #2
    Chaz's Avatar
    Lives in Ickenham, West London, United Kingdom. Last Activity: 20 Hours Ago Has been a member for 4-5 years. Has a total post count of 963. Received thanks 67 times, giving thanks to others 42 times.
    I would recommend putting more strengthening between the left and right profiles that run from front to back.

    The single front and rear ________ beams will only offer some rigidity. Ideally from this shape - | ____ | you want to go to something like O.

  3. #3
    Hello!

    Im certainly no expert but the way I see it you need to think about how you are going to fit your ballscrews..
    They take more room than the linear rails offer and from what I see in the cad there are no spacers or something like that..?

    Skickat från min SM-N910C via Tapatalk

  4. #4
    Also on the Z axis it's stronger to build the rails on the moving plate and the bearings on the stationery side :)

    Skickat från min SM-N910C via Tapatalk

  5. #5
    One thing to watch with that design is that the gantry will need to be shimmed on one side between the gantry and side plates because you have trapped the long X axis rails between the sides of the bed. That is why most people put the rails on top of the profile as the tolerance can then be taken up by slightly over sized holes in the side mounting plate.
    In other words the gantry length will have to be cut very accurately so the side plates are a snug fit into the rail carriages
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  6. #6
    BriceO's Avatar
    Lives in Here, Switzerland. Last Activity: 2 Hours Ago Has been a member for 0-1 years. Has a total post count of 20.
    Nr1madman, you're right there is a space between the linear bearing and the plate. I was thinking to add a 20mm spacer.
    Click image for larger version. 

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    Thanks for your advices, I will do the changes. In my actual design I have a another profile in the middle of the left and right profiles, but I will add more.
    routercnc, nice idea I was thinking that I can order the profile already cutted.

    Thanks everyone ;)

    And what do you think about the linear bearings?

  7. #7
    Your question about linear bearings - do you mean size? If so 20mm on all axes.
    What is the plan on the Y ball screw? It goes straight through the Y and Z axis? With that type of layout some people space the YZ away from the gantry and run the ball screw behind. But this weakens it because of the overhang.
    A more popular design is the L shaped gantry with the ballscrew running behind allowing the YZ to be close into the gantry.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  8. #8
    BriceO's Avatar
    Lives in Here, Switzerland. Last Activity: 2 Hours Ago Has been a member for 0-1 years. Has a total post count of 20.
    Quote Originally Posted by routercnc View Post
    Your question about linear bearings - do you mean size? If so 20mm on all axes.
    I mean which lead should I take, 20 or 10mm lead? I calculated a max speed of 500 IPM, does it seems to be correct? And do I need to have a ballscrew preload ?

    Quote Originally Posted by routercnc View Post
    What is the plan on the Y ball screw? It goes straight through the Y and Z axis? With that type of layout some people space the YZ away from the gantry and run the ball screw behind. But this weakens it because of the overhang.
    A more popular design is the L shaped gantry with the ballscrew running behind allowing the YZ to be close into the gantry.
    I planned to run the ball screw behind the gantry for this axis, but you're right I'll change it for the L shaped gantry.

    For the longest axis, which one is the "best" design?
    Add a spacer to the ballscrew. The ballscrew runs behind the plate and this plate will be near the bearing blocks. Something like this:

    Click image for larger version. 

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  9. #9
    Quote Originally Posted by BriceO View Post
    I mean which lead should I take, 20 or 10mm lead? I calculated a max speed of 500 IPM, does it seems to be correct? And do I need to have a ballscrew preload ?



    I planned to run the ball screw behind the gantry for this axis, but you're right I'll change it for the L shaped gantry.

    For the longest axis, which one is the "best" design?
    Add a spacer to the ballscrew. The ballscrew runs behind the plate and this plate will be near the bearing blocks. Something like this:

    Click image for larger version. 

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    Hmm don't really understand but is "lead" the same as "pitch"?
    Have read a lot about lead on the zone but that seems to talk about trapezoidal screws and not ballscrews?
    Anyway what do you want to cut and in what resolution?

    If you plan on having the ballscrew on the outside of the plate as in the picture then please don't forget that the screw must be longer then the calculated travel as the plate will travel inside the bearings :)

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  10. #10
    BriceO's Avatar
    Lives in Here, Switzerland. Last Activity: 2 Hours Ago Has been a member for 0-1 years. Has a total post count of 20.
    Quote Originally Posted by Nr1madman View Post
    Hmm don't really understand but is "lead" the same as "pitch"?
    Yes, exactly I mean pitch. I would like to cut mainly wood and a few tests with aluminium.

    My goal is to have a resolution of 0.01 and an accuracy of 0.1mm. I tried to calculate the speed with a hiwin 2020 ballscrew, KL23H2100-35-4B NEMA23 and found a max speed of 500 IPM. Is it possible?

    Here is the specs of the motors (4X):
    Click image for larger version. 

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