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  1. #13
    Registered flexbex's Avatar
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    Default Re: Choosing the right motor.

    This would be my solution. To avoid bending beam

    Attached Files Attached Files


  2. #14
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    Default Re: Choosing the right motor.

    That works too.



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    Default Re: Choosing the right motor.

    Is the intention to have the z-axis between the two gantry beams? If so, why? If not, what made you design it with two gantry beams instead of one thicker / sturdier beam?

    When I was researching designs for my build, I found one machine with a long z-axis between two gantry beams. It was for very large (8ft x 12ft x 8ft) 5 axis foam carving. I can see how the double gantry beam might help for a very long Z-axis on a 5 axis machine but.... if it was me, for a very long Z, I would lower the whole gantry instead. I don't like large unsupported overhangs...

    Then again, maybe stiffness is less of an issue if you only cut foam and soft wood... I can make 1" cuts in dense rigid foam with a manual hand router...

    This is the 5-axis foam milling CNC I was talking about:

    %5Burl=https://postimages.org/%5D%5Bimg%5Dhttps://s5.postimg.cc/sla0k8kbr/IMG_3962.jpg%5B/img%5D%5B/url%5D

    and a close-up of the gantry beam design:

    %5Burl=https://postimages.org/%5D%5Bimg%5Dhttps://s5.postimg.cc/xjxiyrvuf/IMG_3961.jpg%5B/img%5D%5B/url%5D



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    Default Re: Choosing the right motor.

    Goemon, your links don't work for me, can you fix them?



  5. #17
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    Default Re: Choosing the right motor.

    Quote Originally Posted by Goemon View Post
    Is the intention to have the z-axis between the two gantry beams? If so, why? If not, what made you design it with two gantry beams instead of one thicker / sturdier beam?

    When I was researching designs for my build, I found one machine with a long z-axis between two gantry beams. It was for very large (8ft x 12ft x 8ft) 5 axis foam carving. I can see how the double gantry beam might help for a very long Z-axis on a 5 axis machine but.... if it was me, for a very long Z, I would lower the whole gantry instead. I don't like large unsupported overhangs...

    Then again, maybe stiffness is less of an issue if you only cut foam and soft wood... I can make 1" cuts in dense rigid foam with a manual hand router...

    This is the 5-axis foam milling CNC I was talking about:

    %5Burl=https://postimages.org/%5D%5Bimg%5Dhttps://s5.postimg.cc/sla0k8kbr/IMG_3962.jpg%5B/img%5D%5B/url%5D

    and a close-up of the gantry beam design:

    %5Burl=https://postimages.org/%5D%5Bimg%5Dhttps://s5.postimg.cc/xjxiyrvuf/IMG_3961.jpg%5B/img%5D%5B/url%5D
    Yes for me the links don't work either. So but to the intention of the design. Where I changed my mind also again and tending to the first one. With one long Gantry beam. Because I want the spindle to run as fast as possible on the long axis. With the first design approach I take the weight of the long axis and though it does not take that much force to accelerate and break. Due to this it can run faster. And to my understanding it makes sense to have motors running at different speeds. As I will always make long strokes over the long axis and Z-axis and Y-axis will only be moved slowly and continously. (maybe to avoid confusion the machine has 3-axis one long one I call X-Axis (the Gantry Beam), one shorter one(1m) I call y-Axis and up and down of the spindle I call obviously Z-Axis )



  6. #18
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    Default Re: Choosing the right motor.

    With one long Gantry beam. Because I want the spindle to run as fast as possible on the long axis. With the first design approach I take the weight of the long axis and though it does not take that much force to accelerate and break. Due to this it can run faster. And to my understanding it makes sense to have motors running at different speeds.

    Not sure where you are getting your information??

    It makes no sense to have the motors running at different speeds.

    And design the machine to move as fast as you need it to. The axis along the gantry should not be any faster than the gantry axis itself.

    Gerry

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    http://www.thecncwoodworker.com/2010.html

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    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


  7. #19
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    Default Re: Choosing the right motor.

    I just try to figure out the best way. I am by no mean an expert in CNC. But to my understanding it would make sense when I know before that I have most of the time a router path similar to the attached image. I also read that my intended Software LinuxCNC supports different mottor types. But I am totally open to other opinions as I am a newby and still in the design phase of my CNC. But concerning the costs I think it would be a good idea. I was considering to use a servo motor on the X-Axis and hybrid steppers on the other axis

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    Default Re: Choosing the right motor.

    Your feed speed should be constant for a given toolpath, so you want both axes to have maximum feeds faster than what ever feed rate you choose. If one axis is slower, it will either slow the whole toolpath down to that speed, or vary in speed depending on which direction it's going (which will have surface quality and tool life implications.) Having a faster rapid speed on the much longer axis makes some sense.
    A lighter gantry will lighter cuts, which either means having to go slower or take multiple passes (so negating any speed improvement.) Also it will make cut quality and surface finish worse.



  9. #21
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    Default Re: Choosing the right motor.

    Quote Originally Posted by skrubol View Post
    Your feed speed should be constant for a given toolpath, so you want both axes to have maximum feeds faster than what ever feed rate you choose. If one axis is slower, it will either slow the whole toolpath down to that speed, or vary in speed depending on which direction it's going (which will have surface quality and tool life implications.) Having a faster rapid speed on the much longer axis makes some sense.
    A lighter gantry will lighter cuts, which either means having to go slower or take multiple passes (so negating any speed improvement.) Also it will make cut quality and surface finish worse.
    Ahh sorry for the misunderstanding term lighter gantry. I attached my first design idea to hopefully clarify things. In this design only the z-axis carrier would move over the long axis. But i would now replace the long beam by maybe two stacked 80x40 Aluminium beams instead of a long steel beam. Hope it makes sense now.

    Ahh and I want to quote the guys I got the idea from. Revolucion Shaping co.

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    Default Re: Choosing the right motor.

    By having the gantry shorter, of course you'll be lightening it, and at the same time stiffening it (assuming the same cross section and material.)



  11. #23
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    Quote Originally Posted by skrubol View Post
    By having the gantry shorter, of course you'll be lightening it, and at the same time stiffening it (assuming the same cross section and material.)
    Ahh ok got it. Sure the shorter gantry is more rigid and lighter then a long one. But in my case with the long gantry the weight of the gantry isn't that important. As the only fast moving part is the spindle carrier on the gantry.
    So my conclusion would be long gantry is good enough for easy to cut material like foam and the short gantry version is more universal as I also can cut harder material.
    Does that sound right?



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    Default Re: Choosing the right motor.

    Quote Originally Posted by flexbex View Post
    Ahh ok got it. Sure the shorter gantry is more rigid and lighter then a long one. But in my case with the long gantry the weight of the gantry isn't that important. As the only fast moving part is the spindle carrier on the gantry.
    So my conclusion would be long gantry is good enough for easy to cut material like foam and the short gantry version is more universal as I also can cut harder material.
    Does that sound right?
    If you're only doing 3d parallel toolpaths that's probably about right. Problem is that for most parts roughing toolpaths are not parallel and want to follow X-Y contours of the part you're cutting, which may go in either the X or Y direction (or anywhere inbetween.) The same holds for 2.5D toolpaths.
    Foam you may be able to get away without even doing a roughing toolpath, so it would probably be ok for that.



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Choosing the right motor.

Choosing the right motor.