Need Help! Choosing y axis design


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    Default Choosing y axis design

    Hello,
    I need help, I hope someone can help to me. I thinking which y axis designs to choose, I have 3 options:
    1. Ordinary: both rails in one row, example: https://www.workshopaddict.com/forum...d-dsc_0763.jpg
    2. Rails in different places, example: https://idea2reallife.files.wordpres...axis-sbr16.jpg
    3. Like this:

    How you think: which design is best (most stable and most accurate). I will use SBR20 support rails.

    Similar Threads:


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    Default Re: Choosing y axis design

    106 views and no answer. Is there someone who can answer to my question: which (1-3) design is most stable and most accurate?



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    Default Re: Choosing y axis design

    I'm also in the planning stages of building a CNC and the Y axis design was something that took me a while to decide on.
    Firstly, if accuracy and strength is your goal, I would consider using square support rails instead of round.
    As for the 3 design options, I think if the right materials are chosen and you take your time with aligning everything, making sure everything is square, neither design is better than the other as far as strength and accuracy is concerned. In my opinion the 3rd design is the easiest and cheapest option when building your own CNC, but I'll be building my CNC using design 1 because unlike designs 2 & 3, the rails are not facing upwards which is bound to catch allot of dust while cutting. I also prefer design 1 over design 3 because you don't have reach over or through the Y axis supports when loading and positioning material. With design 1, it's possible to design your X axis so the spindle can travel past your gantry risers without clashing, allowing you to utilise the full width of your bed.

    [Edit] I forgot to mention (probably because I'll be driving my Y axis using rack & pinon) but design 1 is the only design that allows you drive your Y axis with a single motor/ballscrew.



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    Default Re: Choosing y axis design

    Yes, I know that square support rails would be better, but HIWIN is too expensive to me right now Ok, thanks, so in first place is design number 1 X axis will be 1900mm, Y axis 1300mm and z axis 500mm

    By the way, thanks for your answer



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    Default Re: Choosing y axis design

    More info: cnc frame design will be like in that video ( ), so now I'm thinking about Y axis design



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    Default Re: Choosing y axis design

    I too am doing design 1, however i like design 2, i just cant articulate why...
    I realise this is of no help, sorry!



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    Default Re: Choosing y axis design

    I like design # 1 myself. In any event you need to think about manufacturability of your machine. If the design you choose keeps the rails in one plane then you greatly reduce the complexity of your build.

    The complexity comes from developing a flat surface to mount the rails on that keeps them in the same plane. On design one this can be done via machining or some of the other methods often discussed here like Epoxy leveling. Design #2 is especially bad because you need to mount the top rail on a plane that parallels the other rails mounting surface precisely. Oh #2 arrangement also requires that the top surface that the rial is mounted to is also parallel to the lower rail. As for design #3 the big problems there are two things in my mind. The rials up orientation creates a channel to collect junk and it adds unneeded complexity to the Y axis saddle which will support the X axis.

    In a nut shell when looking at machine designs you need to ask yourself the question "how will I build this". This includes what you can DIY and what you might have to farm out. Also due to the size of these machines farming out work to a machine shop isn't always cheap, especially if you have work that needs to happen on a bigger mill. BridgePort type milling machines are a dime a dozen around here but they really aren't that useful when it comes to machining large gantry beams so all your friends with Bridgeport mills aren't much help.

    In any event #1 is the only viable design approach in my mind. The more you think about it the more the others have design considerations that suggest they aren't the best approach.

    The other thing that bothers me about the selected pictures is the lack of attention to the beam cross sectional size. A fairly large beam , in cross section, is generally your best bet. Stiffness is so important when it comes to getting good machining results and should be the primary driver of your design process. In a couple of those pics there really doesn't appear to be much of a beam at all.

    Last edited by wizard; 01-14-2017 at 01:30 AM.


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    Default Re: Choosing y axis design

    Design 1 is better I think. The machine in the video I don't think will be very rigid. It would help a lot if the square tubes on the gantry had braces welded between them. Then they would act like one single structure and be more rigid, like Design 1.



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    Default Re: Choosing y axis design

    Thanks for all answers! I don't want to make new threat, so I will write in this topic. So: Y axis will be like design #1; cnc size: X axis 1900mm (Ballscrew 2005 and SBR20 from both sides), Y axis 1300mm (Ballscrew 2005 and SBR20), Z axis 500mm (Ballscrew 1605 and SBR16), stepper motors Nema34 1600oz.in. Frame design similar to frame like in this video:

    *What forum members think about this design?
    *What do you think: which steel profile size to use: a.) 70x50mm wall thickness 2mm; b.) 80x60mm wall thickness 2mm; c.) 80x60mm wall thickness 3mm. Or maybe all profile sizes is too small?



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    Default Re: Choosing y axis design

    1600oz steppers are a very bad choice. Using them with 5mm ballscrews is even worse choice. The machine will be very slow.

    Use 2010 or 2025 ballscrews, and 600-900oz motors.

    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

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


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    Default Re: Choosing y axis design

    Thanks for answer 1600oz is about 12 Nm Holding torque, so if speed increase the real torque decrease; I want to mill hard wood, aluminum and sometimes steel, so if motors would be weaker (600-900oz) can they do the job with harder materials (hard wood, aluminum)? Of course speed is important, but if speed is increasing does precision decrease?



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    Default Re: Choosing y axis design

    You won't be cutting steel with that machine - you don't have the right spindle or enough rigidity - aluminum would be questionable. Speed is important for cutting wood; if you go too slowly, the tool starts scorching the wood, leaving dwell marks. High-torque motors tend to have high inductance, which requires more voltage to overcome. But the drivers won't tolerate too much voltage. With any given motor you can increase torque by using finer screws; that gives you more precision at the expense of speed.

    Andrew Werby
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