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  1. #25
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    Default Re: CNC router build

    Hi....that only applies if the bearing blocks on each rail under the table are closer together in the Y axis length......... the spindle has to cover the table Y travel length, the closer together they are on the rails the more unstable they would be, one reason to design with the table long and across the Y axis and short in the up and down length.

    Then a 400mm wide table Y move would need 800mm long in the base as opposed to 1200mm if the table was longways in the Y.....but you can reduce the spacing a smidgeon and get 700 for the wider table design........ not very practical

    This also has it's drawbacks, as now the table bearing block aspect ratio is out of proportion to slideway length/travel formula.

    That is, for a slide way to be a guiding factor it must be longer than wider....a wide table can overcome this to a degree by spacing the rails closer together, but also spacing the blocks on each side further apart in the long configuration.....then you have to have the double length to cover the travel.

    In the end it will be realised that massive cutting forces are not in the picture, so the rail and block spacing becomes a matter of convenience.......I would say though, that if you have the space go for the double length in whatever configuration the table is.

    If you wanted to very pedantic, you could use rails that are a smaller profile but use two of them on each side under the table.(my choice).......that gives you the long slide aspect ratio and apart spacing in one nut shell, also the smaller size brings the overall height down making the table more stable.

    I doubt whether the different slide design factor will put any moving table CNC router light years ahead than if you followed conventional design, it's a matter of personal preference, but you can strive for perfection if that is your whim.

    One very big advantage of the moving table design, and why I like it so much, is with a single central ball screw there can be no slewing of the table when the spindle is to one side as happens to the gantry on a moving gantry design, unless 2 ballscrews are used, either coupled or with 2 stepper motors.
    Ian.



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    Default Re: CNC router build

    Quote Originally Posted by A_Camera View Post
    There are two screws in each bearing to remove the play. Mine are 16mm but I can NOT feel any movement and definitely no distortion.
    I have removed the play with the screws. But what i have found is that if i put pressure on the tool then the bearing block's actually give way/open up...



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    Default Re: CNC router build

    Quote Originally Posted by handlewanker View Post
    Hi....that only applies if the bearing blocks on each rail under the table are closer together in the Y axis length......... the spindle has to cover the table Y travel length, the closer together they are on the rails the more unstable they would be, one reason to design with the table long and across the Y axis and short in the up and down length.

    Then a 400mm wide table Y move would need 800mm long in the base as opposed to 1200mm if the table was longways in the Y.....but you can reduce the spacing a smidgeon and get 700 for the wider table design........ not very practical

    This also has it's drawbacks, as now the table bearing block aspect ratio is out of proportion to slideway length/travel formula.

    That is, for a slide way to be a guiding factor it must be longer than wider....a wide table can overcome this to a degree by spacing the rails closer together, but also spacing the blocks on each side further apart in the long configuration.....then you have to have the double length to cover the travel.

    In the end it will be realised that massive cutting forces are not in the picture, so the rail and block spacing becomes a matter of convenience.......I would say though, that if you have the space go for the double length in whatever configuration the table is.

    If you wanted to very pedantic, you could use rails that are a smaller profile but use two of them on each side under the table.(my choice).......that gives you the long slide aspect ratio and apart spacing in one nut shell, also the smaller size brings the overall height down making the table more stable.

    I doubt whether the different slide design factor will put any moving table CNC router light years ahead than if you followed conventional design, it's a matter of personal preference, but you can strive for perfection if that is your whim.

    One very big advantage of the moving table design, and why I like it so much, is with a single central ball screw there can be no slewing of the table when the spindle is to one side as happens to the gantry on a moving gantry design, unless 2 ballscrews are used, either coupled or with 2 stepper motors.
    Ian.
    Ian, thank you for the information. I will work on a drawing and post it here sometime...



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    Default Re: CNC router build

    My mate sent me a pic of the gantry beam and other bits he cut..



    Attached Thumbnails Attached Thumbnails CNC router build-cncbuild1-jpg  


  5. #29
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    Default Re: CNC router build

    He started doing some welding today...

    Attached Thumbnails Attached Thumbnails CNC router build-cncbuild2-jpg  


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    Default Re: CNC router build

    Hi everyone....i am looking at linear rails and ball screws at the moment. Has anyone bought Hiwin rails and carriages from BST Automation? If so was it genuine HIWIN??
    Also the ball screws that Bst sells....are they reasonable quality?

    Thanks



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    Default Re: CNC router build

    Yes... Rolled or ground and to what standard ordered.
    I have dealt with Fred at BST over the last 4 - 5 years. His factory details Chinese Manufacture for Linear Guide,Ballscrew,Linear Rail & End Support etc.??Zhejiang BST Linear Motion Co.,Ltd as opposed to the https://www.aliexpress.com/store/314742 .
    Send Fred an email, he will respond. The silly question is the one you don't ask. If you have requirements for accuracy and item life tell him, ask his advice. But from experience your tool run out and frame stiffness will be more than the free play in the rails.
    Rule of thumb ..add another truck ( three instead of two with extra space between the trucks so as not to align with the bolt spacing of the rails. )
    Good luck mate

    Paul



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    Default Re: CNC router build

    Thanks Paul



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    Default Re: CNC router build

    Update.....i have decided not to continue with the steel framed machine. My mate will continue it for himself. The machine will be too heavy for my use, plus the size was going to be too small for me. He was going to make the same for himself anyway... Well i decided to go with my original idea of an aluminium framed machine. I ordered 160 mm x 80 mm and 80 mm x 80 mm heavy duty extrusion today. Will post some images soon as i receive them. They will be cut to size and i will use my cnc machine to make the holes for the fasteners...



  10. #34
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    Default Re: CNC router build

    Received the frame parts today. I am very happy with the quality and service


    Attached Thumbnails Attached Thumbnails CNC router build-cnc-jpg  


  11. #35
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    Default Re: CNC router build

    Update, the machine stand is welded up....ready for cleaning and painting. Also bought the adjustable feet for the stand and machine today. Hopefully i will complete work on the stand this weekend and start machining the extrusion and foot plates next week

    Attached Thumbnails Attached Thumbnails CNC router build-img20170929161057-jpg   CNC router build-img20170929161050-jpg  


  12. #36
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    Default Re: CNC router build

    looks beautifully made!



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