Thread: big budget cnc

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  1. #21
    Quote Originally Posted by Desertboy View Post
    I have SBR25 and would recommend that as the minimum for the longest axis and it weighs a ton so I wouldn't want it on my gantry. I'm putting 1.5m 15mm Hiwin clones I got on ebay with 4 carriages for €120 delivered on my gantry to keep the weight down.

    I like my supported rail it's lovely and smooth but it's no Hiwin.
    Thats what i am talking. Its cheap, its not Hiwin but hey, its supported bearing. Thats what i call the real "budget solution". It will work much better than any V and skate bearings. And i have such small machine /V with skate bearing/ from the time when there were no cheap Chinese bearings or machines. And i am telling you this is one of the things in life that have frustrated me most. I dont wish that to anybody. It will go in the museum of Bad engineering
    project 1 , 2, Dust Shoe ...

  2. #22
    Looking at the dimensions more, i can only repeat earlier comments - this is not a machine for what is called "plates and skates" motion - ball bearings running on steel plates. It works reasonably for small stuff - my first plasma cutter was plate & skate but it jammed a lot due to crud on the plates and it was only 650x650mm, over a length of 3000mm the motion will not track square or level.

    This would be a big machine, heavy and expensive I feel, it will need to be if it is to do any sort of work at all. If it were me building big, I would be looking at ball screws, 25mm linear rails, 750W servo motors at least, and a heavy steel frame. I would not even go with the round supported rail at this size. Just my thoughts of course. :)

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  4. #23
    Quote Originally Posted by Davek0974 View Post
    Looking at the dimensions more, i can only repeat earlier comments - this is not a machine for what is called "plates and skates" motion - ball bearings running on steel plates. It works reasonably for small stuff - my first plasma cutter was plate & skate but it jammed a lot due to crud on the plates and it was only 650x650mm, over a length of 3000mm the motion will not track square or level.

    This would be a big machine, heavy and expensive I feel, it will need to be if it is to do any sort of work at all. If it were me building big, I would be looking at ball screws, 25mm linear rails, 750W servo motors at least, and a heavy steel frame. I would not even go with the round supported rail at this size. Just my thoughts of course. :)
    I'm planning an 8*4 machine next for wood only and I was going to use SBR25 and I'm sure it would be very nice but the price of HIWIN 25mm from cnc4you (About 50% more) means I'll just go with 25mm Hiwin on X&Y and 20mm for the Z.

    I costed it at ~1500 delivered from cnc4you for
    2*2.7m HIWIN
    2*1.6m HIWIN
    2 * 2005 2.6m ballscrews with fittings
    1* 2005 1.6m ballscrew with fittings

    but I think I would want to fit a minimum 2510 (Or 2520) ballscrew for the gantry and R&P for the long axis (So I can do a dual gantry, independent drive).

    R&P gets a bad rap but I've seen some very accurate setups out there certainly on par with the C7 ballscrews I would buy and with ballscrew mapping I'm sure well within any tolerances I would ever need with such a machine.

  5. #24
    For your HiWin, look into AliExpress, guy called BST Automation, thats where i got mine from.

    R&P can be done well and is good on long machines - to get good accuracy look to anti-backlash pinions, they are like two pinions with a spring twisting them apart so the tooth is under tension all the time.

    To check what screw, look at the speed/whip rating, longer they go the thicker they need to be, you can also tension the screw to stop whip.
    Last edited by Davek0974; 25-06-2017 at 12:24 PM.

  6. #25
    Just as a side note - 20 size Hiwin for all axis is ok. No need for 25 size. Ball screws: 1605 for the Z, 1610 or faster for the X, 2510 or faster for the Y and A long ballscrews and rotating nut setup. I dont see a point for faster ball screws though than xx10 for a Do-ALL-Machine
    project 1 , 2, Dust Shoe ...

  7. #26
    pet30's Avatar
    Lives in antwerp, Belgium. Last Activity: 3 Weeks Ago Has been a member for 0-1 years. Has a total post count of 24. Received thanks 1 times, giving thanks to others 0 times.
    Very interesting

    https://www.youtube.com/watch?v=fwbkWM0mWfs

    what are your opinions for this type of linair rails? could i use them

    my budget was about 2000€ but i think i will need a lot more.

  8. #27
    Quote Originally Posted by pet30 View Post
    Very interesting

    https://www.youtube.com/watch?v=fwbkWM0mWfs

    what are your opinions for this type of linair rails? could i use them

    my budget was about 2000€ but i think i will need a lot more.
    Looks a lot better than makerslide but still not proper rail! If you want actual production you need to expand you budget

    I think if you double the budget you could build a very decent machine
    Click image for larger version. 

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  9. #28
    That rails could be good for a month, but will need constant tweaking later. Its a better solution than roller bearings or V rails but... I dont know how you value your time but when actually working, any hit and miss day will cost you hundreds of $$$ missed profits.

    My opinion again is to buy used machine, some times people from forum sell good ones. or pay sb to do it for you and start making money from day 1. Yes i build my machine, but it was a do-all-extraordinary and if i have to buy similar i have to pay more than 20k for it so there was a reason for the wait. But for pure woodworking, i wouldn't think twice and buy even Chinese, so to start making money faster
    project 1 , 2, Dust Shoe ...

  10. #29
    pet30's Avatar
    Lives in antwerp, Belgium. Last Activity: 3 Weeks Ago Has been a member for 0-1 years. Has a total post count of 24. Received thanks 1 times, giving thanks to others 0 times.
    Bying a cnc here is stil 20.000 euro or its a old machine etc.
    I will go for the supported rails not the bearings.

    Now the problem is i still have that big gantry of 3000 mm

    How would you guys make that gantry strong so it don't flex and twist?

    if its really difficult then i have to turn the machine 90 so the gantry is 1600 mm .

  11. #30
    I'd extend the frame a little so the gantry can move out the way completely so you can remove the work piece then it's irrelevant which way the gantry is. If you mount the hiwin's and ballscrew on the sides you can enclose them enough that when you access the piece it's not an issue.

    Go for 1.6m gantry NOT 3m simple any other choice is just nuts.
    Last edited by Desertboy; 27-06-2017 at 08:30 AM.

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