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  1. #1
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    Nov 2020
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    3

    Input on DIY budget machine

    I am in the planning stage of building a machine on a student budget.
    Before starting building I'd like some input from people more experienced than me, this will be my first machine.

    Build area is approximately 200*400*225mm.
    I'd want it to be as capable as possible, but I will mostly cut aluminium or softer materials.

    The machine would probably be made of mostly 20mm aluminium, it would be really difficult for me to work on steel, I also do not have the ability to weld.

    I am planning to use a 2.2kw china spindle and HGR20 linear rails, used name brand ones, or generic new ones.

    Motors would be 3nm Nema 23 stepper motors driving ball screws.

    Id like to keep as many doors open as possible, I won't use flood cooling to start, but would want the ability to add it later. Will start with mist cooling.

    The rails would be covered by bellows, they aren't modeled in the CAD.

    The stepper motor mounts are not modeled either.

    To increase the mass of the machine the steel beams that make the main chassis could be filled with sand or something else.

    Any input is greatly appreciated!
    Attached Thumbnails Attached Thumbnails Capture.JPG   Capture2.JPG   Capture3.JPG  

  2. #2
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    Dec 2003
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    833

    Re: Input on DIY budget machine

    Why so much Z?I suggest you draw your spindle with a tool in place and then consider the manner in which the motor body will limit access in terms of both depth and width.That exercise will give you a more useful idea of the work that can be accomplished and you may be encouraged to reduce the Z axis,and consequent loads, by an amount.This automatically gives a stiffer machine.You may need a few more posts before you can post an image of your proposed machine and it will be useful to see it.

  3. #3
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    Nov 2020
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    Re: Input on DIY budget machine

    The z is simply to fit larger materials in the mill. I attached 3 images but they might not be showing. Here is an imgur link instead: https://imgur.com/gallery/4jzHNRs

    The stiffness should only be affected while I actually use high z as it is a fixed gantry design.
    Last edited by Noppishen; 11-25-2020 at 01:33 AM.

  4. #4
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    Dec 2003
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    833

    Re: Input on DIY budget machine

    Distance from tool tip to motor body limits the depth you can machine to from the top surface.Which looks like about 60mm.Nice to see an enclosure has been thought through at an early stage.I get a bit nervous about too much coolant around what is basically a router motor.Do you have any experience of high speed machining of metals?

  5. #5
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    Nov 2020
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    Re: Input on DIY budget machine

    I don't plan on flood cooling any time soon, would probably cover the motor in some way if I did that. I won't use much z while actually machining but the extra height can help if the raw material is kinda large, ~60mm is plenty. Do you think the design is sturdy enough? I don't have any prior experience, will work up slowly to metals, but of course the design must be able to take it. Thank you so much for your input.

  6. #6
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    Join Date
    Nov 2009
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    14

    Re: Input on DIY budget machine

    If the raw material is "kinda' large, consider that it will also be (a) exceedingly expensive and (b) exceedingly heavy. I don't think you're ready for either of those.

    Count on real-world workpieces being no larger than about 70mm in height, then add the spindle / collet length plus the length of a jobber-length drill bit or edge finder. Limit your Z to that. 98% of the wear in your ways and drive system will occur within about a 30mm section of their length because all your real-world work will be very nearly the same height.

    Your X axis will want to be much, much larger than your Z axis.

    Given that such a machine will have limited rigidity... your proposed 2.2KW spindle is huge overkill. You aren't likely to actually use any more than about 0.5KW in actual practice.

    Given the sale of the machine, single-lead trapezoidal (Acme) screws will give you greatly increased precision and torque and wear characteristics and won't tax your NEMA 23 steppers nearly as badly. The tradeoff there is slower traverses, but unless I miss my guess precision is more important in this case than traverse speed is. With single-lead trapezoidal thread screws, you may be able to downshift to NEMA 17 steppers with no loss in performance.

  7. #7
    Gold Member
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    Apr 2004
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    5218

    Re: Input on DIY budget machine

    This doesn't look too different from many of the mini-mill designs out there. I think you should stick with the NEMA 23 motors, but use a different kind of spindle. Those Chinese 2.2KW spindles run too fast for metals; I'd suggest using a regular induction motor and a pulley cluster to reduce the speed while gaining torque. The extra range in Z doesn't seem like a big problem to me, since the Z axis seems pretty well-supported. It's not clear what you're building the main column and base out of, but heavy sections of steel tubing would work best. You wouldn't need to weld it, and it's both cheaper and stiffer than aluminum.
    Andrew Werby
    Website

  8. #8
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    Jul 2018
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    2357

    Re: Input on DIY budget machine

    Hi Noppi - Your Z axis rails are mounted on "air" these will vibrate. There are a few small mill threads in the forum I suggest you read through these. Your current sections are not stiff enough or thick enough for milling effectively. Look at the Milli thread its all about getting a benchtop mill stiff enough... you may be better off starting with a small cheap mill and add CNC to it. By the time you get the frame all done (and generally DIY they are under rigid especially your first one and especially when you will make student decisions based on cost) you would have bought a small imported mill for the same $$$.

    Then once through the learning curve you can use that to build the better one etc etc...Peter

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