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  1. #1
    I thought I'd share my progress on a project that I've been working on for the last few months. I decided that I wanted to build a CNC machine capable of working aluminium. I have an RF45 type mill, but for me, the low spindle speed and limited Y travel make this not ideal for a conversion. I know you can replace the head with a high speed spindle, but I'd rather keep this machine as it is with the gearbox, still suitable for steel and manual work like using big diameter drills in steel.

    It was pretty clear that I'd want a fixed gantry design because stiffness was more valuable to me than a very large working envelope. I thought for a while about using an old surface plate as the base, but given I wanted an X and Y of around 500 and 400mm, this would have needed a surface plate rather larger than the 24" square ones that usually turn up on eBay.

    So I decided to go with a welded steel construction. I'm fortunate to have access to Solidworks through my day job so I used this to do the design work. Unfortunately I didn't take pictures of the various iterations but the current state of the CAD is like this:

    Click image for larger version. 

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    My concept was to fabricate the machine in sections that could be welded, machined where necessary, and then bolted together in ways that would give enough adjustment to allow for the distortion from welding.

    For the linear motion parts I went with cheap Chinese HGR20 rails and bearing blocks, and RM1605 rolled ball screws. I figured if these don't work well enough or last long enough I can replace them with Hiwin parts at a later stage.

    The motors are all NEMA 24 hybrid closed loop steppers from stepperonline, driving the ballscrews via 15mm wide HTD toothed belts. The X and Y are 1:1 and the Z is 1.5:1 to help with the expected weight of the spindle.

    The gantry itself is a 160x80x5 steel tube with a 60x60x5 tube welded to the back to make it into an L shape, and the rest of the frame is mostly 60x60x5 tube with some 30x30x3 for cross bracing.

    A lot of the aluminium came from a large enclosure that came from the company I work for. The enclosures are meant to contain an internal explosion so they're very thick. It was a lot of work to cut the enclosure up and turn it into usable pieces, but I probably saved quite a few quid in metal. Also, the base of the enclosure happened to have a cast in pattern of ribs that I was able to fit between the bearing blocks, so hopefully this will make for a pretty stiff table.

    So as to avoid making a super long post I've attached a few pictures of the progress so far and I'll attach more pictures in a subsequent post.

    Starting with the Z axis:
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    Then the gantry:
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    Click image for larger version. 

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    Bringing the Z axis and the X axis together:

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    Hopefully this is all interesting to someone!

    Oliver
    Last edited by ollied1981; 27-10-2021 at 10:21 AM.

  2. #2
    The table was basically too big for my mill and a real challenge:

    Click image for larger version. 

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    The Y axis rails were also too big for my machine and needed multiple fixturings. This was a recurring theme:

    Click image for larger version. 

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    Motor mounts and belts for the X and Z axis:

    Click image for larger version. 

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    Mocking up the Y rails and screw:

    Click image for larger version. 

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    My friend kindly offered the services of his welding table:

    Click image for larger version. 

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    Then I painted it to match my car:

    Click image for larger version. 

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    Making Z square to X:

    Click image for larger version. 

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    Adding mounts for drag chain:

    Click image for larger version. 

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    And bringing it all together:

    Click image for larger version. 

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  3. #3
    Looking good so far. Looks like there is some adjustment on the upper gantry (I see some plates and holes) ? That will help with alignment.

    For the rear uprights which are near each other - wonder if it would be worth plating the outside and inside of them to form one larger box, especially if overlapped down onto the main frame. These form the stiffness of the gantry support, so worth a thought for not much effort ?
    Click image for larger version. 

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    Keep the photos coming, looks like you are well kitted out to get it done.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  4. #4
    Hi Routercnc,
    Yeah I knew the frame would bend a lot with welding so wanted to allow for alignment of the gantry. I've got M16 bolts in 18mm hole, and have some jacking screws between the gantry and the frame to shift it about before tightening the M16 up hard. This actually worked really well.

    You're right about the plates at the side. This would be a bit harder to do now because I've built an enclosure around the thing that I'll post some pics of later, but I might go back and add the plates at least on either the inside or the outside of the vertical tubes at a later stage if it seems like it needs it 🙄

  5. #5
    Making Z square to Y and X square to Y:

    Click image for larger version. 

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    I got some custom made bellows from AliExpress for the Y rails and the gantry. I've made something to cover the bottom of the Z axis rails up from some flat rubber sheet:

    Click image for larger version. 

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    And I've made a lightweight polycarbonate enclosure to try and catch some of the chips. It just sits in some aluminium rails fixed to the sides. I wanted something that would be easy to remove to give good access for working on the table:

    Click image for larger version. 

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    This is as far as I've got as of today. I've got the stepper drivers hooked up to an Arduino running GRBL, and the machine moves with gcode from Universal Gcode Sender on a laptop. I made a short video of it working here https://www.youtube.com/watch?v=I5fmULRv4vA

    So now I'm waiting for a spindle to come from China, and a Mesa 7i96 to come from the USA. I want to try and get the thing working with linuxcnc in the end. GRBL does work but it seems to have quite a few limitations. On the other hand it was almost free!

    Oliver

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