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Own-Build Design Advice

Discussion in 'CNC Mills/Routers' started by SamanthaJaneyCake, Jun 10, 2019.

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3x 2020 in shown assembly is okay?

Poll closed Jun 17, 2019.
  1. Yes. 3 lengths well spaced should do

    0 vote(s)
    0.0%
  2. No. 2x 4040 is better

    1 vote(s)
    100.0%
  1. SamanthaJaneyCake

    SamanthaJaneyCake Well-Known
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    Hi all, new to the forum and happy to be here!
    I'm working on my second CNC, had to leave the first at my parent's when I moved country for work. It was a Root 3 CNC (Root 3 CNC multitool router 3D printed parts by sailorpete) and while not the best build, with a good number of design flaws, I noted that it used a total of 4x 2020 extrusions and I saw no real issues with sagging or dipping, suggesting to me that for the light milling I intended, it was strong enough. It cut 750x1000mm

    Now, my new CNC is meant to be a light 400W indoor build (as I live in a block of flats and don't want to drive my neighbours insane) with an enclosure and such, and meant to mill just wood, plastic and ply.
    I just wanted some advice/reassurance about using 2020 v-slot in the X axis. I plan to use 3 lengths at ~750mm long, two of which are vertically aligned and which the Z gantry runs along, the third is offset backwards in order to add more rigidity but isn't used for motion.

    I'm planning to get the gantry plates milled out of 6mm aluminium so you can understand why I want to be quite sure before I order them up, but for the same reason I should have decent strength/rigidity:mass.
    The extrusions would be bolted through into the centre and with multiple right angle braces around them. I also plan to use xtreme mini wheels.

    The other option I'm considering is 2x 4040 instead, no third brace.

    I'm attaching a screenshot of the assembly so far. As you can see they're a good 175mm apart so my lever arm is nice and long, plus I'm quite happy with the loading. I'm kind of just looking for some reassurance from the more experienced!

    Thoughts, anecdotal tales and advice welcome, thanks! :)
     

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  2. SamanthaJaneyCake

    SamanthaJaneyCake Well-Known
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    P.S. The Root 3 CNC also uses 2020 box section on the longer Y rails too, which seemed to work just fine. That said, I have 2040 extrusion I was planning to use for those anyway.
     
  3. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    Honestly, it's hard to say as no one here has built one that lightly. Assuming the sections shown in the design are 20x20x3mm thick, the 2020 v-slot will only offer about half the stiffness those sections have to offer so it won't even be close to the same machine. The 4040 v-slot would obviously be a better choice as it has probably 15x the stiffness of the 2020.
     
  4. SamanthaJaneyCake

    SamanthaJaneyCake Well-Known
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    Hi Rick, thanks for your insight! Yes, it’s a lot lighter than a lot of the designs here, but maybe more heavy than most on Thingiverse. I’ll give it more thought but I think you’re right that it would be worth upgrading to 4040. It would also allow me to use more wheels and spread the load.
     
  5. GrayUK

    GrayUK Openbuilds Team Elder
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    Hi.
    SamanthaJaneyCake Welcome.

    Is it light because you want it to be portable and carry it around? :rolleyes:
    Otherwise, why worry so much about keeping the aluminium so small?
    Extra costs of more substantial extrusion are so small compared to the benefits of, stability and stress endurance, to be gained.
    Openbuild machines designed and promoted here are, in reality, quite light as defined by the Hobby label.
    So before you commit to a design, have a good look around the site and remember, small can be very strong if the right framework is used. :thumbsup:
    Gray
     
  6. SamanthaJaneyCake

    SamanthaJaneyCake Well-Known
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    Hi Gray, thank you!

    It’s “light” because I don’t intend to do anything too arduous with it, it’s meant to be just a low powered hobby machine and I’m not going to work it too hard. My previous one used a 700W router as the spindle and was situated in the log shed and you could hear it down the street. I live in the middle flat now so I need to keep noise down and space is a premium! I’m planning to use the top of the enclosure as a table...

    My main worry with the size here and keeping it so small is to try and minimise the dead space (as a premium) but the extra 20mm for that is really not much in the grand scheme of things. And yes, I can get 2x 4040 is about the same price as 3x 2020 so cost-wise it balances out. I can also get 100x Xtreme wheels for 40 quid so that’s good too.

    I’ve taken a good look around and continue to do so at every stage of the design process. I’ve always designed my own machines be they 3D printers (for myself or companies) and my own electric bike/motorbike. It’s a joy to me, my raison d’être! :)

    EDIT: I also just realised one reason I was aiming to keep it small is to avoid design creep as if I start using bigger profiles I start thinking about the capabilities of the machine. “Why stop there? Why not use 150Ncm NEMA23s instead of 65Ncm NEMA17s? Why should a strong machine cut such a small area? I can cut way larger!” Then I run the danger of making something too impractical for my flat/budget!
     
  7. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    If you're intentionally trying to keep it light consider using a 2040 for the lower member of the high/low scheme you have shown above. That will give you a similar lateral stiffness to two 2020s. I would also consider using 2040s for the side rails. That will give you stiffness similar to an Xcarve, a proven system that many swear by.
     
  8. SamanthaJaneyCake

    SamanthaJaneyCake Well-Known
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    What the screengrab doesn’t show is a third 2020 offset backwards from the lower one by 80mm and I was planning on using 2040s for the longer axes. But if I’m upgrading to 4040 then those’ll go up to 4040 as well, most likely. Or possibly c-beam.
     
  9. SamanthaJaneyCake

    SamanthaJaneyCake Well-Known
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    Upgraded the two rails to 4040. Will be upgrading the longer Y rails to 2060 or 4040 as well.
     
    MaryD likes this.

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