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LINEAR RAIL SPHINX 55 (Blue OX plates)

Discussion in 'CNC Mills/Routers' started by that-jim, May 2, 2020.

  1. Steve Hall

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    Hi That-Jim,

    I have been looking at your build and I am currently starting my own build of a similar nature.
    Apolgies for quoting metric, are you using 4080 C beam extrusion.
    If so, what size of ball screw and nut did you use as I am struggling to find ball screw flange nut that will fit in the 40mm space of the extrusion.

    Thanks - WoodKnot
     
  2. that-jim

    that-jim Journeyman
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  3. Steve Hall

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    Thanks JIm -
    I thought i may get away with a thicker ball screw than that?

    However, now i have seen the simplicity of the nut, i may still be able to use my 16mm screws and get something machined up in the UK?

    Thanks

    Steve
     
  4. that-jim

    that-jim Journeyman
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    I don't think that the nut for a 16mm ball screw will fit in the c-beam, perhaps if you build a custom nut block. The other consideration is the pitch of the screws and the motor/controller you plan to use. The openbuilds leadscrew, c-beam, motors and black-box are a plug and play type of solution.
     
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  5. Rhett E

    Rhett E Well-Known
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    What would be the benefit in utilizing ball screws instead of lead for this machine? Speed, accuracy, etc...? Would the cost and labor justify the change?
     
  6. Rob Taylor

    Rob Taylor Master
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    Speed/acceleration, mostly. much lower friction for a given level of backlash. Can run smaller motors because less power is lost as friction. Price isn't that much different any more, ball screws got really cheap.

    Backlash can be just as substantial as lead screws though; DFU nuts are required to get almost-zero-backlash operation, which is particularly important if you're using a control that doesn't provide even basic single-value backlash compensation, like grbl. So that costs more. Some vendors offer "anti-backlash" screws which is where the nut's been emptied and repacked with slightly oversize balls, which take up more room between the two channels and allow for less "slop". They do help, but they're not magic.

    Accuracy/precision is largely the same as lead screws; "C7" doesn't really mean anything, once you've actually mapped screws you see that the true pitch varies wildly as you move along the screw, which is almost certainly the case for any rolled screw, leadscrews included. Ground screws (ball- or lead-) cost serious money though; you could build an entire machine for the price of a couple of ground screws. There are happy mediums, of course, C5, C3, etc. You get meaningful precision guarantees then.

    If you're unsure, want to use off-the-shelf OpenBuilds type products more or less as-intended, and don't want to deal with any additional work combating backlash, lead screw is probably the way to go. If you want significantly higher performance, the possibility of far higher rigidity and power put into the tool instead of the machine (12mm and 16mm screws are enormous compared to 8mm), and are willing to build your machine to the specifications required to actually use that additional performance without simply bending your machine frame, then ballscrews are awesome.
     
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  7. that-jim

    that-jim Journeyman
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    Good quality ballscrews will be more accurate but the openbuilds lead screws are really very good and appropriate for a build like this. the lead screws also work well with the openbuilds motors and controller and are easy. I was plenty happy with the lead screws for this build.
     
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  8. Rhett E

    Rhett E Well-Known
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    Thank you both for the responses. I currently have a lead 1515 but I'm looking to downsize the footprint. I'm leaning towards modifying it similar to this setup and still utilizing my blackbox and other parts.
     
  9. Redouane Saidi

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    Brilliant build, Thank you.
    Would it work if I were to make it bigger, using 1000mm C-Beam Extrusions? I'm worried about the deflection of the gantry by the weight of the spindle and Z-Axis
     
  10. that-jim

    that-jim Journeyman
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    My guess is that at 1000mm wide it would be reasonable for wood and plastics similar to a lead 1010. I built this at the smaller size because I primarily wanted to use it for aluminum and it works good for that. If you are planning on a large spindle and or cutting metal you might look at something like the double beam on the 1515 or some other reinforcement.

    Someone might post a reference to how to calculate deflection, so keep in mind that the above are my un-engineered opinions.
     
  11. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
    Staff Member Moderator Builder Resident Builder

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    Redouane Saidi likes this.
  12. Redouane Saidi

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    Thank you, I'll do some more research on it.
     

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