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Lead Screw or Ball Screw

Discussion in 'CNC Mills/Routers' started by Project Hopeless, Jan 31, 2019.

  1. Project Hopeless

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    All things equal which is preferred for the X, Y and Z drives?

    What lead is generally recommended running Nema23 270 or 4XX oz steppers?
     
  2. Giarc

    Giarc Master
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    How long re each axis? If 1000 mm or under I would use the 8mm lead screws. Ball screws are great, but then you need to modify things. That is no problem if designing from scratch.
     
  3. CNCMD

    CNCMD Veteran
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    Once you go ballscrew you will never go back!
     
  4. Project Hopeless

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    I'm looking at a 1200-1300mm stroke booth X An Y.

    I have seen some relatively inexpensive rolled/forged ball screws online. My thought is the ball screw would have similar back lash and more efficiency than an Acme screw with backlash nut.
     
  5. CNCMD

    CNCMD Veteran
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    Everything has backlash, there is no escaping that. However, a ball screw will have consistent backlash, versus running some plastic anti-backlash nut. The ballscrew is a more robust depending on what we are comparing to. Many run 8mm leadscrew, versus 16mm ball screw.
     
  6. Rob Taylor

    Rob Taylor Master
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    I'm looking at similar lengths of 1605 ballscrew at the minute. Very inexpensive, and IIRC backlash on the regular ones should be consistently around 2 thou/0.05mm, and on the repacked-ball "antibacklash" ones should be under a thou (at the cost of slightly higher wear and/or more stringent lubrication requirements). Or maybe 4 thou and 1 thou, I forget now. It's that kind of relationship, anyway, and it's far smaller than leadscrew, which is why leadscrew typically isn't used for CNC machines- it's easy to take up backlash when manually cranking and measuring single axes, but lash is hard to deal with in a high-speed system.

    It's sometimes hard to find the antibacklash ones in all sizes and lengths, but for a typical extrusion machine it's probably somewhat irrelevant. The ones I got for my mill conversion were all antibacklash though. Technically you could buy whatever and then repack the balls yourself, it's just a bit of tedious small-scale work.
     
  7. Project Hopeless

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    The ball screws I’m looking a claim to be anti backlash. RM1605, C7 standard.

    My first build is a CNC router for wood and plastics so I can accept a couple thou backlash I think.

    If I’m lucky maybe it will work with aluminum.
     
  8. CNCMD

    CNCMD Veteran
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    Those are fine. You will have close to no backlash, and depending on everything else, you will be able to cut aluminum. Check out my build, its a ball screw based machine.
     
  9. Project Hopeless

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    Wow, very nice. That level of build detail is very helpful for a beginner like me. It helps a lot to visually see how it all goes together.

    I can't seem to find a reference table for stroke lengths. On a typical 1500mm ball screw SFU1605 or RM1605 is the stoke 1500mm?
     
  10. CNCMD

    CNCMD Veteran
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    No, not even close. There is a good amount that goes into what your asking.

    You need to know the actual length of the threaded ballscrew section. There is/are parts of the ballscrew that are included in the overall length that are not usable in calculating the stroke. There are parts that sit in the bearings, and then a piece that extends out to connect to the coupler.

    When your asking about stroke, are you asking the working area/cutting area, as that would depend on lots of things.
     
  11. Project Hopeless

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    I found some drawings for another make, I think I'm good.

    The math says 1500mm should get me ~1338mm of travel with 2x lead reserve both ends. I'm targeting 1245mm (49 in.)

    The education continues!
     
  12. Rob Taylor

    Rob Taylor Master
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    Yeah, the two machined ends and the length of the nut have to be taken away from the distance. In total it should be right around 100mm for 1605s (I just measured one, but prints are available in some online listings). Minus the 20mm for thread reserve and you should be right near 1380mm, +/- a couple millimeters.

    Obviously that's dependent on a) your rail length and carriage spacing, and b) other interfering parts of your machine.
     

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