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double z rails?

Discussion in 'Concepts and Ideas' started by James Gao, Apr 29, 2015.

  1. James Gao

    James Gao Well-Known
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    Hey everyone,
    I've been considering ways to stiffen up the carriage on my mini-ox build, and I've been searching for ways to move the spindle closer to the X-rails. Is there any reason why nobody uses this sort of design for the z gantry?
    z_gantry.png
    This eliminates the need for the spacer blocks, moving the whole spindle closer by 12mm. Without spacer blocks, the wheels are also stiffer and can probably bear more compression. This also opens up the possibility of using ball screws or brass lead nuts, since they're typically much thicker than the 12mm nut block.

    Anything I'm missing about this that makes it worse than the current designs?
     
    Nelson Rios and GrayUK like this.
  2. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    There's absolutely nothing wrong with it. The only real catch is that the two rails have to be absolutely perfectly parallel or the wheels will loosen at the narrower end which would allow slop in the system.
     
  3. James Gao

    James Gao Well-Known
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    Ah, good point. The two plates at the top and bottom should hopefully prevent that. I think I'll give this a try in my rebuild...
     
  4. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    Parallel is really not that difficult to achieve. Just cut a short block of 20x40 to set between the ends as a gauge before you tighten the screws on the end plates. I was looking at a similar setup as part of a low profile X-Y table for my drill press.
     
  5. Steve hope

    Steve hope Well-Known
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    I bought a c beam linear actuator for my Z after spending ages fixing an extra piece of 8020 to my X and Z to try to remove movement in both caused by cutting through material (mdf) extending the wheels, using more spacers etc etc.
    It now works a treat with minimum deflection, wish they had invented it sooner.

    Ahhh progress, you got to love it
     
    John Meikrantz likes this.
  6. John Meikrantz

    John Meikrantz Veteran
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    Can you post any pictures of your mod? I've been wanting to to this for a while, but the effort required to disassemble the existing unit is too daunting...

    -- John
     
  7. Traxxtar

    Traxxtar Journeyman
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    Any updates to this thread? @James did you build the Z-Axis slider as you posted about to begin with? Got any pics?
     
  8. John Meikrantz

    John Meikrantz Veteran
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    I finally replaced my existing Z axis with a "Plate Maker" style C-Beam linear actuator. It works great! Totally solved the problems that I was having with deflection, particularly on plunges. I wrote about it in the thread on my machine - Cebu.

    Link with pics: Cebu | OpenBuilds
     
  9. Traxxtar

    Traxxtar Journeyman
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    I have seen other builds that used the C-beams for the Z-axis, but didn't like the way those looked. Since yours is mounted backwards, with max surface area mated to the plate, it sure looks like it would give you a sturdier mount. Perhaps that's the way I will go. Can you shorten those c-beams? Looks like you really don't need all that overhead at the top.
     
  10. John Meikrantz

    John Meikrantz Veteran
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    You can shorten, but I found that you can use all of the height - for instance if you have a really long bit, say 2" of cut length, you can raise the router up high enough so the bit is completely above the bottom of the Z axis. With the original design, I would lose some material height if using really long bits, because I couldn't lift the router high enough.
    -- John
     
  11. Traxxtar

    Traxxtar Journeyman
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    You can raise the router, but doesn't the rail still extend below that? Wouldn't your material contact the rail bottom if your gantry moves towards it? Seems to me you'd still only be able to cut material as thick as the lowest hanging component. Or am I understanding this completely??
     
  12. John Meikrantz

    John Meikrantz Veteran
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    The bottom of the C-Beam is even with the cross brace/rail that links the two Y axis gantries together. So that is the limiting factor for material height. The way the router is mounted, it can go low enough so the collet is almost touching the bed, so very short bits are useable with thin material. It can also go high enough that even with a 2" bit sticking out of the end of the router, at full height the 2" bit doesn't extend below the bottom of the C-Beam. So even with a maximum thickness of material to cut, I can still use the longest bit possible. With the old Z axis design, I couldn't lift the router high enough to use really long bits without sacrificing max material thickness.

    Hope that makes sense!
     
  13. Traxxtar

    Traxxtar Journeyman
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    Got it.

    After looking at so very many designs, I think I've finally settled on one. With your help, I'll do the Z-axis like yours so its stronger and actually looks easier to build and use.

    Thank you very much!!!
     

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