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Z axis platform ideas

Discussion in 'General Talk' started by theodors, Jul 6, 2020.

  1. theodors

    theodors New
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    I want to construct a platform that rides along the Z axis inside a box frame, see image. Are there any other designs you can think of that has done this previously? Will the 4X V slot wheels + 4X lead screw make for a solid platform? Thank you!
     

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  2. Rob Taylor

    Rob Taylor Veteran
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    Looks prone to racking. For rigidity you want sets of wheels a distance apart (the further the distance, the better, limited by the frame's rigidity)
     
  3. theodors

    theodors New
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    Thank you for your feedback. With sets of wheels, do you mean multiple wheels per side of the platform? I've seen that many people use linear rods and bearings for their platforms, like Rob Chesney in his diy laser cutter Is there a reason for going with this design over V slot wheels? My design calls for rigidity over super high precision.
     
  4. Rob Taylor

    Rob Taylor Veteran
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    Maximum rigidity is achieved by building basically twice the machine you want, then using all the excess space to allow wheels/bearings to run into. So each of those wheels in your first design would be made into two wheels, separated vertically, between 100-250mm apart. Imagine your platform as a system of levers. Deflection of one side of the platform wants to rotate the other side of the platform about its mounting point(s). You're gonna put a lot of wear on the nut if your platform isn't build to resist racking (when a dual-mounted beam tries to rotate within the plane of its mounts).

    Linear shaft is highly rigid in the larger sizes- 16mm+- and not that expensive. It's certainly an option, and you wouldn't require as much spacing on your bearings to get the same level of rigidity as V-Slot. Maybe 75mm spacing would be about the same as 250mm spacing, maybe even better. Not 100% sure off-hand, but I suspect it would be in that ballpark. I used 8mm linear shaft on my laser's Z stage with two sets of bearings packed into a ~50mm length and it's extremely rigid- but only has to move about 40mm. You could use fully-supported shaft to mount it to your extrusion framing and use a smaller size like 12mm.
     
  5. theodors

    theodors New
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    Great advice thank you! I’ll make a design using 12mm shafts, since I would like to keep this design as compact as possible.
     
  6. JustinTime

    JustinTime Journeyman
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    If you are moving in the Z axis you could get away with using the 8mm shafts as Rob said he's using on his Z axis. It will be much more compact than the 12mm. There are no significant loads acting on the shafts in the Z axis configuration and you are going to use 4 of them. As long as you mount the rails as solid as possible, using all the pre drilled screw holes, it will be very rigid even on a longer run.
     
  7. theodors

    theodors New
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    Good point. This platform will only have a travel of around 100mm so it should be rigid enough I reckon. Better to start smaller and cheaper and upgrade as needed than other way around. How would you spec the lead screws? 8mm there as well? Btw the dimensions of the platform is roughly 400x400mm
     
  8. Rob Taylor

    Rob Taylor Veteran
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    until 17:05 shows my bearing block boring and fitting

    (24:17 in the same video) shows assembly of the unsupported shaft, you can see the rigidity at short travels
     
  9. theodors

    theodors New
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    Nice. Subscribed :) That machine is a beast!
     
  10. Rob Taylor

    Rob Taylor Veteran
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    Thanks! Appreciate it. You ain't seen the half of it- looking forward to moving to a 6W+ diode, because that thing can haul ***. Belts and NEMA17s, even with a relatively heavy gantry like that, will do crazy accelerations and rapids at 24V. The next video, when I finally get to make it because I'm happy with where the machine's at- last in the series- should show all that fun stuff.
     
  11. theodors

    theodors New
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    Looking forwards to that indeed! I have an Eleksmaker A3 2.5W, but the optics on it are quite bad, so lines are not as crisp as they should be. Maybe I should get a new diode?
     
  12. Rob Taylor

    Rob Taylor Veteran
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    The Nichia diodes in DTR Laser copper housings with G-2 lenses are the way to go for sure. If you have a 6-8A driver that works well already then great, otherwise the BlackBuck 8M has been rock solid for me, it's a great unit and provides headroom for higher power lasers (mine is just a 1.6W NDB7875 for now, even those were a little expensive in 2016 when I started the project :p).

    Next up will be a NUBM44 once I add active cooling to the BlackBuck since it's also a TO5-can laser diode so it'll go in the 12mm copper housing that already fits in my machined laser head.

    I wasted a year and $100+ in diodes trying to figure out why a cheap Chinese driver wasn't working. Horrible false economy, make sure you have a good driver.
     
    Giarc likes this.

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