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Long lead screws

Discussion in 'CNC Mills/Routers' started by Doug, Oct 21, 2014.

  1. Doug

    Doug New
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    Hi All,

    I'm working on designing the second version of a CNC machine I built over the summer. The one I made was very sloppy in how it moved. I attribute this to the belt and pinion approach I used. I just can't help but feel like the belt stretches. That stretching must cause inaccurate movement, especially as it must stretch and contract while the machine runs.

    Because of this, I'm thinking about switching to either a lead screw mechanism or a rack and pinion mechanism, at least for the horizontal axes. I really want to find some long lead screws. At a minimum I'm looking for 1300 mm length (ideally something more like 1800 mm). I probably want larger diameter than the 8mm one OpenBuilds offers.

    I've google the bejesus out of this and there are lots of manufactures, but I'm having a very hard time finding a clear combination of the following:

    1) Metric
    2) >= 1600 mm
    3) Simple off the shelf mounting hardware. IE: The equivalent of the acme nut block and the threaded rod plates offered by OpenBuilds.

    Any suggestions on where to look / who to talk to?

    Thinking about the rack and pinion, I still need to research what sort of specifications would work best for the project at hand. Anyone known anything in this area?

    How would you solve the linear motion on a large CNC machine?

    Thanks for the feedback, everyone!
     
  2. SJD

    SJD Well-Known
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    mcmastercarr.com sells fast travel acme screws and flange nuts ,also check,dumpstercnc.com for antibacklash nuts
     
  3. Steve123

    Steve123 Journeyman
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    I just ordered a couple of these fast start acme rods, not metric, they are 1/2" dia 5 start. I too am designing my machine using acme rods and not belts. Fast start acme rods are suppose to improve the performance of your mill/router.

    http://www.mcmaster.com/#99030a704/=u9ox7e
     
  4. Doug

    Doug New
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    So, what's the difference between fast start vs. standard start? It seems to simply be the number of thread starts. Fast start implies (and I can picture) that the nut travels faster down the rod. Is this correct? Are there any other important facts about this I should know?

    I ask because the metric rods at mcmaster are all standard not fast start. The **** retentive freak in me gets bent out of shape imaging intermingling metric and imperial.

    Thanks for the helpful suggestions, by the way. I greatly appreciate it!
     
  5. Rick 2.0

    Rick 2.0 OpenBuilds Team
    Staff Member Moderator Builder

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    My cheapskate side learned to overrule my **** retentive side long ago. But if you must have metric consider http://www.igus.com/wpck/10893/SD_Gewindetriebe
     
  6. Steve123

    Steve123 Journeyman
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    Multi start will improve performance and reduce backlash. I want my machine to think like me in imperial.
     

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  7. Doug

    Doug New
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    One more question on the topic. How are people attaching the anti-backlash nuts to their machines? None of the flanges I've been able to find have any flanges with holes at 20mm spacing. I haven't been able to think of a way to make it work without having to have a plate or adapter custom milled.

    Also, are you only using one nut per lead screw or do you have a nut on either side of whatever you're attaching to?

    Thanks so much for all of the help, everyone!
     

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