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  1. #11
    Staff Engineer printbus's Avatar
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    May 2014
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    SUGGESTED HOMEWORK AND INDEPENDENT RESEARCH

    While we wait for the conjuring of improved settings that have been validated from someone...

    Consider playing around with the Z axis details in the Prusa leadscrew calculator. Note how using a metric pitch threaded rod to obtain metric linear movement typically always involves an integer number of steps. Switch to using Imperial threads in the calculator and see about all you can do is get close. Use Prusa's Optimum Layer Height calculator to grasp the pain those with Imperial rods have in trying to obtain nice, even metric layer heights. After playing with the calculator, you'll likely never buy a printer with Imperial threaded rods.

    What would happen to the DEFAULT_STEPS_PER_UNIT for the Z axis if the M5 Z rods were replaced with M6 or M8?

    Increasing the difficulty now since at least the Prusa calculator doesn't have a pull-down for it, how would the DEFAULT_STEPS_PER_UNIT change if the Z rods were replaced with 8MM ACME leadscrews that have say a 4mm travel per turn (often listed as Tr8*4) or the harder to find 2 mm travel per turn (Tr8*2)?

    The value of 4000 steps per mm for the Z axis in DEFAULT_STEPS_PER_UNIT seems to be a large number of steps providing an excessively small position resolution. Using higher pitch M8 or 8MM ACME leadscrews would reduce the number of steps required to obtain the same linear movement. Ignoring any other limitations like available motor torque, reducing the number of steps required per mm movement would also increase the achievable feed rate. What kind of achievable feed rate on the Z axis might be possible with the M8 or 8MM ACME with 4mm per turn travel used instead?

    Now repeat as much of this as required to assess what would happen to the Z axis achievable feed rate if you reduced the microstepping on the Z-axis motor to something other than 1/16.

    What would happen if the 20 tooth pulleys on the X and Y motors were replaced with ones that have 16 teeth?

    FOLLOWUP COMMENT: Most of these are pretty straightforward to answer. My point is to get people familiar with the mechanics involved in their printer, or at least provide a one-stop summary with the math and tools that makes it easier to do so. Also note that I'm not necessarily proposing change-out of the Z rods or motor pulleys, since doing so may reveal other issues. My plan is to leave those upgrades outside the scope of this thread.
    Last edited by printbus; 12-21-2014 at 12:16 PM.

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