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Dimensional Accuracy

Discussion in 'Troubleshooting' started by zachary.h.a, Jan 8, 2018.

  1. zachary.h.a

    zachary.h.a New Member

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    Hi All,

    I was just curious if anyone was experiencing/solved a problem with dimensional accuracy on the Robo R2. I have been printing for about a month now pretty well with nearly no problems. Although, when I print parts that need assembly there always is a problem with dimensional accuracy. Things always print to tight and when printing a tolerance test it was only able to work up to 0.3 mm. Any ideas how to fix this?

    Thanks in advance!

    Zack
     
  2. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Slow down the print speed and acceleration.
    Those are the only two things you can do that will impact this since the rest is done in the mechanical design.

    Honestly, 3D printers are not CNC machines and given the vagaries of how filament lays down (expands/contracts when it cools) and other things... you are never going to get better repeat-ability than 0.1 I imagine (you might get lucky, some folks have gotten tolerances down to 0.05). Not in this class of machine. If super high tolerances are your goal or extreme fine detail a DLP or SLA style machine might be needed.
     
  3. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Some of this you learn to CAD around. You design for what you know the tolerances are. You should be able to slow things down and get 0.1 repeatably.
     
    Kilrah likes this.
  4. OutsourcedGuru

    OutsourcedGuru Active Member

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    I've mentioned this before (mostly a Cura issue, methinks...)

    For some recent parts (which fit inside 80-20 extruded aluminum rails), it was necessary to scale them down by 7% for them to fit well.
     
  5. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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    Also depends on the shrink rate of plastics used. To give you an example, LEGO who is the largest user of ABS in the world and has its own chemists developing ABS blends, has to make their molds with errors built in so that the finished Lego block fits every other Lego block ever made. This is what @mark tomlinson is alluding to If you must have dimensional accuracy in all three axes you have to account for the thermal characteristics of the plastic in use.

    Also, for some reason when I examine Robo's version of Marlin I see a purposely inserted error in the number of steps. The line #define DEFAULT_AXIS_STEPS_PER_UNIT { 80.0395, 80.0395, 800.00, 145.5 } has the X and Y axes set to a number that is not mechanically accurate (80 would be the accurate number of steps). They give no reason why this is and honestly it is stupid if they are using it to correct for mechanical accuracy.
     

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