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  1. #1

    Printer Resolution

    Question for the group:
    After having worked with a few low cost 3D printers I have gotten curious about how the resolution is specified. The Solidoodle 4 has 88 steps per mm (.011mm) in the X and Y axis and 2268 steps per mm (.0004mm) in the Z axis. What makes the machines best resolution .1mm? Is it the .4mm nozzle going into the corners? Is it the diagonal where there error from X and Y mid steps are more obvious? Just cuerious - thanks!

  2. #2
    Engineer
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    To be honest, that's the kind of question which isn't answered straight. Too much things can turn those nice resolution into thrash/mean nothing. I once forgot to do change/add new lubricant on the axis rod, and my print have a 2 mm offset on one direction, pretty sure PLA doesn't shrink that much.

    I like to think the spec of the motor, nozzle are only an intermediate among a big process. Which means there could be anything before or after that can screw your "resolution"

  3. #3
    Engineer Marm's Avatar
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    Slightly OT Richard, what type of lubricant do you use?

  4. #4
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    Jigaloo, not the best one since you have to rechange them like everyweek. I am currently trying to play with bearing grease and mineral oil.

    By the way don't try green grease for automobile, those are just too thick and make the stepper work harder.

  5. #5
    Technician -willy-'s Avatar
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    What about using antiseize for automobiles? It is basically turbine oil and grey graphite. A little bit of this stuff goes a long way. I bought a jor of this some 20 years ago and still have a third of it left.

  6. #6
    I guess the question I am asking is more theoretical. Surely Maker, LulzBot, Solidoodle and other manufacturers didn't just build a machine and then test it to see the best resolution it could do. If the machine is running well how do the manufactures design for a specific resolution? Seems like an answer (even if its complicated) that is hard to find.

  7. #7
    Engineer Marm's Avatar
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    Look at how it's driven. My X & Y is belt driven, so it's a 1:1 ratio of motor turns to belt movement. Stepper motors have a minimum step, and then usually +/- 5% (depending on the build). So each step of the motor, the belt is moved by the same amount. In the Z axis, mine is on a worm gear. That means it is not a direct 1:1 of steps to movement, there are a lot more steps per mm than the belt drive.

    Resolution would be actually very simple to find. If they use a motor that has been tested well and well documented, then they know exactly how far it will turn per step, and then using the radius of the belt or worm gears, they know exactly how far the machine will move in each axis.

  8. #8
    ^ So that is the direction I was looking to go. The Solidoodle I have is 88 steps per mm. If it is error in positioning the stepper motor they probably have close to 200 steps per revolution so that would be 2.27 mm per full rotation. A 5% error in 2.27 mm is .11 mm. The rated spec is resolution as low as .1 mm. Not sure if that covers micro stepping hybrid motors.

  9. #9
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    I've been involved with servo positioning systems for many years, but not so much with stepper motors. Your question had me searching for an answer. I may have found a piece of the puzzle with a bit of info found in Wikipedia: "...many modern hybrid step motors are rated such that the travel of every full step (example 1.8 degrees per full step or 200 full steps per revolution) will be within 3% or 5% of the travel of every other full step." Sounds to me like this is where the 5% positioning error comes from. Initially, i thought 'backlash', but that's a significant amount of error to attribute to backlash.

    Also found a good piece called "Microstepping: Myths and Realities", which clearly explains why microstepping does not improve accuracy. That surprised me, but makes perfect sense after reading.

  10. #10
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    Quote Originally Posted by -willy- View Post
    What about using antiseize for automobiles? It is basically turbine oil and grey graphite. A little bit of this stuff goes a long way. I bought a jor of this some 20 years ago and still have a third of it left.
    I have used the one from permatex, aka the green thick grease(label as french one).
    It didn't work well.
    http://www.amazon.ca/Permatex-80078-.../dp/B000AAJTXY

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