Is head movement defined in mm ?



  • Hopefully this is a silly question .
    I presume that head movement in the Web control interface is defined in mm.

    so when I press x+1 the X should move 1 mm ( exactly , I can hope ) .
    I am at the calibration stage and just wanted to double check.

    Thanks


  • administrators

    It's defined in mm, unless you send G20 to change the units to inches.



  • Sorry for jumping in...

    Does it actually matter what it's defined in? I mean, so long as you're consistent.

    The slicer just has to put out coordinates that agree with the units that you have decided to use as your system. You could probably use bu (分) as your base unit (1 bu is 1/330m or about 3.03mm) if you really wanted to do your modeling and printing in traditional Japanese units of measure for whatever reason. I doubt that there's a command built-in to do that, but if that were the unit of measure that my .STL files were in, and therefore what my slicer was actually putting out, and my printer were all set up that way, I see no reason why it wouldn't come out that way. Of course I would need to configure everything else in the same units, having a 0.132bu nozzle, instead of 0.4mm and 0.5775bu filament instead of 1.75mm, I would define my steps/unit as 1212.1212 instead of 400, acceleration as 1980bu/s/s instead of 6000mm/s/s, and print a 6.6bu calibration cube instead of 20mm, and I should come up with very nearly the same final printed object, printed with very nearly the same actual process, within the bounds of rounding errors.

    All in all, I'm most comfortable working in mm everywhere, but in translating the virtual to the physical, we really only need to agree on the mechanical translation. If you multiply all of your steps/mm by 1.05, you would increase the size of your resultant object by 5% in all dimensions. It actually really surprised me that there's a command to make the printer work in inches, unless it's just translating the incoming commands, multiplying (or dividing) by 25.4 in order to translate the output of a slicer, but I did think that should be the responsibility of the slicer to do that. Mind you, I have not really plumbed the depths of what the printer can do, I noticed the other day that all of my Marlin configurations still specify a 3mm filament which I've never used ever for volumetric calculations. This would of course not work if I tried it,but since I've never tried it...

    So really it's just "units" and we're using milimeters as standard units by convention, because they yield reasonable numbers for the sizes that we're dealing with. I do note that when loading .STL files in other software, you can specify that the file uses other things as its unit of measure.

    Anyway, all of the documentation that I've seen on 3D printers and 3D printing seems to assume that the unit of measure is mm, so this is clearly the path of least resistance.

    Anyway, OP question answered as basically "Yes, you should see head movement of 1mm when you press the +1 button on the DWC.:



  • @supraguy said in Is head movement defined in mm ?:

    Does it actually matter what it's defined in? I mean, so long as you're consistent.

    @nickt said in Is head movement defined in mm ?:

    I am at the calibration stage and just wanted to double check.

    Therefore, yes, it matters, because he is going to issue a command, and measure the actual physical movement of the printer.

    It is not "Printer and Slicer must agree"... it is "Printer and ruler must agree".



  • @danal yeah, I get that, and basically the OP question was answered by dc42 (Which I also reiterated at the bottom of my post)

    Just really, when you tell the printer to move 1mm, what the firmware does instead is say "I'm going to send x number of pulses to the stepper motor driver with the forward direction set."



  • @supraguy said in Is head movement defined in mm ?:

    @danal yeah, I get that, and basically the OP question was answered by dc42 (Which I also reiterated at the bottom of my post)

    Just really, when you tell the printer to move 1mm, what the firmware does instead is say "I'm going to send x number of pulses to the stepper motor driver with the forward direction set."

    Agreed!

    However... When the printer is told to move 1 unit, it sends many MORE pulses if there were a prior G20 than a prior G21.


 

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