Using a measured z/steps value vs calculated
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@arhi i know what youre saying but that doesnt answer my question. If the calculated z steps is giving me an inaccurate dimension, is something else wrong or is it just hardware deficiency?
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Dbot, Custom i3, Voron 0&2 -
@Turbo said in Using a measured e/steps value vs calculated:
@arhi i know what youre saying but that doesnt answer my question. If the calculated z steps is giving me an inaccurate dimension, is something else wrong or is it just hardware deficiency?
Hi,
Well there is this in the documentation under M579:
On a Cartesian RepRap you can get prints exactly the right size by tweaking the axis steps/mm using the M92 G Code above. But this does not work so easily for Delta and other RepRaps for which there is cross-talk between the axes. This command allows you to adjust the X, Y, and Z axis scales directly. So, if you print a part for which the Y length should be 100mm and measure it and find that it is 100.3mm long then you set Y0.997 (= 100/100.3).
So if you want to stick to what you calculate as correct for M92 then you can use M579 to tweak things based on measured prints.
Frederick
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How did you measure the correct z steps?
It's a belted z, is there some belt stretch or some backlash in the gearing?
I'd say using the measured steps would be fine in this case. Perhaps that partially explains some of the over extrusion you also recently saw?
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@Phaedrux no belt stretch, using 9mm wide gt2 belts. sturdy stuff. i measured steps using the pitch angle, got values for both pitch angle advertised (smaller final e-step) and the non-reduced motor (80[step ang] * 5-2/11[gear ratio] (larger steps/mm, idk why they are different values)), but those were the calculated steps given the values on the site) , and they were within 4 steps of each other, so i used the larger value (414.5). I found 423 steps to be more accurate, but it feels wrong to use something other than the calculated value.
used this websites calculator: https://blog.prusaprinters.org/calculator_3416/
For calculating the 0.35 step angle, i just edited as html and changed the value because i dont know the actual formula right now. -
I'd probably print a larger object than just a small cube to make sure the measured steps are accurate over a larger range.
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@Phaedrux will be back when 100mm tall cube print is done
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@Phaedrux 100mm tall print (changed to 99.9 due to 0.3 layer height) shows up as 99.6mm. Still 0.3mm off but only slightly. if it was a steps thing wouldn't it be a greater inaccuracy due to the increase in height?
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How thick is a single layer? (as printed)
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@bearer 0.2 mm when requesting 0.2mm. this is before adding a scaling modifier to the z axis.
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You should expect step/mm error to be proportional to the print height. If you're getting the same overall error regardless of the print size it's likely due to something else.
Could be backlash or something mechanical, particularly if the first layer Z plane was approached from the opposite direction of subsequent layers. Most cheap stepper gearboxes have quite a bit of backlash, usually they're quoted at 1.5 to 3 degrees, which would be up to .33mm with a 20t 2mm pulley (40mm/rev).
Steps/mm numbers look correct, my calc gives out 414.545455 steps/mm. Assuming 200 steps/mm motor, 20t drive gear, 5 2/11 gearbox, 2mm belt pitch.
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@Turbo said in Using a measured e/steps value vs calculated:
@arhi i know what youre saying but that doesnt answer my question. If the calculated z steps is giving me an inaccurate dimension, is something else wrong or is it just hardware deficiency?
Well the topic you created is e/steps and then you are talking about Z/steps so it's not really clear what you are asking.
I personally never measure "part" to determine machine properties. Plastic is hard to measure and can lead you astray in many ways. Attach an indicator or caliper to the head, move head known value, read actual moved value from the caliper - compare.
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@arhi my bad, so used to seeing the term e steps and not z steps. fixed in title.
ill try that method shortly. although having part dimensional accuracy is the point, and while i get measuring the printers accuracy like you're saying, it really wouldn't help me if the printer is accurate to 20.00mm for example, but the prints are coming out a different size. -
@Turbo said in Using a measured e/steps value vs calculated:
@arhi my bad, so used to seeing the term e steps and not z steps. fixed in title.
ill try that method shortly. although having part dimensional accuracy is the point, and while i get measuring the printers accuracy like you're saying, it really wouldn't help me if the printer is accurate to 20.00mm for example, but the prints are coming out a different size.more than one thing is influencing part dimensions... you start with making your printer move "properly", ignore part size, make sure you printer move the way it supposed to. then if parts are wrong size find out why (extruder calibration, slicer calibration, shitty slicer, bad print surface, butterflies... ) ... but you can't start to fix other issues unless you are sure your printer movements are accurate..
also if your cube is wrong .1mm on 10mm, is it wrong again .1mm on 100mm or is now 1mm wrong? FDM is not a super precise process, .1mm is not a big issue, 1% is a big issue
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@arhi You were right with regards to the printer not moving "properly". So, after switching to linear rails on the z axis, I found my z axis dimensions to be spot on with the calculated value. I believe there may have been some unwanted friction using the v-rollers, causing the prints to come slightly short.
