Author Topic: 3D printer x/y steps per mm  (Read 5239 times)

ggallant571

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3D printer x/y steps per mm
« on: June 16, 2017, 05:26:32 PM »
I just looked at the motor conversion units on my 3D printer and X & Y are set at 81 while Z is 400. Since these device share components with the laser etchers I find this odd. Measured a 10x20x8 mm cube and it is long on all sides. Any comment?
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Stonemull

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Re: 3D printer x/y steps per mm
« Reply #1 on: June 17, 2017, 01:17:20 AM »
My wanhao rebrand is also 81. Long on all sides is odd, you often get a slight spread if running a little hot or the extruder flow is too high.
If running hot though, it comes out slightly squashed as the material flattens out a tiny bit.

80 makes sense for 20 teeth 2mm GT3 belts, 40mm circumference for one rotation, 200 * 16 = 3200 steps / rotation. 3200/40 = 80 per mm.

So it has always confused me why 81 and not 80.
Dropping it to 80 is going to make the object larger as it will do more steps for a given size.

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Re: 3D printer x/y steps per mm
« Reply #2 on: June 17, 2017, 01:46:16 PM »
I do not understand it either. For my Printrbots the default is 80. 20 tooth gears. I had to increase it slightly when calibrating the machines.
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ggallant571

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Re: 3D printer x/y steps per mm
« Reply #3 on: June 17, 2017, 03:51:55 PM »
Dropping to 80 will make for shorter distance traveled. Think of it from the respective of the motor/gear/belt. If 80 ticks equates to 1 mm then 81 ticks is going to go 1/80 mm too far. The CPU will convert mm to ticks.
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Re: 3D printer x/y steps per mm
« Reply #4 on: June 17, 2017, 04:43:51 PM »
I had to set a high value for my Z steppers on my 3D printer frame converted to a laser machine. The Z axis definitely wasn't 80 like the X and Y steppers are. I measured the Z axis travel to verify my setting was correct. Put some tape on where the z axis bracket was and sent a g-code command to move the Z axis up 10mm and then measured. I finally got the right setting and tested a range of mm distances: all came out perfect.

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ggallant571

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Re: 3D printer x/y steps per mm
« Reply #5 on: June 17, 2017, 04:54:53 PM »
I have a need to get 60 mm center to center on 8mm holes. Guess I will do the same and hope for good results and/or fudge the numbers.
 
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wild.bill

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Re: 3D printer x/y steps per mm
« Reply #6 on: June 17, 2017, 05:03:19 PM »
the 80,80,400 are good starting points but none of these printers are exact.
You need to calibrate, and Method 2 is a little harder (trying to measure exactly how much the head moves) but is more accurate because the different plastic you use all have different amounts of shrinkage. But that being said if you always use the same plastic (which most of us do not do) you can get good results with method 1.

All of my printers were a few % off from the calculated numbers until calibrated.

 
Method 1)
With those numbers print a test cube (the bigger the better) and then measure it.

Find the ratio of what you got vs what you expected for each axis and use that fraction to adjust the numbers.

Repeat until happy.

Method 2)
Mark the rails and tell it to move something like 100mm. Again get the fraction of what you expect vs what you got, adjust and try again.
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Re: 3D printer x/y steps per mm
« Reply #7 on: June 17, 2017, 06:05:34 PM »
On a  4inch square, I had it accurate within 6 thousandths in the X and 4 thousandths in the Y direction with no adjustments. A one-inch cube is within one thousandth in all three axes.

Luck of the draw I guess.
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Stonemull

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Re: 3D printer x/y steps per mm
« Reply #8 on: June 17, 2017, 11:06:19 PM »
Dropping to 80 will make for shorter distance traveled. Think of it from the respective of the motor/gear/belt. If 80 ticks equates to 1 mm then 81 ticks is going to go 1/80 mm too far. The CPU will convert mm to ticks.

Oh yeh .. doh!

The gcode sent to the machine tells it how many mm to move,
if it has to go 100mm then 81 steps/mm means it will move exactly 81000 steps.
drop to 80 steps/mm and it will now move 80000 steps. less..

What can I say, I had a brain fade lol...

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Stonemull

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Re: 3D printer x/y steps per mm
« Reply #9 on: June 18, 2017, 04:41:45 AM »
I had not bothered tuning in the sizes, just left it at default for the time being.
Finally got around to printing the calibration/testing cube https://www.thingiverse.com/thing:1278865

and what do you know .. my verniers say it is 20.25mm on the X and Y.

81 * 20/80 = 20.25mm..

So no idea why they set 81 steps, it is plainly a mistake.
Set to 80 and reprinting to see if it does anything to my slightly short Z .. which on a revisit is actually not that bad, I thought it was 19.88mm but it varys from 19.88 up to 20.01mm with most measurements coming in at 19.9 something, I did not level my bed beforehand which is a must do for accurate results.

Data from my 2 cubes...

Second cube just finished, measurements are better .. a measurement taken from each side of each axis.. same gcode used each print.

First cube (81 steps)..
X 20.21 20.09 20.24 20.13
Y 20.23 20.25 20.21 20.15
Z 19.85 19.82 19.81 19.82

Second cube (80 steps)
X 19.98 19.85 20.01 19.96
Y 19.90 19.85 19.84 19.85
Z 19.85 19.80 19.82 19.81

« Last Edit: June 18, 2017, 05:47:56 AM by Stonemull »
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ggallant571

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Re: 3D printer x/y steps per mm
« Reply #10 on: June 18, 2017, 07:27:41 AM »
And I was beginning to think that the Chinese 3D printers ran a higher quality software than the laser etcher/cutter. Looks like there might be a market for T2-3D.
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Stonemull

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Re: 3D printer x/y steps per mm
« Reply #11 on: June 18, 2017, 08:24:22 AM »
Huh, none of the software is chinese, these printers are running Marlin firmware which is open source and western, it is a hardware configuration error easily rectified. Neither marlin or the slicer set these values, they are machine specific.
I just don't  understand why they used 81 unless they determined the value by brute force methods (printing a test cube and deciding 81 is the correct falue lol) and simply have no idea how to calculate the correct value by just looking at the hardware.



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ggallant571

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Re: 3D printer x/y steps per mm
« Reply #12 on: June 21, 2017, 11:38:07 AM »
It has to be Chinese for the spelling mistakes on the user interface.
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Stonemull

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Re: 3D printer x/y steps per mm
« Reply #13 on: June 21, 2017, 12:10:50 PM »
Ok, The UI is probably tacked on by some chinese people :)
If you connect to my chinese UI'ed printer with realterm it reports Marlin 1.1 firmware in the boot text.

Someone released new custom firmware for the wanhao i3+/ cocoon touch a few days ago, might have a crack at it shortly.
These printers all have colour screens and none of them use it.

https://github.com/Silverquark/i3PlusPlus
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