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jordan.c
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Prints slightly small

Jan 09, 2017 1:39 pm

I have noticed a slight size discrepancy in my prints and I am wondering if this is expected or maybe my calibration is busted?

Dimensions on the x y axis seem to be very slightly smaller than what is specified in the models. I see about a .15 to .25 reduction in widths and inside holes / boxes. Z seems to be slightly larger by about the same amount. I thought maybe I was model things wrong, so I printed one of these

http://www.thingiverse.com/thing:1363023
IMG_20170108_170155916.jpg
IMG_20170108_170155916.jpg (4.19 MiB) Viewed 854 times
And see the same results. Is this an expected? Or a symptom of something else?

david.t2
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Re: Prints slightly small

Jan 09, 2017 2:16 pm

I use this http://www.thingiverse.com/thing:1818250 for dimensional calibration. Use M92 gcode command to set new values of axis steps/mm and M93 for displaying current values. http://reprap.org/wiki/G-code#M92:_Set_ ... s_per_unit

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jordan.c
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Re: Prints slightly small

Jan 09, 2017 4:19 pm

David, this is a great print for calibration, I will print it today. But how do you fix the issue? Say you need like .15 mm larger on the X?

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jordan.c
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Re: Prints slightly small

Jan 09, 2017 4:28 pm

for instance, in slic3r i see this custom gcode

Code: Select all

M115 U3.0.9 ; tell printer latest fw version M83 ; extruder relative mode M104 S[first_layer_temperature] ; set extruder temp M140 S[first_layer_bed_temperature] ; set bed temp M190 S[first_layer_bed_temperature] ; wait for bed temp M109 S[first_layer_temperature] ; wait for extruder temp G28 W ; home all without mesh bed level G80 ; mesh bed leveling G1 Y-3.0 F1000.0 ; go outside pritn area G1 X60.0 E9.0 F1000.0 ; intro line G1 X100.0 E12.5 F1000.0 ; intro line
I don't understand where the calibration variables come in? Does the firmware automatically modify every coordinate to keep the calibration? What about for bumps in the bed only in certain places? How does it know to +.002 the Z there?


david.t2
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Re: Prints slightly small

Jan 09, 2017 6:01 pm

jordan.c wrote:David, this is a great print for calibration, I will print it today. But how do you fix the issue? Say you need like .15 mm larger on the X?
Easy. First display current value using M93. Let's say it is 100 (100 steps per mm).
You printed 100mm object which came out not 100mm but 99.85mm (.15mm smaller). You need to set X steps to 100 * 100 / 99.85 = 100.15, so use "M92 X100.15". Put it anywhere in starting gcode script.

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jordan.c
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Re: Prints slightly small

Jan 09, 2017 7:18 pm

Well, one is waiting for me when I get home...
Screen Shot 2017-01-09 at 2.14.06 PM.png
Screen Shot 2017-01-09 at 2.14.06 PM.png (369.75 KiB) Viewed 817 times
david.t2 wrote:Put it anywhere in starting gcode script.
So this is something I will need to inject into every gcode script? Via Slic3r?

Call me crazy but isn't the this what the calibration is for? I don't remember seeing dimensional calibration in the kit assembly, or the manual.

david.t2
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Re: Prints slightly small

Jan 09, 2017 8:22 pm

jordan.c wrote:I don't remember seeing dimensional calibration in the kit assembly, or the manual.
That's OK because it is not there. ;-)
In perfect world calculated steps/mm should be accurate enough. Those people living in real world have to calibrate the printer.

On the other hand, having correct constants placed in starting gcode script eliminates the need of restoring them into eeprom every time you upgrade the firmware.

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jordan.c
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Re: Prints slightly small

Jan 09, 2017 9:52 pm

Whoa... ok game on

But in fairness, I guess they expect that if you are building your own printer, you are one hardcore maker and should know these things. I am still learning.

So just to recap..

Z Calibration - Make sure the you don't drive the hot head into the bed, built in and vars are saved to eeprom
XYX Calibration - Make sure your bed isn't bumpy or dippy or skewed and you don't drive your hot head into the bed, built in and vars are saved to eeprom
Dimensional Calibration - Make sure your prints are dimensionally accurate so you can print useful things, NOT built in and vars are saved to gcode prefix script

Any other surprise calibrations I should know about ;)

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jordan.c
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Re: Prints slightly small

Jan 10, 2017 5:49 pm

david.t2 wrote:First display current value using M93
The M93 doesn't seem to return anything...

Code: Select all

Send: M93 Recv: ok
What am I doing wrong?

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