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Author Topic: Kossel Mini Z Calibration  (Read 4888 times)

Ladvien

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Kossel Mini Z Calibration
« on: April 22, 2017, 08:09:06 PM »
Hey, a question for those with a Kossel Mini.  My Z height on prints is way falling a little short.  For example, on a 20mm cube I'm getting:

X = 21.23 mm
Y = 21.56 mm
Z = 19.70 mm

I'm using Marlin / AstroPrint for the firmware.  And Cura for the Slicer.  Anyone know how to calibrate it correctly?  Just don't have a lot of time now days for troubleshooting.

I'm working on a print now for pictures.

X


Y


Z
« Last Edit: April 22, 2017, 09:04:25 PM by Ladvien »

MEgg

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Re: Kossel Mini Z Calibration
« Reply #1 on: April 24, 2017, 05:48:39 PM »
I am not a 3D printer pro, but as I also have a delta this might be similar.
At least my latest cube also is not exactly 20mm:





When calculating how many % your measurements are away from 20mm
(I am not sure if X,Y,Z are mixed up between picture and text, but you'll know what I mean):
X -20mm=1.23mm = 6.15%
Y- 20 =1.56= 7.8%
Z- 20=0.3   = 1.5% off

I'd say your Z is more ok than your Y therefore.

I also found this one somehow refreshing:
"No, it's actually done in the firmware or through the menus on the control box. (not at home at the moment to tell you where exactly, but google is your friend)

However, the real solution is to stop printing calibration cubes and get over it. You're within 1% in all directions, and you may simply not be able to do better than that. Your print nozzle is 0.4, and your largest variance is 0.19. That's a small enough variance that a variation in the thickness of your filament could cause it.

This is a prime example of why calibration cubes are a waste of time."
https://www.thingiverse.com/groups/i3/topic:7614 ]

I do not agree 100% but he is somehow right: there are tolerances everywhere and in my case I cannot really
say what is caused by measurement error of the caliper and what is caused by my printer:
20.08mm for sure is ok
20.12 =  0.6% off is also ok.

I also guess that you already know this one:
https://www.3dhubs.com/talk/thread/delta-printer-printing-dimensions-wrong
and afair Jinx told me this one:
http://reprap.org/wiki/Triffid_Hunter's_Calibration_Guide

May the more pros like Jinx or Bajdi correct me if I am completely wrong.
 ;)

P.S.: does anybody know where to get the cables for this caliper?
I tried a Cable, DRO Mini-DIN at http://littlemachineshop.com but they were not able to
deliver.
« Last Edit: September 02, 2017, 05:05:25 PM by MEgg »
1st project: Dagu 5 Rover + Dagu - 4 Channel DC Motor + Red Back Spider robot controller + Raspberry B+
Chassis + wheels: https://picload.org/image/dggroior/20150831_028.jpg
current: https://www.keepandshare.com/userpics/m/a/r/k/usegg/2016-04/sb/img_3480-79682018.jpg

jinx

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Re: Kossel Mini Z Calibration
« Reply #2 on: April 24, 2017, 06:22:38 PM »
spent few evening with this guy in the background.

cheat reduce the flow rate to 98 shave off .6!
another is use slicer and scale the axis! though its still better to calibrate.
Lad post your  axis steps and delta section need to remind myself how I calibrated mine  ::)
..........................went to bed.........................
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jinx

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Re: Kossel Mini Z Calibration
« Reply #3 on: April 25, 2017, 03:42:00 AM »

@lad

 your axis step look like that, I found it in the  kossel pro section of marlin. I love it leaves only getting the belt tension matched.
be careful bud I find changing one part  of a delta config  you may well require tweaking the whole thing again. stay close to the off switch.
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Ladvien

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Re: Kossel Mini Z Calibration
« Reply #4 on: April 28, 2017, 07:57:57 AM »
Thanks gents!

@Megg, well, I'm pretty sure my caliper has more variance than I like (my gut says around 1mm).  But I'm thinking Jinx is on track with the settings.  I'd be ok with with .5mm off, but the 1mm off on the Y axis turns into 8mm with a large print.

@ Jinx, just flew back in from D.C., so I'll probably start working on the printer in the morning.  I'll start by posting my axis and delta sections here.  Definitely with you on the off switch.  I've crashed my head a few times; it's always unsettling.

Ladvien

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Re: Kossel Mini Z Calibration
« Reply #5 on: April 29, 2017, 09:31:37 AM »
Below is the current delta settings.  I'm thinking I need to lower the pitch slightly?

//// MOVEMENT SETTINGS
#define NUM_AXIS 4 // The axis order in all axis related arrays is X, Y, Z, E
#define HOMING_FEEDRATE {200*40, 200*40, 200*40, 0}  // set the homing speeds (mm/min)

// default settings

#define XYZ_FULL_STEPS_PER_ROTATION 200
#define XYZ_MICROSTEPS 16
#define XYZ_BELT_PITCH 2 //
#define XYZ_PULLEY_TEETH 17
#define XYZ_STEPS (XYZ_FULL_STEPS_PER_ROTATION * XYZ_MICROSTEPS / double(XYZ_BELT_PITCH) / double(XYZ_PULLEY_TEETH))

#define DEFAULT_AXIS_STEPS_PER_UNIT   {XYZ_STEPS, XYZ_STEPS, XYZ_STEPS, 100}
#define DEFAULT_MAX_FEEDRATE          {200, 200, 200, 200}    // (mm/sec)
#define DEFAULT_MAX_ACCELERATION      {9000,9000,9000,9000}    // X, Y, Z, E maximum start speed for accelerated moves. E default values are good for skeinforge 40+, for older versions raise them a lot.

#define DEFAULT_ACCELERATION          3000    // X, Y, Z and E max acceleration in mm/s^2 for printing moves
#define DEFAULT_RETRACT_ACCELERATION  9000   // X, Y, Z and E max acceleration in mm/s^2 for retracts

// Offset of the extruders (uncomment if using more than one and relying on firmware to position when changing).
// The offset has to be X=0, Y=0 for the extruder 0 hotend (default extruder).
// For the other hotends it is their distance from the extruder 0 hotend.
// #define EXTRUDER_OFFSET_X {0.0, 20.00} // (in mm) for each extruder, offset of the hotend on the X axis
// #define EXTRUDER_OFFSET_Y {0.0, 5.00}  // (in mm) for each extruder, offset of the hotend on the Y axis

// The speed change that does not require acceleration (i.e. the software might assume it can be done instantaneously)
#define DEFAULT_XYJERK                20.0    // (mm/sec)
#define DEFAULT_ZJERK                 20.0    // (mm/sec)
#define DEFAULT_EJERK                 20.0    // (mm/sec)

jinx

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Re: Kossel Mini Z Calibration
« Reply #6 on: April 29, 2017, 10:51:34 AM »
thats giving you 21mm cube.. think you gonna need to tweak the DELTA_DIAGONAL_ROD  may have to adjust the DELTA_RADIUS as well.

printing something with details first.  if its a really good walls and stuff, leave it  and use scale in the  slicer's. :o :o :o inner voice cry's out dial it in!!. but dont worry about  XY axis's being  off by .3


On a delta...here is what matters
Quote
-Build it right!  Accurate dimensions are far less important than symmetry.  The towers must be parallel and equidistant.  The six diagonal rods must all be equal in length.
-Turn off EEPROM and auto bed leveling when tuning.
-The only firmware tweaks that are important are steps per mm (which controls general X and Y movement, and Z height), DELTA_RADIUS (which controls "flatness" ) and DELTA_DIAGONAL_ROD (which controls X and Y dimensional accuracy).  Set and tune these values in this order. 
-I see a lot of conversation about carefully measuring DELTA_SMOOTH_ROD_OFFSET, DELTA_EFFECTOR_OFFSET, and DELTA_CARRIAGE_OFFSET.  These only matter when starting to dial in DELTA_RADIUS.  Use them as starting information.  See #3 above.  After all, what matters is that the printer is printing flat and accurately in X,Y, and Z dimensions.
-Tune the firmware so that the printer prints correctly.  Tuning firmware to match the (presumed) "as built"measurements of the printer is not the fast-path to a smooth and accurate printer.
Only turn on EEPROM and auto bed leveling when tuning is complete
                                                  http://minow.blogspot.co.uk/index.html#7516958070168615082
« Last Edit: April 29, 2017, 11:57:17 AM by jinx »
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Ladvien

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Re: Kossel Mini Z Calibration
« Reply #7 on: May 07, 2017, 08:40:19 AM »
Thanks for the advice, Jinx.

To resolve the issue I've lowered XYZ_BELT_PITCH from 2mm to 1.9mm.  This seems to have resolved the build height issue. Although, I've not printed anything over 1/4 of my build volume.  After, because like you said it throws everything else off, I recalibrated XY dimensional accuracy using DELTA_DIAGONAL_ROD.

While I was at it I calibrated the extruder flow by removing filament tubing from the extruder, clipping it flush to the edge of the tubing, then extruding 10mm of filament and measuring the output with digital calipers.  Then, adjusting the last element in DEFAULT_AXIS_STEPS_PER_UNIT.  This was set to 186 and I found an even 450 to give me exactly what I needed.  Before adjusting the extruder I was compensating in the slicer by adjusting flow rate.

Next step will be to start on addressing what I think are retraction issues.  Also, I'm noticing there are some issues where infill is not connected to walls.  But this seems to be rare.

Also, I was having an infuriating problem with print edges curling while printing ABS.  This seemed to be completely dependent on ambient temperature.  I live in Texas (not by choice) and the printer is in my workshop which doesn't have AC.  In the mornings, when ambient is lower, the prints would curl every damn time.  In the heart of the afternoon they curled much less if at all.  From what I've read, this is best solved by building an enclosure, but I don't have time for that--so I cheated and got a big-ass heat lamp.  That seemed to do the trick, buuuuut... the heart started playing havoc with printer parts.  E.g., the clips holding the bed in place started to warp.  So, I've moved the heart lamp from shining indirectly on the printer and have it near it, to heart the air.  This seems to be working OK.

Next, I'll probably print the advanced delta calibration print you suggested to MEgg.  I'm sure I've still some adjustments to make to DELTA_RADIUS, however, I think they are minimum.

Three years later, I've got to get this printer dialed in.

« Last Edit: May 07, 2017, 08:52:47 AM by Ladvien »

jinx

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Re: Kossel Mini Z Calibration
« Reply #8 on: May 07, 2017, 11:09:17 AM »
Quote
Next step will be to start on addressing what I think are retraction issues.  Also, I'm noticing there are some issues where infill is not connected to walls.  But this seems to be rare.

you could combine the two bridging and retraction with the bridging cali.  http://www.thingiverse.com/thing:284380   but a couple of hollow cubes you nail retraction
 with http://www.thingiverse.com/thing:30171 what you looking for is hair free sides while extruding enough after retraction for the small walls of the columns " you can't really see it in the bridge test ". there a setting in slicer for it as for speed as fast as you can without stripping fila, start at 60 most extruders  do 60 just fine. " bajdi observation on speed ".

  funny thing with hairs on the prints sometime it work against you and other you want  it can be useful in catching the odd overhangs where you dont need supports by defaults, its a judgment call!.

ABS just nasty for curling of the bed  though  prit stick can hold for an hour or two, but making ABS juice or buying one of those stick mats best option for abs. personal dont buy a mat yet you'll possible score it to death before calibration right. PLA  a better choice right now while calibrating last thing you need is picky abs to test with drive you  mad  >:D   
« Last Edit: May 07, 2017, 11:15:55 AM by jinx »
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