Calibrating Extruder

Shawn Fitzpatrick

May 29, 2016 03:28 Edited

I found that the OpenGB Calibration process varies slightly from the GB process in the re3D Wiki. This worked for me, but is not approved by re3D so use your discretion in following my guide.

Calibrating the filament feed

Correct extrusion quantity is important for quality prints. If the extruder is pushing too much plastic layers will overfill resulting in bumpy and uneven surfaces. Extruding too little plastic will cause weak bonds and gaps between layers resulting in a weak structure.

1. Connect Open Gigabot's USB cable to your computer
2. Turn on Open Gigabot
3. Start Pronterface
4. Click on <Connect> button at the top of the screen

Read the current extruder calibration number in Pronterface

Pronterface will display:

Connecting...
echo:Stored settings retrieved
echo:Steps per unit:
echo:  M92 X118.52 Y118.52 Z4031.50 E1000.00

...

1. Check that filament is installed in extruder
2. Heat hot-end to suit your filament
3. When hot-end is up to temperature extrude 10mm of filament at 60mm/sec until you see filament coming out of the hot-end
   
   NOTE: I found the recommended 100mm/sec feed to be too fast for OGB and cause the extruder drive to jump teeth.

1. Mark the filament 100mm and 150mm from rear filament tube shelf
2. Extrude 80mm of filament using Pronterface
3. Measure actual extrusion distance
   
   Deduct what is remaining from either your 100 or 150 mm marks
   i.e. 100 mm mark with 15 mm remaining equals 85 mm of filament feed
   
   
4. Perform Calculation
   
   (Commanded distance x old calibration number) / actual extrusion distance = new calibration number
   
   (80 x 1000) / 85 = 941

In Pronterface:

1. Type “M92 E941” <enter>
2. Type “G92 E0” <enter>

Repeat the steps above to verify the extruder moves exactly 80mm when commanded.

In my case I ended up with my second calculation being

(80 * 941) / 81 = 923.4

I rounded up to 930 which seemed to work perfectly

Save the new extruder calibration (M92 Exxxx)

Simplify3D >> Edit Process Settings >> Scripts tab >> Starting Script tab >> Fourth line - Change "M92 E1000 ; calibrate E" to reflect whatever your E number is

or

Slicer-> Printer Settings -> Custom G-code -> Start G-code (M92 E1000 ; calibrate E)  (Unconfirmed...)

or

Open the OpenGB Config File in Notepad or Notepad++ and replace the four instances of "M92 E1000 ; calibrate E" with "M92 Exxx ; calibrate E" substituting your calculated E value

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  Matthew Fiedler

  May 29, 2016 04:23

  Hi Shawn, I appreciate your taking the time to share your findings! Can't wait to see your next print and impression of any change in quality after the extruder calibration.

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  Shawn Fitzpatrick

  May 29, 2016 16:29 Edited

  

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  Robert Oakley

  May 29, 2016 18:21

  For the cold ends I would suggest you print them with base down for the best results

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  Shawn Fitzpatrick

  May 30, 2016 22:36

  Base down with support I assume? Given that my first attempt had a fair amount of fallout under the motor mount...

  
  I had already started the print with it flipped so I left it run so I could see the
  result and compare.

  
  It warped more than i expected which I presume is an effect of printing on top of all of that more or less unheated support - especially given I wasn't going to print ABS with the hood closed again.
  
  Still pretty cool that I was able to make a half way decent repair part with a damaged machine LOL
  
  
  
  Didn't really think about how much the iPhone lens distorts things till I looked at these pictures. These surfaces are all very nice and square, overall aside from the one surface mentioned above, the print came out extremely well.
  
  
  

   

   

   

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