Calibrating XYZ

Shawn Fitzpatrick

May 29, 2016 15:06 Edited

Calibrating XYZ

Correct calibration is important for accurately sized prints. This is not that important if you are just going to be printing artistic or fun things. It is important if your prints have to fit with parts coming from other sources, such as metal or machined parts.

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. Print the 20mm-box.stl file
   
   
3. Before removing the box from OBG, mark sides X and Y
4. Measure X,Y and Z using a caliper or micrometer and record
   
   
5. Perform calculation:
   
   (Commanded size x old calibration number) / actual size = new calibration number
   
   In my case here are the calcs I ended up with:
   
   X - (20 x 118.52) / 20.35 = 116.48
   Y - (20 x 118.52) / 20.3 = 116.77
   Z - 10 x 4031.5 / 9.8 = 4113.78
   
   
6. Save the results
   
   Simplify3D >> Edit Process Settings >> Scripts tab >> Starting Script tab >> First through third lines - Change:
   
   

   M92 Xxxx ; calibrate X

   M92 Yxxx ; calibrate Y

   M92 Zxxxx ; calibrate Z
   
   To reflect the results of your calculations.

7. Repeat steps 2 through 4.
   
   If the cube now measures exactly 20 x 20 x 10 then you have successfully calibrated your OGB. If not, then repeat the rest of the process.

8. When you have the calibration completed
   
   Update your copy of the OpenGB Config File so that if you need to reimport it into Simplify3D again in the future you won't loose your calibration. Open the .fff file in Notepad or Notepad++ and replace the four instances of:
   
   "M92 X118.52 ; calibrate X,M92 Y118.52 ; calibrate Y,M92 Z4031.5 ; calibrate Z,"
   
   with your calculated results, i.e.
   
   "M92 X116.48 ; calibrate X,M92 Y116.77 ; calibrate Y,M92 Z4113.78 ; calibrate Z,"

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  Matthew Fiedler

  May 29, 2016 15:31

  Shawn, I would urge you to look at a few more things before changing the x,yor z calibration numbers. Those numbers are based upon belt and pulley specifications for x and y and the leadscrew specs for z.

  When you performed the extruder calibration it was just a rough calibration. To fine tune your extrusion print a 40mm box, hollow except for 2 bottom layers and no top layers, single wall thickness. Measure the wall thickness with a good quality calipers or micrometer (you will spend more than $30 for a decent calipers). Be sure to measure the wall thickness of only one or two layers because if you measure over too many layers at once then you are also measuring movement variability in x or y. For the z axis please keep in mind that if the layer height is not an even multiple of the overall height then Simplify3d will round up or down when adding the top layer. Second thing that affects overall height is the bed home position. The bed needs to be touching the nozzle to give you a true z height.

  When you change the calibration numbers you are essentially correcting for any variability from the belt, pulley and threaded rod manufacturing process. I don't recommend changing the x,y,z calibration numbers until you can rule out all other possible sources of variability.

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  Shawn Fitzpatrick

  May 29, 2016 16:23

  Thank you for the excellent feedback and advice Matthew, it is much appreciated. I will do the test you suggested this afternoon using my micrometer - I bought a set from a tool and die fellow that was selling out last summer.

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