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Three-Axis Calibration Unit Object

by wildseyed, published

Three-Axis Calibration Unit Object by wildseyed Nov 15, 2012

Description

Feature dimensions are multiples of one millimeter, so you can scale the object in any direction prior to slicing, to get the desired object size.

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Instructions

Set your scaling. You can go as low as your layer height, or as large as your build volume, or anywhere in between. Slice, and print

The method I describe below helps to stradle the calibration between inner and outer loops. In some cases, the slicer is already making some allowances for inner loops, so this method may be affected by that.

For any given axis:

Cspmm = Current Steps Per Millimeter (This is the value presently being used by the machine. Typically in firmware EEPROM settings.

Nspmm = New Steps Per Millimeter (This is the value you will arrive at once you have performed the calibration. It will take the place of Cspmm)

Cdo = Commanded Distance Outer (This is what the part's outer diameter should be, if it were accurate.)
Ado = Actual Distance Outer (This is what the part's outer diameter measures out to be in reality. Taking an average of Ado's along the edge of the calibration object is recommended.)

Cdi = Commanded Distance Inner (This is what the part's inner diameter should be, if it were accurate)
Adi = Actual Distance Inner (This is what the part's inner diameter measures out to be in reality. Taking an average of Adi's along the edge of the calibration object is recommended.)

Sro = Scaling Ratio Outer (this would be the corrective multiplier to use if all you cared about was the outer part dimension)
Sri = Scaling Ratio Inner (this would be the corrective multiplier to use if all you cared about were the hole dimensions in the part being accurate)

Asr = Averaged Scaling Ratio

Cdo/Ado = Sro
Cdi/Adi = Sri

Asr = (Sro+Sri) / 2

Nspmm = Cspmm * Asr This new value will be very close to perfect, assuming everything was measured properly.

Once the new value has been entered into the Firmware/EEPROM, you can re-print the calibration object, and repeat the whole process to verify, or itteratively improve on the previous result. You will probably never get it 100% spot on, due to the infinite number of variables that can affect the print extrusion, but it will be very close.

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