Measurement/Circle Test

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Incomplete Working Notes (Please log in and edit)


Short version: this is a cheap but clever trick to measure squareness of your machine. You really want a 1-2-3 block and an edge-finder, but that adds $50+ to the price of your machine.

We need pictures of this.


  • 2x Inline Skate Bearings
  • 1x Precision Calipers, (Digital or oldschool)
  • (Contact electronics - optional)


  • Bolt down one bearing, the Bed Bearing the upper face of your print bed.
  • Attach the other bearing, the Test Bearing to the lower end of your extruder, or using TestBearingMountingHardware.
  • Using the software, move the Test Bearing so that is roughly lies above Bed Bearing.

Now move the test bearing to the eight corners of an octagon centered on the bed bearing, measuring the outer bearing-bearing distance with the calipers.


Using your favorite spreadsheet (table showing mockup), you now know the off-squareness in the xy plane.

Now plug in the generated correction matrix fudge factor into your machine definition, and the software will correct for your diagonal machine parts and make square parts. To this accuracy: