Tried this method which seems to go more smoothly than previous tries. The Cura printer definition file and the modified version of Marlin 1.1.9 can be found here. They seems to be working fine. I re-sliced the model using Cura 3.3.1 and that seems to work fine now.
From the comments in this thingyverse thread
OK, I've re-flashed the firmware and carefully took notes on the video you posted on this thing, and now the bed is perfectly level everywhere.
I've made a list of exactly all the steps in the video, in the correct sequence, and I'm going to post them here as a reference to anyone who comes looking for it in future (in case they miss the video):
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Connect Probe
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Prepare -> Delta Calibration -> Auto Calibration
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Prepare -> Delta Calibration -> Set Delta Height
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Prepare -> Delta Calibration -> Store Settings
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Remove Probe
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Prepare -> Move Axis -> Soft Endstops: Off
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Prepare -> Move Axis -> Move Z
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Put paper on bed. Move Z down towards bed until nozzle just grabs the paper. Write down the Z-height at which the nozzle touches the paper. We will call this "touchdown Z" Prepare -> Delta Calibration -> Delta Calibration -> Subtract contact height from "Height"
Formula: Height - (touchdown Z) = New Height
E.g. if touchdown z was -0.1 and delta height was 334, new delta height is 334 - (-0.1) = 334.1 If touchdown z was 0.1 and delta height was 334, new delta height = 334 - 0.1 = 333.9
- Prepare -> Auto Home
- Control -> Motion -> Probe Z offset -> Adjust it using this formula: New offset = Old Probe Z offset - touchdown Z) =
E.g. If old offset was -16 and touchdown z was -0.1, new offset = -16 - (-0.1) = -15.9 If old offset was -16 and touchdown z was 0.1, new offset = -16 - 0.1 = -16.1
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Control -> Store Settings
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Prepare -> Auto Home (to apply new Z-height and probe offsets)
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Verify Z-height with paper again (i.e. lower nozzle to Z=0, make sure it just grabs the paper)
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Auto Home
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Connect Probe
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Prepare -> Level Bed
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Control -> Store Settings
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Auto Home