How accurate should the AXIS_STEPS_PER_UNIT number be?

The company that installed Marlin on my machine said 71.6

but this is maybe the real calculation:
(200 * 16) / (2.032 x 22) = 71.58196134574087

How accurate does the number have to be?

#define DEFAULT_AXIS_STEPS_PER_UNIT {71.6,71.6,1067.8,97.5} // default steps per unit for ultimaker 123 //2014/02/28 105->100 105->90

I printed a 10mm cube and got
x 10.21mm
y 10.40mm
z 10.27mm

What is to best way to get more accurate results?

The value of 71.6 steps/mm is only 0.02% lower than the value you calculated, so not significant. Your cube is about 3% too large. There are a few likely reasons:

1. External perimeters tend to come out a bit too big (and internal perimeters too small), because the plastic does not form a nice rectangular cross-section, but bulges at the sides. This will increase the size of a test cube by a constant amount. Over-extruding will make it worse.

2. The extruded plastic shrinks after cooling, by a factor depending on the plastic and the temperature change.

Try printing a 20mm cube to see how much larger that one is, and hence calculate the contributions of effects (1) and (2).

You can compensate for (2) by reducing the configured steps/mm.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I uploaded my firmware changes and now my LCD doesn't work (T-T)

http://a4jp.com/3d-files/marlin-2015-01-06th-23-28-00.zip

Any help on getting the LCD to work again would be greatly appreciated.

Edited 2 time(s). Last edit at 06/10/2015 03:59PM by a4jp.com.