Symptoms: Xeno calibrate sometime, and failed sometime, sometime it bite the tongue after "try" to calibrate.

Root to the issue: loose lock bolt on the gear, casing the gear to spin on axle.

Fix: rotate the gear on the axle to so the flat area on the axle is under the umbraco bolt and tighten.

This was solved with help from Jesper Graver Jensen  @ Sis Enterprise ApS (