Not certain, but: Based on 'typical' Myford engineering, the handle probably acts as a lock-nut … Hold the hexagon with an open-ended spanner, and 'bump' the handle with the butt of your [other] hand.
MichaelG.
[don't blame me if I'm wrong]
.
Edit: corrected a typo.
Edited By Michael Gilligan on 13/10/2015 20:04:06