Rob,

I found that there is a little 'slop' in the lower arm where it attaces to the main motor case. By loosening the two bolts that attach it to the case you can move it up or down slightly thereby adusting the position of the lower arm to either lengthen or shorten the distance between the blade holders. Due to the length of the arm a very small adjustment at that end translates to a much larger adjustment at the blade holder end.

 

Tom