It’s a while back now. I think it was to do with getting enough movement on the cross slide. I normally have the topslide offset at 6 degrees, to give a x10 on the topslide dial, ie the feed is 0.0025mm/div instead of 0,025mm as calibrated.
I had to do the same thing when I turned the flywheel for the Victoria, I had to swing the top slide right round to get the tool to the edge of the work.
Steve