As I mentioned above, I have the same milling head as Bob, but mine is, at the moment, bolted onto the back of my lathe.
Before going the whole hog and emulating Bob's set up with the X,Y table, I decided to try using it as it was originally intended; on the lathe. I haven't done this before as I have the Micro Mill for my small jobs.
So, I removed the lathe topslide and found that I could just about fit my small milling vice to the top of the cross slide if I drilled and tapped some new holes to fix the hold-down clamps.
With this done, and the vice mounted I did a trial run. Milling the surface of a 15 mm wide aluminium block.
(start simple). I was using a 10 mm cutter.
Then I discovered a snag.
You can't lock the cross slide.
Locking the saddle will prevent most of side to side motion, and tightening up the slide gibs helps.
But you encounter a problem. The back lash in the cross slide lead screw.
If, say, you do a cut along the rear of the job (left to right), and you are conventional milling, the cutter will pull the job towards the rear of the machine.
If you now try to repeat the operation along the front (right to left), the cutter again pulls the job. This time towards the front.
Come to think of it, it will also do this when you are milling along opposite sides of a job in the which ever way you are cutting.
Short of fitting some kind of clamp and always ensuring that the backlash is taken up in one direction I can't see an answer to this. There will always be backlash in the lead screw, and unlike the gib slides, it can't be taken out easily.
I posted this here because it may be something Bob has an answer to.