I have some info on your A axis problem, but you may not like it... I went through the same thing recently. What model VF do you have? Do you have the high speed option inthe control?
I have a 1999 VF0-E (now VF-2) with the high speed option in the control. When I bought the machine, I asked if it would be possible to run a 4th axis also at high speed. They said "sure". Yeah, right.
Later I bought a 4th axis. And, lo and behold, once hooked up, it exhibited exactly the same symptoms as you describe. After much back and forth, I was finally informed that it was indeed not possible to have high speed performance with a 4th axis without having a co-processor on the main board. This would require replacing the main board and installing new machine software. I managed to get a deep discount on this because they had promised me it would work, but I still had to pay a good chunk of cash to do it.
Once that was installed, the 4th axis was tested - and whaddya know - it was exactly the same as before. Then, after much head scratching, the tech went in and adjusted a parameter for the 4th axis - I don't remember exactly which number now, but it was something like the number of encoder steps within which the control would consider the 4th axis to be "in position". i.e. he opened up the position window. Once that was done, it ran very smoothly.
So, I have no idea if the co-processor was really necessary - of course, they swear it is. I might try adjusting this parameter first. But I don't remember which one... Also I have no idea if that will significantly affect accuracy when running at high speed. I don't need to be that accurate, fortunately.
Anyway, maybe this helps, maybe not... --ch  |