I have a BP Series 1 that I just recently bought off of ebay and have finally got to start making chips with it. I have noticed that it is consistently off of the target dimension by .006-.007 in X and .004-.005 in Y. This comes with milling a circular pocket, rectangular frame, etc.. it doesn't matter what you are doing, it's always off close to the amount listed above.
I found that the spindle had some scoring inside of it near the top of the taper (NMTB30) so I polished it with a die grinder/flap wheel arrangement and it made the consistent chattering go away.. but didn't help the accuracy any to speak of. It even made it rattle the collet nut loose and drop the tool in mid-cut, but that seems to be gone too.
So, I figured there must be some sort of compensation tables in the centriod controls - and there is, but there is no description on how to adjust them and the numbers don't really have any rhyme or reason to their meaning. The programming manual just mentions calling Centroid for help.
I haven't looked real close at it, but are there any manual adjustments to the ball screws that can help take up the slack?