Here is another test piece, which I've called the wall of death.
It mills either side of a circle and should, theoretically, leave no material. In a similar way to the last pattern, my machine does leave some traces in wood.
This seems to come from about a thou of play in the chinese ball screw on the gantry. I already had to change the ball bearings since it had about 2.5 thou new. It seems the Chinese make these cheap parts with lesser precision then some poor guy has the job of trying different ball sizes until it's about right. In this case I must have got someone who was ready to jump out of a window and didn't really care any more. Luckily, I have a selection of balls: 3.15, 3.16, 3.17 ..... Hopefully the next size will not be too tight.
Looks like another strip down.
Anyway the pattern may be a useful diagnostic, focussing on what I saw in the previous , without the multiple passes of the other shapes possibly destroying part of the evidence. When cutting a harder material like ali, this will quickly show up problems due to lack of rigidity.