Problem with line of available punching zone in angle line 1

Recently, there are several precision problems(around 2-3mm) happened to the line of available punching zone in angle line. After checking at sight, check the line of available punching zone of B axis by vernier caliper, 130-->120-->130-->120-->130-->120 forward/reverse positioning, we noticed that the gap of screw reached 0.6mm, as for an old angle machine with consideration of error, which is 3mm of processed workpiece of, the gap of the screw doesn’t affect single-row hole error.

Let,s see how does the workpiece look like. Just in time, the processed workpiece still existed, after measuring them, a moment was discovered, a 7-meter workpiece, on one head of A side line of available punching zone, there is a 2mm shortage, on one end of B side line of available punching zone, a gradually varied reversal errors happened to a 75X5 angle with a 6-year-old angle machine, the mode is JX2020 enhanced.