I just received a Sigma from matter hackers. The y axis was having some problems. First is that it crashes the end of travel at the left front of the machine. It turned out the gantry was 5mm off square. I fixed that by rotating the left pulleys.
How tight should the belts be? I can squeeze the y axis belts so they touch midspan with almost no force. Maybe an ounce.
Next is that every printed object is a little short on the y axis. Circles are out of round about 0.015". Circles have a flat spot front and back. I was trying to check the backlash by issuing g codes and monitoring a dial indicator. I installed pronterface. X axis G commands work as expected but Y axis commands will not move the stepper motor unless they are about 5mm or more. A G0Y1 from Y=0 does nothing. 10mm works though. This is not the case with the x axis where it responds as expected.