This is the single most important build step on a 4-axis machine. If the towers are not parallel and their X/Y axes not aligned, the wire is skewed and every cut is off. Build both tower carriages identically, mount them on a common, flat base, and measure diagonally (corner to corner) to confirm the frame is square — equal diagonals mean square.
Use a steel rule or a known-square block to set the rails parallel, and check that the wire is perpendicular to the base at both ends with the carriages at the same coordinates. Re-check after tightening everything. A dial indicator or even a tape measure across several positions catches drift before it ruins foam.
Use a steel rule or a known-square block to set the rails parallel, and check that the wire is perpendicular to the base at both ends with the carriages at the same coordinates. Re-check after tightening everything. A dial indicator or even a tape measure across several positions catches drift before it ruins foam.