So I have been trying to set up a jig to cut a 4-1 merge collector using 1.5 inch pipe for an SAE project. I set it up so that it would cut at a 15 degree angle, and I was able to rotate the pipe exactly 90 degreesin the jig to make the second cut. I practiced on pvc first, however I cannot get the merge to meet up well in the center. each cut is ~5-10 degrees off in the center. When I adjust for this, the outlet diameter becomes very small but the centers meet up.

What am I doing wrong? I have gone through about 10 feet of pvc trying to figure this out!