Y axis problem now solved after putting a heatsink onto the Y axis driver chip. Y was slipping when test cube got to walls, and now is steady. Colin recommends avoiding heatsinks, and I can see why. The tape that comes with the driver boards looks to have a metal film as the substrate, which could cause shorting issues. I was careful. Now that printer is working, will print fan mounts tonight. Maybe a fan can eliminate the need for the heatsinks.