Okay, I got it fixed. The short answer is that I’m using a terminal block to connect the 4-conductor cables from the steppers to the dupont connectors that plug into the ramps. Two of the wires for the z axis were clamped on the insulation instead of the wires. Works great now!
I looked up the model number on the steppers and got the data sheet. It said rated voltage was 4.2. I tested the power going to each coil of the steppers. The x and y axes were plus or minus 1.60v. The z axis was plus or minus 3.56v. Should be good, right?
Thanks for your help! I’m getting ready to tape a piece of paper to the work surface and let the machine write with a sharpie.