[jerryrigge]

Regarding direct drive stepper to rack systems, although workable, present several issues that can become problems. Because they use a high gear ratio (mine is .75 to 1, overdrive) they operate on the margins of needed power. If they cannot accelerate as fast as needed they will miss steps. You might tune the motors using Mach2 or other program and make it workable. I did. But it is not flexible. My acceleration and velocity setting must be set right.

Motors seems to be a little bit warmer than it should. Demands on the motor will be higher, although some motors will certainly provide enough power. Don't expect to use an under powered motor direct drive.

Direct drive will dart back and forth like a rabbit. It will go faster than is practical.

Bearing load is another concern. If the rack has any irregularities in it then the bearing on the motor will get that extra pressure. If the bearing binds a little it might miss steps.

Just my initial thoughts after 3 hours of testing.