HermannSW:
Reason is that minimal voltage of A4988 is 8V, and I am not sure what the tiny stepper of sliding-table rated 5V does when powered with 8V.
It is normal to use much higher voltages with an A4988. I think it can go up to 35v.
The way the motor is protected is by setting the current limit on the A4988 to (or below) the max that the motor is designed for.
...R