Hello I wonder if it is a bad idé to connect two nema 23 steppermotor to one port of the controller board? I have tried it and it works if I don't drive the motors to fast. Can I harm the controller board or something else if I do like this?

As long as your controller board is set up to limit the current to the value of one motor it is unlikely to sustain any damage.

It is not, however, considered a very good idea to do this and it would much better for each stepper to have its own controller axis. There are many reasons but the modern controller chips measure back emf and reduce current when motors are stationary etc and connecting two motors (series or parallel) tends to confuse the poor little chip's logic.

Tweakie.

How would you hookup 2 stepper motors  to one port.

How would you hookup 2 stepper motors  to one port.

Either connect each coil bank (A,B) form each motor in series or in parallel to the 4 terminals on the controller.
 
Tweakie.