Here is my stepper motor controller. I assembled it from a kit made
by Camtronics.
It is in a box I made out of masonite with a particle board base. I would probably be better to put it in a metal case to keep any EMF emissions from causing any interference, but I was unable to find any metal cases for a price I was willing to pay.
The controller is cooled my a 24 VDC fan located on the upper left side in the picture and it is set up to exhaust air from the case. There is an air intake on the middle of the right side. The V shaped piece on the right next to the air intake is a baffle. Before I put the baffle in the heat sinks were running quite hot. With the baffle in place I would guess that the temperature on the heat sinks has dropped 30 - 40 deg F and now the heat sinks get just barely warm to the touch.
The shiny silver item running from the lower left through the center are the step and direction signal wires that come in from the parallel port. When I moved up to the 550 in/oz stepper motors and increased the amperage to 5 amp per axis I started getting odd random movement on one axis. After messing around with it for a month trying to figure out what was wrong I struck upon the idea that I was getting a signal fed into the step input from the EMF coming off the mosfets and heat sink. So, I tried wrapping the incoming step and direction wires in strips of aluminum foil and connecting it to ground as a shielding. After this modification all random movement went away. The moral of the story is, if I had to build it again I would use shielded wired inside the controller.