Here is a way to make a computer controlled milling machine. That puts the real power of a computer control build a kids desk into the hands of the average human.
Small enough to set on the desk but scalable to any size. All most all the parts can be purchased in local retail stores. I used one inch pipe just for fun but as it turned out it was pretty handy too. When I needed to make adjustments I could just tap it with a hammer.
As you can see the post that holds the Z axis doesn’t have to be in the center. Next its time to add the rails for the X axis stage. 4 inch U chanel aluminum that you can get from the hardware store. Put a washer under each end to space the rail off the pipe just a bit. Don’t worry about the rails being perfectly parallel. Now mount the stepper motor with a bracket like you see here.
The round thing is a bearing. You can get them out of motors or buy them at a hardware store. Mount it to a short piece of aluminum like so. Here’s a video on making the bearing fixture. The Y stage is just like the X stage but turned 90 degrees. Mount two rails and a motor on the X Stage and then take another piece of flat material and a U channel and make the moving Y stage. Make the little bearing thing and a coupling nut for it too.
When your done it should look like this. Again we are going to reproduce the X and Y Stage to create the Z axis stage. Take a flat piece, here I used a piece of white Plexiglas. Mount some rails and a Motor to it. Then make a moving stage piece with a u channel and a roller bearing. The four posts you see on the stage will hold the motor tool. Now we slap the motor tool into the Z stage.