You could try building a simple CNC machine. Then you could test your fabrication skills and use it afterwards to make cool stuff. It wouldn't have to be anything complicated either. Use a simple drill for the blade and make some sort of arm to move it around. Then write a basic program to run it. Follow YC's style. Make something simple as fast as you can that just works and then as time goes by improve it. Man, I think I know what I'm doing this weekend.