I have a Milwalkee 7 1/4" circular saw. When I tighten the nut to secure the blade it continues to turn never completely stopping. Then when I run the saw it comes loose again every time. I've taken nut and washer out, cleaned and shop vac'ed it and it still won't tighten. Can hear it turn mototr inside. Suggestions? Thanks Jim
Either you're not using the arbor lock feature (look for a button or lever nearby which engages a hole or slot in the arbor as you turn), or your bolt is stripped.
Use the arbor lock or replace the bolt.