Get into the habit of only using the Brake when you need it instead of an automatic reaction if that is possible on your saw. The nut loosening is most likely from braking and those older Deltas had a very strong brake. If the blade spins on the arbor enough saw is useless as the cost of repair is too high to justify. Saws with brakes require a very tight arbor nut as the braking forces want to make the nut back off.