You put the rivet in hot and the fan is room temp. Throw in the hot rivet, set the head on an anvil and pound it over with a 3 lb engineering hammer.
When it cools down it will be tighter than a SOB . . .
And the rivet will be strong as you just work hardened and realigned the molecules and relieved the stress at the same time from the pounding.
Win, Win !
