It would be great if we could animate visibility!!
I do a lot of food processing equipment and it's nice in max to change a large chunk of cheese's visibility to 0 while changing smaller chunks to 1. This creates the illusion of cutting the food product or at the end of a conveyor instead of running off the screen the product gets to the end and disappears.
We will add this in v5. In the meantime you can add a translation to the part that will move it a large distance in very little time; effectively making it invisible (as an emergency solution).
Or even translate it a) off screen and b) very quickly underneath a Ground plane with 'Clip geometry below ground' enabled.
That will effectively make the parts underneath the Ground plane invisible.
Dries