Jim & Sharon wrote:

In my unheated garage i have 4 big tools with cast iron tops, a unisaw a
jet 18" bandsaw, a jet shaper and a powermatic 54a joiner. with a monthly
application of topcoat the unisaw bandsaw and the shaper
stay rust free but the joiner needs to be recoated at least once a week. Any
idea why the joiner is different than the other three?
....

Difference in metallurgy and finish probably...