I have never use tung oil (mainly due cost) on all my projects,
instead I use varnish than finished it with as many coats (sanded
between each coating) of polyurethane as needed to get good finished.
However, if for example I need to finish a heavy use, long-lasting
cabinet door knob, shall I first varnish it, sanded and finished it
with as many coats of tung oil?

Please advice and thanking all in advance for replying.