I managed to get it in one try using the following approach.
Screw crown on full length stem (make sure it bottoms/is threaded all the way on.)Install in movement, thru case.Measure distance with caliper between top of tube, and base of crown.Unscrew crown from stemCut [insert measurement] from stem.Hand file burrs.Test fit.(Lather, Rinse, Repeat as needed)When right, use Loctite 290 between stem and crown.Use stem lube before final assembly.
This is for Rolex style that has the 'spring' push in and turn. The above method should get you to the point where the spring action takes up the slack necessary to get a successful screw down.
If this leaves you a little long, just use a hand file to slowly take a little off as needed. If you only have one stem available, err on the long side (shorten your measurement) and hand file as needed. Diamond files work great.