I don't think you "have" to tap the center support. Read this thread on what others do for their center supports. Personally, I use a Lowes "roll pin cut to length and then use a long rivet through the center and hammer the end opposite the head. It has worked great on my first build.
http://www.gunco.net/forums/showthread.php?t=1105&highlight=center+support+sleeve
http://www.gunco.net/forums/showthread.php?t=1105&highlight=center+support+sleeve