Do you think I need a trackball mounting plate?
Unless you have an Ultimarc U-Trak or change to a metal control panel, the answer is almost always yes.
Have you found a build with a wood control panel that uses the same trackball that you have (Happ? Betson?) but doesn't use a mounting plate?
How much material would you have to route out of the underside of the CP to make the trackball usable without a mounting plate? (quite a bit to get the trackball high enough to keep your hand from scraping on the edge of the hole)
How much material would that leave and would the resulting trackball mount be strong enough to withstand vigorous play? (not much and probably not)
Scott