Wedge the platter upward to the end of its travel and then gently tap the spindle with a hard cover book or a tack hammer. Operative word is “gently”.
Some platters do bear threaded holes which facilitate their removal.
Help! Monolith turntable platter removal
I'm preparing to move house and wanted to pack up my Monolith turntable so I began what I thought was a simple process of disassembling the turntable. OK - it's not that simple. Can anyone guide me in removing the platter? I made the mistake of first disconnecting the drive belt, and now it's loose under the platter.
I emailed Monoprice, but don't know if their customer service is any good, so I thought I might get advice here.