this is a good stuff, and need a tailstock for too..
please note it has harmonic drive, what actually used for at 5 axis machines for B and C axis..
relative high gear ratio 1:50 or 1:100 makes possible small stepper sufficient..
CNC Router Rotational Axis The 4th Axis A Axis for The Engraving Machine 1650 | eBay
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another option beltdriven, faster, also has very little or neglectible backlash, but require larger stepper..
CNC Router Rotational Axis The 4th Axis A Axis Claw Set for Engraving Machine | eBay
you also can lloking for a combined type..
where 2 motor applied onto one rotary attachment..
a stepper for controlled movement, and a regular electric motor for turning task.. where you use lathe cutters instead endmill