I want to make a Tangential knife with a stepper controlling the tangential rotation.

First step is to make a working "drag knife" that can be used as a tangential knife later.
Since my router's ER11 Spindle can already provide rotation, I made a Working Drag knife by
lathe machining down part of a $2.95 Craftright Scapel knife holder that has an 7.8mm diameter Aluminum down to 6.8mm to fit a 7mm ER11 collet.  Then cutting it to length.
The scalpel blade was found to be too soft for cardboard. So I just snap off one section of 18mm wide Olfa cutter, grind off part of it so that it will fit Craftright Scapel knife holder
and I have a $4 dollar Drag-knife.

Works like a dream based on "caster-wheel principle" cutting packing cardboard.
Of course the THE SPINDLE must be switched off.

Excellent