You will probably need something to lock it as well unless maybe you have the spindle set up like a servo somehow.
My Fadal uses a small air cylinder with a roller on it, and theres a ring on the spindle with a notch in it. Theres also a hall effect sensor that activates when notch lines up. Probably wouldnt be hard to make a setup like this.
On my machine now to orientate i turn spindle on slowly, delay for a while to let it reach speed, wait for it to see sensor, delay again until close to notch in next rotation, then turn off spindle and enguage air cylinder. Adjust speed and delay until it stops in notch smoothly. good luck with it