Yes, there will be set screws at the encoder mount to set a belt tension.
I’ll be making the new rotary table from scratch.
Ok. Are you going to use cast iron as most tables use that to dampen vibrations?
The green section will be steel but the gray surfaces will be cast iron to damp vibration.
That project is several steps above hobby grade projects. Have you looked at Haidenhain encoders for rotary components?
What is the ratio of teeth on the table pulley to teeth on the encoder pulley?
The machining is more advanced, but that’s my strong suit. The electrical business is what I struggle with. It seems like displaying degrees from an encoder should be hobby level stuff.
The Heidenhain stuff looks nice, but I’m still left with the problem of displaying degrees. Does the TTL signal work better for this?
I haven’t made the selection yet, but probably 3:1.
Sounds like you best get started learning programming for your Arduino. TTL is best or higher voltage for use around operating machinery. Programming is just as much fun as machining and a lot more forgiving!
If you want hundredths of a degree resolution you would need 36 thousand encoder pulses per table revolution. With a 3:1 pulley ratio, you might use a 3000 pulse per rev encoder and a library that reads all 4 pulse edges so 12000 pulses per encoder rev times 3 = 36000 pulses per table rev. The Arduino encoder library by Paul Stoffregen would probably work fine, it's in the IDE library manager.
As far as wiring, I would choose an encoder with NPN open collector outputs and use external pullup resistors (10 k) at the Arduino pins.
Better than what?
What they call TTL is actually RS422.
So you will need to built an interface circuit.