Step 11: Build a Coupler

UPDATE: I abandoned this design later as I replaced the threaded rod with a lead screw

Drill 1/4 inch hole straight thru.

Drill 5/16 inch hole half way thru. Drill from same side as 1/4 inch hole was drilled, this keeps them perfectly aligned (assuming you are using a press drill)

Tap the 5/16 hole with a 3/8 tap. I use a press drill with a weight on the handle to start the tap by hand (no, the drill is not turned on). Otherwise the hole will NEVER be tapped straight and this is critical.

Drill and tap thru side for 8-32 bolts.

Bingo, add a couple bolts as set screws and the 3/8 threaded rod is coupled to the stepper motor, and straight too! (Only took 4 attempts… though I wasn’t trying very hard the first couple)