Here are the first couplings I made using 1/4" I.D. brass tubing and two part epoxy to attach them to the stepper motor shafts.
The motors had round shafts (no flats) and I applied the epoxy and rotated the sleeves while holding the motor shaft stationary to evenly spread the epoxy between the shaft and sleeve. These are the type of couplings used in the original Nut & Volts Automatic Coil Winder article.
The epoxied on sleeves are on really straight, but I really didn't like the idea of permanently mounting the sleeves to the motors so I started looking for other inexpensive solutions that I could make from materials that I could buy locally.
The stepper motor above is one of two small and under powered stepper motors that I bought from a local surplus store to use temporarily while building the coil winder. I made my first removable couplings from nylon spacers but the spacers have a loose fit to begin with and deform when you tighten the set screw.
The second coupling I made from an aluminum spacer I had is better but I can't buy them locally.
The bronze couplings I made from bronze bearings have the best fit of the removable couplings and are made from materials that can be purchased from a local home center or hardware store.
A negative of the bronze couplers is the wall thickness of 1/16". Very little wall thickness to tap threads into for the set screws, although I have put quite a bit of torque on the small hex key wrench tightening the set screws several times without having any issues with them stripping. At this point I don't know if it will become a problem in the future.
My latest couplings are made using 1/4" x 3/8" x 1" bronze bearings (bushings) and are attached to the motor shafts with #8 - 32 x 3/16" set screws.
I also used #18 x 3/4" brass escutcheon pins to secure the coil winder threaded and brass rods to the couplings.
I cut the brass pins to size and filed the end smooth than used vinyl tubing with a 3/8" inside diameter (1/2" O.D.) and cut the tubing to about 1/4" width to hold the shaft pins in place.
I heated the vinyl tubing with a hot air gun to straighten it and to make it easier to cut through the tubing with a utility knife.
In the images to the right you can see the 1/4" O.D. polystyrene tubing being used as a bushing between the 1/4" I.D. coupling and the 3/16" O.D. brass rod. The polystyrene tubing I used is made by evergreen scale models, Item no. 228 .250 diam (6.3mm). I bought it from a local hobby shop.
The rods are not rigidly held inside the polystyrene tubing. There is still some space between the rods plastic tubing allowing tolerance for alignment issues. To remove the end-to-end play in the carriage and winder rods, I cut two small pieces of soft cell foam and inserted the foam into each of the motor couplings
These bronze bushings are porous and impregnated with oil so the first thing I did was submerse them in isopropyl alcohol for a couple of days to degrease them because I am using them as couplings not as bearings.
The bronze bushings have a better fit than the nylon or aluminum spacers I used for the 1/4" stepper motor shafts and the 1/16" wall thickness doesn't seem like it will be an issue for this winder but it may be an issue for more demanding applications.
The cost of the bronze bushings locally are about $2.50 each. You can over sleeve them with another bronze bushing or a cheaper steel spacer to double the wall thickness.
Since making the bronze couplings I have since added nylon bearings to the motor coupling side of the coil winder so the construction of the motor couplings are less critical.
I have since improved my drawing and added a few more at my coil winder Coil Winder Updates Page.