Why would you make anything? Shaft couplings are readily available off the shelf, including inch to metric versions? The exact variety of coupling will depend far more on how precisely the two shafts are aligned, speed, torque and tolerable backlash than on the small size mismatch you have.
Edited in light of the comments below
Then you need one of two things; a reducer bushing/bore reducer or a shaft adapter
A reducer bushing is a sleeve much as you propose with the exception that it has a "C" shaped cross section to allow for tolerances and the shaft key. I've only used them with mating a metric shaft to a inch bore, but I'm sure you can google something. Worst case is you have a custom one made. They're typically brass or aluminum. The torque should not be transmitted through the adapter. If you have a keyed shaft, you'll need a special step key, which you can buy or if you have a mill, they're simple to make from key stock for the larger of the two slots.
If you have axial space, you can get a 1/2" to 14mm shaft adapter which has a female side that accepts your 1/2" shaft and a short 14mm shaft on the other side.