Some more unfocused work for today.
First I parted off 5" of 1/4" drill rod that will serve as the crankshaft. Rather than tuning down from larger stock to leave the mounting for the flywheel, my plan is to turn/drill/glue that mount to the crankshaft. The flywheels I bought at Cabin Fever have 7/16" center holes with the ability to tighten onto the shaft with clamp screws. Therefore, no key needed to retain the flywheel. I'll wait to attach the mount to the shaft at assembly time, and as well I'll wait to fit the crank at the other end once that part is made.
Next I revisited the issue of providing the end of a 3/32" eccentric rod narrowed to 1/16'. I mounted my tapping chuck on the lathe with a short length of 3/32 rod, and was successful in drilling a 1/16" hole.
I inserted a length of 1/16" drill rod in the hole and secured it with Loctite 620. I'll let it cure for a day and then see if I can thread the end 3-48 without cutting into the smaller rod.
Last part of the day is the crosshead. I decided to make it from brass rather than steel, but I doubt it matters. Starting with some 1/2" diameter brass rod, I drilled and tapped 2-56 for the set screw.
Then turned down the spigot.
Then over to the Bridgeport to machine the sides. I was originally going to do this part on CNC but decided this way would be faster. In reality it was about the same amount of time.
Then drill and tap the sides for 3-48 and then drill/ream the top for the 1/8" piston rod.
Then all that was left was to part off on the lathe and sand off the nib from parting.