After realizing that I could not make a new pump rod for my Monotype caster on my lathe (the lathe bed was not long enough), I considered several ways to get around this problem.
As it turns out the solution was easy: make a small extension to lengthen the existing spring rod.
I started with a shorter piece of 5/8″ round steel, turned one end down to 7/16″ and threaded it to match the lower end of the existing spring rod. I used a hacksaw to rough-cut the rod to length.
The other end of the rod was faced to the correct length, drilled, and tapped. I had a little trouble getting the bottoming tap started in the hole so the first turn or so of threads is a bit rough. A short 7/16″ counterbore accommodates the unthreaded portion of the end of the spring rod.
The photo at left shows the extension installed on the spring rod. The joint is tough to see, but it is a little over two inches from the lower end of the rod (which is at the top of the photo). Once I am sure everything fits correctly I will put some removeable threadlocker on this joint so that future removal of the spring rod does not leave the extension behind. If this were to happen it would be very difficult to remove since there would be no place to use any tool to turn the rod extension.
There is a small possibility that this joint might be weak enough to break eventually, but I would hope that by then I would either have a larger lathe or have found a genuine part to replace the home-made one.
Now the only job left is some mill work on the extended-stroke piston rod.
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