I've been contemplating how to go about making those too. Making replacement brass nuts for the compound and crossfeed seem trivial by comparison. In looking at the piece to be made, I'm wondering, do I cut the block to size, then cut out the half thread and then mill the final shape? Or, and I'm leaning in this direction, use a rectangle that will have the thread cut in the middle, mill the ends to match the half nut configuration, then cut it in half with a bandsaw. Not having much experience with a vertical mill the most expedient solution doesn't jump to mind.
Then there's the question of where to obtain the appropriate size acme thread tap. I ran across an idea utilized by someone else, where they took the screw which matched the thread pattern they wanted, tapered the end slightly, cut in two furrows with a bit of a rake on the cutting edge, and used that. Fed it in as if it were a boring bar and claimed the results were perfect. As ACME thread tappers are hardly what I would call inexpensive, and add to that I would need three different sizes. That being said, I happen to have a few bits of pristine ACME threaded rod in 2 of the required sizes already, and will happily experiment to see if that method is viable.
Terry
