A Classic Exercise
Captive Nut
© Frank Ford, 2006; Photos by FF

I'm still at that "lucky" stage of my efforts to learn machining technique that pretty much every project is something of an adventure.  Today, though, I felt like doing something different - a little exercise that doesn't result in a tool, fixture or other useful item. Just for fun I made this little classic machinist novelty.

I cut a couple of pieces of 5/8" diameter 304 stainless steel, faced and drilled one end of each:

Then I tapped them 5/16-18, using my hand tap aligned at the tailstock:

I took special care to face off the ends as smoothly as I could:

After screwing in a short section of threaded rod, I could screw the sections together:

The sections went together nicely, with no gap:

Mounting the assembled rod between centers, I took a light pass over the length to true up the sections:

My lathe had most recently been set to cut 20 tpi threads, so I just left it set that way and proceeded to cut some threads centered at the joint in the piece where I'd turned down the diameter a bit:

Then I stuck a short section of 7/8" brass hex stock in a collet, drilled, bored, and tapped it to match the threads I'd made on the rod:

Separating the two sections of the rod, I was able to check the threads as I cut, and when I got a nice loose fit, I trimmed up my brass nut.

Here's the whole thing, after I buffed up the rod ends and the nut:

Screwing it together with a bit of blue Loctite, and cleaning the threads completed my little puzzle:

With its loosely fitting nut, this gizmo is irresistibly fun to twiddle, and it's a little conversation starter. Even with my myopic close up vision, the joint is invisible.

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