View Full Version : Captive Nut Variation (Thanks Frank Ford)

01-22-2009, 11:16 PM
Nearly a year ago, I saw a project on the "Frets" (Frets.com) site and asked Frank Ford if I could use one of the projects for my class to learn threadding. Feel free to look on his site for how to do this, but I made some variations on the project as I tend to do when I get things going.

(two pic in this)


The basic idea is this. The rod is a 3/4 inch diameter - either brass, aluminum or stainless (I have made all three, but used 1117 and brass nuts for the students). They make the rod, which you see how in the site, but I changed dimensions. The thread on the rod is a 5/8-18 thread. made so to show a difference between the outer diameters and the inner thread diameter. The teaching in this is they have to figure the thread relief depths +.030 for the radiused grooves, and use Machinery's handbook to find out the allowable thread diameters and the pitch diameter. The student can't make this successfully if they do not measure the thread diameters with a calibrated pitch mic, you just can't get the nut to fit otherwise because you don't have the luxury of "trying the nut" on the thread.

Hint, if you turn turn rod in brass, use a single bar, brass color between bars varies.

Even the way it has to go together from the start requires finely turned single point threads with a sharp honed tool throughout and some very fine and precise facing and even re-facing throughout. Concentricity for allis critical, and the finished thread and ends are turned from either colletts (OK), or between centers with a drive dog (best for learning).


The nut is a simple tapped 5/8-18 thread in a 1" x 3 inch long or more round piece on the lathe, then set up in a 5-c index head and milled to .875 +/- .005 to leave very slight "rounds" on the corners - not dead sharp. even after milling, parts are re-faced, re-tapped, then back to the lathe for cut-off, re facing ect.

I made these examples today for my father, who loved the project. If you do this right, probably would take about two th three hourws for a good HSM. For the students, it took 9 hours to 11 hours with lessons (one week plus)

I am making two more tomorrow evening for myself. The stainless steel one is the shop show-off model, the two others will be for me around the home.

Thanks Frank Ford for this idea, I hope this is acceptable to you and shows how your work has helped a few students

01-23-2009, 04:00 AM
So, how does the nut end up on the threads between the shoulders?


Or, after the exercise, do you turn down one shoulder, install the nut, and solder on a sleeve to make the shoulder?


01-23-2009, 06:25 AM

The trick is that there is a thread inside the rod, see the link here http://www.frets.com/HomeShopTech/Projects/CaptiveNut/captivenut.html

01-23-2009, 10:01 AM
couple of ideas......

have a unthreaded section at the end of each end of the thread, like a real bolt.....observers are looking for where the seam is and with think one of the heads comes off, but if the nut is on a thread section with the ends unthreaded, full dia material, well, what thats a mystery.

secondly, have the ends hex head and turn the little chamfer on the end so they look like a real bolt.

I'll hand mine to someone and say "I need some more double ended bolts but they're really hard to find". Some will immediately grasp it with a " hey how'd you get that on"....others will hand it back with a "that's nice" look on their face. We can't all be mechanically inclined.

Frank Ford
01-23-2009, 12:34 PM
spope -

You're hat's a fine student project - your bolts look great. I think I first learned about it right here at HSM a few years ago. Funny, but I've all bot forgotten about it, Now that I'm hanging around the TechShop maybe I'll suggest it to them for consideration as a class project.

01-23-2009, 10:58 PM
I made 2 of those, gave one to my uncle.