Captive Nut Installer

This tool helps to install a captive nut in a cavity during a build. A captive nut is set in a cavity during a print, and the print continues around it, leaving it trapped inside. This is a great way to include a threaded joint in a 3D print, but it can sometimes be hard to get the nut into the hole. Depending on how the print is place on the plate the hole can be way at the back. The build plate is often close to the top and sometimes hot. The nut has to be placed squarely in the hole. If it's cocked it won't go in.

We often use neodymium magnets, but they are actually too strong for the purpose. They want to hang onto the nut and flip it out. This uses magnetic tape with adhesive. It's strong enough to hold a #6 square nut, but not so strong that it won't let go. I used Magnet Source Magnetic Tape with Adhesive, which is 12.7 mm wide (½ inch) and about 1.6 mm thick. I made the stick with a cavity that is wide enough to hold a square of the tape, and just a little bit less deep than the tape. This means you can set the nut in place, then slide the tool away. The magnetic strip is just a bit proud, so the nut slides right off and onto the unmagnetized part of the tool. The idea is to place the nut, then while continuing to press down pull the tool away, wiping the nut off the magnet. This places the nut, and the tool keeps the nut placed until the magnet is well away from it. 

I made this to install a thin #6 square nut (that's about M3.5 x 2.6 mm thick), but it will hold up a full size 5/16 hex nut (about M8), as shown in the pictures.

Print with the cavity up. No supports are needed.

There's a version with a lip at the back to keep the nut aligned. I'm not sure if it's beneficial.

It has a 100 mm long handle. It needs to be turned into SCAD model out of it so it can be parameterized.