Fixture for Installing Threaded Inserts

by: Ben Blackwell
AWA member 

About a decade ago, the Albuquerque section of the American Institute of Aeronautics and Astronautics (AIAA) built a flight demonstrator for the Explora Science Museum in Albuquerque, NM. The refurbished flight demonstrator was on display at the museum grand opening in December, 2003. The design called for about 200 threaded inserts. After some simple experimentation, it was quickly realized that some kind of fixture was required in order to get the threaded inserts properly installed in oak. The pieces of the fixture that evolved from this project are shown below:

The material list for the fixture to install 1/4-20 brass inserts is as follows:

1. 1/4-20 threaded rod, about 3 inches long; precise length is not very critical
2. 3 each 1/4-20 nuts
3. 1-1/2 inch length of copper tubing, ID slightly larger than OD of threaded rod
4. enough masking tape on the upper OD of the threaded rod so that the copper tubing fits snugly

A 3/8 inch pilot hole is drilled in the board to receive the threaded insert. The assembled fixture is shown below; it is mounted in a drill press chuck with the threaded insert in place. Make sure the power to the drill press is turned off during the entire operation. Do not over tighten the chuck as the threaded rod must be free to rotate inside the copper sleeve. Downward pressure is applied to the chuck while the wrench is used to rotate (thread) the insert into the wood. The fixture simply keeps the threaded insert perpendicular to the work piece. The purpose of the masking tape is to keep the threaded rod from falling out of the copper sleeve. If you are working with a hardwood, there will probably be some lifting of the wood around the hole; if this is a problem for your application, then consider chamfering or counter sinking the hole.

For comparison purposes, the same size stainless steel threaded insert is shown in the first figure. The stainless steel insert is obviously stronger than the brass. Another difference is that the stainless steel insert has an allen head and the internal hole/thread size is smaller than 1/4-20. The slot on the (soft) brass insert is next to worthless while the allen head on the stainless steel insert could actually be used to tighten (or loosen) it.

A few years ago, Fine Woodworking had an article on a similar fixture (I do not remember the date) but at the time I thought this design was better. If you have suggestions for further improvement, feel free to email me or phone me at 505/897-5090.