Saturday, April 2, 2011

An Unorthodox Tee-Nut Application

A typical tee-nut is a threaded barrel with a big spiky flange at one end of it. Tee-nuts are great for installing steel female threads in wood for fastening things together; but there are other ways they can be put to use. Here's an example.

I needed a nut plate recently to span a 1 1/8" diameter hole in the back of a piece of furniture, so I could secure an ill-fitting lamp cord grommet. On the face of it, such a thing can be easily made -- just drill and tap a hole in a suitable length of 1/8" thick mild steel flat and there's your nut plate. But tapping even mild steel with a small diameter tap like 6-32 is fraught with peril, and I avoid doing it if there's a reasonably elegant alternative. Here's a way to make a nut plate using a tee-nut. The resulting part is actually superior to one with a tapped thread.

Pictured below are the ingredients.

At the left is an unmodified 6-32 tee-nut. Beside it to the right is an identical nut that's had its spikes broken off, and the resulting rough spots filed. At the very right is a two-inch length of 1/2" wide, 1/8" thick steel flat that's been prepared to accept the modified tee-nut. Note the countersink to partially accept the radius at the base of the tee-nut's barrel.

There are two ways you can go about this. That hole in the steel flat can be drilled for a slip fit, or for an interference fit for the tee-nut's barrel.

In this case, the tee-nut I'm using has a barrel diameter of 3/16". So, for a slip fit in the steel rectangle you'd use a 3/16" (0.1875") drill. A No. 13 (0.185") drill gives an interference fit. Either case requires press-fitting in the vise to mash the radius at the base of the nut's barrel into the countersink. Here's a shot of the parts in the vise being pressed together using a 5mm socket wrench as a pressing 'anvil'.

An interference-fitted version will be ready for use right out of the vise. A slip-fitted version needs to be glued together with CA adhesive.

Here are finished examples of both versions.

The upper one is a glued, slip-fitted nut plate. The lower one is the press-fitted version. Either one will work fine.

Here's a shot of the glued, slip-fitted item on the job.

A very strong nut plate, and no tap got broken or dulled to make it. ('Sorry about the glary photo. I still have much to learn about photography.)

This technique is an inexpensive alternative to Rivet Nuts in any situation where the back of the material is accessible.

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