, ,

I wanted a tap follower for an upcoming project to make aligning the threads easier. They retail for about £7, but I decided to make one instead. This is a simple project and set a goal of making it in one day.

The main principle of the tap follower is a spring loaded pin that presses against the back of the thread tap being used to hold it in place, making sure to cut straight threads.

Tap follower cross section

The design I’m going with uses a 9mm spring pushing a pin/plunger, held in via a captured set screw. The length and diameter of the pin are the only critical parts of the design. The plunger length needs to be long enough to provide a solid support and not move when fully extended. A rule of thumb when designing plungers is to have more of the plunger length supported inside the body than outside. This design will have 20mm travel so the pin length inside the body should ideally be at least 40mm.

Spring length sizing

The uncompressed spring length is 40mm and compressed is 9mm. Having a maximum cavity length for the spring slightly smaller than the uncompressed length will give a slight pre-load and ensure the spring does not bounce around freely when not in use.

Plunger retention

The plunger of the follower is held in via an M4 set screw which slides along a groove in the body.

Finished tap follower
Tap follower
Plunger retention
In use

I set a goal of designing and fabricating this in a day, in total it only took a few hours, with most of that time spent boring out the body using ever increasing drill sizes. This was an easy project but will come in useful for future projects to create nice straight threads.