Home made TDI for Huvema lathe

Because I want to do more with threading I wanted a TDI (Thread Dial Indicator) for my Huvema lathe.

I realized a TDI is really only a cog to follows the longitudinal guide. You link the longitudinal guide at the moment the dial has a predetermined position. After disconnecting and moving the longitudinal guide you can reconnecting when the dial has returned to the same predetermined position.

My spindle has a pitch of 1.5mm. After a little math, I decided on a 30 mm circumference so 20 teeth. It allows me to use it for threading of 0.75 1.0 1.25 1.5 and 2 because each of these has a multiple that is exactly 1 time the circumference of my gear (30 mm)

So using an existing reduction and improvised a 4th axis and machined the sprocket. This can also be done without CNC router by using a tap with the correct pitch.