MT3 Spring Centre

[dazz]

Hi

This is the result of a project to make a precision spring centre. The spring centre is used when tapping threads on the lathe to ensure the tap is properly aligned. The spring centre keeps pressure on the back of the tap as threading advances.

All of the clearances are minimised to ensure that the centre doesn't wobble about in use. The close tolerances also help keep dirt out of the internals.

The MT started out as a cheap $1 MT3 / JT3 arbor. I started by tempering the arbor to blue and ensuring an even hardness through the arbor. I drilled the arbor out and then made a D-reamer to accurately bore and finish the hole. The D-reamer was made from a piece of 12.4mm round HSS.

The end of the arbor was threaded to take a cap piece. The cap retains the stepped pin and guides the pin to keep in on centre. The cap guide hole was bored using a slot drill.

The centre pin is made from silver steel.

I made the spring because I can't buy a suitable size here.

The outcome is a spring centre with virtually no play. This will make tapping and other operations easier to do on the lathe.

As part of this project, I had to make other tools (making tools to make tools).
I made a small boring bar from a piece of key steel. This was used to bore and thread the cap piece.
I made a split clamp, also from key steel, that was used to hold the slot drill in the tool holder.


This design is more complex to make than others I have seen. There are plenty of opportunities to make mistakes. It has achieved the aim of an accurate spring centre.

Dazz