If you've read my blog post about my woven gear shifter, then you know the process of tapping the shifter didn't go according to plan. The tapered connector is tricky to hold properly in a vice. I used paint stirrers to function as a soft material to grip the shifter, but the majority of the gripping force was still concentrated on the widest point of the taper. In the end, sparks flew from my vice when it chipped because the force concentration was so great. The proper way to hold a tapered object is to make a matching taper in a fixture that can properly be held by a vice. Over father's day last year, my dad was in town and we took on the task of making such a fixture so I could properly tap a gear shifter for a friend.
The Pocket NC, a desktop 5-axis CNC machine, is the perfect tool for making such a taper. I wrote a script to generate the G code necessary to cut the taper. In April of last year, I also started working full time for Pocket NC. One of the projects I’ve been working on is a simulator for the Pocket NC, which is a great way to test G code programs before running them on the machine. It can also be used to teach machining by loading G code into an embedded version of it. You can see my taper program in the simulator below:
The feed rates in my program needed some adjusting, but the taper came out great:
With the tapered hole in hand, we made another smaller hole with the drill press and a quick slot with the bandsaw. The slot allows the fixture to flex so the gripping forces on the flat sides from the vice transfer to almost the entire surface area of the tapered connector.
With the fixture complete, we mounted it in the vice and had no issues tapping the threads! The knob made a great gift for a friend.