Potentially, I am pleased to say that I am about finished with this shaft, having got it to fit yesterday.
I've made a few observations on blog post I've written about it, but one might be of interest to you John.
Thanks for the excellent write up and pictures on your indexing / spline cutting equipment. One of the most important things I observed on my last attempt was related to tool height - it's absolutely critical to get the tool in the same position if you have to regrind part way through a splining job. Maybe, if I had made a clapper box I wouldn't have chipped the tool; maybe, if I had cut a run-out in the shaft, I wouldn't have chipped the tool.
Question for you though John - does the hinge on your clapper box allow the tool tip height to vary much?