You are right, Yorik, the tool is not staying centered, and the resulting end is unacceptable. I’ve tried a couple of different ball diameters and didn’t get good results.If it cracked, that leads me to believe that the tool wasn't centered properly or it was over tightened. I've had that happen to me once and had to get a replacement master link.
Blame the tool. I had a similar issue with my cheap chain tool. If you are going to do this every blue moon then don't spend 100 bucks on a quality chain tool just pay a shop and be done with it. On the flip side don't expect to get good results with a cheap one.I have a couple of cheap tools, but they seem decent. My problem appears to be that I’m not crushing the end evenly, even when I started with a smaller ball then moved to a larger one once I had a mushroom started. Part of the problem is my lack of experience doing this process, but it appears I’m doing it correctly. I can’t really blame it on the tool, it has all the plates etc.