FWIW, Jeff Henise and I spent the afternoon machining two TZ350 heads to convert them to replaceable combustion chamber inserts for his Bonneville LSR project.
I did a simple program at the mill and machined the first head and everything went along fine -- not as fast as possible (no flood coolant on my mill) but no excitement either.
The second head was a different story. It either at some point got hot enough in use to completely anneal it or that batch of heads was from a different alloy or HT spec from the first. Nasty gummy aluminum, building up on the cutter to the point of making the head extremely hot from rubbing as well as pushing it out of position (4 clamps, the first head had no problem) 2/3 of the way through the cycle.
It would be interesting to know what was going on. The same end mill that worked a treat on the first one immediately went into "I'm not happy" mode on the second one so we're pretty sure it was the head casting and not anything we were doing (same program as the first head). Slowing the feeds and RPM down by about 2/3 took some of the "why is the coolant smoking so much?" heat out of the head but even with that the EM was clearly pushing metal around instead of cutting it.
I guess it is just part of the mystique of old race bikes.
cheers,
Michael
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