Started machining up a nice fixture plate for my TC22. It is 24x12, with about 350 1/2-13 holes. I purchased a 1/2-13 form tap (OSG, steam oxide), and did a half dozen tests to dial in the proper drill/bore/tap cycle. Got the hole dialed in perfectly in the middle of the recommended size. Tapping seemed to work great. When I went to tap my real plate (MIC 6 Aluminum) it snapped the tap on the 3rd hole!
Now I'm nervous to try this again. The spindle sounded a tad different when it tapped this time. Maybe a bit more load, although I'm not sure why this would be. The plate is 1" thick, so the tap was fully engaged. Tap broke soon after the spindle reversed. The first two holes it tapped look great.
I used a standard ER32 collet holder. I don't see any sign of slippage on the body of the tap. Using flood coolant with the same synthetic coolant I use for everything.
I checked through the G code, and it is using an M29 G95 G84 cycle. This is "feeds per revolution" which the DX32 programmers manual calls "FANUC mode".
The programmers manual also says:
"Note that the G95 works only with desired spindle speeds, it does not self adjust if the spindle speed varies due to load or operator actions"
This kinda implies that G95 is not closed loop? Or maybe it means that it isn't closed loop without M29?
Now I'm worried something is up with the machine. I have a floating tap holder but it doesn't go up to this size. Maybe the steam oxide was inappropriate for aluminum?
Anything I should check?