Seeing as this area is specifically for bench top mills, generally meaning small to mid range bench top mills in the posts I see, I figured I'd probably be best off asking for S&F's around here. Mainly in that we are never going to hog like the big boys do, and so those of us who get to work on these machines should be better suited for this conversation. Additionally, I converted to TTS in the fall and while that has been pretty good so far, last night I managed to experience the famous TTS tool pull out twice in an hour. Meaning the TTS tool holder slipped out of the collet. I know many people have converted to TTS, even if you doing manual tool changes.

I don't claim to be a S&F wizard, but over the years I have gotten a feel for it. Since I am running a G0704 that is at this point fairly souped I am aware that I can exceed the limitations of my machine fairly easy, but what I am really trying to establish are general rules of thumb for step down and step over, assuming my F&S are giving me the correct chip load.

Now I try to pay very close attention to chip load, for example, I've had great luck in 6061 with a 2 flute 3/8" carbide endmill running at 36ipm and 6000rpm, providing .003" feed per tooth. I run flood coolant. This is what Harvey and all the major manufacturers recommend for chip load. Last night however I ran this same setting at .15" step over and .3" depth of cut it yanked the TTS tool holder right out of the collet. I caught it, the end mill was pretty much squeezed into the aluminum. I wouldn't say that it was chip welded, but the aluminum definitely started to stir a bit. Luckily I was right there. It should be noted that I don't currently have my PDB on as I was actually machining some new parts for the PDB itself, so I used the standard drawbar and TTS. So lack of PDB force shouldn't be an issue, I crank the drawbar down by hand about as tight as I can with the 4" long wrench.

I noted that there was a good bit of chatter, the part may have been too far out of the vise... It was a 1.25"X5"x"5 plate on end in a 4" vise, I was cutting the 1.25" face. Even running at 30% feed the chatter remained, but the tool pullout issues went away. So the thinking here is that I just had too much stepover last night on the 3/8" end mill, that resulted in chatter, and the chatter may have created enough resonation to help the TTS wiggle loose? Will less stepover ease chatter? If I run less stepover can I get away with more DOC? If I add DOC but remove stepover wont I ultimately see similar tool loads?

I hope that this can be a discussion were we share information. I plan to machine a few more parts tonight and I'll report back with results.