I am using the TTS ER20 collet holder. Yes, I crank down the ER collet pretty darn tight, as well as the drawbar. Yes, I jam the holder all the way up until it hits the spindle nose. Yet under certain circumstances I get horrible chatter with a 3/8" end mill. To solve the problem, I just run the end mill in a regular R8 collet and the problem goes away. Is there anything I am doing wrong, or is the TTS system not that stiff because it sticks out too much?