Change your roughing insert to a positive geometry rather than a negative geometry. Negative inserts are not good for thin walled parts due to push off and such. Play around with your feeds and speeds to get a tight little chip. I cut 4140 HT all day long but you have to push hard to get a chip. The positive insert will shear the material rather than rub it raw which leads to stringy shavings. How do you like the 2500? Is it the TL or the TT? I am thinking about buying a TL2500.