I have found that I have had to "fine tune" the torque settings and others and in some cases tune the servo motor depending on the version of C-320. Plastics and titanium in small diameters like to whip when given 21 mm dia channels to play in especially when not supported by the rollers.You may be able to fine tune the settings or for the best results goto the smaller channel set ,sometimes you can even get away with the 16 mm set.
good luck