This is a good place to remind folks, especially those who have never used a collet chuck, that there is nothing magic about a collet chuck. It has the potential to hold a work piece accurately, yes, but the contact surface of any collet is rather small compared to a jawed chuck. The collet will hold the work solidly enough to resist cutting forces up close to the chuck but the farther you are from the chuck, the more the potential for deflection. This is especially true if you are using a carbide tool, which will deflect the work piece all by itself. (EDIT: Not fair; a HSS tool will deflect the work piece, too, but not as much as a carbide insert will.) It is wise to extend the work piece only as far as you need to, and if that extension is greater than 1-1/2 to 2 times the diameter of the work piece then consider using a live center to support the work. This matters when the work must be held to close tolerances but it is also good workmanship if that is important to you. In fact, this advice also applies to a jawed chuck as well. Deflection is a real thing and it has several sources, primarily the size and material of the work, cutting tool and the way we support the work piece. By supporting the work piece properly we eliminate one factor and minimize the effect of the other. When accuracy matters and tolerances are tight, do all you can to minimize deflection.