FIGURE 5-Standard vs. climb milling. (For clarity, consider the cutter moving, although it is actually the part that moves while the cutter remains in one place.)
WORKING TO SCRIBED LAYOUT LINES
A common practice when working with a mill is to lay out the hole centers and other key locations using a height gauge and a surface plate. A coloring (usually deep blue) called layout fluid or "Dykem" is brushed or sprayed on a clean surface of the part. A thin layer is best because it dries quicker and won't chip when a line is scribed. The purpose of this fluid is to highlight the scribed line.
Don't prick punch the scribed crossed lines representing a hole center. Using a center drill in the mill spindle and a magnifying glass, bring the headstock down until the center drill just barely touches the scribed cross. Examine the mark left with a magnifying glass and make any corrections needed to get it perfectly on center. You should be able to locate the spindle within .002" (.05mm) of the center using this method.
Once the first hole is located in this manner, the additional holes can be located using the handwheels. (This is where the optional resettable "zero" handwheels are handy.) Now the scribe marks are used as a double check and the handwheels take care of the accuracy. Don't forget the rules of backlash and always turn the handwheels in the same direction as you go from one point to the next.