BACKLASH - Distance that you must turn the handwheel before the leadscrew engages the threads of its nut. Usually encountered when reversing table direction, it's the "slack" in the screw. A large amount of backlash is undesirable.
CNC - Computer Numerically Controlled. A system that uses a computer to control the X-Y-Z motion of the mill to automatically machine parts.
COLUMN - Supports the head. Common types of columns are dovetailed, cylindrical, etc.
DRAWBAR - Threaded rod that engages the rear of a collet or other tool holder, allowing the tool holder to be tightened into the spindle.
DRO - Digital Readouts. Scales that will digitally record the distance the table or head is moved. Usually seen in sets of X, Y, and Z scales.
GIB - A metal plate that sits between the table and its ways and can be adjusted to take up slack. Usually found on table, saddle, and column.
GIB SCREWS - Locking screws that can be turned to increase or decrease the pressure on the gib.
GIB LOCK - A device, often a screw, that applies enough pressure to the gib to lock the table in place. Used to prevent the table from inadvertent movement.
HANDWHEEL - A handle that is attached to the leadscrew, which moves the tables back and forth.
HEAD - Part of the mill that sits atop the column, and houses the spindle and its motor. Often it can be moved up or down, in the "Z" axis. Some heads tilt, some swivel.
KNEE - A platform on which the table and saddle are mounted, it can be moved up or down in relation to the rest of the mill. Often seen on larger mills, it is very handy for getting enough clearance to set up and clamp the workpiece without moving the quill.
LEADSCREW - Long screw mounted to the table that travels through a fixed nut to move the tables back and forth.
MT#1,2,3 - Morse Taper. An industry standard, it is used to ensure compatibility between tools and mill spindles (or lathe spindles). Often seen on lathes as well, it has fallen into disuse on most mills in favor of the R-8 taper. An MT-3 spindle will accept only an MT-3 tool; different Morse Taper numbers are not interchangeable.
PHASE CONVERTER - A device that allows three-phase motors to operate on a single-phase circuit. There usually is a loss of efficiency when using a converter.
POWER FEED - Motor that engages the leadscrew to automatically move the table back or forth. A very handy feature for a production environment.
QUILL - Usually refers to a spindle that can be moved up or down. I.E., "quill travel is 10 inches."
R-8 - Industry standard tooling taper that is the most common at present. Most large mills use this taper. Incompatible with Morse tapers.
SADDLE - A block of metal that the table sits on. The saddle has a leadscrew providing "Y" axis travel.
SINGLE PHASE - A form of electrical power, commonly used in residential wiring. House current is single phase. Mill motors will usually be single phase or three phase.
SPINDLE - The part of the mill head that actually turns and holds the tooling that you're using to cut with. Spindles will generally have either an R-8 or Morse Taper to accept tool holders. Some mills use proprietary or obsolete tapers.
SWARF - Metal chips, debris generated from cutting operations. Why they needed to make up a word for it is beyond me.
T-SLOT - Slots cut into the mill table that resembles an inverted "T" and accept T-nuts. The method of fastening workpieces to the table.
T-NUT - A threaded block of metal that resembles an inverted "T", and fits into T-slots. They can be moved back and forth, and clamping tools can be screwed into them to help clamp workpieces down. Unfortunately they are not universal in size, you need to get the ones that fit your mill's T-slots.
TABLE - The long, rectangular flat surface that workpieces are clamped to. The table moves left to right, has T-slots in it to facilitate clamping, and is, ideally, perfectly flat.
THREE PHASE - A form of electrical power that is most usually encountered in industrial environments. As it allows more current to be delivered to a motor, three-phase motors are usually installed on larger industrial mills and machinery. A three-phase motor can be used on a single-phase power system with the use of a phase converter.
WAYS - The flat metal "tracks" that a table or saddle slides against. They should be lubricated at all times and kept free of chips and trash.
X-Y-Z - Used to describe the three axes of movement in relation to the moving parts of a mill. The mill table moves in the "X" axis (left-right), the saddle moves in the "Y" axis (in-out), and the quill moves in the "Z" axis (up-down).