• A machining center is a very versatile machine, using a variety of cutting tools, that can be run with limited operator intervention during the cutting cycle.

• Machining centers are classified into two main types, vertical machining centers (VMC) and horizontal machining centers (HMC).

• The workpiece must be securely fastened, and the setup must be rigid enough to withstand the forces that will be present during the machining operation.

• Cartesian or rectangular coordinate system can describe any specific point in mathematical terms from any other point along three perpendicular axes.

• Two types of programming modes are used on CNC machines: the incremental system and the absolute system.

• CNC programming falls into two distinct categories, point-to-point and continuous path machining.

• When programming arcs and circles, the MCU requires only the coordinate positions (the XY axes) of the circle center, the radius of the circle, the start point and end point of the arc being cut, and the direction in which the arc is to be cut (clockwise or counterclockwise).

• Home position on a CNCmachine tool is often called the machine reference position. This is a precision position designed by the machine tool manufacturer.

• The reference point of the part is called the program zero or the part zero.

Machining centers

1. What are the two main types of machining centers?
2. Name five machining operations that can be performed on a machining center.

Machining center Parts

3. What is the purpose of the MCU?

Cartesian Coordinate system

4. Why is the Cartesian coordinate system used for machine tools?

Machine axes

5. Using a machining center, define the X, Y, Z axes of movement.

Programming System

6. What is the main difference between incremental and absolute part programming?
7. Name the two classifications of positioning systems.
8. Why is linear interpolation not generally used to program arcs or circles?
9. What four pieces of information are required for programming arcs or circles?

Machine axes

10. Name the three most common axes on a machining center and give the function of each.
11. What is the reference point for the part usually called?
12. What is the home position of the machine usually called?

Preparatory functions

13. For what purpose are G codes used?
14. Identify the following G codes: G00, G03, G17, G20, G42.

Miscellaneous functions

15. What functions do M codes control?
16. Identify the following M codes: M01, M02, M05, M06, M30.

Copyright 2004, Industrial Press, Inc., New York, NY