Tips for CNC Programming

1. Tips for CNC Programming Jason Emerson

2. Introduction • Handy references for the CNC programmer. • Student will learn formulas and codes for CNC machines. • Students will apply lesson to develop a program for a CNC machine.

3. Agenda • Speed and feed formulas • Common G codes • Common M codes

4. Overview • The student will learn the basic foundation to developing a CNC program. • Each lesson will work together to produce the final outcome. Speeds Feeds M - codes G -codes

5. Vocabulary • CNC – abbreviation of computer numerical control. • Chip load – the thickness of the chip the tool creates for each revolution of the tool. The thicker the chip the greater the tool pressure, which causes the tool to bend. • Circular interpolation – enables the programmer to move a tool up to 360 degrees in an arc using only one block of information. The circular path may be generated in any two planes.

6. Vocabulary • Cutter compensation – provides a means of using a cutter from a different diameter than originally intended in a program. The programmer may use either an oversized or undersized cutter and still maintain the programmed geometry.

7. Vocabulary • Feedrate – A code containing the letter F followed by digits. It determines the machine slide rate of feed. • G-code – A word addressed by the letter G and followed by a numerical code defining preparatory functions or cycle types in a numerical control system. • Linear interpolation – the movement of the tool in a linear (straight) path.

8. Vocabulary • M-code – A miscellaneous function, which includes actions necessary for machining, but not those that are actual tool movements. • RPM – abbreviation of revolutions per minute.

9. Speeds and Feeds • RPM = surface feet per minute (SFM) / tool diameter x 3.82 • Total chip load = number of flutes x desired chip load

10. Speeds and Feeds • Feedrate = RPM x total chip load • Example RPM = material : aluminum; End mill : .375 diameter: SFM : 800; (800 / .375) x 3.82 = 8149.3332 or 8149 • Example total chip load = tool diameter : .375; Number of flutes : 4; Chip load : .002; 4 x .002 = .008 TCL • Example Feedrate = RPM : 8149; Total chip load : .008; 8149 x .008 = 65.192 or 65.

11. Common G Codes • G00 – position in rapid • G01 – linear interpolation • G02 – circular interpolation (CW) • G03 – circular interpolation (CCW) • G17 – XY plane

12. Common G Codes • G40 – cutter compensation cancel • G41 – cutter compensation left • G42 – cutter compensation right • G80 – cancel canned cycle • G81 – drilling cycle • G90 – absolute positioning

13. Common M Codes • M00 – program stop • M01 – optional program stop • M02 – program end • M03 – spindle on clockwise • M04 – spindle on counterclockwise

14. Common M Codes • M05 – spindle stop • M06 – tool change • M08 – coolant on • M09 – coolant off • M30 – program end, reset to start

15. Summary • The student now has learned the basic foundation of creating a basic CNC program. • The student will now write a basic program using the formulas and codes learned in this lesson. • Students are encouraged to keep this lesson as reference for future programming lessons.

16. Where to Get More Information • Many machinery suppliers offer factory training classes, workshops, and seminars. • More information can be found through internet searches, Modern Machine Shop magazine, The CNC Workbook (Addison-Wesley Publishing Company), Computer Numerical Control: Concepts and Programming (Delmar Publishers Inc.).