CNC Tips and Techniques. Peter Smid
Threading
Threading Methods Compared
Going Helical with Threads
Multi-Start Threading
Limitations in Threading
Programming a Long Thread
Threading with G76 Cycle — Basics
Threading with G76 Cycle — Details
Tools
Tool Length Setup — Three Methods
Automatic Tool Change — ATC
Maximum Tool Specifications
Live Tooling on CNC Lathes
Turning
CNC Turning — Why Are There So Many Errors?
PROGRAMMING
Why Should I Know Manual Programming?
CAD/CAM or CAD and CAM?
Short Suggestions for Long Programs
Keep Records — Document Your Programs
Minimizing Program Length
Well-Structured Program Structure
Control Features — Optional or Standard?
Programming Process — When Is It Completed?
Quality in CNC Programming
Short Ideas and Observations
Interpreting a CNC Program
Safety and CNC Programming
Programming Techniques
Part Program Upgrading and Updating
Shifting Program Zero — Part 1
Shifting Program Zero — Part 2
Imaging a Mirror Image
Automatic Corner Breaking
The “Other” Work Offset
Programming a Long Thread
Feedrate Adjustment on Arcs
Programming a Full Circle
Subprograms
(Extreme) Power of Subprograms
Toolpaths
Simulating the Toolpath
CODES, FUNCTIONS, AND MACROS
Codes
Special Purpose G-Codes
Homeward Bound with G28
G76: Two Formats, One Cycle
Create Your Own G-Code
Lathe Cycles G70–G72 — Part 1
Lathe Cycles G70-G72 — Part 2
Threading with G76 Cycle — Basics
Threading with G76 Cycle — Details
Functions
Mastering M-Functions
Block Skip Adds Flexibility
Macros
Default Settings in Macros
Special Tapping Macro
CYCLES
Lathe Cycles — To Use or Not to Use?
Conversion of Lathe Cycles
Fixed Cycles Repetition
Lathe Cycles G70–G72 — Part 1
Lathe Cycles G70-G72 — Part 2
Threading with G76 Cycle — Basics
Threading with G76 Cycle — Details
THE MATHEMATICS OF CNC
Focus on Numbers
When 1 Thou Equals 65 Dollars
Easing Up on Calculations
Feedrate Adjustment on Arcs
CNC GEOMETRY
Working in Planes
A Case for Polar Coordinates
Programming a Full Circle
WORKING IN THE FIELD
Are You a CAM Machinist?
CNC Programmer/Operator — Should One Person Be Both?
Using CAM Software in Small Shops
APPENDICES
Appendix 1 Interpreting a CNC Program
Appendix 2 Default Settings in Macros
Appendix 3 Create Your Own G-Cod
Appendix 4 Scaling Option
Appendix 5 Safety and CNC Programming
Appendix 6 Lathe Cycles G70-G72 — Part 2
INDEX
 | CNC Turning — Why Are There So Many Errors? January 2004, updated February 2013 |
Even in this era of CAD/CAM, many of the part programs that are available for two-axis CNC lathes are still developed manually. There is a good reason why. Purchasing a CAD/CAM system just for a lathe may not be the primary choice of many managers. Modern CNC lathes offer many time-saving features. For example, all centerline operations — such as drilling, reaming, and tapping — are simple point-to-point motions. Lengthy turning and boring cuts can be dramatically shortened by the use of very powerful machining cycles. Special cycles are also available for external and internal threading operations, even for machining castings and for simple grooving.
Yet, with all these programming tools at our disposal, many lathe programs suffer from a number of errors. It is not unusual to see frustrated CNC operators frantically changing programs at the machine, at a great cost to productivity. Why do so many lathe programs suffer this fate?
When I talk to programmers and operators, I get many opinions but seldom real answers. All it takes is a careful look at many of their lathe programs to see that the same type of error appears over and over again. Let’s look at them in groups, with some views on what can be done to prevent them:
Calculation Errors
For all their power and simplicity, no lathe cycle will provide calculations of the contour points. When an error is evaluated, typically the programmer either “guessed” or miscalculated. Brushing up on trigonometry is the first step toward improvement in this area. Of all the math subjects, trigonometry is relatively the highest knowledge programmer should possess. I know a few programmers who avoid this obstacle by asking their engineers to give them the contour points from Autocad or some other program.
Other types of calculation errors are accumulated ones caused by incorrect rounding. To avoid this problem, round only the final result — not the intermediate calculations. Many calculations can be confirmed by selecting a different mathematical approach.
Syntax Errors
Syntax