CNC Tips and Techniques: A Reader for Programmers - Softcover

Smid, Peter

Softcover

ISBN 10: 0831134720 ISBN 13: 9780831134723

Verlag: Industrial Press, Inc., 2013

Inhaltsangabe

During the past decade, Peter Smid wrote dozens of column for Shop Talkmagazine that addressed the full gamut of CNC topics, such as tapping and threading and knurling; program length and memory needs; G-codes, M-functions, cycles, macros … and more still. 

Ever since Shop Talk ceased publication, these columns have been unavailable. Now, in CNC Tips and Techniques, we are delighted to bring them back—over 60 of the best of Peter’s columns --- all under one cover, so that you can have full and easy access to the advice Peter has been sharing during the past decade.

CNC Tips and Techniques is a treasure trove of Peter Smid’s “lost work” that is certain to be an invaluable addition to your CNC toolkit.  We hope the advice and instructions contained in these readings will help you do your job more efficiently and more effectively – and that you find them a good read besides. 

Features

• Offers more than 60 focused columns which have been thoroughly reviewed since its initial publication and updated as needed to reflect ongoing changes in the field.
• Columns are presented here in chronological order of when they first appeared.
• Includes an alternative table of contents, organized by topic.
• Provides several useful appendices and an extensive index.
• Appeals to both veterans and newcomers with tips and techniques that can be applied at work and speed up the learning curve.

Über diesen Titel

Über die Autorin bzw. den Autor

Peter Smid is a professional consultant, educator and speaker, with many years of practical, hands-on experience, in the industrial and educational fields. During his career, he has gathered an extensive experience with CNC and CAD/CAM applications on all levels. He consults to manufacturing industry and educational institutions on practical use of Computerized Numerical Control technology, part programming, Autocad®, Mastercam® and other CAD/CAM software, as well as advanced machining, tooling, setup, and many other related fields. His comprehensive industrial background in CNC programming, machining and company-oriented training has assisted several hundred companies to benefit from his wide-ranging knowledge.  

Mr. Smid’s long time association with advanced manufacturing companies and CNC machinery vendors, as well as his affiliation with a number of Community and Technical College industrial technology programs and machine shop skills training, have enabled him to broaden his professional and consulting skills in the areas of CNC and CAD/CAM training, computer applications and needs analysis, software evaluation, system benchmarking, programming, hardware selection, software customizing, and operations management.

Over the years, Mr. Smid has developed and delivered hundreds of customized educational programs to thousands of instructors and students at colleges and universities across United States, Canada and Europe, as well as to a large number of manufacturing companies and private sector organizations and individuals. He has actively participated in many industrial trade shows, conferences, workshops and various seminars, including submission of papers, delivering presentations and a number of speaking engagements to professional organizations. He is also the author of articles and many in-house publications on the subject of CNC and CAD/CAM. For six years he had a monthly column in the ShopTalk Magazine related to CNC programming. During his many years as a highly respected professional in the CNC industrial and educational field, he has developed tens of thousands of pages of high quality training materials.

Von der hinteren Coverseite

Written by one of the most authoritative experts in the field, this compilation is organized by topic and

Offers more than 80 focused articles.

Covers all aspects of CNC, such as hardware, software, programming, codes, and macros.

Features articles reflecting recent developments in the field.

Appeals to both veterans and newcomers with tips and techniques that can be applied at work and speed up the learning curve.

Auszug. © Genehmigter Nachdruck. Alle Rechte vorbehalten.

Sample Readings

1.   Programming a Long Thread
2.  Trial Cut for Measuring
3.  Special-Purpose G-Codes
4.  Running the First Part — Economically, That Is  
5. Programming a Long Thread

1.    Programming a Long Thread

In the essay Limitations in Threading, the main focus was on limitations in single point threading caused by spindle speed that is either too high or too low. In this essay, we look at the effect of threading feedrate, particularly how it applies to long threads.

 What exactly is a long thread may be a subject for some discussion. For the purposes of this article, a long thread is a thread with a ratio of rather small diameter to long threading length. In most everyday threading operations, you will work with threads that have a length relatively short respective to their diameter. These threads, which do not require any physical support at the machine, generally do not present any problems in programming or machining. Machining long threads does have a few challenges, however. Long threads often require suitable support devices, at least a tailstock for basic support, but often a follower rest or a steady rest as well, in order to prevent deflection of the part.

 Many CNC machine tool builders provide lathes specially designed for machining long parts, such as shafts and tubular stock. These lathes (often of the flat bed type) are also capable of threading over their entire Z-axis travel. From the CNC programmer's perspective, a possible problem lies with the feedrate for certain imperial threads. Feedrate for threading is always the thread lead, and no rounding is necessary for metric threads. Some imperial threads have to use rounding for feedrate calculation, when the threads per inch (TPI) are converted to the thread lead (cutting feedrate).

 As an example of a possible problem of feedrate rounding, consider a single start, standard form 60 degree thread 6.0-12, over the threading length of 70 inches (actual use of the thread is not important for the illustration): 

• Thread diameter = 6.0 inches
• Thread per inch (TPI) = 12
• Length of thread = 70 inches

 Assuming a suitable tooling and part setup, the thread cutting program is easy:

 N51 T0500

N52 G97 S550 M03  (SPINDLE SPEED 550 RPM)

N53 G00 X6.25 Z0.4 T0505 M08  (START POINT CLEARANCE)

N54 G76 P011060 Q005 R0.002  (G76 - BLOCK 1)

N55 G76 X5.8978 Z-70.0 R0 P0511 Q0120 F0.0833  (G76 - BLOCK 2 - 0.0833 IPR)

N56 G00 X12.0 Z5.0 T0500   (TOOL CHANGE CLEARANCE)

N57 M01

All program data look reasonable, but let's focus on the programmed feedrate of F0.0833. For twelve threads per inch, the pitch is 1/12 = 0.08333333, which is also the thread lead and programmed feedrate. Now, consider the feedrate actually used in the program, F0.0833. It has been rounded to four decimal places, as is customary for imperial dimensions.

Inevitably, the rounding has brought in a certain amount of inaccuracy. Over one inch length, the error is:

1 - 12 * 0.0833 = 0.0004 inches

In most cases, this error can be absorbed by the thread tolerances. Now, consider the same error over a significant thread length, such as our example of 70 inches:

70 * 0.0004 = 0.0280 inches — this is a significant error

Because the 0.0833 amount was the correct rounding to four decimal places, any other rounding would make the accumulative error even worse. The solution to this problem is quite simple — just change the programmed feedrate of F0.0833to a new feedrate of F0.083333, from four to six decimal places. Fanuc-type controls allow this method, for the exact purpose of minimizing the accumulative error for long threads. With F0.083333, the error over 70 inches will be:

1 - 12 * 0.083333 = 0.000004 inches * 70 = 0.00028, which is less than three tenths.

Older Fanuc and similar controls could not use F-addresses with six decimal places, but the control provided E-addresses, specifically for threading, which did allow six decimal places. The six decimal place accuracy is not required for threads that have lead divisible into four or fewer decimal places, for example 16 TPI = 1/16 = 0.062500.

The G76 threading cycle itself will be discussed in two other essays looking at basics and details.
 

2.    Trial Cut for Measuring

Precision CNC machining is always a cooperative effort between CNC programmers and CNC machine operators. Programmers can employ certain program features that will enable the machine operators to perform functions that would otherwise be difficult or even impossible. One such method is programming a trial cut for measuring.

There are many factors in machining that influence the final size of a part, such as heat, tool deflection, tool wear, and even lubrication to some extent. For those parts that require very tight tolerances, the negative effect of these factors may result in an out of tolerance size and even a possible scrap. Another problem that is quite common is machining certain hard-to-measure shapes, such as a cone on CNC lathes. By using a simple programming method known as the trial cut, CNC programmers can greatly influence the final size of a part.

Take the already mentioned cone as an example. Without a suitable custom gauge, a cone is a difficult shape to measure at the machine, as there is no flat spot for the micrometer to use. Even if such a special gauge is available, it will be too late to find out that the cone is out of tolerance. The method of using a trial cut is to provide a special flat area (diameter) that can be easily measured, before the final cone is machined, following a few simple rules.

Normally, a cone machined from round stock, such as the 5.0 inch diameter used in the following example, will include G71 roughing cycle and G70 finishing cycle in the part program:

N1 G20 T0100 (ROUGHING TOOL)

N2 G96 S300 M03 (CUTTING SPEED)

N3 G42 G00 X5.2 Z0.1 T0101 M08 (START POINT FOR CYCLE)

N4 G71 U0.15 R0.025

N5 G71 P6 Q8 U0.07 W0.02 F0.015

N6 G00 X2.8 (CONE START)

N7 G01 X4.6 Z-3.5 F0.008 (CONE END)

N8 U0.2 (RETRACT FROM PART)

N9 G40 G00 X10.0 Z4.0 T0100 (CLEAR POSITION)

N10 M01

N11 T0300 (FINISHING TOOL)

N12 G96 S500 M03 (CUTTING SPEED)

N13 G42 G00 X5.2 Z0.1 T0303 M08 (START POINT FOR CYCLE)

N14 G70 P6 Q8

N15 G40 G00 X10.0 Z4.0 T0300 (CLEAR POSITION)

N16 M30

%

Although correct, the program above does not offer any means to measure the conical part efficiently. By adding several blocks of trial cut in the program and using the finishing tool (T03), a suitable straight cut can be machined first.

When measured, various offsets can be adjusted as necessary — all this is done before any roughing cuts take place:

/ N1 G20 T0300 (FINISHING TOOL)

/ N2 G96 S500 M03 (CUTTING SPEED)

/ N3 G42 G00 X5.2 Z0.1 T0303 M08 (INITIAL POSITION)

/ N4 X4.925 (DIAMETER TO BE MEASURED)

/ N5 G01 Z-0.35 F0.008 (LENGTH OF CUT FOR MEASURING)

/ N6 U0.2 (RETRACT)

/ N7 G40 G00 X10.0 Z4.0 T0300 (CLEAR POSITION)

/ N8 M00 (MEASURE DIAMETER - MUST BE 4.925)

N9 G20 T0100 (ROUGHING TOOL)

N10 G96 S300 M03 (CUTTING SPEED)

N11 G42 G00 X5.2 Z0.1 T0101 M08 (START POINT FOR CYCLE)

N12 G71 U0.15 R0.025

N13 G71 P14 Q16 U0.07 W0.02 F0.015

N14 G00 X2.8 (CONE START)

N15 G01 X4.6 Z-3.5 F0.008 (CONE END)

N16...

Details zur Ausgabe

• Verlag: Industrial Press, Inc.
• Erscheinungsdatum: 2013
• Sprache: Englisch
• ISBN 10: 0831134720
• ISBN 13: 9780831134723
• Einband: Taschenbuch
• Auflage: 1
• Anzahl der Seiten: 238
• Kontakt zum Hersteller: Nicht verfügbar
• Verantwortliche Person: preigu; mail@preigu.de; ; Lengericher Landstr. 19; Osnabrück; 49078; Deutschland