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July 6, 2010

Dear Subscribers,

We've got two new turning center manuals to go with the recently released machining center manuals - information is provided in the Product Corner section. 

Instructors will find the two new curriculums for turning centers to nicely compliment those we have for machining centers.  Again, you can find information in the Product Corner.

We hope you find the information in the articles for this issue to be of value.

As always, enjoy!

Mike Lynch

IN THIS ISSUE
Product Corner: New turning center materials and curriculums
Instructor Note: Determining what a student must know
Manager's Insight: Who are your gatherers?
G Code Primer: Two applications for L0
Macro Maven: How does G66 work?
Parameter Preference: Making user defined G codes modal
Safety First: Watch out for that G28 command!

Product Corner: New turning center materials and curriculums

We’ve recently introduced two self-study manuals for people wanting to learn about CNC and the corresponding instructor curriculums to help instructors teach CNC classes:

We have already developed similar materials for machining centers, and these new products round out the product line.

You may know that we also provide materials in one self-study manual and instructor’s curriculum for programming, setup, and operation (one for machining centers and another for turning centers) – and you may be question why.

Which is right for you?

While pricing is about the same for each set of materials (about $120.00 for each if you buy everything), we recommend that the buying decision be based upon current experience level:

If the student has no previous shop experience, we recommend the setup and operation manual, followed (if necessary or desired) by the programming manual.
If the student has previous shop experience, we recommend the programming, setup and operation manual and workbook/ answer book combination.
Here’s the rationale behind our recommendations:

Many newcomers to CNC need only learn how to run machines, not necessarily how to program them (at least not yet). This is especially true for people hired on in entry level manufacturing positions. In the past, we’ve tried to provide tips for using our materials for programming, setup, and operation to learn or teach only setup and operation, but admittedly, these suggestions have been met with limited enthusiasm. Instructors and students alike clearly want separate materials – so we’ve responded.

Additionally, there are certain basic machining practice topics that are omitted from the programming, setup, and operation materials (shop safety, shop math, blueprint reading, tolerance interpretation, measuring devices, and machining operations). Our thinking was that these topics are prerequisites to learning about CNC, and most schools have other courses that cover these topics.

I think this still holds true for a person that wants to master all three tasks required to become proficient with a CNC machine tool (including programming). But I have to admit that a person who will be simply running production on a machine (CNC operator), or even a person making simple setups, doesn’t need to know nearly as much about basic machining practices as a programmer – at least not as they begin their CNC careers.

So we have created two separate curriculums. Each will stand nicely on its own – though the materials for programming do assume that the student has gone through (or will be going through) the setup and operation curriculums.

The first major difference between the materials is a strong emphasis on basic machining practices in the new setup and operation manuals and curriculums. We now include a lengthy presentation about basic machining practices. Key Concept number one (You must get ready to learn about CNC machining/turning centers) includes two lessons. In lesson one, we introduce shop safety, shop math, blueprint reading, tolerance interpretation, and measuring tools. In lesson two, we present the most common machining operations that are performed on a CNC machining/turning center. While presentations for these topics will not be equivalent to full classes your school may have for them, they will be sufficient to ensure that students understand enough about basic machining practices to begin working with CNC – especially as a CNC setup person or operator.

Practice makes perfect

The second major difference between the materials is related to practice exercises. With the programming, setup, and operation manuals, there are a few quizzes and exercises included right in the text, but the bulk of exercises and programming activities are included in a separate workbook – and answers are provided in a separate answer book.

With the new materials, the exercises (with answers) are provided right in the manual.

The new CNC curriculums

The instructors’ curriculums for each include a Lesson Plans manual, a For the Instructor manual, and PowerPoint slide show presentations. And as with all of our instructor’s curriculums, the instructor’s materials will be shipped free of charge with your first order for student materials. In fact, we’ve lowered the number of student manuals for the initial order that must be purchased to qualify to only ten.

If you teach for a school, be sure to request a free checking copy. We’ll send you one of these manuals to help you judge whether it will be appropriate for your classes.

 

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Instructor Note: Determining what a student must know

As you get ready to teach any new class, you must first figure out what material should be included in your curriculum. While some schools dictate the curriculum to be taught, many instructors – especially those in manufacturing programs – are left on their own to determine what should be included in their classes.

The decisions you make in this regard are of paramount importance if you classes are to have any real meaning or value to your students. And curriculum content is especially important for classes related to vocational skills – as opposed to general education classes. Students graduating with Applied Science degrees or certificates will be expected to do something from the day they graduate.

Trying to develop content on your own can be a dreadful mistake. While you may think you know what it takes for a person to become successful in your field, your students will pay a terribly high price if you’re wrong. With classes related to manufacturing, for example, students must be able to step in and be productive from they day they start. While a student may fully understand and master what you’ve taught them, if what you’ve taught them is not appropriate to what they actually need, the manufacturing company that hires them will find them to be of little value.

Frankly speaking, thinking that you know enough to determine class content completely on you’re own can border on arrogance. I’ve met several instructors with a god-like sense of (over) confidence. While these instructors truly believe that students are benefiting from their classes, in reality, students may seldom need much of what they’ve learned.

I’ve heard from at least one university professor that strongly believes that universities should be driving what happens in industry. If the school is progressive enough, they should be well enough versed in the areas they cover to provide not only appropriate, but ground-breaking concepts to their students. Graduating students will have a profound and immediate impact on the companies for which they work.

This kind of thinking is appropriate for our very best schools – like M.I.T. They have the resources and respect needed for this approach. But this thinking will not be appropriate for the majority of technical schools and community colleges with CNC programs. The fact of the matter is that most CNC instructors simply don’t have the knowledge base needed to create a CNC curriculum that will be of the highest benefit to students completely on their own. They need help.

So where do you turn for help?

My best suggestion has always been to seek help from local CNC-using manufacturing companies. The people who will be hiring your graduates should be given the first say in what is taught in your school. This may fly in the face of some educators, but if you want to boast a high placement rate for graduates, you better be able to satisfy the people doing the hiring. If they don’t approve of (or know about) what you’re doing, they won’t be hiring your graduates.

If you haven’t already, I’d urge you to create an advisory committee, made up of knowledgeable people from companies in your area. They’ll be able to tell you what they expect of their workers. At the very least, provide them with an outline of what you are currently doing (or propose to do), and ask them to provide comments and suggestions. And be ready to respond to their ideas.

The more diverse the industry in your area, the more diverse will be their suggestions. You will likely be surprised at the differing needs in your area. But the closer you can come to satisfying these needs, the more likely it will be that your students will be placed.

Another place to turn for help is the National Institute for Metalworking Skills (NIMS). Their website is nims-skills.org. Using a national advisory committee made up primarily of people working in industry, they have developed a skill-set a person must master in order to work with CNC mills and lathes. Actually, they have done this for two levels – one for CNC operators and another for CNC setup people. And as stated, knowing what students must master is the first step to developing a great curriculum.

At the time of this writing, the NIMS website doesn’t freely post specific information about the actual skills included in each Credentialing Achievement Record (NIMS abbreviates this as CAR). You must register to see it. Lifetime registration is $40.00.

Though it may be beyond the scope of this article, NIMS even offers accreditation for the skill sets they provide. That is, they can show you how to prove that your students have mastered the skills included in each skill set.

Any CNC instructor should be very interested in the NIMS materials. Though NIMS doesn’t promote their materials in quite this way, you can show perspective employers exactly what is included in your CNC programs – the NIMS standards. At the very least, employers will know what they will have to supplement with on-the-job training for a student achieving the NIMS credential. Or you can also work with local industry to build upon these standards to further suit your area’s more specific needs. And if your school becomes accredited by NIMS, you can prove to perspective employers that students have mastered the skills in each skill set.

My last suggestion is to stay flexible. Your curriculums cannot be cut in stone. If you find that (by working with local industry) a given topic or skill included in your curriculum could be eliminated or improved, by all means, make the change. In this way, your curriculums will always be evolving toward the ideal curriculums for your area.

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Manager's Insight: Who are your gatherers?

If you place a high priority on keeping your CNCs running, you better ensure that the people running them are able to keep up. When a machine finishes a cycle, someone better be immediately available to get the next cycle running. Obvious tasks include removing the previous workpiece, cleaning the workholding device, loading the next workpiece, and pressing the cycle-start button.

In similar fashion, when a machine completes a production run, someone better be immediately available to start the next setup (assuming you have work for the machine). Obvious tasks include tearing down the previous setup, putting things away, making the next setup, and verifying the program to get a good workpiece.

While it takes time to complete the tasks necessary to restart a cycle and make a setup, this time can be reduced by making sure that all items a setup person or operator need are available at the instant they need them. It doesn’t make much sense to have a very expensive machine sitting idle waiting for a critical component (insert, fixture, wrench, etc.) to be located and brought to the machine. And it makes no more sense to have the highly paid and experienced setup people and operators doing the gathering.

As you watch your CNCs, look for times when they sit idle because a needed component must be found. Determine what can be done to eliminate this down-time. If, for example, you have a CNC helper gather needed components, you can eliminate the related downtime.

The person doing the gathering must, of course, be able to locate needed components. In some (lesser organized) shops, this can be quite a challenge even for experienced people, meaning your gatherers must have more experience. If your shop is organized – everything has a place and is always put back in its place – a person with lesser skill can be hired to do the gathering. Regardless of what you must do in order to have a separate person do the gathering, when you consider the benefit you’ll achieve, it will be worth the effort.


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G Code Primer: Two applications for L0

With most Fanuc controls, the L word is used to specify the number of repetitions for a subprogram call. The command

  • M98 P1000 L4

for example, will make the machine execute program O1000 four times. Again, this is the most common use for the L word.

If the L word is omitted (M98 P100), the machine will execute the program one time. That is, the machine will assume L1 if it is not explicitly stated in the command.

Though not as commonly known, the L word can also be used with canned cycles. As with subprogramming, the machine will assume one execution of the canned cycle if the L word is left out. So the command

  • N050 G81 X1.0 Y1.0 R0.1 Z-1.0 F4.0

will drill one hole.

When programming incrementally, the L word can be used to specify that a series of equally spaced holes will be machined. Consider these commands:

  • .

  • .

  • .

  • N010 G54 G90 S400 M03

  • N015 G00 X1.0 Y1.0

  • N020 G43 H01 Z0.1 M08

  • N025 G81 R0.1 Z-1.0 F4.0

  • N030 G91 X1.0 L9

  • N035 G90 G80 M09

  • N040 G91 G28 Z0

  • .

  • .

  • .

In line N025, the first of ten equally spaced holes on one inch centers is drilled. Line N030 drills the other nine.

But this article is about using L0. When could this be helpful? Maybe you want to have a subprogram that includes a series of holes to be drilled. All of the hole locations are included in the subprogram. Here is the subprogram:

  • O1000

  • N1 X1.0 Y1.0

  • N2 X4.5

  • N3 Y4.5

  • N4 X1.0

  • N5 G80 M09

  • M99

Again, all of the holes to be drilled are in this subprogram. Consider this portion of the main program:

  • .

  • .

  • .

  • N010 G54 G90 S400 M03

  • N015 G00 X1.0 Y1.0

  • N020 G43 H01 Z0.1 M08

  • N025 G81 R0.1 Z-1.0 F4.0 L0 (Tell the machine how to drill the holes)

  • N030 M98 P1000

  • N035 G91 G28 Z0

  • .

  • .

  • .

Line N025 sets up the canned cycle but does not drill a hole. Not until the machine executes the subprogram will the first hole be drilled.

Another application for L0 is helpful when you need to clear obstructions between holes. You probably know that G98 and G99 can be used to clear obstructions by moving above them in Z between holes, but in some cases, it may save time to clear obstructions by moving around them in X and Y. Consider these commands:

  • .

  • .

  • .

  • N010 G54 G90 S400 M03

  • N015 G00 X1.0 Y1.0

  • N020 G43 H01 Z0.1 M08

  • N025 G81 R0.1 Z-1.0 F4.0 (First hole)

  • N030 X1.5 (Second hole)

  • N035 Y2.0 L0 (Move forward in Y to clear obstruction)

  • N040 X3.0 L0 (Move right in X to continue to clear obstruction)

  • N045 Y1.0 (Drill next hole)

  • N050 G90 G80 M09

  • N055 G91 G28 Z0

  • .

  • .

  • .

No holes will be machined in lines N035 and N040. While you can achieve the same effect by canceling and reinstating the cycle between holes, this technique requires fewer commands.


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Macro Maven: How does G66 work?

G66 is one of the more misunderstood custom macro B commands. Fanuc calls it a modal custom macro call. It looks just like a G65 command. Consider these two commands:

  • N045 G65 P1000 X3.0 Y3.0 Z0 A45.0 H8.0 F4.5

  • N045 G66 P1000 X3.0 Y3.0 Z0 A45.0 H8.0 F4.5

If you’ve worked with custom macro B, you know the G65 command will set the values of local variables #24 (X), #25 (Y), #26 (Z), #1 (A), #11 (H), and #9 (F) and then execute program O1000. With G65, that is, the program specified by the P word will be executed as part of the command.

While the G66 command is written in exactly the same manner, there is an important difference. Program 01000 will not be executed as part of the G66 function. G66 will set the values of local variables 24 (X), #25 (Y), #26 (Z), #1 (A), #11 (H), and #9 (F). But that’s it. G66 also puts the machine into a modal state. Every CNC command it executes from the G66 command (until G67 that cancels G66) will call program O1000 and the local variables will be set as specified in the G66 command).

When is this helpful?

G66 can be helpful when you have a given machining operation that must be performed at several locations on a workpiece. Maybe you must mill a round counter-bore or mill a square pocket in several XY locations. Consider these commands in the main program:

  • .

  • .

  • .

  • N070 G66 P1001 X1.0 Y0.5 R0.1 Z-0.5 F6.0

  • N075 X5.0 Y5.0 (First pocket location)

  • N080 X3.0 Y3.0 (Second pocket location)

  • N085 X1.0 Y1.0 (Third pocket location

  • N090 G67 (Cancel modal call)

  • .

  • .

  • .

In the G66 command, X represents the pocket length, Y the pocket width, R the approach position, Z the pocket depth, and F the feedrate for milling. And #24, #25, #18, #26, and #9 will be assigned. The custom macro (O1001) will include the necessary motions for one of the pockets. But again, N070 will not machine a pocket. Line N075 will cause the machine to first move to X5.0 Y5.0 and then call program O1001. This will be repeated until the machine executes the G67 in line N090.


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Parameter Preference: Making user defined G codes modal

As you probably know, is possible to create user defined G codes with custom macro B. That is, you can cause the machine to execute a particular custom macro whenever a G code of your choosing is executed. As with all parameters, the specific parameter numbers will vary from one machine to another. Look in the custom macro section of your Fanuc manual to find the related parameters.
Programs O9010 through O9019 are involved. If the first available parameter is set to a value of 80, for example, the machine will execute program O9010 whenever G80 is read.

The simple trick to making a user defined G code modal is specifying a negative value as the parameter value that specifies the G code number. If you set the second available user defined G code to a value of -12, the machine will execute program O9011 whenever G12 is read. It will continue to execute program O9011 in each CNC command until it reads a G67 to cancel the modal calling command.

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Safety First: Watch out for that G28 command!

As you know, the G28 command is used to send the machine to its zero return position. At the completion of a G28, the machine will be at its zero return position in any axis included in the G28 command.

However, how the machine gets to its zero return position can be a bit confusing. You may know that G28 is actually a two-step command. First the machine will move to something called an intermediate position in any axes included in the G28 command. Second the machine will go to the zero return position in these axes.

Most programmers are taught to make the intermediate position the machine’s current position. The simplest way to do so is to include a G91 incremental mode G code in the G28 command (machining centers). So the command

  • G91 G28 Z0

tells the machine to first, move incrementally nothing in Z (staying where it is) and second, to move to the Z axis zero return position.

The safety-related warning has to do with forgetting the G91. This command

  • G28 Z0

will first, send the Z axis to the program zero surface in Z (crash) and second, send the machine to its Z axis zero return position. This assumes, of course that the machine is in the absolute mode when the G28 command is executed.
For turning centers, most programmers use the command

  • G28 U0 W0

to accomplish the same thing. The machine will move incrementally nothing in X and Z, then it will go to the zero return position in each axis. But if you give the command

  • G28 X0 Z0

you are telling the machine to go to program zero in X and Z (again, crash), and then go to the zero return position in each axis. 

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