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January 12, 2009

Dear Subscribers,

Welcome to issue 77 of The Optional Stop newsletter. You may have noticed that there was no Fall 2008 issue (we did receive a few comments). Things have been pretty busy and I simply didn’t have time to create it. Part of the reason why we’ve been so busy is related to this issue’s Product Corner. Instructors take note – we have two new CNC curriculums aimed at helping you teach CNC classes!

As always, we appreciate your continued interest and support.

Enjoy!

Mike Lynch

IN THIS ISSUE
Product Corner: Two new CNC curriculums to help instructors teach CNC classes
Instructor Note: What CNC students must know about basic machining practices
Manager's Insight:  Assigning sensible responsibilities to CNC people
G Code Primer: Multiple machining operations on holes
Parameter Preference: Controlling when the machine stops reading a program
Safety First: How much safety training do you provide?
 

Product Corner: Two new CNC curriculums to help instructors teach CNC classes

The two new curriculums include:

At present we have approximately forty schools using our CNC curriculums to teach CNC classes. These include vocational high schools, community colleges, technical schools and universities. By far, our two most popular curriculums have been Machining Center Programming, Setup, and Operation and Turning Center Programming, Setup, and Operation. These existing curriculums help you teach all three tasks a person must master in order to become fully proficient with CNC machine tools – programming, setup, and running production.

Some of you have questioned our methodology. For instance, we have been asked why we begin with programming, leaving setup and operation until the end. Our thinking has been that most people who are starting out with CNC have some basic machining practice experiences. Most of these people already know how to setup and run conventional machine tools, like drill presses and milling machines. And since setting up a CNC machine – at least the physical tasks – are very similar to those used with conventional machines, it only made sense to start with programming. Up until now we have made understanding basic machining practices a prerequisite for our curriculums.

Many of you have pointed out, however, that more and more of your students have no previous machine shop experience. They are entering the field of manufacturing at CNC level. It is not be necessary to teach people to setup and run conventional equipment before they start learning about CNC. However, there are many important basic machining practice topics they must understand before digging in to CNC. Many of you have found it necessary, for example, to teach students about shop safety, shop math, blueprint reading, tolerance interpretation, and measuring devices before you can start teaching CNC-related topics. One of our new curriculums – the Machining Center Setup and Operation curriculum – now includes an introduction to these important topics.

We have also assumed that people starting out with CNC want to learn all three of the related tasks – again, programming, setup, and operation. We have always felt that a person with skills in all three of these areas will be of the most value to their employers.

But again, some of you have pointed out to us that many students are not (yet) interested in learning how to program, especially if they are just starting out. They’ve seen in the local want-ads that companies are looking first and foremost for setup people and (especially) operators. This is where the most jobs are. And when entering the field of CNC, most people will not start out as programmers. While they will eventually want to learn how to program, they (and their potential employers) want setup and operation skills first.

For these reasons, we’ve developed two new curriculums – one for setup and operation (intended to be presented first) – and another for programming. Currently these new curriculums are only available for machining centers. We are working on the turning center versions and they should be ready for the Fall semester of 2009.

If you are currently using our curriculums, these new curriculums will allow you to flip-flop the order by which you teach CNC – setup and operation first, then programming. They also allow you to start in a much more basic fashion, assuming much less prior knowledge of your students when they begin.

Much of the content in our new curriculums remains the same, meaning if you are currently using our curriculums, things will stay pretty familiar. We still use the Key Concepts approach (and almost all of the Key Concepts remain the same). We still break the Key Concepts into lessons (12 lessons in the setup and operation curriculum and 16 lessons in the programming curriculum). Most of the slide show presentations remain the same – though we’ve given them a face-lift. And, the new curriculums still come with instructor materials (CD-rom that has the PowerPoint slide shows, Instructor Manual, and Lessons Plans Manual).

The main differences are:

  • Basic machining practice discussions included in the Machining Center Setup and Operation curriculum

  • Shop safety, shop math, blueprint reading, tolerance interpretation, measuring tools, and machining operations

  • While our materials aren’t as comprehensive as a book or class for each individual topic, materials are pretty substantial – taking 100 pages in the student manual

  • Each curriculum now stands completely on its own

  • You can teach only setup and operation or only programming

  • If students have no prior shop experience, start with setup and operation

  • If students have shop experience, you can skip or skim the basic machining practice discussions in the Machining Center Setup and Operation curriculum

  • If student have shop experience, and you will be teaching all three tasks, continue to use the Machining Center Programming, Setup, and Operation curriculum (we will not be discontinuing this curriculum)

  • Very few discussions about setup and operation are discussed in the programming curriculum

  • We’ve removed all setup and production-run discussions from programming topics like tool length compensation, cutter radius compensation, and fixture offsets – they are included only in the setup and operation curriculum

  • All of the exercises, programming activities, and answers that have traditionally been in separate books are now included in the student manual

  • If you will be grading your students’ work, you can ask them to remove the answers from the manual on the first day of class

  • Improved navigation in the slide-show presentations

  • New startup slide gives quick access to all lessons

  • The first slide of every lesson is the Lesson Topics slide

  • This slide has links to all major topics addressed in the lesson

  • Every slide provides a link to the Lesson Topics slide and the next major topic

These two new curriculums are available because we’ve received so many requests for a separate setup and operation curriculum. But if you intend to continue to use our current curriculums, don’t worry. We will continue to make them available. Again, they are very well suited to schools that offer prerequisite classes for basic machining practice topics.

Here are the links to our machining center curriculum web pages that describe the curriculums in more detail:

Special thanks – We’d like to say thank you to BIR Training Systems in Chicago, Illinois for their help while developing these curriculums. While we’ve incorporated ideas from many sources, BIR Training Systems has been beta-testing the setup and operation curriculum for the last few months. Their input has been well appreciated.

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Instructor Note: What CNC students must know about basic machining practices

Most CNC people would agree that the more a person understands about basic machining practices as they relate to the kind of CNC machine they will be working with, the better programmer, setup person, or operator they will be. In almost all situations, understanding basic machining practices is of paramount importance to a CNC person’s success. Indeed, most technical schools that have CNC courses also have some courses aimed at teaching basic machining practices.

While I’ve always been an advocate of learning basic machining practice skills prior to learning CNC, the question often comes up about just how much basic machining practice training a person should have prior to starting out with CNC. In the past, my general answer has always been “more is better”.

But with more and more people entering the field of CNC with limited or no shop experience, it does make sense to include some basic machining practice discussions in our CNC curriculums. What follows is a summary of what I feel are the “bare minimums” when it comes to preparatory training in basic machining practices prior to starting with CNC. Admittedly, this is a somewhat controversial subject – your opinions may vary from mine.

Some basic machining practices topics are universal. That is, they apply to just about part of the manufacturing environment. While there may be some facets of each topic that are specific to a particular type of machine or process, the main ideas will apply to just about any machine or process. We’ll begin with the most universal topics.

Shop safety

Students must be aware dangers in the machine shop environment and know how to avoid accidents. They must know about, among other things:

  • Protective equipment
    Protective eyewear
    Clothing
    Hearing protection
    Safety shoes
    Helmets
    Gloves
    Respirators and facemasks
    First aid kits
    Fire extinguishers
    Cranes and hoists
    Warning signs

  • Safety practices
    When in doubt, ask!
    Raw material handling
       Heavy, sharp, greasy, slippery, dirty, sharp edges, chip residue, awkward shape
    Finished workpiece handling
       In addition to raw material handling:
          Hot items
          Spring

  • Tightening and loosening fasteners

  • Getting around in the shop

  • Behave in a professional manner
    No horseplay!

  • Machining-center-specific safety issues
    Safety interlocks, guarding, signs, safe operating procedures

You can probably come up with more considerations. And again, these are general items the often come under the heading of “common sense”. But don’t assume that your students already know how to stay safe in the shop environment.

Shop math

Frankly speaking, the math used by most setup people and operators is pretty simple. Addition and subtraction are the most common arithmetic operations, and there is some need for multiplication and division. But that’s about it. Manual programmers additionally require some right angle trigonometry, but computer aided manufacturing (CAM) system programmers may not even need trig.

The real trick is consistently performing simple calculations – over and over again – without making any mistakes. An arithmetic mistake, of course, can result in a scrapped workpiece, a damaged machine, and even an injured operator. So it’s pretty important that CNC people can do basic math.

And don’t assume everyone can use a calculator. When teaching a class of newcomers to the shop environment, I am often amazed at how many different answers people come up with for relatively simple calculations – even when they are using calculators.

Blueprint reading

Students must be able to interpret a three-dimensional shape from a series of two dimensional views. They must also be able to approximate the size of each workpiece attribute from the dimensions placed on the blueprint. This basic machining practice topic can fill an entire class by itself, but in our new setup and operation curriculum, we concentrate on just a few important skills.

Orthographic projection – Students must understand that the alignment of views on the workpiece is key to understanding what the workpiece looks like. Students must understand that most design engineers will show the bare minimum number of views needed to fully define the workpiece.

Line type – An understanding of the various types of lines on a blueprint (visible lines, hidden lines, center lines, section lines, etc.) is necessary in order to visualize the shape of the workpiece.

Dimensions – Knowing how long or large a workpiece linear or angular attribute is ensures that the student knows how big the workpiece is. Student should understand size in both the Imperial (inch) system and the Metric system.

Other information on the blueprint – including what is in the title block, notes, and revisions.

Understanding these topics, I feel, is enough to get a person to the point that they can begin working as a setup person or operator, especially if they have an actual workpiece to look at when interpreting the blueprint (most operators and some setup people will have a completed workpiece when they start working on a job). Having an actual workpiece can really help a person interpret what the blueprint is telling them.

Tolerance interpretation

Some people feel this is part of blueprint reading. Indeed, tolerances for every dimension are specified (or implied) on the blueprint. But I like to separate the task of interpreting tolerances from the task of visualizing a three dimensional workpiece from a series of two dimensional views. I think it’s hard enough for beginners to do one without having to think about the other (yet).

In my experience, tolerance interpretation can be quite difficult for newcomers to the shop environment. They must understand that there are two types of tolerances, dimensional tolerances and geometric tolerances (which I like to call surface relationship tolerances). In most cases, they can only control (or change) workpiece attributes with dimensional tolerances. In general, if a workpiece attribute is not within its geometric tolerance, there is usually something wrong with the process – and will be out of the control of a typical setup person or operator.

So I focus – first and foremost – on dimensional tolerances.

Even for dimensional tolerances, there are three different ways they can be specified. The most common – and the easiest to interpret – is the plus or minus tolerance. If students are struggling at all, I’ll limit my discussions to this form of tolerance – at least until they are fully comfortable with it. But of course, tolerances can be specified in a plus one value, minus another manner – or they can be specified with a high and low limit. Again, trying to learn all three methods at the same time can be confusing.

Students must understand how to determine the high limit, the low limit, and the mean value for each dimension they machine. They must also be able to determine whether the measured value for a workpiece attribute is within its tolerance band. If it is not, and even sometimes when it is, they must be able to determine the deviation from the measured value to the target value (the target value is often, but not always, the mean value). The deviation will be the amount of change that is required when adjustments must be made.

Admittedly, there is quite a bit to learn about tolerance interpretation. But it is at the heart of being able to setup and run a CNC machine tool. Without the ability to interpret tolerances, a person will not be able to make good parts.

Measuring devices

Again, a course in measuring devices can (and may in your school) fill a class by itself. For the purpose of learning CNC mills and lathes, students should be able to use some basic variable gauges, like micrometers, calipers, depth gauges, telescoping gauges, and others of your choosing.  Students must understand the various ways gauges can display the measured value, including digital displays (easiest to read), dials (a little harder), and Vernier scales (hardest). They must also get a feel for using the various variable gauges. I like to gather a set of example parts with known sizes on which they can practice. A set of gauge blocks and pins works nicely for this.

Machining operations and cutting tools

Setup people and operators should be familiar with the various machining operations that can be performed on the machines they setup and run. While they may not have to know as much as a programmer, they should know enough to be able to tell when cutting tools get dull, and what it takes to replace them.

Conclusion

Again, these suggestions are the bare minimums needed to get ready to learn about CNC setup and operation. And as I’ve said, more is better. But this should suffice to get a person started, as long as they understand that there will be much more to learn as they begin working with a CNC machine in the real world.

 

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Manager's Insight: Assigning sensible responsibilities to CNC people

Many shops assign one person to be totally responsible for the CNC machine/s they run. With the possible exception of creating programs – which some companies also expect – this person will do everything needed to get the machine running and keep it running. Tasks commonly include – but may not be limited to:

  • Gathering components needed for setup and production runs

  • Make the workholding setup

  • Assign program zero

  • Assemble, measure, and load cutting tools, and enter offset values for cutting tools

  • Load program

  • Verify program

  • Run first workpiece

  • Inspect first workpiece

  • Complete production run, maintaining sizes and replacing dull tools

  • Complete paperwork (like SPC data reporting) during and after the production run

  • Preventive maintenance – cleaning machine, way lube replenishment, etc.

Suffice it to say that these tasks will keep even the best CNC people busy – especially with multiple machines to run, complicated jobs, short cycle times, and low volumes.

Look for times when your machines sit idle. If you have one person doing everything, there’s probably a lot of idle time while this person is gathering components, doing inspections, loading programs, cleaning the machine, etc. I often question the wisdom of having a highly skilled CNC person performing tasks that just about anyone can do. If you can team-up on the overall task of getting and keeping a CNC machine in production, you can often get much higher productivity out of the machine, without too much of an increase in labor cost.

Consider, for example, the task of gathering components. To me, having a highly skilled setup person gathering cutting tools, workholding devices, and gauges (while the machine sits idle) is like requiring a surgeon leave the operating room – right in the middle of a surgery – to find a scalpel. Just as the surgeon has a team of people around to ensure that they can concentrate on the job at hand, so can a CNC person benefit from having helpers to perform simpler tasks that will allow them to concentrate on getting and keeping the CNC machine running production.

Think of other times when people team up to get tasks done faster. A NASCAR team has a pit stop crew to minimize pit stop time. Fast food restaurants have a team of people in the kitchen to minimize the waiting time for their customers. In these cases, of course, there is an urgency related to getting the job done as quickly as possible. If your goals are to get the highest productivity from a given machine as possible, and to do in a timely manner, teaming up on responsibilities will ensure that your reach your goals.

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G Code Primer: Multiple machining operations on holes

It is not uncommon to perform several machining operations on a group of holes. You may, for example, have to spot drill, drill, and tap several holes. The more holes you must machine, the more redundant commands there will be in your program. And if you are programming manually, each operation will be quite error prone. This means you must cautiously verify each tool.

This is an excellent application for using sub-programs. The more holes that must be machined, the more this technique will help. And, if the first operation is correct – hole locations and obstruction clearing – you can rest assured that all other operations will be correct as well. After all, the same commands will be used.

How to do it

In the main program, you will include a command for each cutting tool that machines the first hole, specifying how the holes are to be machined (cycle type, hole bottom, rapid plane, feedrate, etc.). Then you will command the related subprogram to be executed. In the sub-program, you will include all of the other hole locations, as well as any other commands that might be necessary (like G98 and G99 words to clear obstructions).

Example

Here is an example main program:

  • O0046

  • N005 T01 M06 (CENTER DRILL)

  • N010 G54 G90 S1200 M03 T02

  • N015 G00 X1.0 Y1.0

  • N020 G43 H01 Z2.0

  • N025 G81 R0.1 Z-0.15 F3.0

  • N030 M98 P1000

  •  

  • N035 T02 M06 (27/64 DRILL)

  • N040 G54 G90 S700 M03 T03

  • N045 G00 X1.0 Y1.0

  • N050 G43 H02 Z2.0

  • N055 G73 R0.1 Z-0.7 Q0.1 F6.0

  • N058 M98 P1000

  •  

  • N060 T03 M06 (1/2-13 TAP)

  • N065 G54 G90 S229 M03 T01

  • N070 G00 X1.0 Y1.0

  • N075 G43 H03 Z2.0

  • N080 G84 R0.25 Z-0.75 F17.6

  • N085 M98 P1000

  • N090 G28 Y0

  • N095 M30

Here is the sub-program:

  • O1000 (1/2-13 holes)

  • N001 X6.0

  • N002 X11.0

  • N003 X10.0 Y5.0

  • N004 X4.0

  • N005 X1.0 Y10.0 G98

  • N006 X6.0 G99

  • N007 X11.0

  • N008 G80

  • N009 G91 G28 Z0 M19

  • N010 M01

  • N011 M99


In lines N020, N050, and N075, notice that the tool is brought to within 2.0 inches of the work surface. This sets the initial plane for clearing obstructions with G98 and G99. In lines N025, N055, and N080 of the main program, the appropriate canned cycle command is given and the first hole is machines. In lines N030, N058, and N085, subprogram O1000 is executed, which contains the balance of the holes to be machined. Notice the G98 in line N005 of the sub-program. There is an obstruction (maybe a clamp) between this hole and the next. In line N006, the R plane is reset so the tool will not continue to retract to the initial plane (only one obstruction to clear). Finally, notice that certain tool ending commands are redundant and included in the subprogram (lines N009 and N010) to minimize the number of commands required yet further.

The only problem with this technique is that more than one program is required for a given job. Indeed, if you have five different kinds of holes that must be machined, you’ll have six programs if you use this technique for each. It can be difficult enough to track one program per job, let alone many. And loading individual programs may be difficult.

We can solve the program loading problem by including all of the programs in one file on your DNC system. A parameter within the machine controls whether the machine will stop reading a program at the program ending word (M02, M30, or M99), or whether it will continue reading until an end-of-file delimiter (a percent sign - % is read). This parameter will be the topic of the Parameter Preference article later in this newsletter.

Additionally, some Fanuc compatible controls (but not most Fanuc controls) allow you to include the sub-programs right in the main program, before the end of program command. This allows you to keep all of the commands related to a job in one program – simplifying the tracking and loading of your programs..

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Parameter Preference: Controlling when the machine stops reading a program

All CNC machines made today allow you to transfer program to and from a distributive numerical control (DNC) system. Indeed, you probably transfer programs on a regular basis. An important consideration when reading programs – that is, loading them into the machine – is when the machine will stop reading from the file being sent from the DNC system. With Fanuc controls, one of two settings is possible in this regard. A parameter controls which of the two methods will be used.

First, it is possible that the machine will stop reading as soon as an M02, an M30, or M99 word is seen. These words, of course, are all program ending words. And it may seem logical that the control will stop reading as soon as it sees the first end-of-program word. In my experience, most machine tool builders make this the default setting for the parameter.

Second, it is possible that the control will not stop reading until the end-of-file delimiter is read. For Fanuc controls, the end-of-file delimiter is a percent sign (%). Again, in my experience, this is not how most machines are set.

If you are only loading one program at a time, it really doesn’t matter how this parameter is set. Even if the parameter is set to stop reading when a percent sign is read – and even if there is no percent sign in the program, the control will still read programs (though the machine may not automatically stop reading – you may have to press the reset key).

But if you want to load more than one program at a time – as may be the case when loading a main program and several sub-programs (see the G Code Primer article earlier in this newsletter), you’ll need the parameter set to stop reading when the percent sign is read. If, of course, the parameter is set so that the machine stops reading at M30, M02, or M99, only the first program will be loaded.

To find this parameter, look for the category “CRT/MDI EDIT” in the Fanuc parameter table. For a 16 series control, it happens to be bit seven of parameter number 3201, and has the label NPE (labels tend to be pretty consistent from one Fanuc model to the next). If this parameter is set to a 0, the machine will stop reading at M02, M30, or M99. If set to a 1, the machine will read until a percent sign is seen.

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Safety First: How much safety training do you provide?

Most companies assume quite a bit of their employees when it comes to safety issues. They assume their employees know how to stay safe in the shop environment. This can be a terrible mistake. Most people won’t know the right questions to ask – indeed – newcomers may not even recognize the fact that they have been placed in a dangerous working environment. As the employer, it is your responsibility to alert and inform them.

There are three common times when this training should be done – though you may elect to do even more. First, safety training should be done with new hires. You don’t know what kind of safety habits (good or bad) a person brings with them from their previous employer/s. New people should be afforded the opportunity to learn your company’s safety practices – not to figure them out on their own.

Second, safety training should be done whenever a situation changes. Changes could stem from the implementing of new machines or new processes – or a person could be moved from one area of the company to another. Different situations have different safety issues. Be sure that your people know the safety implications of their new situation.

And third, I recommend that you do continuing refresher courses on safety issues to ensure that people stay up to speed. A brief (and incomplete) list of safety topics is included in the Instructor Notes article earlier in this newsletter. It shows the kinds of topics your people should be aware of. Surely there will be more specific considerations for people working in your company.

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