Product Corner: Self-study manual offers cost-effective self paced course

We’ve been offering these manuals for just about as long as we’ve been in business. They are the same manuals included with our video courses and CD-rom courses. They are also the ones used with our CNC curriculums. Again, we’ve always made these manuals available separately – and when combined with the corresponding workbook / answer book combo, they make excellent and inexpensive self-study courses.  Our two most popular self-study manuals are:

• Machining center programming, setup, and operation (CNC drilling and milling equipment)

• Turning center programming, setup, and operation (CNC lathes)

Each is tutorial in nature yet comprehensive. We assume that the reader knows nothing about CNC prior to reading them and present the three tasks that must be mastered (again, programming, setup, and completing a production run) from the ground up. We do assume that the reader has some basic machining practice experience (blueprint reading, shop math, knowledge of shop tools, etc.), but nothing about their previous CNC skills.

While a few exercises are included in each of these manuals, to completely confirm comprehension we recommend purchasing the appropriate workbook / answer book combination. Each manual is divided into lessons (twenty-three lessons in the machining center manual, twenty-eight in the turning center manual), and after each lesson there is an exercise to do in the workbook. Some exercises include programming activities. Answers, of course, are provided in the answer book.

We also thoroughly cover each topic. When a person finishes, they will have a very good understanding of what it takes to program, setup, and run a CNC machine.

Cost for each manual is $70.00 (again, one for machining centers and another for turning centers). Each workbook / answer book combination sells for $49.90. Total cost per set is $119.90 plus shipping. And again, there is one set available for machining centers and another for turning centers.

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Instructor Note: Do you introduce parametric programming in your CNC classes?

As you probably know, parametric programming provides computer-programming-like capabilities at G code level. Variable, arithmetic, and program flow control are but three of the features available when the CNC control has parametric programming. (Learn more about parametric programming here.) There are also many CNC-related parametric programming features that help make it such a powerful programming tool – a tool that all CNC students should, at the very least, be introduced to.

At some point in your CNC class – most preferably a programming class – you should spend a little time explaining what parametric programming is and describing its applications. While students may not have to be well versed with its use, they should be able to recognize good applications when they see them.

As you also probably know, the most popular version of parametric programming is custom macro B. This version is used by Fanuc and any control manufacturer that claims to be Fanuc-compatible. For this reason, I’d recommend that any specific examples you show be in custom macro B format. But do explain that every control manufacturer has a version of parametric programming that allows the same techniques used with custom macro B. Okuma calls it user task 2. Fadal calls it macro. The point is: Some version of parametric programming will be available (possibly as an optional feature) regardless of what CNC machine and control are being used.

I like to introduce parametric programming during the discussion of special programming features – which is included in our “key concept” number ten. Since it can be quite similar to sub-programming, we include a brief introduction to parametric programming at this point in our CNC curriculums and student manuals. Again, we simply introduce its features and applications. Only a page or so is provided for this purpose in our manual. You may want to do more – showing a real life example/demonstration on one of your lab machines.

Admittedly, it may be difficult to get too specific about parametric programming during a basic CNC programming class – as parametric programming can get pretty complex. But even if you keep your presentations pretty general in nature, students should be able to see the benefits of this very important feature.

If you don’t feel well enough acquainted with parametric programming to introduce or teach it, there is plenty of free information on our website to help you understand. Look on our CNC Tips page for several real-life examples. We also offer a self-study manual and a CD-rom course that completely covers parametric programming in detail. And we can provide you with a curriculum including instructor and student materials that will allow you to teach a parametric programming class – should you decide to provide a separate class on this subject.

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Manager's Insight: What percentage of time are your machines in production?

I’ve done quite a bit of in-plant consulting and training over the years. While walking shop floors, and as you can imagine, I’m always very interested in the CNC processes taking place. As long as it doesn’t bother the people running the machines, I’m always looking over someone’s shoulder to see what’s going on and peering into machines to see the cutting operations being performed.

I’ve noticed something pretty consistent from one company to the next. CNC machines never seem to be in production for as much of the time as management and engineering staff seem to think they are. At some point during my visit, I’ll always ask for some general percentages of setup time compared to production run time. And during production run time, how much time the machines are actually running (as opposed to being down for part loading, tool maintenance, adjustments, etc.).

I hear some pretty conflicting things from management and engineering people. According to management in one company I recently visited (data taken from computer printouts), setup time was about 12 percent and production run time (machines actually running) was about 78 percent. I was quite impressed with the efficiency they had achieved. Yet the next time I toured the facility, over half the machines were sitting idle!  During the week of my visit I kept making my way through the shop at various times (and over the course of two shifts), and never were more than half the machines actually running.

This didn’t sound right to me so I questioned whether something special was happening during my visit. Maybe more people than normal had called in sick. Maybe there were a lot of people taking vacation days. Maybe there wasn’t enough work for the machines while I was there. Whatever. But I was assured that things around the plant were quite normal.

Admittedly, my stay was relatively short – surely I was getting just a snapshot of what was probably happening in the company over the long haul. But as I said, I’ve found the estimated production running time to be consistently high in many of the companies I’ve visited.

One of the first tasks to undertake when considering making any improvement, of course, is objectively assessing the current state of affairs. Machine downtime should be an obvious target for improvement, but if you are not getting a true picture of what is happening on the shop floor – for whatever reason – you may not even recognize the need to improve.

My suggestion is to question and test your production run-time numbers. Simply do what I did. After determining what the accepted run-time percentages are, go out into the shop and determine what percentage of machines are sitting idle at any given time. If you find discrepancies, it should be taken as a signal that there may be some errors in your data collection and reporting system. They shouldn’t be too difficult to spot.

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G Code Primer: Try not to think incrementally

I’ve had over five hundred students come through my on-line courses to date. In my programming classes, there is one common misunderstanding that a great percentage of students share. They tend to think incrementally. By this I mean when programming a cutting motion, they ask themselves the wrong question. The question they should be asking is “To what position do I want to move the cutting tool?” This position is always relative to the program zero point location. And of course, when you specify positions relative to program zero, you are working in the absolute mode.

But instead, they ask themselves “How far do I want to move the tool?” This is thinking incrementally. While there are good applications for the incremental mode, the vast majority of motions should be programmed in the absolute mode. Indeed, I urge entry-level programmers to work exclusively in the absolute mode while they write their first few programs.

With machining centers, G90 specifies absolute mode while G91 specifies incremental mode. With many turning centers, X and Z words specify absolute motions while U and W words specify incremental motions (U causes incremental X axis motions and W causes incremental Z axis motions).

The method by which absolute and incremental modes are specified, however, is hardly the cause of the thinking-incrementally problem. Instead, the confusion usually stems from the way prints are dimensioned. Consider, for example, two holes that are specified as 2.5 inches apart from one another. Maybe one of the holes is dimensioned directly from the program zero point – and the programmer won’t have a problem correctly specifying its location. With the tool currently above the first hole, and since the print dimension shows the 2.5 inch distance between the holes, many entry-level programmers will mistakenly specify the motion to the next hole with 2.5 inches. Again, this is thinking incrementally.

Some programmers will temporarily shift to the incremental mode and specify the motion to the second hole – and this will actually work – but we don’t recommend it. This is not one of the good applications for incremental mode that we mentioned earlier. Instead, we recommend keeping the machine in the absolute mode and specifying the position of the second hole just as you do for the first hole – from the program zero point. This means calculating the position of the second hole relative to program zero – probably requiring the addition of the 2.5 inch between-the-holes dimension to some other value.

So – what are good applications for the incremental mode? One is related to sub-programming. When a series of commands must be repeated, it is usually a good application for sub-programming. Say five identical pockets must be milled. The same motions needed to machine the first pocket will be used to machine each of the others. But if the subprogram is written in the absolute move, the same pocket will be machined five times.

One way to overcome this problem is to write the subprogram in the incremental mode. After moving to the starting point of the pocket in the absolute mode, the incremental subprogram can be called. (Note that there is another way to handle this application that does not require writing incremental commands. It involves the G52 temporary shift of origin command.)

Though we’ve strayed a bit from the focus of this short article, our main point is that most program should be written exclusively in the absolute mode. The sooner an entry level programmer can stop thinking incrementally, the sooner they will become a proficient programmer.

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