To subscribe: Simply email us (email@example.com) and let us know you'd like to be added to our distribution list.
To unsubscribe: Respond to this email, typing REMOVE in the subject. Please accept our apologies if we have disturbed you.
On-Line Courses Update: Our on-line classes - Here's how it works...
We offer six online CNC classes:
The format for our on-line courses is quite consistent for all courses. We're using the on-line training platform from UniversalClass.com. If you haven't already done so, check out this site. It is truly amazing. There are countless classes you can take that relate to just about any conceivable topic (though few are related to CNC or manufacturing). UniversalClass.com provides a robust virtual classroom environment, one that will allow us to relate all course material with ease. And since our classes are on-going and self-paced, you can start immediately - as soon as you enroll!
Here's what you'll be doing during the class. Activities include:
Remember, these courses are self-paced. You'll be progressing through the course as quickly or slowly as you like. You control the pace. Once you enroll in the class, you'll begin (of course) with lesson one. We want you to get the most out of this course, so we require that you complete all activities in one lesson one before you'll be allowed to continue with the next.
G code primer: Some special feature of G76 (the threading command)
Fanuc's threading command is pretty powerful - and very helpful. It will allow you to completely machine a thread with one command in your program, regardless of how many passes the threading tool must make. The G76 command is given after the threading tool approaches the diameter to be threaded - away from the diameter in Z and above or below the diameter in X (above for outside diameter threads and below for inside diameter threads).
Though the actual words given for G76 will vary even among Fanuc controls, the functions they control include:
Again, the functions just described are pretty basic, and consistent from one thread to another. Here is an example command that machines an OD thread (approach position is above X value in threading command).:
If you have been using the G76 command on a regular basis, so far we haven't told you anything new. But there are some special, lesser-known functions of G76 that we'd like to relate.
When machining a taper thread, of course, the tool must make a tapered move when threading. The amount of taper is specified with an I word or R word, depending upon control model. This word does not specify the taper angle. Instead, it specifies the distance and direction from the end point of the thread to the start point of the thread along the X axis. For OD threads, this value will be negative - for ID threads, it will be positive (assuming you are machining in the negative Z direction, as is normally the case).
To calculate the value of this word, you must know the taper angle, which is 3.718 degrees for National Standard threads. You multiply the tangent of the taper angle times the total distance in Z that the tool will be moving during each pass (including approach).
Multiple start threads
Some controls require that you specifies more than one G76 command when machining a multiples start thread (one for each thread start. This requires a Z axis movement between threading commands. The amount of movement is the pitch of the thread (total lead divided by the number or thread starts). For a four-start thread with a 0.5 inch overall lead, the pitch is 0.125.
In some cases, it may not be possible to move in Z between passes (consider a thread at the end of the workpiece that is supported by a tailstock). And the extra motion does take time, making for a somewhat inefficient cycle.
Newer controls have overcome these two limitations. A Q word in each G76 command specifies the angle of entry for the treading tool. For a four-start thread, an example set of Q words is Q0, Q90.0, Q180.0, and Q270.0.
Not always programmable
There are some thread functions you should know about that may not be programmable. They are only programmable for control models that use a two-line G76 command (many 0T controls use this method). For controls that use the one-line G76 command, a parameter controls the function. If you want to change its value, you must change a control parameter.
Instructor note: Mastering the presentation of CNC skill sets
Our CNC Curriculums help you teach how to master all three skills needed to become a proficient CNC user:
When a student completes your CNC course, they will posses the basic skills needed to begin working with all three facets of CNC machine tool usage. We start with programming and work our way toward setup and operation. This method works best for students intending to master all three skills.
There are many presentations made during the programming portion of the course that apply to setup people and/or operators. For example, a programmer must understand that program zero it the location from which all coordinates in the program are taken. But a good programmer should also know how program zero is assigned. In many companies, program zero assignment is the responsibility of the setup person. But since a CNC programmer must be able to direct the CNC setup person (providing setup sheets and help to setup people at the machine), we include this presentation during our discussion of programming.
This is but one example. All through the programming discussions, we present implications related to setup and operation. When the student finishes the programming portion of your course, they will already know many of the principles related to setup and operation.
While our curriculums have been designed to teach all three skills, we know that you may want to keep some of your classes may be more basic. You may, for example, want to teach a class on setup and operation - or just operation. For this reason, our curriculums include some special help for these situations.
Here are two links to the Lesson Plans Manuals Again, note how much emphasis is placed on mastering each skill.
Along with our Key Concepts approach, these functions make it easy for a CNC instructor to teach all three skills in one class or to pick and choose those skills they want to cover.
G code primer: Which fixture offset should I use?
This is a question that recently appeared in the CNC Tech Talk forum on our website.
As you know, Fanuc controlled CNC machining centers use fixture offsets to assign program zero. You'll have at least six fixture offsets, though Fanuc provides an option to get more. For most applications, especially with machines that do not have a rotary device (indexer or rotary axis), six is more than enough.
When your machine has six fixture offsets, they are instated by a series of G codes, ranging from G54 for fixture offset number one through G59 for fixture offset number six.
In many applications, only one fixture offset is required - and if this is the case, we recommend using fixture offset number one (instated by G54). The reason why we recommend this that when you power up the machine, it automatically instates G54. That is, G54 is initialized. Should you forget to include a G54 in the program, the machine will still select the correct fixture offset.
Macro maven: Using the machine's current absolute position in a custom macro
One of the application categories for custom macro is user created canned cycles. In this category, you're creating your own canned cycle. As you know, most control-based canned cycles (like G81 - drilling) can use the machine's current position for certain things within the canned cycle. With G81 for example, if you leave out the X and Y value (hole center position), the machine will assume that the hole will be drilled in the current XY position. With three special system variables, you too can access the machine's current absolute position and use it from within your custom macros.
Let's look at an example. Here is a custom macro for thread milling from issue 62 of The Optional Stop newsletter.
Again, how this custom macro works is presented in an earlier issue. Please see issue 62 if you want to learn more about it.
With this custom macro in its current form, X and Y are used in the G65 command to specify the hole center. They are currently mandatory variables - an alarm will sound if they are not specified in the G65 command.
Say you want the this custom macro to behave more like a G81 canned cycle. If X and Y are left out of the call statement, you want the custom macro to assume that the hole center in X and Y is at the machine's current XY position. Here is the custom macro again, modified to use #5001, #5002, and #5003 that will do this.
The highlighted commands provide the desired function. If either or both of X and Y are left out of the call statement, the values of #24 and/or #25 will be set to the machine's current absolute position in X and/or Y.
Parameter preference: Limiting offset changes on turning centers
A very common mistake when operating a CNC turning center is misplacing a decimal point. When changing offsets, such a mistake can be disastrous. If an operator means to type 0.001 and instead types, 0.1, at the very least, a workpiece will be scrapped. Worse, the machine could crash.
While there is no way to eliminate mistakes, you do have a way to minimize the amount of offset amount per entry. With most Fanuc controls, a parameter determines the maximum amount of offset entry. If a value greater than the offset amount is entered, with most machines, nothing happens. With newer machines, a message appears in the entry area to tell the operator that they entered too large a value.
Finding the parameter
As with all parameters, it can be difficult to find the parameter in question. Look in the list of parameter functions for parameters that control tool offset and start scanning. With a 16T control it happens to be parameter 5014, and its description is: Maximum value of incremental input for tool wear compensation. Again, the parameter number and description will vary from one Fanuc control model to another.
For this particular parameter, you'll be entering the actual value to which you want to limit offset entry. Note that most controls do not allow a decimal point in this value and the value must be specified with a fixed format. If you're working in the inch mode (G20), a value of 0200 specifies 0.020 inch, which is what we'd recommend that you set the parameter to. In the metric mode, a value of 500 specifies 0.50 mm. (Note that in the inch mode you work with a four-place fixed format - in metric mode you work with a three-place fixed format.