As the previous illustration shows, there are three major selections that can be made by a setup handle, regard less of its actual design:
As an example shown in the initial illustration, the rotary switch points out to the Y-axis as the current selection. That means all axis motion generated by the dial will apply to the Y-axis only. Also, the range selection will apply to the Y-axis as well.
Selects axis to be set
Selects minimum motion amount for one handle division
Selects the axis direction, based on axis and range selections
While the chapter title may be a bit ambiguous for the programmers with limited interaction in actual machin ing, its meaning should be quite clear to CNC operators at all levels. What is generically described as ‘the setup handle’, is commonly known under several other names or descriptions. The name of the device defines the main purpose of this ubiquitous hardware, ‘officially called – manual pulse generator – also known as the MPG device by its initials. Other names commonly used in machine shop users are ‘handle’, ‘dial’, ‘pendant’, and some other descriptions. For the purposes of this chapter, the all-in- clusive term ‘handle’ will be used.
Once the working axis has been selected, the next se lection relates to the handle range. This part of any CNC operation is often most misunderstood. The selection range is commonly identified with certain X-codes. They may look like some ‘mysterious’ specification, for example, X1, X10, and X100 are typical. Contrary to some interpretations, there is no mystery in these selec tions at all. The key to understanding such designation is that the letter ‘X’ does not refer to a particular axis – the letter X is nothing more than a symbol for the multiply ing factor, meaning ‘times’. So X1 is actually ‘times one’, x10 is ‘times ten’, and X100 is ‘times one hundred’.
Of course, the qualifier ‘times’ in the expression has to have some more detailed additional definition. If X1 means ‘times one’, and X10 means ‘times ten’, then the natural follow-up question is – times what? The answer is simple – ‘X-times the minimum increment’ of an axis motion.
While the answer is correct in principle, it should be enlarged – after all, what is the ‘minimum increment’?
Most control manuals use the term ‘minimum incre ment’ when they really mean ‘the smallest axis motion possible’. Either definition refers to the smallest motion the machine can make within the scope of the selected units (Metric or Imperial). In practice, that means the smallest amount of axis motion is 0.001 mm or 0.0001 of an inch;
Although their main purpose does not change from one CNC machine to another, handles used for setup do vary quite a bit in their design. On small CNC machines, the handle is often built in the operation panel or the con trol panel. For smaller machines, this design hardly pres ents any problems, as the handle is always within comfortable reach of the CNC operator, during part setup. On the other hand, medium and large CNC ma chining centers (as well as many CNC lathes) do not pro vide the same ease of handling, so they provide a handle that is detached – such a handle is not a part of the oper ation or control panel, but a unit that is connected to the control panel via a coiled cord. In this case, the handle pendant also includes switches that allow remote set tings. Many modern handles are fully digital and can play much more information than traditional handles.
It should be understood that all three features always work together – there is no such thing as ‘set one, ignore the others’.
Handles with digital display have additional features, typically those that would require looking at the main display screen. Good examples are tool position screen, work offsets, even a program listing.
In order to make the handle functional, proper mode must be selected from the machine operation panel. There are four MANUAL mode selections shown at left and four AUTO selections, shown at right. Some con- trols use reverse orientations of the two modes.
Regardless of how a particular machine handle is de- signed, it always serves the same purpose during actual machine setup. When setting up a part for CNC machin ing (milling or turning), the CNC operator needs to use the control and operation panels of a CNC machine to in put various offsets, to move the machine slides by a cer tain distance, or make many other settings. In the category of ‘other settings’, the most common is setting the work offset using an edge finder or a similar device.
The single purpose of handle is to allow CNC operator
to control axis motion(-s) during setup away from the main operation panel
JOG , EXT / DNC
Minimum increment is equivalent to the smallest amount of motion => 0.001 mm or 0.0001 inches
SELECT MODE – HANDLE
As the definition indicates, the purpose of the handle is to allow various axis motions to take place during setup, when access to the operation panel is too far from the work area or is otherwise restricted.
Whether built into the machine enclosure or used re motely, the handle is normally used in manual mode of operation, selected from the operation panel by a switch set to – HANDLE
The typical handle is a mechanical device sending electronic signals to the control system. Each signal rep resents the amount of motion to be performed along each axis selected. The use of the handle is generally limited to machine and tool setup.
Once the desired machine axis had been selected and the range of motion specified, the handle dial becomes the most important instrument during part setup. The handle dial is divided into one hundred equal divisions, generally called increments or resolutions or notches – or – divisions.
In order to make a motion in a certain direction, the proper axis has to be selected first. Handles of any de sign offer minimum selection of XYZ axes on CNC milling machines and machining centers, and minimum selection of XZ axes on CNC lathes. Typically, the selec tion will reflect the actual axes available on the CNC machine, such as the fourth axis. If this axis is shown on the handle but does not exists on a particular machine, the selection on the handle will be disabled.
One division (notch) always represents the minimum increment within the selected range
CNC Control Setup for Milling and Tuming SETUP HANDLE
CNC Control Setup for Milling and Tuming
Another way of using the handle is to think of the dial in terms of amount of axis motion in full djal turns.
Keep in mind that once a certain cutting tool is manu ally moved during program execution, it no longer rep resents the required position from the part program. This is where the major benefit of Manual Absolute is most apparent.
The setup handle is not normally used during actual production (while the part program is being processed). The only time that the handle may be used is to provide manual motion when the program processing is inter rupted. This can happen, for example, if you want to in spect a hole, but the cutting tool is in the way. Switching to manual mode and using the handle, the tool can be moved away into a clear position and the hole can be in spected.
Although the handle design will vary from machine to machine, and control to control, its content, purpose, and applications remain the same, regardless of the model.
The following series of tables illustrate the results of various settings and their influence on machine motions. They should answer the most important question a CNC operator might ask is – what is the length of axis motion when different settings are applied.
The following tables show the length of motion per dial division (notch) for metric and imperial units re spectively, as well as motion amount per turn of the dial.
Motion Length per Handle Turn – Metric
This is a variation on the metric version for motion length of an axis per one division. In the previous metric table, 100 notches represent one full turn of the handle dial in any range setting (360° turn of the dial).
When Manual Absolute is turned ON, any manual tool motion will UPDATE
the work coordinate system
Number of turns
1 full turn
| 10.000 mm
Manual Absolute in its ON setting allows a manual motion during program processing. Any manual motion will always update the coordinate settings, which means the control system always ‘knows’ what is the current tool location from part zero.
There is hardly any practical reason why this switch (if available) or the parameter setting should ever be turned off.
Note that when using x100 range, even a small turn causes large axis motion
10 full turns
Make sure the MANUAL ABSOLUTE switch is ON when moving an axis during program processing
100 full turns
Motion Length per Handle Division – Metric
When a CNC machine is set to metric mode of mea surement, the units of axis motion are in millimeters (mm). In metric system, the minimum increment (axis motion) is one millimeter divided by 1000, into microns:
Manual Absolute Switch
The previous warning should be taken very seriously. The majority of modern CNC machines do not have the feature called Manual Absolute at all, at least not in the form of a switch on the operation panel. This feature can be controlled by system parameters, if necessary.
At the same time, on some older CNC machines (con trols), there is a physical switch, usually located on the operation panel, and identified as Manual Absolute. This switch can be turned ON or OFF. It is very important to understand the purpose of this switch and its ON and OFF settings.
Motion Length per Handle Turn – Imperial
This is a variation on the imperial version for motion length of an axis per one division. In the previous impe rial table, 100 notches represent one full turn of the han dle dial in any range setting (360° turn of the dial).
Manual Absolute OFF
Keep in mind that if Manual Absolute switch is turned OFF, any manual motion performed during part pro gram processing will NOT update the coordinate sys tem. The unpleasant result of such a situation is a likely scrap due to wrong positioning of the cutting tool.
One mlcron = 1 mm / 1000 = 0.001 mm
Number of turns
1 full turn
As a general rule, Manual Absolute setting should always be ON
10 full tums
100 full turns
| 1.000 mm
Number of Divisions for a Given Axis Motion
Manual Absolute ON
Setting the Manual Absolute to ON makes the only sense in practical applications. Suppose that you need to inspect a part while the part program is still in progress. This is a common activity between tool changes, usually associated with the M01 (Optional Stop) function.
As is often the case, the part area to be inspected is ei ther too far for comfortable inspection, or the tool itself may be in the way of viewing, or some other obstacle prevents the inspection. In any case, it will be necessary to switch from Memory mode to manual mode (such as HANDLE mode) and move the tool manually from the programmed position.
The setup handle can be used for any amount of axis motion, from the smallest increment up. The table below shows formulas to calculate number of handle divisions required to move the selected axis by specified distance:
Using a handle does not require any special skills, but it does require a certain degree of caution. Study the four tables presented in this chapter and especially focus on the range setting of x100.
With such a high range setting, it is very easy to make an axis motion too long and possibly hit the part during setup, for example. Even a small turn of the handle can produce a long tool movement in the x100 setting range.
Keep in mind that a handle is an electronic device – there is no human feel of touch in the handle. The main purpose of the handle is to transfer electronic signals to the CNC system as manual axis motions.
Motion Length per Handle Division – Imperial
When a CNC machine is set to imperial mode of mea- surement, the units of axis motion are in inches (in). In imperial system, the minimum increment (axis motion) is one inch divided by 10000, into one ten thousandths of an inch, commonly known as ‘one tenth’:
Number of divisions for distance in millimeters
Number of divisions for
distance in inches
One ten thousandth of an inch = 1 inch / 10000 = 0.0001″
Motion x 1000
Motion x 10000
Motion x 100
Motion x 1000
Motion x 10
Motion x 100