Disclaimer: CNC Concepts, Inc. accepts no responsibility for the use
or misuse of techniques shown in this web page. We simply publish information
we feel will be of interest to CNC users. In all cases, the reader is totally
responsible for considering the implications, good and bad, of implementing one
or more of the techniques we show.
Using custom macro to streamline tool length measurements
This rather advanced technique assumes your control has parametric
programming (example shown in custom macro B). If you have this feature, you
can eliminate the error-prone calculations and tool length compensation offset
entry needed for tools on machining centers!
In the Fall 1994 issue of The Optional Stop, David Engel of H & K
Incorporated in Waukesha, Wisconsin submitted an excellent idea for using an
edge finder as a kind of manual probing system. This technique dramatically
reduces the time, effort, and potential for operator error when measuring the
program zero position during setup. In this article, we use the same principle
to help with on-line tool length measurements.
While nothing beats the efficiency of measuring tool lengths off-line, there
are times when production quantities are so low that there is no real advantage
to measuring tool lengths off-line, and many companies have their CNC operators
measuring tool length values on-line. Like the suggestion from Mr. Engel, this
technique uses custom macro B to allow us access to the machines current
position and to tool length compensation offsets from within the CNC program.
System variable #5003 gives us access to the current absolute Z position and
the #2000 series system variables give us access to the tool length
compensation offsets. This particular example assumes you are using the length
of the tool as the tool length compensation offset value. However, it could be
easily modified if you use the distance from each tool tip down to program Zero
in Z as your tool length compensation value.
To keep this program simple, we assume a vertical machining center and work
in sequential tool order starting with tool station number one. The operator
will simply stop the program when the last tool length is measured. More
elaborate techniques could be used if you wanted the operator to be able to
designate which tool stations require measuring. Additionally, this program
assumes all tools to be measured are in the machine's tool changer magazine and
that there is no tool in the spindle at the time this program is run.
Program
O9100 (Program to touch off tool lengths)
#3006=101 (TOUCH SPINDLE NOSE TO BLOCK)
#5003=0 (Set current Z position as program Zero surface)
To use this program, the setup person loads all tools to be measured into
the tool changer magazine. Then, just as when measuring tool lengths completely
manually, they will place a block on the table to be used as a reference point
in Z (the top surface of the work holding setup is commonly used). They will
then position the machine in X/Y so that the spindle nose (no tool in spindle)
is above the block. When this program is run, the operator will be asked to
touch the spindle nose to the block. Just as when measuring tool lengths
completely manually, the operator will place the machine in manual mode, use
jog to quickly position the spindle nose close to the block, and then
cautiously touch the block (or gauge block) with the handwheel.
When this is done, they will place the machine back in automatic mode and
press cycle start. The control will record this position in Z as the current
program zero point (just like the operator does when manually resetting the Z
axis display to zero) and then automatically move the machine to its tool
change position. Tool number one will be placed in the spindle and the machine
will stop again. The operator places the mode switch back to jog and cautiously
touches the tool tip to the block. When this is done, they place the mode
switch back to automatic and press cycle start. The length of tool is
automatically stored in offset number one! This process is repeated for each
tool until the last tool length is measured. This technique dramatically
simplifies the tool length measuring process for the operator and eliminates
tool offset entry mistakes.
