The most basic application for mirror image is when machining left and right hand workpieces. Say you want to set up and run 500 of one hand, tear down, and then set up and run 500 of the opposite hand. In this case, it is possible to use the same program to machine both right and left hand parts. In fact, this application does not even require programmable mirror image. We’ll simply turn mirror image on and off in a manual fashion.
We must point out one severe limitation when it comes to using mirror image that has to do with contour milling. If the same cutter is used for both hands, any conventional milling operations done with mirror image turned off will become climb milling operations when mirror image is turned on. In many applications, this limitation may eliminate the feasibility of using mirror image to run one of the hands. (One somewhat far-fetched solution would be to use a right hand cutter for one of the hands and a left hand cutter for the other.)
The figure below shows the workpieces for our example. Note that this application will be using mirror image in the X axis. When mirror image is turned off, the program will run in the normal manner. When X-axis mirror image is turned on, the control will reverse the sign (plus or minus) of all X-axis coordinates it sees. So all that’s really happening is that the control will make any X plus value an X minus value as the program is executed.
Say for example, the program is written for the left hand workpiece. Note that since program zero is the lower left hand corner, all X coordinates will be positive. When setting up to run this hand, the setup person will do nothing out of the ordinary. The program zero assignment value for the X axis will be measured and entered into the fixture offset in the normal fashion (the fixture offset values are commonly negative values with Fanuc and Fanuc-compatible controls).
With the production run for the left hand workpiece completed, the setup person will make the setup for the right hand workpiece. This will, of course, include the determination of the X-axis program zero assignment value. However, when entered into the fixture offset, the setup person must remember to reverse the sign for this entry (by entering it as a positive value with Fanuc or Fanuc-compatible controls). Additionally, X-axis mirror image must be turned on. With Fanuc and Fanuc-compatible controls, this must be done while the machine is at its X-axis zero return position.
When the program is run, the control will simply reverse the sign for all X-axis movements, machining the right hand version of the workpiece.