Not so long ago, the jig grinder was one of the workhorses of precision tool grinding. While it was primarily used in die making, many mold shops also made extensive use of these highly precise machine tools.
One reason mold making has a limited use for jig grinding is because injection molds just don’t have that many through holes. Instead, most details are cut into the steel, but are “blind”, that is they do not to entirely through the steel.
While this does limit the applications, in actual practice there are countless uses for the jig grinder. The wire EDM is able to nearly all of the hole making, such as ejector pins or core pins, but very often there are shut off details or molding details that are done by jig grinding.
The counter bores for core pins are one such application. While these could be finished before heat treat, it is difficult to grind the blocks to suit the depth of the counter bores. Another option is to hard mill them, but this often causes an interruption in the more important machining of cores and cavities.
A common predicament is when a mold or die is damaged in production. Usually the surface is welded and reworked. A skilled jig grinder operator can do this rework in a fraction of the time that a CNC mill requires. There are no complicated programs to generate, and it is much easier to visually blend in the new surfaces with the existing ones.
This is the perfect application for this precision machine tool. Most stamping dies have an abundance of through holes that can easily be ground. The shapes and contours can also be ground to a very high degree of accuracy.
The extensive use of wire EDM has dramatically reduces the need for the jig grinder, but the demand still exists. The use of carbide limits the types of machines that can be used, but with diamond wheels and CBN wheels, this is no problem.
Together with the WEDM, these workhorses can manage almost all the precision work required in a stamping die. A CNC grinder is capable of some very impressive machining and can make short order of many details.
Production machining of precision parts requires the use of highly accurate gages and fixtures to inspect the dimensional accuracy. This is a great application for the jig grinder. Sometimes it is actually the only practical way to create the shape and contour of the gage.
Conventional milling is not accurate enough, EDM is not accurate enough, but these precise tools can manage easily. In fact, they are so accurate that the government uses them to establish standards of accuracy. In a sense, they are a part of national security.