Jig-grinding is almost always overlooked as a meaningful machine tool for injection mould making. Yet, from my experience, it is a very valuable machine that gets the job done quickly and very accurately.
Injection mould makers everywhere are always looking for ways to improve their operations. Any way you can shorten your delivery date and improve your quality should be seriously investigated.
One reason jig grinding is overlooked is because most toolmakers view it as an out-of-date machine that is only good for round holes or time consuming contours that should be done on a CNC milling machine or WEDM.
True, milling and WEDM now do much of the work previously done by jig grinding, yet it is still indispensable for many operations in the tool shop. The fact that it is overlooked also makes it a kind of secret weapon. Some shops run their jig grinder all day long, doing a variety of tasks.
I have never investigated, but I suspect that there are many used jig grinders not being used. You might be able to pick one up at a bargain price, though you will have trouble finding a qualified operator!
Jig grinding can save you money
Examples of the time consuming tasks it can do well
Blind hole floors. These are always a pain to do; either you mill them extra deep before heat treat and grind to fit, or you leave stock for post heat treatment machining. Either way, it is a bother to get the depths right in a timely manner. By jig grinding, you leave them shallow before heat treat, and simply use a CBN wheel or carbide cutter to very quickly grind the depth perfectly. This is much faster and easier than hard milling or guessing at the depths when grinding.
Bosses and similar details
Why use EDM machining them when you can do it in a fraction of the time? Jig grinding is fast.
Adding relief to cores and core pins
You can either use a Ded-Tru machine, or a spin fixture on a surface grinder, or hard turn your cores. Or you can do much of the work by jig grinding.
Ejector and core pin holes
While almost all knock out holes are WEDM’d these days, there are still applications when it makes sense to jig grind them.
Pockets, whether round, square or rectangular
It is hard to beat a jig ground pocket. This is a great application for locators in the core and cavity blocks. This way you are assured of perfect alignment.
You can try the new approach and use hard milling and high speed milling to imitate the jig grinder and it does work for many applications.
Getting started with jig grinding
This is a problem; if you don’t already have one and a qualified guy to run it, you may not be able to find either one! As previously stated: you might find the machine, but good luck finding somebody who is accomplished running it.
This is one of those vanishing old school skills that does not seem to be a candidate for training and replacement. Jig grinding is also part of our national defense strategy because of it’s accuracy. NIST is responsible for the dimensional integrity of manufacturing.