Jig Grinding: One Of The Secret Weapons In Injection Mould Making

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.

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.

Why is the jig-grinder overlooked?

It is overlooked partly because most toolmakers view it as an out of date machine that is only good for round holes or time consuming contours that should be done on a CNC milling machine. It is true, it is not very common, it is primarily used for round holes, and it does excel at contours such as you might find in a gauge for inspection.

This is why it is a secret weapon for building a plastic mould. Because it is so overlooked, so efficient and so accurate, you should take a second look at this tool of the not so distant past. Some shops run their jig grinder all day long, doing a variety of tasks.

Jig grinding can save you money

Some good 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. With the jig grinder, you leave them shallow before heat treat, and simply use a CBN wheel 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?

• 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 on a jig grinder.

• Ejector and core pin holes. While almost all knock out holes are WEDMd 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.

How can you get started with jig grinding?

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. You might have some trouble finding a qualified operator though! Experience is what makes this a valuable addition to the modern injection mould making shop. The basic operation is rather simple and straight forward, but the almost endless list of uses is a direct reflection of the skill of the jig grinder machinist.

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