Knowing how to grind ejector pins is one of those basic injection mold making skills that is often overlooked. Why is it that one guy takes a few minutes to grind them and the next guy seems to take all day?
Besides that fact that some people are just plain slow at what they do, there is also a difference in how things are done. After all, there is almost always a better way to do anything. Good mold making training for the surface grinding process is not that easy to find, which doesn’t help matters much.
If you only have 8 or 10 pins to do, technique doesn’t matter much, just get it done. But if you are talking about 120 pins or doing them nearly every day, then it pays to find an efficient method of grinding ejector pins or core pins accurately.
There are really only a few main methods that I’m aware of: vertical, horizontal, Ded-Tru and using a production type cut-off/grinding machine.
Most people use some type of V-block to hold the pin vertically and grind it to size with the bottom of the wheel. There are as many ways to do this as there are toolmakers and some places have custom V-blocks that accommodate multiple pins to save time.
This works fine, except for pins that are too long for the machine. In that case you need to hold the pin horizontally and preferably use a cupped wheel. There are several good commercial fixtures made for this purpose, such as the Royal pin grinding fixture.
Grinding small diameter pins
Grinding very small ejector or core pins can be a challenge. One solution is the Wee-block. This set includes two small V-blocks that can hold very small pins in any number of grinding fixtures. Be sure to use the little accessory between the clamping screw and the pin when holding small ejector pins. This prevents the screw pressure from distorting the pin.
Many shops have custom made V-blocks to mount on 1-2-3 blocks in order to hold tiny pins. These are always a good choice because they are made to order.
If you have production level quantities you should invest in a production machine to grind pins quickly and accurately.
The only drawback is the initial expense. I’ve often wondered just how long the payback actually would be, but few shop owners seem inclined to find out! Gromax makes a quality machine for this purpose.