uestion: Why do I break bushings in my lamination plates?

The first thing you might ask is "Why do I have bushings in my lamination plates to start with?"

The main reason to have bushings is that they enable you to renew the precision in your plates at a very low cost. This goes a long way in helping to extend the usable life of these expensive plates.

What are bushings?
Bushings are precision components which are press fit into lamination plates to provide the means of keeping lamination pins aligned and in the right location. They are about 1/2" diameter by 0.275" long, Multiline Bushings have a head of 0.080" thickness. In this head is a precision ground radius which is used to key the bushing to prevent rotation. This key is needed in slot bushings only, not in rounds.

Bushings are precision ground all over to a tolerance of +/- .0002". The hole In the bushings is just as precise as the body since the fit between the lamination pin and the bushing is of utmost importance.

There seems to be two common ways for bushings to break. The first way is one in which the head is broken off of the body. The head which is 0.080" thick breaks off and looks like a washer with the shape of the lamination pin in the center. This break is caused normally during depinning. By misplacing the depinning pin and striking the head of the bushing instead of the pin, which can cause the head of the bushing to be broken off.

The second way is not as simple, and shows up as cracks running from the lamination pin hole to the outside diameter. These cracks usually start in the sharp corners of slots. The cracks go all the way through the bushings, but the bushings will remain in the plate because they were pressed into the plate. Pieces ofthe bushings will fall out at different times. Bent lamination pins or mushroomed pins are the main cause of this problem. Anytime the lamination pin has to be forced with a hammer into the hushing this type of breakage can occur.

The best way to prevent the first problem is with the proper depinning methods. Use a good hydraulic depinner or, if you have to use a hand punch make sure there is some sort of a cushion over the thin part of the punch (rubber or urethane) so that the handle of the punch can't strike the bushing head.

There are also pin and bushing gauges available to check the condition of lamination pins which will indicate pins that may cause a problem. A worn or defective lamination pin or bushing may be difficult to detect especially by the naked eye. A lamination pin, after some usage, may become worn, mushroomed or bent. Lamination bushings are also susceptible to wear such as hole enlargment or closing. While some of these defects may be determined by uses of conventional inspection equipment, it can be very time consuming and often confusing. Using the carefully designed Multiline gauges, all the problems associated with the inspection of pins and bushings can now be determined. If you wish to order a Multiline Lamination Pin and Inspection Kit the part number is 30-D246.

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