From Mechanical Database

Whether to save money, time, or creating a gasket that is otherwise not available in stores, sometimes creating your own gasket is a better option.

Using a hammer

This technique only works on sharp cornered gasket surfaces, so it will not work on smooth cornered surfaces such as steel oil pans. All you need is a hammer (the smaller the better) and gasket material. This works best with thicker gasket material such as the combination of rubber and paper material in the pictures below.

1. Place the gasket material over the surface, and begin to tap the hammer lightly on the edges, the sharp edges will cut the gasket material resulting in the perfect shape.
2. Place a bolt with the same thread over the area where holes for the bolts will need to be made. Tap on the bolt lightly until it punches a smooth hole through the gasket material.
3. If done correctly, you will be left with a nearly perfect gasket equivalent in quality to one that can be purchased from a store. At the very most, certain areas can be slightly trimmed with a razor blade to make them more smooth. This method produces much better looking results and much faster than tracing and cutting gaskets with a blade.