Before any glass can be cut for installation, there must be a pattern made to accurately depict the finished size and shape. This sounds like a simple task, but there are some things that must be realized and practiced to reduce waste and problems with installation.

There are four types of patterns; trace, measurement, pinchweld and geometrically drawn. The trace is the easiest pattern to make, but it must be done properly.

To make a pattern properly you will need some tools:

• A flat surface for drawing;
• Pattern pencil or drawing pen
• Poster board or cardboard big enough to capture the size; and
• Tape measure.

A trace pattern is simply the tracing of an existing piece of glass for duplication. If the glass is in one piece, it can be removed and placed onto a heavy sheet of paper or cardboard and traced to create a template for reproduction. However, the trace must be exact to the outside dimensions of the existing glass for the cutter to accurately cut the glass to fit. If there is a discrepancy of only a 1/8 inch, it is multiplied on both sides and on the top and the bottom.

This change in size will make a difference in how the piece will fit in the opening. If a typical pen or pencil is used to make your trace, then you must compensate for the thickness of the barrel of the writing instrument which is typically about a 1/8-inch. One method is to angle the pencil or pen to compensate for the barrel thickness or communicate the method of trace to the cutter so adjustments can be made when fabricating. There are special pattern pens that make this compensation for you so accuracy is more exact.

What if you are caught with no cardboard or drawing paper? Make measurements and draw radiuses. Remove the glass and make measurements vertically and horizontally. Make sure that you check the vertical and horizontal measurements near the top of the part and the bottom and near the far right and far left of the two sides. Some parts have a very subtle angle and checking the measurements at different points will assure proper configuration. Use a small piece of paper to draw the radiuses of the four corners. Don’t forget to mark each radius with its location on the part. Again, there can be slight differences in the radiuses and if you get the wrong radius in any corner the part will not fit. Correct measurements and accurate drawings will give the cutter the information necessary to fabricate a part that fits perfectly.

Next week we will discuss pinchweld pattern techniques.