by Bob Beranek
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The last step in fabricating an auto glass piece is finishing the edges. There are four edges that are used in auto glass fabrication, the edge number one, edge two, edge three and edge four. Let’s take a look at each finishing edge and how they are accomplished by the cutter.

Edge #4 (90 degrees)

Edge number four is sometimes called a clean-cut edge. Its distinguishing feature is that the edges are 90 degrees to the surface of the glass. This edge is used when the glass edge is not exposed or when the glass is to be bonded or fitted into a channel.

Once the glass is cut to size, the cutter will use a belt sander or vertical wet sander to create a flat ground edge.

 Bob Finishing Edges 1

Edge #3 (seamed)

Edge number three is sometimes called the seamed edge because the sharper edges are seamed or dulled off. This type of edge is the easiest way to prep the glass for installation into a gasket or weather strip. The dull edge does not bite into the rubber of the gasket that can hinder the ease of installation.

It is accomplished by first attaining edge four and then using the belt sander at a 45-degree angle to seam the sharp edge. If a vertical wet sander is used, simply lift the glass to a 45 degree to the belt and run it the length of the glass piece.

Bob Finishing Edges 2

Edge #2 (rounded)

Edge number two is a rounded edge sometimes called a pencil edge. This edge is used when the glass edge is exposed and possible injury or damage can result. This unpolished edge is used in vehicles that have a high risk of frequent breakage but require the edge to be exposed. An example of this might be the door glass for a delivery vehicle.

The “two” edge is accomplished by first attaining the “four” edge and working the belt sander the length of the piece starting at the flat edge and slowly changing your angle until a rounded edge is achieved. Then turn the glass over and repeat on the other layer of the glass. The edge will appear dull in finish.

If a vertical wet sander is used, start the glass on the flat edge and run the glass the length of the edge. Then lift the glass slightly and repeat. Continue to lift and run until the top layer of glass is rounded. Then turn the glass over and repeat on the other layer of glass.

Bob Finishing Edges 3

Edge #1 (polished)

The number one edge is a polished edge used on exposed edges where a person’s arm may come in contact, such as in a door glass or vent glass. This type of edge may be used for collector vehicles or for vehicles that require a higher degree of detail.

It is accomplished by first attaining the edge three and then polishing the rounded edge with a cork or fine diamond grinding belt. Use the same tool action as described in the edge three procedure.

There you have it, the conclusion of the lost arts of an auto glass professional. I hope you enjoyed the step back in history and the possibilities of profit enhancement. I have no idea what to write about next week so please send in your ideas.

Comments (2)

  1. daniel said on 21-03-2013

    Professional as always. However, I would suggest the edge sanding opperation to be performed not perpendicular to the side, but somehow along the lenght, as sharp sanding angles might bite the glass. When situation makes this possible. Best wishes for all readers !

  2. Glasseye said on 21-03-2013

    I think it is worth pointing out that rounding off the edges, increases the edge strength of the glass reducing the risk of breakage during fitting.

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