Mastering the Cold Knife

You may be thinking cold knives? Why is Bob writing about cold knives when there are power tools and wire-out tools that are taking over the automotive glass removal process? The answer is because it hasn’t happened yet, as much as tool companies and safety advocates would like to make that case. The cold knife is still the most popular tool for glass removal.

The productive use of a cold knife can be nearly as difficult to learn as hitting a golf ball straight, or hitting a baseball on every pitch. There are angles to find, leverage to master, and muscles to develop before a rookie technician can be proficient.

It takes some training. I call it the “sweet spot.” If a technician is able to find that sweet spot, he (or she) is able to cut through urethane like butter. It is amazing the first time a tech gets it just right. Only experience allows you to find it every time.

In one of my classes I taught a 14-year-old girl (no more than 70 pounds soaking wet) to pull a cold knife in two days. However, that isn’t always the case. I had a former employee who took six months to finally learn the technique. The problem with my ex-assistant is that he was a body builder in his spare time. He had a lot of muscle, so he thought that should be the secret to cutting out glass. Because he didn’t want to consider angles, leverage and the use of body weight, it took him a lot longer to learn than it could have.

Another component involved with the efficient use of a cold knife is the blades we choose. One of the most popular blades is the pointed and tapered sided blades invented and manufactured by UltraWiz.


Their blades have been the choice of many new technicians country wide if not globally. They are easy to insert into a hardened urethane bead. The company offers super thin steel construction and the coated blades, pictured above. This is the blade style of choice by many. However, one thing I noticed as a trainer is that the tapered design does pose an inherent problem for the new and learning technicians. As the blade is pulled or pushed, it has a tendency to move out from under the glass and move towards the wall of the pinchweld. This wasn’t a problem when we had reveal mouldings to cover any mishaps in paint scratches but the modern “exposed-edge” glass mounting requires that the technician pay attention to the blade making contact with the exposed wall of the pinchweld.

When I started as an installer, we had the standard style of cold knife blade with parallel sides.


This blade was substantially more difficult to insert and to pull. In fact, we needed to regularly use the shortest to the longest blade progression to comfortably cut out the glass. Even then, the blade itself was not always easy to remove from under the glass.

If you are relatively new to the industry and you use the tapered blade in your knife, please be aware of the action of your tool. Tweak the vertical handle in at the base to keep it under and against the glass edge during the cutout. Have the vertical handle of the knife with a slight backward angle while pulling and a slight forward angle when pushing the tool. Positioning the tool in this way will allow for the most efficient use of the cold knife without damage to the wall of the pinchweld.

Please let me know if you have other suggestions for mastering the cold knife. I am always interested in hearing your experiences.