The cold knife is one of the most difficult tools to master but still is the most commonly used cut out tool. It takes strength, leverage, and proper angles all used in conjunction with one another to easily cut the glass from the adhesive bead. It may take as many as 20-30 cutouts to become comfortable in its use. Here are a few tips to get you started.
Pulling the knife is always easier than pushing it. When you pull the knife, you can utilize your body weight to make the cutout easier. The tool is designed for two-hand use. The vertical handle is the blade angle control and the cabled handle is the power. Look at the blade in relation to the cable handle mounting.
As you can see, the cable handle is mounted to the side of the blade that is just under the horizontal part of the blade. This handle mounting is for the best leverage and torque. The tool design requires that hand positioning be changed from one side of the vehicle to the other. When pulling the tool on the driver side top, the right hand is controlling the vertical handle and the left is the power. On the passenger side top, the hands are reversed. This is necessary to produce the best cutting position of the tool.
Although pulling the tool is the best for most cutting procedures, the pushing of the tool is sometimes required because of the close tolerances between the glass and the wall of the pinchweld. If pushing the tool is called for, start the tool in an area that affords you the best leverage and easiest insertion. This is usually the top or bottom corner.
Once the blade is inserted into the urethane, the blade is midway into the bead. The best place for your blade to be, during cutout, is just to the glass surface. To get it there, angle the vertical handle back slightly and pull. This directs the blade to the glass surface.
Once the blade touches the glass surface, adjust the vertical handle to be perpendicular to the body. This will then shave the urethane bead from the glass surface and facilitate cutout.
It is very important that once you have your blade into position under the glass, that it stay there. Too much backward angle will cause the blade to fracture the glass; too much forward angle will cause the blade to dive into the urethane bead and cause difficulty. Once the blade is into position and is shaving the urethane from the glass surface, keep your hand on the vertical handle perfectly steady. If you allow the power handle to influence the vertical handle, the cutout will be difficult. If the blade does fracture the glass, angle the blade forward and pull to get the blade back underneath the glass.
Another technique to use is to push down on the vertical handle and pull. The rubberized urethane allows the blade to indent the urethane and position itself back under the glass. Then return to perpendicular and finish the cutout.
Remember that the glass is curved. It may be necessary to position your body in relation to the glass curvature. It is easier to position your body than to adjust the tool.
Cold Knife Blades
Here is a tip that helps when the urethane is thick and hard to cutout. Cold knife blades come in varying lengths. Purchase these different sized blades and use them in progression from the shortest to longest blade. In this way, you are only cutting a small amount of adhesive at a time and it makes the cutout much easier.
When it comes to cutting out an exposed edge glass, it is also a good idea to protect the paint of the vehicle by padding or taping the vertical leg of the blade. There are cold knife blades that have padded vertical legs manufactured into them and does provide a certain amount of paint protection. However, the coating does wear off and then they can damage paint like normal blades, so keep an eye on them and change them often.
Long-handled utility knife
The other commonly used hand tool for removal is the long-handled utility knife. Make sure that you change the blade before each use. Protect the dashboard from possible damage with the use of a plastic or metal pad.
Apply pressure from the inside out with the use of a helper or leverage tool. While the pressure is applied, use the knife to release the bond in the two corners first. This allows the glass to be pushed up further for easy access to the rest of the bead. If it is possible to cut the corners from the outside, do it. This will be less likely to damage interior upholstery. Start on the driver side corner first, the steering wheel will be a hindrance, but by doing this you will have more room to maneuver when you cut out the passenger side. Make sure that the blade shaves the glass surface and keep the blade away from the edge of the dashboard. Use long controlled strokes; do not try to cut the entire bead with one stroke. The backstroke is the most damage-producing act. Be careful on your backstroke. Cut the driver side corner free and then move to the passenger side corner. Cut that free and then while in position on the passenger side reach the tool to the area that was freed on the driver side and pull toward you in a long slicing action. You will feel the glass give a little on every stroke you make. Once the glass is separated from the urethane bead, carefully remove the glass from the vehicle’s opening.