Knockout Punches: The Perfect Hole

by Andy on February 4, 2008

Greenlee Slug BusterMany people in and out of the electrical industry often search for a tool that will cut holes in metal both accurately and quickly, while leaving smooth edges. An ideal tool for the job is a knockout punch.

Punches do their job well and are easy to use. Typically there are three parts to a hole punch. There is the punch itself, which actually does the cutting, then there is the die, which is placed on the opposite side of the metal for the punch to be pulled against, and lastly there is the draw stud, which is used to pull the punch and die together in order to cut the hole.

Once you have determined what size hole you need and it’s desired location, simply drill a pilot hole in the center of the area. When drilling your pilot hole, be sure that it is big enough to pass the punches draw stud without it binding. The draw stud should be inserted through the die and then through the pilot hole. The open side of the die should be facing the metal. Once the draw stud has been inserted through the pilot hole, you will need to thread the punch onto the other end, with the cutting edges toward the metal, until both die and punch are snug to the metal. Now that you have your punch in the desired position, simply use a ratchet wrench to tighten the two sides together. As the draw stud is tightened with the ratchet wrench, the die and the punch are pressed together to cut a perfect circle in the metal.

You have several options when it comes to choosing a type of knockout punch to purchase. First you have to choose from a standard knockout punch or a Slug-Buster knockout punch. A standard punch keeps the waste or slug from the hole intact while a Slug-Buster punch will split the slug in half while cutting the hole. The benefit of a Slug-Buster punch is that the waste is easier to remove from the die when it is in two pieces.

A new punch line Greenlee has introduced is the Slug-Buster SC self-centering punches. These punches will not only split the slug in half like the normal Slug-Buster punches, but will also align themselves on the pilot hole, saving you time and ensuring accuracy. Greenlee has even created a detailed Slug-Buster SC demonstration video so that you can see these new and improved punches in action.

The second deciding factor is whether you want a manual knockout punch or a hydraulic punch driver. The manual punches are driven by a ratchet wrench that pulls the punch through the metal. Hydraulic punches are usually pricier than manual knockout punches but these punches can develop up to 11-tons of hydraulic force, depending on the specific hydraulic driver used, to make fast, easy punches.

Greenlee is a company known for making both quality manual and hydraulic punches.

All-Spec now stocks several Greenlee punch kits, including the 735BB, the 737BB and the 7238SB.

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