How to cut a hole in ductwork with aviation tin snips

When building HVAC plenums or installing a duct takeoff collar on a ventilation system, you will need to cut into the ductwork to fit different parts. Sometimes you may cut rectangular holes and other times round holes and curves.

While you could use a hole saw, dremel, or jig saw to cut holes and shapes in ductwork, there is one hand tool that does the job perfectly all the time. This is the offset aviation tin snips.

What are offset aviation tin snips?

Offset aviation snips are a type of tin snips with an angled head. They come in three different types namely, straight-cut (yellow), left-cut (red), and right-cut (green). While the 45 degrees angled aviation snips are the most common, there are also 90 degrees offset snips. Both types are useful for making long cuts along the edges and cutting patterns inside the sheet material.

Please check out this article to learn more about tin snips.

The reason why offset aviation snips are the best for cutting holes in ductwork, metal studs, and sheet material is that the head and the handles are on different planes. This allows you to cut any shape anywhere on the workpiece without the handles coming in the way. It is the same reason that makes offset tin snips the best for cutting long curves in sheet material.

The other reasons that make offset tin snips suitable for cutting holes in ductwork are that they are easy to use, have sharp blades, and are easier to control when making precision cuts. Needless to say, offset tin snips are safer to use because the angled head helps keep your hands from the workpiece. However, it does mean that you use the pliers without protective gloves. Always wear leather gloves when cutting with tin snips.

How to cut a holes in duct work?

Aviation tin snips are the best tool to cut a hole in ductwork. To use them to make a nice, neat, round vent hole, you first need to know how to select the right type of tin snips. In this section, I share how to choose the right aviation tin snips for the job and how to use them to make neat circular holes in ductwork for your HVAC fittings.

Which type of aviation snips are the best for cutting metal duct?

As I mentioned earlier, offset aviation snips are the best tool for cutting holes in metal ducts. More specifically, the green and the red offset snips are the best for cutting curves. They allow you to make nice continuous curves on sheet material. The yellow snips are just good for straight notches because they only cut as deep as the jaws.

Although you can use the green snips and red snips to cut in either direction, each type cuts best in one direction. The green snips or right-cut snips are best for cutting counter-clockwise while the red snips or left-cut snips cut best in the clockwise direction. So, depending on the position of your air duct and your orientation, you might use one type or both.

Steps to cut a hole in a metal air duct

Once you select the right type of offset snips, you are now set to start making holes in ducts. These are the simples steps to follow and the tools you will need.

Tools

  • Right-cut or left cut offset aviation snips
  • Screwdriver or drill
  • Hammer (optional)

Steps

1. Mark the round shape on the ductwork

Set the takeoff collar on the ductwork and trace its shape. It doesn’t matter what shape the collar is, just try to trace it as accurately as possible. If you are working with a template, place firmly on the ductwork where you want to make a hole and mark the duct with a marker.

2. Drill a pilot hole

Use a power drill to make a pilot hole inside the round shape that you want to cut out on the duct. If you do not have a drill, use a flat screwdriver or chisel and a hammer to punch a hole into the ductwork.

Hold the screwdriver or chisel at an angle against the duct and strike it with a hammer to make a hole. If the ductwork is steel, you may need to strike harder with the hammer.

3. Pick the right snips and start to cut out the hole

Depending on your position of operation, you can pick either the right-hand snips or left-hand snips and start cutting. If you pick the left-cut snips, you will cut in a clockwise direction. And if you choose the right-cut snips, you will have to trace the marking in the counterclockwise direction.

If you choose the wrong snips, you will not only struggle to cut all around but you will also end up with a jagged edge. Moreover, cutting with the right snips in the wrong direction will also produce very rough edges. So, make sure you have the right pair of offset tin snips and that you are cutting in the right direction.

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