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Cutting metal panels on site is a part of installing metal roofing and wall panels. However, the right tools and methods must be used to ensure the panels remain protected from damage and their longevity is sustained. Using the wrong tools can result in rust, rust stains, the voiding of warranties and diminished building service life. In this blog post, we’ll share several common field-cutting techniques and best practices that help ensure good results.

Maintaining Longevity When Cutting Metal Panels On Site:

When metal panels are produced in a manufacturing facility, the tools and methods used to cut the coated metal coil help protect the cut edge from deterioration like corrosion. When cutting metal panels on a jobsite or in the field, protecting any cut edges is just as important. To understand how field-cut metal panels should aim to meet the quality of metal cut in a manufacturing facility, you must first understand that metal roof and wall panels are most often fabricated from Galvalume®-coated steel coil because of its proven longevity. Not only does the Galvalume® coating protect the surface area of the metal panels, it has also been shown to be effective along the thin edges of the metal too, as long as those edges are cut properly. 

During fabrication, the coated metal is cut to length either by shearing while flat before entering the roll former, or by means of a profile shear as the panels exit the roll former. Either method tends to “wipe” the Galvalume coating across the cut edge of the metal panels. This provides superior cut-edge protection from corrosion.  

Likewise, when the panels arrive on site, any needed field cutting should address the same concerns of protecting the edge of the steel from corrosion. Of course, there are ways of doing the field cutting correctly. However, there are also poor strategies that can lead to real problems. The following are some examples of common tools used to field cut metal panels and the best practices for good results.

Common Tools and Methods for Cutting Metal Panels On Site:

Aviation Snips Red and green aviation snips are often used for small cuts on metal panels, such as around pipe penetrations. These snips will wipe the Galvalume® coating in the same way as factory shears, making them a good choice.

Electric Shears Electric shears are typically used when making lengthier cuts along the steel, such as cutting a wall panel at a corner or at a door opening. These shears will take a ¼” strip of metal out of the panel during the cutting process, which tends to leave both sides of the panel smooth and flat along the cut. Like the aviation snips and factory shears, electric shears will wipe the Galvalume® coating and protect the edges.

Mechanical Shears Mechanical shears are an add-on tool that fit onto a battery-operated impact or screw gun. These shears do not take any metal out of the panel and will leave a slightly wavy edge. Mechanical shears are an excellent choice for bevel cutting standing-seam panels at hips and valleys, since they too wipe the Galvalume® coating over the cut edges to offer protection.

Nibblers A nibbler is a great tool for cutting across corrugations in wall panels to create openings for windows, doors and similar additions to a structure. A good nibbler will typically cost $500-$700 (currently), but is well worth it if you cut a lot of corrugated metal panels. The punch and die in the nibbler tends to wipe the Galvalume® across the cut edge as it punches out small, half-moon shaped pieces of panel. However, because these little metal pieces will fall away from the cut, it’s important to contain them so no one walks on them. Otherwise, these pieces can become embeded in the soles of shoes and create scratches in roof panels as they are walked over. 

Skill Saw Skill saws are often used to cut metal panels since they are versatile and enable cuttingtobe done either across or parallel to corrugations, whether straightor at an angle. When using a skill saw, it is critical to use a saw blade that cuts cool. Otherwise, the Galvalume® coating can melt along the cut edge and become ineffective. In particular, do not use an abrasive blade, which will generate heat and damage the coating. 

Panels cut with abrasive blades corrode. A cool-cutting blade leaves a smooth edge.

Additionally, its very important to avoid cutting panels on the roof or above other panels, because a skill saw blade will throw considerable amounts of steel debris into the air and down onto any panels below. This debris, called swarf, will quickly rust and ultimately cause rust spots in the panels. If enough swarf gathers in one spot, it can rust through the panel.

Steel swarf, like this collected at the ridge will rust through the panel.

Which Tools Should Never Be Used When Cutting Metal Panels On Site:

Tools that should never be used include:

All of these tools will melt the Galvalume® coating, causing edge rust just like an abrasive blade would (as shown above). These tools also throw a lot of steel debris (swarf) onto the panel being cut. This debris will be hot and will embed into the panel coating, causing rust spots and bigger problems down the road as shown above.

In conclusion, using the right tools and following the recommendations provided by the metal panel manufacturer when cutting metal on site will help ensure that the panels are protected from damage and the final installation will be a fairly seamless process. Using the wrong tools can result in rust, rust stains, and the voiding of warranties. To find out more about the best practices and recommendations for on-site cutting and installation of metal panels contact your local MBCI representative.

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