How to Cut Metal Roofing With Power Shears and Nibblers
Cold cutting keeps the paint and the coating intact. Pick the right tool, support the panel and clean up every sliver.
- Intermediate
- Depends on the job
- Updated
The short answer
Power shears and nibblers cut metal roofing without heat, which preserves the paint and zinc coating. Shears make fast straight and gently curved cuts and leave a clean edge. Nibblers punch out a narrow strip and handle ribbed panels, tight curves and cutouts. Support the panel, mark the line, cut steadily, wear eye, ear and hand protection and sweep away all swarf.
Every metal roof needs cutting: panels to length, along valleys and hips, around penetrations, at walls and at the ridge. How you cut decides how long the roof lasts. A cut that leaves heat marks, burrs and scorched paint starts to rust in the first wet winter. A clean cold cut leaves the protective coating intact right up to the edge.
Three tools do most of the work. Snips do short cuts and touch-ups. Power shears make long straight cuts quickly. Nibblers chew a narrow slot out of the metal, which lets them cut ribbed panels and tight curves. This guide explains when to use each one, how to make the cuts and how to manage swarf, the metal chips that can ruin a finish. For cutting by hand, see how to choose and use tin snips, and for layout and cutting of panels see how to cut metal roof panels.
Tools
- Electric or battery shears for sheet metal
- Electric or battery nibbler
- Aviation snips for touch-ups
- Tape measure and square
- Permanent marker and straightedge
- Sawhorses with a soft surface
- Safety glasses, hearing protection and cut-resistant gloves
Materials
- Metal roofing panels and trim
- Scrap panel for test cuts
- Magnetic sweeper or broom for swarf
- Soft cloth or foam pads for the work surface
Safety first
- Wear safety glasses, hearing protection and cut-resistant gloves. Cutting throws chips and the cut edge is razor sharp.
- Clamp or support the panel so it cannot move. A panel that shifts while you cut can cut you.
- Do not use an abrasive cut-off wheel or an angle grinder on prefinished metal roofing. The sparks and heat burn the paint and scorch the coating, and the burnt areas rust.
- Keep the cord clear of the cut, unplug or remove the battery before changing a blade or punch, and never wear loose clothing or gloves that can catch.
Step by Step
Step 1: Choose the right tool for the cut
Shears cut by shearing the metal between two blades, and the waste curls away in a strip. They are fast and leave a clean edge, but cannot easily cut across a ribbed profile. A nibbler punches out a thin slot of metal, leaving small chips. It cuts ribbed, corrugated or standing seam panels, tight radii and cutouts for pipes. Snips are best for short cuts, corners and trimming.
Some jobs use all three. Check the tool's rated capacity for the metal gauge you are cutting.
Step 2: Measure, mark and plan the cut
Mark on the back of prefinished panels where you can. Account for the width of the cut, called the kerf, with a nibbler. Note that some panels have a direction and cannot be cut from either end. Check the panel layout drawing and cut a test piece first if the profile is complicated.
Step 3: Support the panel and protect the finish
A panel that sags or vibrates gives a rough cut and can be damaged. Use a soft surface such as carpet or foam on the sawhorses to avoid scratching. The finish side may need to be face down with some tools to keep chips from scratching the paint. Check the tool's manual. Keep the work area clean, since one piece of grit under the panel can mark the finish.
Step 4: Put on protective equipment and check the tool
Inspect the blades or punch and die for wear, and replace them when they are dull, since a dull tool makes a rough cut and works the motor hard. Check that the guard is in place and the cord is in good condition. Remove loose clothing and jewellery.
Step 5: Make straight cuts with shears
Let the tool cut at its own speed. Forcing it overheats the motor and leaves a wavy edge. Keep the shears aligned with the line and watch where the blade, not the handle, is. Hold the waste strip away from your body as it curls off the cut. For a long cut, support the panel on both sides of the cut so it does not sag and bind the blades.
Step 6: Cut ribs, curves and openings with the nibbler
A nibbler removes a strip about a few millimetres wide, so it can turn tight curves. Keep the tool flat on the panel and move it steadily. For cutouts, drill a pilot hole inside the waste area, insert the nibbler and cut to the line. Work from the waste side of the line so a slip does not damage the panel. Nibblers make many fine chips, so work over a tray or sheet where you can.
Step 7: Deburr, inspect and protect the cut edge
A burr is a sharp lip left by the tool and can cut hands and scratch neighbouring panels. Remove it lightly with a file or a deburring tool. Do not file the paint off the face. Touch up bare edges with a touch-up paint the panel manufacturer approves, to slow rust.
Step 8: Sweep up every chip of swarf
Hot metal chips that land on prefinished panels can embed in the paint and leave rust spots, and loose swarf rusts, stains and cuts feet. Wipe panels and clean the roof before the end of each day. In the Fraser Valley's wet climate, swarf left overnight will mark the roof by morning. Check gutters and valleys at the end of the job.
Why Not an Abrasive Wheel?
Angle grinders with cut-off wheels are fast, but they heat the metal, throw hot sparks that burn into the paint and strip the zinc and paint coating at the edge. The resulting rust stains are hard to remove, and they often void the panel's finish warranty. Cold-cutting tools avoid all of that. If you must use a saw, choose one made for metal roofing with a blade designed to cut cold.
Shears Versus Nibblers
- Shears: fast, clean edge, long straight cuts on flat stock, limited for ribbed panels.
- Nibblers: slower, leave small chips, can cut ribbed panels, tight curves and cutouts.
- Snips: best for short cuts and trimming, tiring on long cuts.
- Standing seam and ribbed panels: often best with a nibbler or a sheet metal shop cut.
Common Mistakes
- Using an abrasive wheel on prefinished panels. The sparks ruin the paint and the edge rusts.
- Leaving swarf on the roof or the panels.
- Forcing the shears and leaving a wavy edge or burning out the motor.
- Cutting on the wrong side of the line so the panel is too short.
- Working without ear and eye protection. Cutting is loud and throws chips.
- Cutting unsupported panels that bend and bind the tool.
When to Call a Professional
If you are cutting a whole roof of panels, complex hip and valley cuts or standing seam profiles, a roofer or a sheet metal shop will have the tools and experience. A miscut panel is expensive, and mistakes in cutting are not always fixable.
For custom-length panels, many suppliers will cut panels to length for you, which is often the most accurate option.
Fraser Roofing does free roof inspections across the Fraser Valley, from Hope to Abbotsford. See our Roof Replacement service or the towns we cover.
How to Cut Metal Roofing With Shears and Nibblers: Questions
What is the best tool to cut metal roofing?
It depends on the cut. Power shears are fast for long straight cuts on flat stock, nibblers handle ribbed panels, tight curves and cutouts, and aviation snips suit short cuts and touch-ups. All of these cut cold and protect the paint. Many roofers use more than one, and some ask the supplier to cut panels to length.
Can you cut metal roofing with an angle grinder?
It is not recommended. An abrasive wheel heats the metal and throws hot sparks that burn into the paint and strip the protective coating at the cut edge, which leads to rust. Panel manufacturers often say that abrasive cutting can void the finish warranty. Use shears, a nibbler, snips or a blade made for cold cutting.
What is the difference between a nibbler and shears?
Shears cut through sheet metal with two blades and leave a thin strip of waste, which is fast and makes a clean edge, but it is best on flat stock. A nibbler punches out small chips along the line. It is slower but can cut ribbed panels, curves and openings that shears cannot.
Why do metal chips matter on a metal roof?
Steel chips and filings left on the roof rust quickly in damp weather and leave brown stains that can be permanent. Hot chips can also embed in the paint. Sweep them up with a broom or magnetic sweeper after cutting and at the end of each day, and check gutters and valleys.
What safety gear do you need for cutting metal roofing?
Safety glasses, hearing protection and cut-resistant gloves are the minimum. Power shears and nibblers are loud and throw chips, and the cut edge of the metal is razor sharp. Wear long sleeves, avoid loose clothing, and clamp the panel so it cannot move while you cut.
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This guide is general education. Always follow the product manufacturer's installation instructions, the BC Building Code and WorkSafeBC requirements, which take priority over anything written here.
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