How To Cut Sheet Metal With Snips

Content Menu

● The Engineering Behind the Shear

● Decoding the Taxonomy of Snips

● Ergonomics and Human Factors in Manual Cutting

● Material Specifics: Navigating Alloys and Gauges

● The Professional Cutting Workflow: A Step-by-Step Guide

● Advanced Techniques: Circles, Notches, and Internal Cutouts

● Maintenance and Longevity of the Tooling

● Troubleshooting Common Cutting Defects

● The Future of Manual Shearing in Manufacturing

 

The Engineering Behind the Shear

To understand how to cut sheet metal effectively, we first have to look at what happens at the microscopic level when the blades of a pair of snips meet the metal. Unlike a saw, which removes material in the form of chips or swarf, snips utilize a shearing action. This process involves two offset blades that pass each other, creating a localized fracture in the material.

When the blades begin to close, the metal undergoes initial plastic deformation. The pressure from the blades exceeds the yield strength of the material, causing it to flow. As the blades penetrate deeper, the stress concentrations at the edges of the blades exceed the ultimate tensile strength of the sheet, causing a controlled crack to propagate through the thickness of the material. This is why the quality of the blade edge and the clearance between the pivot point are so critical. If the clearance is too wide, the metal will simply “fold” or “draw” between the blades, leading to a jagged, crushed edge rather than a clean cut.

In manufacturing engineering, we refer to the “burnished zone” and the “fracture zone” of a sheared edge. A high-quality cut with snips will minimize the fracture zone and maximize the smooth burnished area. This is particularly important when working with materials like stainless steel or high-grade aluminum, where a rough edge can act as a site for fatigue cracking or corrosion initiation. Understanding this mechanical interaction allows a technician to adjust their technique based on the gauge and alloy of the sheet they are handling.

Decoding the Taxonomy of Snips

One of the biggest mistakes a novice makes in a production environment is grabbing the first pair of snips they see. For a manufacturing engineer, tool selection is a matter of efficiency and safety. We generally categorize snips into two main families: Tinner’s snips and Aviation snips.

The Robust Simplicity of Tinner’s Snips

Tinner’s snips are the traditional, long-handled tools that look like heavy-duty scissors. They are typically forged from carbon steel and are designed for making long, straight cuts in thinner gauges of metal. Because they lack the compound leverage of modern aviation snips, they require more physical force from the user. However, their long blades allow for a much smoother, continuous cut over a long distance, reducing the number of “re-bites” which can leave tiny burrs or notches in the metal.

Think of a scenario where you are fabricating a large drainage pan. Using Tinner’s snips allows you to glide through a 48-inch sheet with minimal deviation. The lack of serrations on most Tinner’s snips also means the edge of the metal remains smoother, which is vital for parts that will be exposed or handled frequently by end-users.

The Precision of Aviation Snips

Developed originally for the aerospace industry to help technicians work on complex airframe curves, aviation snips feature a compound-leverage pivot. This mechanical advantage allows you to cut much thicker or harder materials with significantly less hand fatigue. The most distinctive feature of aviation snips is their color-coding, which is a standardized system across the industry.

• Red Snips (Left-Cutting): These are designed to cut curves to the left. For a right-handed user, the waste material will curl up and out of the way to the right, providing a clear view of the cut line.

• Green Snips (Right-Cutting): These are meant for right-hand curves. The waste material curls to the left.

• Yellow Snips (Straight-Cutting): These are designed for straight lines and very large-diameter curves.

In a manufacturing workflow, using the wrong color for a specific geometry is not just an inconvenience; it can ruin a workpiece. If you attempt to cut a tight right-hand circle with red snips, the jaw of the tool will bind against the metal, forcing the sheet to warp and potentially causing the blades to “nick” the finished part.

Ergonomics and Human Factors in Manual Cutting

From a manufacturing engineering perspective, the ergonomics of tool use are just as important as the tool’s mechanical output. Repetitive strain injuries (RSIs) are a major concern in assembly lines and fabrication shops. Aviation snips were a revolutionary leap forward because they reduced the required grip force by nearly 50% compared to traditional shears.

When selecting snips for a production team, we look at the “grip span.” If the handles open too wide, the user’s hand is at its weakest point when they begin the cut, leading to rapid fatigue. Modern industrial snips often feature bi-material grips that provide a non-slip surface and dampen the vibration or “snap” that occurs when a cut is completed. Furthermore, the orientation of the handles—whether they are straight or offset—plays a huge role in worker comfort. Offset snips allow the user to keep their hand above the material, which not only provides better leverage but also protects the knuckles from the sharp edges of the metal as it curls away.

Consider a technician who has to trim a hundred galvanized steel brackets per shift. If they are forced to use poorly designed, non-ergonomic snips, their accuracy will drop by the third hour, and the risk of a “slip-and-cut” injury increases exponentially. Providing the right tool for the human factor is a core tenet of lean manufacturing.

Material Specifics: Navigating Alloys and Gauges

Not all sheet metal is created equal. A pair of snips that glides through 26-gauge galvanized steel might struggle or even sustain damage when faced with 18-gauge stainless steel. Manufacturing engineers must understand the “Hardness” and “Work Hardening” characteristics of the metals being processed.

Galvanized and Mild Steel

These are the bread and butter of most sheet metal shops. Mild steel is relatively ductile, meaning it shears easily without excessive force. Galvanized steel, which is coated in zinc, behaves similarly but requires attention to the coating. When you cut galvanized sheet, the “smearing” of the zinc over the cut edge can actually provide a small amount of cathodic protection against rust, which is a nice secondary benefit of the shearing process.

Aluminum Alloys (6061 vs. 5052)

Aluminum is softer than steel but can be “gummy.” When cutting aluminum, particularly softer alloys like 5052, the metal can sometimes build up on the blades of the snips, leading to a ragged edge. A light application of tool lubricant or even a bit of wax on the blades can significantly improve cut quality. However, be careful with 6061-T6; it is much more brittle and can “crack” ahead of the blade if the snips are not sharp.

Stainless Steel (304 and 316)

Stainless steel is the ultimate test for manual snips. It is significantly harder than mild steel and has a high rate of work-hardening. This means that if you hesitate during a cut or use dull blades, the metal actually gets harder as you try to cut it. For stainless applications, engineers must specify snips with induction-hardened blades. Using standard snips on 20-gauge stainless will likely dull the serrations in a single afternoon.

The Professional Cutting Workflow: A Step-by-Step Guide

To achieve results that pass a rigorous Quality Assurance (QA) inspection, the cutting process must be systematic. Here is how we approach a precision manual cut in a professional setting.

Layout and Marking

Precision starts with the line. In manufacturing, we rarely use a blunt pencil. A fine-point permanent marker is standard, but for the highest precision, a carbide-tipped scriber is used. A scribed line creates a physical “groove” that the blade of the snip can actually feel, helping to guide the tool. When marking, always account for the “kerf”—the tiny amount of material lost or displaced by the thickness of the blade.

The Initial Bite

Position the metal deep into the throat of the snips. Cutting with the tips of the blades is a common mistake; it provides the least leverage and is the most likely to cause the blades to twist. By placing the metal near the pivot point, you maximize mechanical advantage and stability.

Managing the Waste

This is where the distinction between “finish side” and “waste side” is vital. One side of the metal will always stay flat, while the other side will curl or bend away. You must orient your snips so that the finished part remains flat while the scrap piece is the one being deformed. For example, when using green snips to cut a straight line, the right side of the metal remains flat, while the left side curls.

The “Golden Rule” of Closing the Blades

Never close the blades all the way to the tip when making a continuous cut. If you “click” the blades shut, you will create a small “fish-tail” or notch at the end of the cut. Instead, stop about 1/4 inch before the end of the stroke, slide the snips forward, and begin the next stroke. This technique produces a perfectly smooth, continuous edge that looks like it was cut by a machine.

Advanced Techniques: Circles, Notches, and Internal Cutouts

While straight cuts are straightforward, manufacturing often requires complex geometries.

Cutting Circles and Radii

When cutting a hole or a radius, the “approach” is everything. You don’t just start cutting on the line. First, you should remove the bulk of the waste material with a series of straight or tangential cuts, leaving a “tab” near your final line. Then, using your red or green aviation snips, you make a final pass. This reduces the pressure on the blades and allows for a much tighter, more accurate curve.

Notching for Bends

In sheet metal box fabrication, you often need to cut “notches” where the metal will be folded in a brake. These notches must be precise. If you over-cut, you create a point of failure where a crack can form. Manufacturing engineers often specify “relief holes” at the corner of a notch. You drill a small hole at the intersection of the lines, then cut into the hole with your snips. This replaces a sharp, stressed corner with a smooth, rounded one.

Making Internal Cutouts

If you need to cut a rectangular window in the middle of a sheet, you can’t start from the edge. The professional method involves using a cold chisel or a heavy-duty punch to create a starter slot. Once the slot is large enough to accommodate the tip of your aviation snips, you can begin the cut. For internal holes, “offset” aviation snips are a lifesaver, as they keep your hands clear of the sharp edges within the cutout.

Maintenance and Longevity of the Tooling

A manufacturing engineer knows that a tool is only as good as its maintenance schedule. Hand snips are often treated as “disposable,” but high-quality forged snips can last for decades if cared for properly.

• Blade Sharpening: Never use a bench grinder on aviation snips. The serrations are precision-engineered. Instead, use a fine diamond file to lightly hone the flat side of the blade. If the serrations are worn flat, the snips will start to “push” the metal forward rather than cutting it.

• Pivot Adjustment: The nut and bolt at the pivot point should be tight enough that there is no lateral play in the blades, but loose enough that the tool opens easily under spring pressure. A drop of high-viscosity oil on the pivot and the spring mechanism once a week will prevent “stiction.”

• Cleaning: Sheet metal often comes with a coating of mill oil or protective film. This gunk can build up on the blades, attracting metal dust and creating an abrasive paste. Wiping the blades down with a solvent at the end of the day is a simple but effective habit.

Troubleshooting Common Cutting Defects

Even with the best tools, things can go wrong. Recognizing these defects early is key to maintaining production standards.

The “Burred Edge”

If your cut is leaving a sharp, jagged edge, it is usually a sign of one of two things: dull blades or excessive blade clearance. If the metal is being “torn” rather than sheared, it’s time to adjust or replace the tool. In a pinch, you can remove a burr with a deburring tool or a file, but in a high-volume environment, this is wasted labor.

The “Wavy Edge”

This occurs when the operator is not keeping the snips perpendicular to the metal. If the snips tilt to one side, the shear angle changes, causing the metal to ripple. This is often seen when someone is trying to cut a thickness that is beyond the tool’s rated capacity.

Blade Drift

Sometimes the snips will “drift” away from the marked line, no matter how hard you try to stay on it. This is often caused by a nick in the blade or a misalignment in the pivot. It can also happen if you are trying to use straight-cut snips to follow a curve.

The Future of Manual Shearing in Manufacturing

As we move toward Industry 4.0, you might wonder if there is still a place for hand tools like snips. The answer is a resounding yes. While robots handle the high-volume production, the “tailoring” of components—fitting a duct in a tight ceiling space, trimming a prototype automotive panel, or performing emergency repairs on a factory line—still requires the human touch.

The development of new materials, like ultra-high-strength steels and advanced composites, is pushing tool manufacturers to innovate. We are seeing snips with titanium-nitride-coated blades and handles made from carbon fiber to reduce weight. The core principles of the shear remain the same, but the tools are becoming more refined, more ergonomic, and more capable than ever before.

In conclusion, cutting sheet metal with snips is an art backed by rigorous engineering principles. It requires an understanding of metallurgy, a respect for mechanical advantage, and a disciplined technique. For the manufacturing engineer, these tools are a bridge between the digital design and the physical reality, a way to make those final, critical adjustments that ensure a perfect fit every time. Whether you are cutting a simple piece of flashing or a complex aerospace component, the right pair of snips and the right technique will always be your most reliable assets on the shop floor.