Learn to make straight cuts, curved cuts and even round cuts in sheet metal with tin snips. With proper tool selection you can do it with ease.
The angle of the shear tips allows you to keep your hand above the sheet metal as you cut.
Cut a round duct from the right-hand side with green-handled compound snips. Use this technique if you're right-handed or in tight quarters. Keep the top blade aligned parallel to the cutting line to cut a straight line around the duct.
Cut a round duct from the left side with red-handled compound snips. Use this snips if you're left-handed or in tight quarters. Mark round ducts by measuring in from the end at intervals and drawing a broken line with a permanent marking pen.
Cutting sheet metal with snips can be tricky and frustrating. The edges are sharp, the cutoffs are stiff and get in the way, the snips bind or you just can't seem to negotiate the curve. These problems are common for those of us who don't work with sheet metal every day. But you don't have to be a tinsmith to cut sheet metal successfully. With the right tool and a few simple techniques, you can make almost any cut with ease.
We'll recommend a pair of tin snips that will get you through 90 percent of the jobs you'll run into. But we'll also indicate the best tin snips to use for each type of cut we show. Then when the time comes you can decide if it's worth investing in another pair of snips to simplify your job.
One snips can do it all … well, almost
There are at least a dozen types of tin snips, and choosing just the right one can be confusing. I'd recommend starting your collection with an offset compound snips (Photos 1, 1A and 2). The cutters are offset below the handle so you can keep your cutting hand above the work, and the compound action allows you to cut thicker material with less effort.
Compound snips, also called aviation snips, are color coded. Green snips are designed to cut clockwise curves and red snips to cut counterclockwise curves. You can use the snips with either hand, but if you're right-handed you'll find it easier to use green snips for many types of cuts (Photo 1A). If you're left-handed, approach the cut from the opposite direction with red-handed snips (Photo 2). Notice the clockwise and counterclockwise directions of the curved starting cuts (Photos 1A and 2). Each snips can do one direction well, but not the other.
Sheet metal edges are razor sharp. Always wear leather or other sturdy gloves when you're working with sheet metal.
Nestle thick material deep into the wide open jaws before you squeeze the handles. Straight-cutting compound snips work best for cutting thick or doubled-up sheet metal. They don't cut curves well.
There are two ways to cut round ducts. First, if you want to cut a duct near the middle and use both ends, mark and cut the duct before snapping it together. Any tin snips will work for this. But when you come to the thicker locking seam, you'll need the extra leverage of compound snips. Photo 3 shows how to cut through thick metal. If you have to squeeze the handles with excessive force, use a hacksaw instead to avoid damaging your tin snips' blades.
If you only need to trim a few inches from a round duct, it's just as easy to snap it together first. Then use the technique shown in Photos 1A and 2 depending on which color snips you're using. This is an easy cut to make with the curve-cutting snips shown, but making it with a straight cutting snips would be a challenge. Once again, you may need a hacksaw to cut the thick seam, or use the technique shown in Photo 3.
Long, straight cuts are easier to make with large tin snips. Open the cutters as wide as you can at the start of each stroke, and make long, smooth strokes. Lift the cutoff strip and roll it to the side to prevent it from binding on the tin snips' handle.
Make long strokes for long, straight cuts. Compound snips are designed more for leverage and maneuverability than for straight cutting. If you're using compound snips, open and close the jaws fully with each stroke to maximize the length of the cut. Even so, your cut will probably be a little ragged. If you've got a lot of straight cutting to do, buy tin snips like the one shown in Photo 4. It cuts metal almost as easily as a scissors cuts paper. And the long blades make it easy to cut straight and leave a smooth edge.
As you cut, one side of the sheet metal will ride up and over the lower jaw. Roll this piece back and to the side as you go to keep it from binding on the blade or getting in the way of your hand (Photo 4).
Punch a starter hole for a circular cutout with a straight-blade screwdriver. Pound on the back of the screwdriver with a hammer to puncture the metal and create an opening for the tin snips.
Start the curved cut by nibbling at the gash left by the screwdriver with the tip of offset compound snips until you can slip the lower blade under the metal. Then cut a gradual curve until you reach the curved line. Guide the top blade of your snips along the line to complete the cutout.
Use a curve-cutting snips to cut circles. Making a circular cutout in a duct is simple using the techniques shown in Photos 5 and 6. The key is to use red-handled offset compound snips to cut counterclockwise or green-handled snips to cut clockwise. This is one cut where it really pays to have snips that cut curves. It's difficult to cut a hole like this with straight-cutting snips. Even if you succeed, the resulting hole will probably have a ragged edge.
Combine red and green snips for difficult cuts. If obstructions in a work area prevent you from completing a cut with one set of snips—red-handled snips, for example—switch to green-handled snips and complete the cut by going in the opposite direction. Situations like this, which usually occur when you're modifying heating or air conditioning duct work, are about the only reason to own both red- and green-handled snips.
The next time you tackle a project that involves cutting sheet metal, head to the hardware store or home center and pick up a sharp new pair of snips that's right for the task. You'll be glad you did. The savings in time and frustration will more than make up for the cost of the new snips.