Sheet Metal Basics

Aviation snips cut curves or straight lines. Arrows indicate the direction we cut to make the curves with the snips shown. The trammel with scriber comes in handy for layout, and gloves will protect your hands.
As a woodworker, you may feel slightly lost venturing into the foreign territory of sheet-metal fabrication.

You may have some of the tools required already: a portable drill, twist-drill bits, scratch awl, center punch, and measuring tools. For large-diameter curves, a trammel like the one in the photo right will come in handy.

You'll also need snips for cutting the metal, along with pop rivets and a pop-rivet tool for joining the pieces of metal you cut. You can buy them at home centers or hardware stores.

Snips. For cutting sheet metal, we prefer aviation-style compound snips, shown above right. Avoid the old-style tin snips with long handles and short jaws; it's a hard tool to cut curves with.

Aviation snips cut in specific directions--straight, left curve, or right curve. Handle color signifies the direction.

Pop rivets. We like steel pop rivets 1/8" in diameter for light sheet-metal work. (The diameter indicates the size of the hole the rivet fits through.)

You'll find these rivets available in three lengths--short, medium, and long, corresponding to grip lengths of 1/8", 1/4", or 1/2". Choose the nearest grip length longer than the thickness of the materials you're joining.

Pop-rivet tool. You can't install pop rivets without a special tool, shown in the photo below. The tool is inexpensive, and any manufacturer's tool works with any brand of rivets, as long as they're the same diameter. Most pop-rivet tools feature interchangeable nosepieces, allowing one tool to set rivets of any diameter. A long nose like the one shown reaches into tight spots, making the tool easier to use and more versatile.

Safety gear. Sheet metal has sharp edges. And because it's springy, it sometimes seems to jump at you maliciously. Without protection, that can lead to a cut. Just as bad, tiny metal splinters can get under your skin, and they're harder to get out than wood splinters.

So, wear gloves. The yellow Kevlar-fiber cutproof gloves shown afford great protection. But any kind of work glove, even cotton gardening gloves, can save you from a painful cut. Wear long sleeves to protect your arms, too, especially when cutting curves in metal with snips. And you should always wear eye protection.

You can't count on your trusty sharp pencil for drawing layout lines on sheet metal. Pencil marks won't show up well enough or last long enough to be of much help. Felt-tip pens and permanent markers write well on metal, but their wide lines hinder precision. Instead, scribe cutting lines with a scratch awl.

You'll also need a straightedge with a nonskid back. If you can't find one at a hardware store, try an art-supply store. Or, you can make a suitable substitute by sticking strips of double-faced tape to a steel ruler. Press the exposed face against your sleeve a few times to reduce the tape's tack before use.

Straight-leg dividers or a trammel works well for scribing arcs or circles on metal. To prevent the pivot point from skidding off center, stick a piece of masking tape or duct tape at the center. If the inside of the circle will be waste, you can simply centerpunch the centerpoint to prevent skidding.

Before making the parts for your project, lay out some straight and curved practice lines on a piece of sheet metal. Then, cut along them to get the feel of your snips. Some snips, like the yellow-handled one shown top of the page, shear out a narrow strip to make a cut. (Often called duct snips, this one cuts straight or curves, and works well on stovepipe or other cylinders.) With this type, make sure you take the strip from the waste side of the cutting line.

When cutting with snips, closing the jaws all the way leaves a jagged-looking edge on the metal, which looks crude and is difficult to eliminate. Instead, close the jaws most of the way, release pressure on the handles to let the jaws open, then push the jaws forward to continue cutting.

A lap joint is the simplest way to join sheet metal. And pop rivets provide a quick, effective means of fastening a lap joint, as shown right.

To make the joint, simply overlap the parts by at least 1/4" (or as specified by project instructions). Then, drill rivet holes through both pieces.

Mating holes must align exactly, so the best approach is to drill through both pieces at once. To do that, tape the pieces together or clamp them, using C-clamps or bar clamps and clamp blocks.

Mark the hole positions, and centerpunch them. For a neat job, align the rivet holes and space them evenly. Drill the holes with a twist-drill bit the same diameter as the rivet. Drill the first hole through both parts, then insert a rivet (without setting it) to keep the parts from creeping out of alignment while drilling the remaining holes.

(Designer/builder Jan Svec used tape a little differently for the cyclone project. He cleaned the joint area on the top face of one piece with lacquer thinner, then applied a strip of double-faced tape to it. Next, he cleaned the underside of the piece on the other side of the joint, and brought the pieces together. The tape held both parts in position while he drilled the holes and helped seal the riveted joint.)

It's easy to remove a pop rivet, too. Simply drill through the rivet head with the same size bit you used to drill the rivet hole.

Squeezing the handles of a pop-rivet tool expands the tail end of the rivet to make a tight joint. The mandrel that extends from the rivet breaks off when the rivet is pulled tight enough.

Read more about

Tip of the Day

Piece of pipe makes button sanding a cinch

Wooden buttons often need to be sanded before use. But it's sure tempting to stick them into... read more