The Nuts and Bolts of Metal Joinery

No welder? No problem. Build sturdy metal furnishings the old-fashioned way.

For fast, convenient metal joinery, nothing beats welding. But if you lack the space, equipment or skills for welding, you have another option: using metal fasteners.

Building metal furnishings with nuts and bolts may be a bit more tedious than welding, but it offers a few advantages. Because you can make adjustments during the process, it allows for very precise work. Unlike welded joints, connections made with screws or bolts can be disassembled easily if you need to move or alter the item. In addition, you may come to appreciate the clean, contemporary (even industrial) appearance you can create using metal and exposed heavy-duty fasteners. Best of all, anyone with the most basic carpentry skills can build metal projects using metal fasteners.

A metal cutoff saw is by far the best tool for cutting angle iron and strap metal for your building project. If you're buying or renting one, look for a saw with clamps that can be set for miter cuts, too.

Building with angle iron
Although you can join practically any two pieces of metal together by welding, a relatively small number of sizes and types are suitable for joining with mechanical fasteners. For most metal furnishings, angle iron is an excellent choice. It is possible to form mechanical joints with metal tubing (square or round) too, but trying to align the entry holes and exit holes complicates the assembly process. (If you can use a drill press, a sliding drill-press vise can help you do accurate work on those joints.) Strap iron or plate steel can be used effectively, but if it’s 1/8 in. thick or thinner, avoid using it in structural locations where it could bend.

A drill press is best for boring metal, but most of the drilling for this vanity required a portable drill. In either case, drill a small starter hole first, and use plenty of machine oil or cutting oil.

From a design standpoint, angle iron must be handled with some savvy unless you want your furniture project to look like a stationary tool stand. One or two simple embellishments, such as the strap-iron crossbucks on the sides of the vanity base shown here, can go a long way toward dressing up a plain design.

Angle iron comes in many thicknesses and widths. Building centers and hardware stores stock a limited selection of 1/8- and 1/4-in.-thick angle iron, usually in 12-, 36- and 48-in. lengths. Steel yards usually sell angle iron in 20-ft. lengths, but they’ll cut it down to more transportable lengths for you. (They may charge a small cutting fee.) The metal I used for this vanity base cost about $40 at a local steel yard. At a building center or hardware store, you should expect to pay twice as much.

The design prototype for this vanity base was built with 1-1/2 x 1-1/2-in. angle iron, but that size has inadequate surface area if you want to use more than one bolt in each joint. I switched to 2 x 2-in. angle iron, and I’d recommend this size for most metal furnishings. When building with angle iron, be aware that the crotch of the angle is rounded, so you can never make a perfectly square butt joint. If this troubles you, consider using aluminum angle iron, which has crisp inside corners.

Drill both bolt guide holes in the outer member first, but drill only one of the guide holes in the inner member. Clamp parts with a vise grip while you work.

Once the project is squared and adjusted exactly, fully tighten all of the bolts and then extend the guide holes for the second bolt in each joint through the inner joint member. Add bolts and nuts as you work.

Hex-head bolts are the principal fasteners in this vanity base. When working with 2x2 angle iron, you can use 1/4 or 3/8-in.-dia. bolts, but I found that 5/16-in. bolts (3/4 in. long) are a perfect compromise: They’re big and strong yet small enough that you can fit two for each joint and still have room to fit a socket wrench around the nuts or bolt heads.

The tight confines of the metal joints don’t allow for the use of washers or lock washers in most cases. To keep nuts from loosening due to vibration, apply a thread-locking compound to the bolt threads before tightening the nut.

Tack all joints with one bolt for each joint, and assemble the project. The second guide hole in each inner member should still not be bored. Apply thread-locking compound to bolts threads (inset photo) to help prevent loosening.

The completed metal vanity base is ready for service supporting the concrete vanity top shown in this additional article.

When using bolts to join metal, there is no way to avoid exposed fastener heads. Because the heads are so prominent, it’s important to maintain uniform spacing and patterns at each joint. I made a drilling template from a piece of angle iron for this purpose.

Make a drilling template from a piece of scrap to ensure that you maintain even spacing between fasteners. A lumber crayon works well for marking metal.

In some cases, the heads of the metal fasteners must be flush with the surrounding metal surfaces. In this vanity, for example, the strap-iron stretchers on top of the base cannot be fastened with bolts because the heads would touch the vanity top first, preventing the stretchers from distributing the weight of the top. Instead of bolts, I used flathead machine screws (No. 6 x 1/2 in.) driven into countersunk guide holes. I considered simply using small nuts to secure the screws, but I chose to tap threads into the guide holes. I used the same technique to fasten the crossbuck straps to the sides of the base.

Tap threads into the screw guide holes in the crossbucks and the top stretchers. Cut countersinks at each hole with a metal countersink reamer, and drive machine screws so the heads are flush with the surrounding metal.

Assembly strategies
Whether you’re welding or fastening, the biggest challenge when building with metal is keeping projects square. It is especially tricky when using fasteners because tightening the nuts exerts multiple directional forces on the joint. And if your guide holes aren’t aligned perfectly, the parts will shift out of position when you bolt them together.

Start by cutting all parts to length. I used a metal cutoff saw for the job and then deburred the cut ends with a file. After marking drilling points with the template, I used a drill press to bore 5/16-in. holes in the aprons at each apron/leg joint location. Although boring metal is much easier with a drill press than a portable drill, these were the only holes it was practical to make on the drill press. Whichever tool you use, drill a small starter hole first (1/8 in. or so) and use plenty of cutting oil to lubricate the bit.

With the holes in the apron drilled, clamp each apron to a pair of legs using locking pliers. Drill through the leg at one hole location only at each joint using a portable drill. (Marking a center point with a center punch is a good idea.) It is important that you do not drill the second hole yet. Insert a bolt into the hole and secure with a nut to pin the joint together. Drill both guide holes in the outer member of each joint (but only one guide hole on the inside member) and tack all of the joints together. Take care to square the joints as best you can as you work.

Once the entire project is tacked together (one bolt for each joint), fine-tune the joints until the entire project is precisely square. Then drill the second guide hole in each joint. Secure each joint with a second fastener. Finally, add the top stretchers and the crossbucks using the tapping technique described above.

Once assembly is complete, scrub all metal surfaces with steel wool and mineral spirits; then wipe clean. Paint or clear-coat the metal to prevent rusting. I used two coats of black hammered-finish Rustoleum spray paint for a finish with some texture. With any metal project that relies on mechanical fasteners, it’s a good idea to occasionally test the nuts and retighten them as needed.

Working with metal is always a messy process, and it’s even messier when you’re drilling dozens of holes for fasteners. The drill filings are very sharp and can easily cut your hand if you try to brush them away. Use a workbench brush or, better yet, a shop vacuum to remove the filings after each hole you drill. Wear gloves when handling metal, but not when operating power tools. Gloves and most power tools do not mix. And be careful not to touch metal with your bare hands immediately after cutting or drilling. Give it time to cool down.

This project is part of HANDY's Top 5 Collection: Metalworking Ideas & Tips.
Click here to check out the other four metalworking articles in this collection.