Riveting stainless steel: tips for tough jobs

Stainless steel rivets are the go-to choice when a joint has to survive British weather, road salt and the occasional jet wash. Whether you are patching a sill on a project car, repairing a boat trailer or building a garden gate that will outlive you, stainless gives you corrosion resistance that mild steel simply cannot match. The catch is that the same properties that make stainless so durable — high strength and a tendency to work-harden — also make it awkward to set. Get your technique right, though, and the results are excellent.

Understand what you are working with

Stainless steel work-hardens. The moment a drill bit spins without cutting cleanly, the surface beneath it gets harder, and the hole becomes progressively more difficult to finish. That is the single biggest cause of burnt-out bits and ruined panels. Two rules follow from it: keep the drill speed down, and keep the feed pressure up.

Grades matter, too. A2 (304) stainless covers most general workshop and automotive work. A4 (316) is the marine-grade option, with better resistance to salt and chlorides, and it is worth the extra cost on anything that lives outdoors near the coast. For the rivet itself, you will mostly be choosing between plain stainless rivets with a stainless mandrel, and sealed or closed-end versions that keep water out of the joint.

Pick the right riveter for the job

Stainless rivets need noticeably more pull force than aluminium ones, and the difference is not subtle. A standard light-duty hand riveter that copes happily with 4mm aluminium will struggle and often fail on 4.8mm stainless. Options, roughly in order of capability:

• Heavy-duty hand riveter — fine for 3.2mm and 4mm stainless in short runs, but hard work on the hands.
• Lazy tong riveter — long handles give useful leverage for 4mm and 4.8mm stainless, though it needs room to operate.
• Lever or concertina riveter — a good compromise for workshop use where you have several dozen rivets to place.
• Hydraulic or air-hydraulic riveter — the sensible answer if you are setting more than a handful of 4.8mm stainless rivets, or using structural monobolt-style fasteners.

Also check the nose tips. Stainless mandrels wear tooling quickly, so keep spare tips in the sizes you use most. A worn tip lets the rivet skew, and a skewed stainless rivet is a pig to remove.

Drilling stainless without wrecking the job

Use sharp HSS bits with a cobalt or TiN coating if you can get them, and run the drill slowly — somewhere around 600 to 1,000 rpm for a 4mm hole in thin sheet. Too fast and you will polish the metal rather than cut it. Push firmly enough that the bit is always biting, and back off the pressure the instant it breaks through.

Lubrication is not optional. A dab of cutting paste, tapping fluid or even a drop of neat cutting oil on the bit keeps the temperature down and dramatically extends bit life. Reapply every few holes. If you are drilling a stack of stainless to stainless, clamp the pieces together properly — a wandering bit will oval the hole, and an oval hole gives a poor rivet set.

A step drill is brilliant for enlarging holes in thin stainless sheet, because it cuts a clean edge without grabbing. For spot weld or panel work, a dedicated hole cutter designed for stainless will save you a lot of frustration.

Joining stainless to other metals

Mixing metals invites galvanic corrosion, and while stainless against aluminium is far less aggressive than plain steel against aluminium, it is still a pairing worth thinking about. The aluminium becomes the sacrificial anode, and in a wet environment it will slowly give up material around the joint.

• Use stainless rivets in stainless sheet as a matter of course.
• For stainless sheet to aluminium, consider aluminium rivets with a stainless mandrel where strength allows, or seal the joint properly.
• Apply a bead of polyurethane sealant or a jointing compound around the rivet before setting it — the rivet squeeze pushes sealant into the gap.
• Use nylon or plastic isolating washers under the rivet head where the joint is exposed to road spray or salt water.
• Prime and paint the joint afterwards where the finish allows.

Setting the rivet cleanly

Hold the tool square to the work. If the riveter is even slightly off-axis, the mandrel pulls sideways and the rivet sets lopsided, with a head that sits proud on one side. Squeeze in one smooth, firm stroke — a hesitant, stop-start pull on stainless is how mandrels snap early or rivets fail to clamp.

Aim for rivet spacing of roughly four to six times the rivet diameter, and keep the hole at least twice the diameter away from any edge. The hole should be a snug fit for the rivet body; a sloppy hole lets the rivet expand into the gap instead of clamping the sheets together. Once set, the mandrel should snap cleanly and the head should be tight against the surface with no gap under it. If you can rock the joint, drill it out and start again.

Removing stainless rivets

Drill the head off rather than trying to lever it. Use a bit the same diameter as the rivet body, or a fraction smaller, and drill just deep enough to release the head. Push the remains through with a pin punch. Take your time: stainless work-hardens under a spinning bit, and a blunt drill here will skate across the panel and cost you far more time than the removal itself. A centre punch mark first keeps everything on track.

Done properly, stainless riveting gives you joints that shrug off years of weather and look smart while doing it. Slow drills, sharp bits, a bit of lubricant and a tool with enough grunt — that is the whole trick.