How to set a pop rivet without damaging material

Why pop rivets let you down — and it is rarely the rivet

Pop rivets are one of the most forgiving fasteners in the workshop, which is exactly why so many installations go wrong. The rivet itself is nearly always fine. What fails is the preparation: the wrong drill size, a gap between the panels, or a tool held at an angle. Crushed heads, dimpled panels, loose joints and rivets that spin in the hole all trace back to one of those three faults.

The good news is that setting a rivet properly takes seconds more than doing it badly. Once you understand what the mandrel is actually doing inside the joint, you can set dozens of rivets in aluminium sheet, steel chassis rails or plastic bumper trim without leaving a mark.

Match the rivet and drill to the material

A pop rivet is a hollow body with a mandrel through the centre. When you squeeze the tool, the mandrel pulls a ball up through the body, expanding it behind the panels. That expansion is what clamps the joint together — and it needs somewhere to go. Too big a hole and the body mushrooms uselessly; too small and you split the sheet or shear the mandrel.

As a working rule, allow around 0.1 mm of clearance over the rivet diameter:

• 3.2 mm rivet — 3.3 mm drill bit
• 4.0 mm rivet — 4.1 mm drill bit
• 4.8 mm rivet — 4.9 mm drill bit

Then check the grip range. Measure the total thickness of both panels with a calliper and pick a rivet that covers it comfortably in the middle of its range. A rivet at the very end of its grip range will not clamp properly, and one that is too long will leave a loose tail that rattles and never tightens the joint.

For material choice, keep the rivet close to the parent metal. Aluminium rivets suit aluminium sheet, steel mandrels give more strength in chassis work, and sealed or closed-end rivets are the sensible pick anywhere water, dust or a wandering mandrel would cause trouble. Where steel meets aluminium, a smear of sealant or a barrier washer reduces galvanic corrosion.

Drill the hole without stretching it

Mark the position and centre-punch it. A punch stops the bit skating across the surface, and a skating bit makes an oval hole — the single most common cause of a rivet head pulling through the panel.

Use a sharp bit, run the drill at moderate speed with light pressure, and keep it perpendicular to the work. Support the back of the panel with a block of wood or a second pair of hands; unsupported thin sheet flexes, grabs, and the hole ends up ragged and oversized. Wrap a piece of tape around the bit as a depth gauge so you do not punch through into a wiring loom or a fuel line behind the panel.

Deburr both sides of the hole with a countersink bit or a larger drill twisted by hand. Burrs sit between the panels and hold them apart, which is the second most common cause of distortion. Blow or brush the swarf away before you bring the panels together.

Clamp, align and hold square

Bring the panels together and clamp them, or hold them with a couple of clecos in the first holes. A rivet pulls the sheets together as it sets, but it cannot close a big gap, and forcing it to try is what bows a panel out of shape.

Plan the pattern before you drill. Keep edge distance to at least twice the rivet diameter, and space rivets roughly three to four times the diameter apart. Rivets set too close together concentrate stress and can tear the sheet between them.

Push the rivet fully home so its head sits flat against the panel. Then fit the correct nosepiece for the rivet size, offer the tool up square to the work, and press forward lightly until the head is seated. If the tool is angled even slightly, the mandrel bends, the head lifts on one side, and you will set a rivet you have to drill out again.

Set with steady pressure, not brute force

Close the handles in one smooth, firm motion rather than a series of short bites. The mandrel should pull through and snap with a sharp crack. That snap is the signal the rivet is correctly set — the body is fully expanded and clamped against the rear of the panel.

If the mandrel grinds and takes forever to break, the rivet is too long for the grip range or the hole is oversized. If it snaps almost immediately with no resistance, the rivet is too short and the joint will be loose.

Keep the tool pressed against the work throughout the squeeze. Letting it drift back lets the rivet ride up out of the hole, which is a classic route to a crushed head. Catch the spent mandrel or let it drop into a tray — a stray steel mandrel rattling around inside a door skin is a job for another day.

Fixing crushed heads and distorted panels

• Crushed or sunken head: almost always an oversized hole or a rivet at the end of its grip range. Drill out the rivet with a bit the same diameter as the body, remove it, and refit one size up with the correct drill.
• Wavy or distorted panel: the sheets were not clamped tight, or the rivet spacing is too wide. Clamp harder, add an extra rivet or two, and check for burrs holding the panels apart.
• Spinning rivet: the tool was angled or the hole is oval. Replace the rivet and, if the hole is worn, step up to the next size.
• Loose joint after setting: the rivet was too long. Remove it and fit one with a shorter grip range.

To remove any bad rivet, drill into the centre of the head just until the head releases, then tap the body out with a pin punch. Support the panel behind it and go slowly — it is far easier to drill a fresh hole than to repair a hole you have just enlarged by accident.