How to hot rivet steel in a home shop

If you want to know how to hot rivet, the idea is simple. You heat a steel rivet until it is soft, push it through holes in the pieces you are joining, and hammer the protruding end into a second head. As the rivet cools it shrinks, and that pulls the joint tight. The skill is in the sizing, the timing, and holding the head still while you hit the other end. Most failed rivets I have seen, mine included, come down to a rivet that was the wrong length, too cold when struck, or not supported underneath. This guide is owner-to-owner shop practice from a hobby smith, not engineering advice. Do not trust a hand-set rivet in anything where a failure could hurt someone, such as a hook that carries a person's weight.

What hot riveting does and when to use it

Hot riveting is a mechanical joint. Nothing is melted or welded. The rivet shank fills the hole, the two heads clamp the pieces between them, and the cooling shrink adds clamping force on top of that. That is why smiths have used hot-set rivets for centuries on tongs, hinges, straps, brackets, and fittings.

It sits between a few other ways of joining metal:

• Cold riveting works for small rivets and soft metals like copper. Larger steel rivets take far more force cold, so heat makes them easier to set.
• Forge welding makes a solid joint but needs the right heat, flux, and practice. If that is where you are headed, see how to forge weld.
• Threaded fasteners can be taken apart. A hot rivet is meant to stay put.

There are jobs where you should not hot rivet at all:

• Hardened or tempered steel. Heating a finished, heat-treated part undoes its heat treatment. Knife handle pins are normally set cold for this reason.
• Galvanized or plated stock. Heating zinc coatings gives off fumes that can make you sick. Read forging galvanized steel before putting any coated bar near a forge.
• Anything with a hazard you cannot inspect. If a rivet carries real load and you cannot tell whether it filled the hole, use a different joint.

Choosing rivet stock and sizing the hole

Blacksmith rivets are almost always made from mild (low-carbon) steel round bar. It is soft at heat, upsets easily, and forgives mistakes. High-carbon or alloy steel is harder to upset and more likely to crack in the head, so keep it for tools and blades. If you are using bar from a scrap pile and do not know what it is, test a short piece first. Heat it, upset it, and see whether it behaves like soft steel or splits at the edges. If you need a deeper answer about what a steel is, that is a question for testing sources like Knife Steel Nerds and the Steel selector tool, not for guesswork at the anvil.

For diameter, pick a rivet that looks right for the work. Too thin and the joint can shear or the rivet can bend. Too fat and you weaken the strap around the hole. A common shop rule of thumb is to keep the hole center well back from the edge of the piece, at least a couple of rivet diameters. For practice work, round rod around 3/16 to 1/4 inch is easy to handle. That is a practice suggestion, not a specification. If you need a diameter you do not have, you can draw out a larger bar to size.

The hole matters as much as the rivet:

• Drill when you can. A drilled hole is clean and straight. A punched hole is fine too, but it tapers, so check which end is wider before you decide which side takes the set head.
• Make the holes line up. Clamp the pieces together and drill through both, or use the first piece as a template for the second. Holes that do not line up bend the rivet and open gaps.
• Leave a little clearance. The cold rivet should slide through with a light push and no forcing. The hot shank swells as you upset it and fills the hole. A rivet that is a tight fit cold will jam as soon as it is hot and scaled.
• Deburr the edges. A burr under the head keeps the pieces from seating flat.
• Countersink for a flush finish. Cut a shallow cone at the hole's mouth so the upset metal has somewhere to go and the head ends up level with the surface.

Working out rivet length

Length is where most beginners go wrong. The rivet must be long enough to fill the grip and still leave enough metal to form a head. The grip is the combined thickness of every piece you are joining. The rivet length is that grip plus the stick-out beyond the last surface.

Ask around and most smiths will tell you to leave a stick-out of about one and a half times the rivet diameter for a round head. For a flush, countersunk rivet, you need just enough extra to fill the countersink. Treat these as starting points, not law. Different head shapes and hole clearances change the answer, so test on scrap from the same stock.

If you are unsure, err on the long side:

• A rivet that is too short cannot form a head that clamps anything. You have to cut it out and start over.
• A rivet that is a bit long can be trimmed or just spread into a larger head.
• A rivet that is far too long tends to fold over sideways instead of upsetting straight.

Measure the stack with calipers or a rule, add your stick-out, and cut the rivet a little over. Then keep that length consistent from one rivet to the next so you stop making calculations at the anvil.

Making a rivet head before you set it

You can buy rivets with a head already formed, but most smiths make their own from rod. The method is the same move covered in how to upset: you gather metal at the end of a bar.

You need a heading tool, which is a thick steel plate with a hole drilled to the rod diameter. A simple one can sit in the hardy hole or be clamped in the vise. Hold the plate on edge or lay it flat over a support, whichever your setup allows. Then:

1. Cut a length of rod longer than you need, so you have something to hold.
2. Heat the end you will head until it glows a bright orange, and hold the other end with tongs. A set of good blacksmith tongs that grip the rod's diameter all the way along will save you from a rod that spins at the wrong moment.
3. Drop the hot rod through the hole so a short stub sticks out above the plate.
4. Strike the stub straight down so it swells and spreads into a head against the face of the tool. Aim the blows down the axis of the rod. Off-axis hits bend the stub.
5. Pull the rod out and cut the rivet to length, either with a hot cut at the anvil or a cold cut after it has cooled.

When you cut the rivet off hot, the slug can fly. Cut with eye protection on and make sure nothing flammable lies where the piece could land. A few trial heads on spare rod teach you more about how much metal makes what size of head than any rule can.

How to set a rivet hot, step by step

Once the stack is drilled and the rivets are cut and headed, lay out everything you need before the rivet comes out of the fire, because the heat will not wait for you.

1. Dry-fit the joint. Push a cold rivet through the stack and look at the stick-out. Check that the holes line up and the pieces sit flat against each other.
2. Heat the whole rivet. The entire shank needs to be soft, not just the tip, so the metal inside the holes can swell and fill them. Take it to a bright orange. Judge color in your own shop light and keep it consistent, because the same steel looks different in a bright room and a dim smithy.
3. Knock off the scale. Tap or wipe the rivet to shed loose scale. Scale trapped between layers leaves a joint that rattles.
4. Place it quickly. Slide the rivet through from the head side, seat the head on your support, and bring the stack down tight. Cold pieces pull heat out of the rivet fast, so the time between the fire and the first strike should be a few seconds.
5. Upset first, shape second. Use light, straight blows from a flat-faced hammer to swell the shank and close any gap between the pieces. This is the step that makes the joint tight. Do not start by hammering the tip flat.
6. Spread the head. Switch to the peen of the hammer and work around the stick-out, moving metal from the center outward and building a dome. A cross pein hammer works well for this, and many people prefer a ball peen on small rivets.
7. Finish the head. Dress it with the hammer face or a dished rivet set, which is a punch with a rounded hollow in the end. Tap it down until it sits snug against the surface.
8. Watch the color. Once the rivet fades from bright orange to a dull red, stop. Hammering a rivet that has gone dull invites cracks in the head. If the head is not finished, put it back in the fire and try again.
9. Let it cool in air. Leave the joint on a heat-safe surface. Steel at a black heat looks much like cold steel, and many burns come from picking up a piece that seemed finished.

If both pieces can go in the fire with the rivet, heat them together. A joint that is hot all through holds heat longer, so you have more time to shape the head. For a pivot such as the joint in a pair of tongs, rivet it snug and then work the joint back and forth while it is still hot to free the movement. That is common practice among smiths, not a measured process.

Supporting the head while you work

A rivet gets hit hard on one end, so the other end needs support. If the head can move, the blow goes into bending the shank instead of upsetting it. There are a few ways to handle this:

• A pritchel hole. If the head is small enough to drop into the anvil's pritchel hole, the stack lies flat on the face while the head hangs below it. Check that the hole is bigger than your rivet head before you rely on it.
• A dished block or swage block. A hollow or divot that matches the head shape supports a round head and keeps it from flattening.
• A rivet dolly or bucking bar. This is a heavy steel block or bar pressed against the head. A helper holds it, or you clamp it in a post vise.
• The anvil face. For a flat head, laying it on the face is fine. For a domed head it will flatten the dome, so decide what you want before you set up.

Think about how you will hold the work. You may need one hand on the tongs, one on the hammer, and the stack pinned in place. If you are working alone, a clamp or a vise to hold the stack saves a lot of fumbling. Place the hot work where you can hit it comfortably, not at the end of a stretched reach.

Fixing rivets that go wrong

Every smith has set a bad rivet. Most problems have a clear cause and a simple fix.

• The rivet folded over in the hole. The stick-out was too long, the hole was too large, or the blows came in off-axis. Cut it out and redo it with a shorter rivet and straighter strikes.
• The joint is loose or rattles. The rivet was too short, the shank never swelled to fill the hole, or the rivet had cooled before the head was finished. Scale between layers can also cause it. Remove the rivet and try again with the pieces clean and the rivet hotter.
• The head has cracks. You worked it too cold or the stock was a harder steel than you thought. Reheat sooner, and test your rod on scrap.
• The head is off-center. The stack shifted or your blows landed on one side. Support the work better and strike straight down the axis.
• The head is too small. There was not enough stick-out. Next time leave more metal above the surface.

To remove a bad rivet, grind or file the head flat, or cut the head off with a chisel. Then drive the shank out with a punch or drift. Wear safety glasses for every step, because chiseled and ground steel flies. Check that the hole is not damaged before using a new rivet. If it has gone oval or burred, clean it up or drill it out a size bigger and use a fatter rivet.

Safety at the anvil

Hot riveting is mild next to some smithing work, but the hazards are real.

• Eye protection. Wear safety glasses rated to ANSI Z87.1 every time you strike hot steel. A hammer blow knocks scale loose and throws it off the rivet as a spray of hot flakes. See blacksmith safety gear for what to wear around the forge and anvil.
• Clothing. Natural fibers such as cotton and wool are better than synthetics near heat. Synthetic fabric can melt and stick to skin. Keep sleeves out of the fire and out of the way of the hammer.
• Hearing. Repeated hammering on steel is loud over a long session. See hearing protection for blacksmithing.
• Dropped rivets. A hot rivet that bounces away can start a fire in sawdust, paper, or dry leaves. Keep the floor around the anvil clear and look for a dropped rivet before you do anything else.
• Hot steel does not always look hot. Always hold with tongs and treat any piece you have just worked as hot until you have confirmed otherwise.
• Coated stock. Do not heat galvanized or plated material. Strip or avoid it.
• Hammer condition. A hammer with a chipped face or a loose head should go in the bin or get fixed, because a head that flies off during a swing is a serious hazard.

If something goes wrong, such as a burn or a piece in the eye, stop work and get medical help. Nothing here replaces medical advice or proper training.

A practice joint to try first

The best way to learn is a few cheap joints on scrap. Cut two short strips of mild steel flat bar, clamp them together, and drill one hole near the end. Cut a few rivets from round rod in the sizes mentioned earlier, make heads on them, and set one in each joint. Change one thing each time: the stick-out, the heat, or the support. After each rivet, write down what happened.

Then cut the joint open. Saw straight through the rivet with a hacksaw and look at the cross section. If the shank filled the hole with no gap, that is a good sign the rivet set well. If you see a gap beside the shank, the rivet was probably too cold, too short, or hit off-axis. A few of these sawn-open practice joints teach you how the metal moves, and no description does that as well.

Once your rivets are consistently tight, try a real project such as a small pair of tongs or a hinge. If you are still building the basics of your shop, the Getting started topic hub collects the articles that cover the first tools, skills, and safety habits a new smith needs.