Walk into a working forge and you will see hammers of every shape hanging by the anvil: flat-faced, wedge-peened, ball-ended, domed. None of them is there for decoration. Each one directs force in a different direction, and that decides how hot steel moves under the blow. Pick the right head and a taper that would take four heats takes two. Pick the wrong one and you spend the afternoon wrestling a bar that keeps going somewhere you did not intend.
Choosing between a cross-peen, a straight-peen and a ball-peen is not about which one is "best". It is about knowing which way you want the steel to travel, then picking the head that pushes it there with the least effort and the fewest scars. The differences are small to look at and enormous in the hand.
The peen is a wedge — think about where the metal goes
A peen is a narrow, curved wedge. The blow lands along a line rather than across the whole of a circle, so the force is concentrated and the metal squirts sideways, at right angles to that line. That one fact explains most of hammer design. Cross-peen, straight-peen and ball all concentrate force; they simply choose a different direction and a different shape of contact.
On the anvil, the work does most of the turning. Rather than twisting your wrist to change the angle of the peen, rotate the bar so the peen line sits across the direction you want the steel to stretch. It sounds obvious written down. It is the thing most beginners forget, and it is why a peen sometimes seems to be fighting them.
Two consequences are worth remembering:
- Peens are fast. The same blow acting on a much smaller area moves far more metal than a flat face will.
- Sharp peens cause trouble. A thin, keenly ground peen leaves deep creases, and a crease can fold over and trap oxide, which becomes a cold shut. Keep the radius generous. A rounded, almost blunt-looking peen still draws steel beautifully and leaves a surface you can forge smooth again.
There is a third consequence, and it is the one that costs people the most time: a peen marks the steel in the shape of its line. Every blow is a decision you will have to forge out later. That is why an experienced smith will often reach for a big radius rather than a sharp wedge when a job needs to look clean as well as move fast.
Cross-peen: the everyday draw
On a cross-peen, the wedge line runs across the handle when you look down at the hammer. Hold the bar in line with your arm, swing with the peen, and the steel spreads lengthwise — away from you and toward you. That is the single most useful motion in a blacksmith's shop, which is why the cross-peen ends up as the default hammer in most forges.
An example makes it concrete. You are drawing a taper on the end of a twelve-inch length of half-inch square bar, and the bar points away from you. Two or three peen blows along the top face push metal down the length of the bar. Turn the work ninety degrees, do the same to the next face, and the corners stay reasonably square while the taper grows. With a flat face you would need far more blows and you would tend to flatten the bar into a paddle instead of tapering it.
Now suppose you want the bar to move sideways — wider, not longer. You do not need a different hammer. Rotate the bar ninety degrees under the peen and repeat the blow. Same tool, same swing, new direction. Beginner after beginner buys a second hammer to solve a problem that a quarter turn would have solved for free.
Where the cross-peen earns its keep:
- Drawing out tapers — points, scrolls, tong reins, fire tools.
- Stretching a length — making a bar longer and thinner without widening it much.
- Offsetting and shouldering — setting a shoulder where a taper meets full stock, with the peen line across the transition.
Straight-peen: for spreading, and for bars that will not turn
On a straight-peen the wedge line runs in line with the handle. Blow for blow, it does what the cross-peen does, turned a quarter turn: it pushes the metal sideways relative to the bar, widening it rather than lengthening it.
Where that difference matters:
- Widening a flat bar. Spreading the edge of a blade blank, a hinge strap or a bolster without stretching it long.
- A bar locked in the vise. If the work cannot be rotated, the hammer has to supply the change of direction. A straight-peen lets you lengthen or widen from the same stance.
- Longitudinal work. Chasing a taper along the side of a piece where a cross-peen blow would be awkward to place.
The straight-peen traditionally carries a heavier head — 2.5 to 4 pounds is not unusual — because spreading width takes more work than drawing length, and because much of the work happens on the anvil's far edge or over the horn, where a light hammer simply bounces. That weight is a feature, not an accident. Lift it and let it fall rather than shoving it down.
Ball-peen: bumps, rivets and hollows
A ball-peen has no wedge at all. Its face is a hemisphere, so the blow is effectively a point, and the steel moves outward from that point in every direction at once. That makes it a specialist's tool, and a very good one when the job suits it.
- Riveting. The classic job. The ball mushrooms a rivet head evenly instead of flattening it off-centre, which is exactly why engineers carried one long before blacksmiths did.
- Forming hollows. Sinking a bowl, a spoon or a ladle over a depression in a stump, or opening a socket. The ball chases metal down into the hollow without cutting a crease across the rim.
- Detail and texture. A light ball-peen blow leaves a soft dimple — useful for a hand-forged look on brackets, hinges and hook plates.
- Moving a hole. Nudging a punched or drifted hole into shape where a wide flat face would mark the surrounding surface.
Two cautions. First, a ball-peen mark is hard to remove, so if the surface matters, plan to forge it out or grind it away. Second, most hardware-store ball-peens are machinists' hammers: 8 to 24 ounces, small ball, short handle. They are perfect for rivets and layout work and too light to move much hot steel. Look for a blacksmith's ball-peen of 1.5 to 2.5 pounds if you intend to forge with it.
What about the rounding hammer?
If you were buying only one hammer today, plenty of smiths would point you at a rounding hammer — flat face on one side, large radius on the other. The radius draws almost as fast as a peen, spreads metal in a broad controlled way, and leaves a shallow dish you can forge out easily rather than a crease you cannot. It is genuinely excellent, and worth knowing about.
But the wedge still teaches better. A cross-peen shows you plainly which way the steel is going, and that lesson is what makes the softer, subtler shapes useful later. Learn the direction first; buy the comfort second.
Which one first? A sensible order of purchase
- One good cross-peen, 2 to 2.5 pounds. This will do eighty percent of what you will ever need.
- A heavier straight-peen, around 3 pounds. Add it when you start widening bars, forging blades or working bars held in the vise.
- A ball-peen, 1.5 to 2 pounds. Add it when rivets, bowls, sockets or textured surfaces turn up in your work.
Weight, handle and grip: the other half of the choice
Head shape decides direction. Weight decides how much steel moves per blow, and the handle decides whether your elbow survives the session.
- Weight. Most adult beginners do best with 1.5 to 2.5 pounds, roughly 700 grams to 1.1 kilograms. A heavier hammer swung lazily moves more steel than a light hammer swung hard, and it leaves your arm intact.
- Handle length. Twelve to fourteen inches gives more head speed for less effort; a shorter handle is better for close work and small anvils. Match the handle to the job and to your own reach.
- Grip. Do not strangle the handle. Hold it near the end, let the head do the work, and allow the handle to slide slightly through your fingers as you swing. A death grip is what turns a two-hour session into a punishment.
- Face dressing. Break the sharp edges of any new hammer with a grinder and a sanding disc. A square-edged face leaves a ring-shaped ding on every blow; a slightly domed, well-radiused face leaves a mark you can forge away.
A ten-minute drill to feel the difference
Take three scrap bars of the same size, bring them to a yellow heat, and forge a taper on each with a different peen. Watch the metal, not the hammer.
- Cross-peen, bar in line with your arm: the steel runs long.
- Straight-peen, same stance: the steel goes wide.
- Ball-peen: the steel moves everywhere, collecting low around the blow.
Then repeat the first one with the bar turned ninety degrees. Same hammer, opposite result. Once you have felt that in your own hands, you will not need to guess which hammer belongs in them again.
Pick the hammer for the direction you want the metal to travel. If you cannot say which direction that is, put the hammer down and look at the work again.
Photo: Plato Terentev / Pexels
