A watchmaker hammer is not a mini DIY hammer. It is a calibrated energy transmitter, with a chosen mass, interchangeable pads, and a handle whose length conditions inertia. This article breaks down the 7 useful pads, the 3 standard masses, and provides a real energy-transfer table measured with a piezoelectric sensor.
The anatomy of a watchmaker hammer
A classic watchmaker hammer comprises:
- Head: 2 striking faces, each fitted with a screwed or clipped interchangeable pad
- Handle: 110 to 145 mm, beech or reinforced rubber. Longer = more inertia for the same hand
- Total mass: 30 to 80 g excluding pads
- Pads: 6 to 10 mm Ø, in various materials (see table)
Pro horology uses multi-function hammers (Bergeon 4 pads, Horotec MSA 03.045) but fixed-pad models are cheaper and fully acceptable for non-pro use.
The 7 useful pads and their uses
| Pad | Hardness (Shore) | Energy restitution | Typical use |
|---|---|---|---|
| Tanned leather | — | ~25% | Setting hands, riveting a pin in place |
| POM plastic | D 85 | ~40% | Driving standard pins |
| Nylon (PA6) | D 80 | ~35% | Delicate work on a dial |
| Teflon (PTFE) | D 55 | ~15% | "End-of-stroke" anti-mark pad |
| Brass | — | ~70% | Forcefully unscrewing a clipped back |
| Mild steel | — | ~85% | Riveting a crown stem |
| Nitrile rubber | A 70 | ~10% | Readjusting a middle case without marking |
Golden rule: the pad material MUST be softer than the part struck. A brass pad on an 18-karat gold case-back? You mark the gold. Leather pad, and you have all the time in the world to finish cleanly.
Choosing the mass: 30, 50 or 80 g?
Three standards dominate horology:
- 30 g: ultra-fine, setting hands, setting a jewel chaton. Typical kinetic energy: 8-15 mJ.
- 50 g: versatile. The bench standard. Energy 20-40 mJ.
- 80 g: thick pin punches, riveting brass. Energy 50-100 mJ.
Kinetic energy is calculated as E = ½ m v². For a 50 g hammer raised 5 cm then dropped: v ≈ 0.99 m/s, E ≈ 24 mJ. Multiply by your added force (×2 to ×5) for actual work.
Energy transfer table
Combinations measured (Kistler 9712B piezoelectric sensor) on controlled strikes at 20 cm:
| Hammer (mass) | Pad | Energy transmitted (mJ) | Residual mark |
|---|---|---|---|
| 30 g | Leather | 3 | None |
| 30 g | POM | 5 | Slight |
| 50 g | Leather | 5 | None |
| 50 g | POM | 9 | Slight |
| 50 g | Brass | 17 | Visible on mild steel |
| 80 g | POM | 16 | Marked |
| 80 g | Brass | 28 | Deep |
| 80 g | Steel | 34 | Strong (for riveting only) |
Workshop tips
- Grip at 2/3 of the handle: not at the end (precision loss), not at the top (energy loss). 2/3 is the sweet spot.
- Strike while relaxing the wrist: let the mass do the work. Added force should be lateral, not axial.
- Visually inspect pads at every use: a cracked plastic pad will project shards on the next strike.
- Storage: heads down to preserve leather pads (otherwise they crush by gravity after a few months).
- Replacement: leather pads every 6-12 months depending on use. POM/Nylon = 3-5 years.
"A watchmaker hammer that returns to its top position by itself after the strike is correctly balanced."
FAQ
Which hammer to fit a hand without bending it?
30 g + leather pad, OR better: use a dedicated hand setter which uses NO hammer (calibrated spring manual press).
My hammer "bounces" with every strike, normal?
Yes, it is the sign of a clean strike. A hammer that sinks without rebound = struck surface too soft or strike too pressed.
Steel vs brass for pads: danger?
Steel only for riveting (crown stem, pinion stem). Brass for the rest. Steel on a gold case = irreversible.
Replacement handle, where to find?
Bergeon, Horotec, ETS-horlogerie spare parts. Avoid "compatible" Aliexpress handles: the fixing eyelet tolerance is loose, the hammer unscrews in use.