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The Age Old Technique of Peening Sheet Armor (Applied to Clasps)

by J.Edwards


There are certain types of work that seem to come in batches. Months may pass where I won’t see a single Patek, Omega, or Breitling come in for service and then suddenly 3 or 4 may come in within the span of a week. Sometimes I won’t see a single broken crystal for weeks, and then one day I’ll have half a dozen come in before the noon hour hits. These past few weeks, the recurring theme seems to be Rolex clasps. Prior to September, I hadn’t seen a single Rolex come in that required any noteworthy amount of clasp work since shortly after Christmas. After the first one came in in early September, though, several more followed within a matter of days. All from different clients under completely different circumstances.

Very little attention was paid to the subject of clasps, let alone their maintenance or repair, during my days in watchmaking school. Fortunately, to fill that void, a full afternoon was devoted to the topic during my time spent training at Rolex, which I am very grateful for. Even with that hands on training, though, there was one area of clasp repair I have consistently been frustrated by until just recently, and that is riveting.

For starters, I found my rivets never looked as clean as those from the factory. In fact, I’d say my rivets used to look downright ugly – especially under a loupe. Aesthetic problems aside, making new rivets was a time sink. There have been days where I’ve spent on near an hour trying to put a new rivet in the fliplock of a Rolex Oyster bracelet. Part of the reason it would take so long is that the rivet wouldn’t mushroom properly. Furthermore, Rolex uses such strong steel (which is absolutely fantastic) that I’d be pounding on it so hard, for so long that the pin would oftentimes bend under the brunt of successive blows before the top would billow. Worse still would be the occasional time that the clasp would cave in slightly on itself as the pin bent.

Fed up with past results, and with the sudden onslaught of fresh clasp repairs to perform, I decided to formulate a new approach. I pulled my copy of The Complete Modern Blacksmith off the shelf in hopes of finding some abetment there, but to no avail. Other typically helpful resources online weren’t much help either. Perplexed, I inquired with a friend who dabbles in recreating medieval armor, and it was in his technique that I found the near failsafe and breezy solution I’d been looking for. I could hardly believe my eyes when I saw the beautifully formed rivet that resulted through the application of his technique.

Here is what I learned:

  1. Assemble the clasp with the new pin to be riveted
  2. With the clasp assembled and closed, support the bottom, preformed portion of the pin on a block of soft metal such as brass or lead
  3. Mushroom the top of the pin into a rivet by hammering on it with a small, ball peen hammer, first with the blunt side then with the ball side

The soft block of metal supporting the rivet will keep the preformed end from being marred and will also absorb enough of the power from each blow to keep the main body of the rivet from giving under pressure and deforming.

When peening, don’t treat the rivet like a nail. Go ahead and start with a few blows straight down on the pin with the flat end of the hammer, to balloon the top of the pin, but then work the edges of the pin with gentle, uniform blows using the ball end of the ball peen hammer. The objective is the roll the edge of the cylindrical body of the pin over itself.

Thanks to the above tips, I no longer dread forming rivets. In fact, I really enjoyed working on all of the clasps that we were recently barraged with using the new techniques. I hope you, too, find the above pointers as helpful as I did.

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  1. J.Peter
    Posted October 5, 2010 at 1:59 pm | Permalink

    J. Edwards, you could have given me a call. I too had to learn this “out in the field.” One day one of our jewelers fed up with hearing me bang on the clasp taught me how to properly form a rivet. In addition to what you have mentioned I would add that the tendency is to hammer much harder than is needed. More softer taps work better than fewer big hits. I fairly lightly hit the top of the pin, dragging the hammer from the center out, but the ball side of the hammer pretty much takes care of that action as it wants to slide off the head of the pin.

    Lastly, a rotary tool with a concussion tip (like a miniature jack hammer action) with the appropriate tip makes easy work of the rivet, but alas, I don’t have one of those at my bench.

  2. Posted October 5, 2010 at 4:12 pm | Permalink

    Thanks, J.Peter. You can expect to hear from me the next time I’m stumped.

    It definitely doesn’t take much force. The ball peen does a great job of focusing the energy of each blow.

  3. Posted October 26, 2010 at 11:45 am | Permalink

    Not sure if this applies to riveting relatively hard metals, but I suspect it does. Having past experience with peening softer materials, such as gold, having highly polished hammer faces makes for a cleaner looking job. It would certainly cut down on the amount of polishing required to finish the rivet head.

  4. Posted October 26, 2010 at 8:48 pm | Permalink

    Great point, James. The ball peen hammer I used was highly polished and I’m sure that contributed to the final finish. Can’t say I’ve done enough ‘proper’ riveting yet to know how long that high polish will last when dealing with harder metals, like steel, but my guess is that the hammer will more than likely need refacing over time. Thanks for the insight.

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