Destructive testing of the new Luminox Mil-spec watch

We received the new Luminox Mil-Spec Series – 3351.SET for testing, given the instructions to destroy the watch. We happily took up the challenge, and took the watch out for a real spin.

Luminox has been known for making really tough watches, this one probably topped it. The Luminox Militry Specification (MIL-SPEC) watch is built to the performance specification standard of MIL-PRF-46374G. We give a brief introduction about this standard, but in short, it is built to withstand some really harsh environmental conditions expected of military operations. Luminox challenged us to destroy this tough watch.

Destructive testing of the new Luminox Mil-spec Series – 3351.SET watch

The Luminox Mil-Spec Series – 3351.SET has a retail price of SGD 1,200 inclusive of GST.

Introduction

Prior to this review (or experiment), the watch was already abused. We don’t have the full history of the watch but it was probably thrown off a few stories, run over by a truck, iced and boiled, and then rubbed against tarmac. We don’t have the exact history, but the watch was already in bad shape. The minute rail was dislodged at 7 o’clock. The tube on the minute hand was assumed broken, as it did not glow. There were serious scratches throughout the bezel and at some parts of the crystal. With some hard knocks, the movement would stop. But a few more knocks on the crown would start the movement again- we suspect the stem might have been slightly dislocated inside.

Before we absolutely destroy it, I put the watch through a rather realistic scenario of surviving the harsh outdoors. The watch accompanied us on a 9-day hike to Uhuru Peak on Mt. Kilimanjaro- the highest peak in Africa. My 5.25” wrist was way too small to wear this watch, so I got a model with a 6” wrist to test the watch all the way up to Uhuru Peak, and we reviewed its toughness during this adventure. After this adventure, I took some extreme actions to destroy it as tasked.

MIL-PRF-46374G

There are MIL-SPEC for almost everything. Weapons, vehicles, aircrafts, materials, clothing etc. MIL-PRF-46374G is especially for wrist watches, and the full document can be found here (https://quicksearch.dla.mil/qsDocDetails.aspx?ident_number=25404). The scope of this specification reads: This specification covers analog wrist watches intended for general use, that are intended to be continuously read, without any action required on the part of the wearer, for periods in excess of 8 hours in low or no light situations. It’s a 21-page document that details all the necessary conditions to meet, and the methods of testing. It covers requirements for watch design, bezel design, materials, accuracy, synchronization of hour and minute hands, hacking and the environmental conditions to withstand. This version was written in 1999, superseding the previous version that was written in 1991. The first version was first published in 1964, specified as an accurate and disposable watch. Requirements for “dark viewing”, font, radiation safety, strap types and other features were slowly introduced in the later versions. Notable brands that have been supplying certified MIL-W-46374 watches include Hamilton, Timex, Stocker & Yale and Marathon. 

Case and straps of the 3351.SET

Let’s start with the overall looks. The military style font is appealing- and this was one of the specifications in earlier MIL-W-46374 versions. White font and lume tubes on a black dial was highly legible. On him, the 47mm case was too large, and got in the way occasionally when putting on the backpack or reaching back to get a water bottle while walking.

The straps are tough and it was good that it came with two keepers.The strap was too long and came out of the movable keeper. Luckily, the stationary keeper helped secure the strap at the tang buckle even when the movable keeper came loose and the strap was flapping around. 

Dial and lume

The black dial and white font added to the military and tactical aesthetics. The whitish appearance of the Luminox Lighting Technology (LLT) tube did not interfere with the design during day time. The convenience of the LLT tubes was the best feature. It was pitch dark in the tents every night, and there’s no light pollution except for the soft moon glow. Normal phosphorus lume would hold their glow for about 30 mins to an hour- too short for time-telling hours after sunset. On smart watches and phones, there would be fumbling around to switch on illumination. But on the Luminox, the LLT would perform. On top of time telling, it also gave us a sense of orientation and space inside our tents. 

Our summit hike was during a (almost) full moon. The moonlight was shockingly bright, but not quite bright enough to read a watch. The LLT worked consistently and helped us with our steady pacing to reach the summit for sunrise.

Working in the environment

Because of previous trauma, the watch would stop if there’s a big impact. But this was easily fixed by knocking the crown. Other than that, the watch kept good time throughout the 9 days. We also used the bezel to time our water purification duration of 30 mins. We were exposed to four seasons in 9 day where temperature ranged from -15°C to 34°C, and these had no effect whatsoever on the watch. We buried and rubbed it in the fine dirt, and the dirt came right off without getting  stuck in the crown or the bezel. We had more dirt stuck in our nails and cuticles that took a few days of washing to remove.

Ultimately we made it to Uhuru Peak. To be honest, I was too tired and cold to bother with photographs, but luckily, our wrist model felt obliged to take an iPhone wrist shot. It was a glorious day, and looked warmer than it was. Being born and raised in sunny Singapore, -15°C was definitely too cold for me to take off my mittens to handle the camera. 

Death blow.

Since natural outdoors was no challenge to the watch, we decided to use artificial means of destroying it. We could either cook the watch (beyond boiling), or compress it to bits. If we were to roast it, I suspect the batteries would be the first to blow up. If we compress it, then it would probably be flattened at some point in time, and we would expect the case to crack open and then the movement squeezed flat. Given that most of our readers would likely have access to a barbeque pit to perform their own burning experiment, we decided to compress the watch instead with a Universal Testing Machine (UTM). Besides, there were unknown health hazards such as toxie fumes if we burned the watch. Therefore, we would recommend against burning your watch even if you got curious..

Benchmark

To give a sense of how much this watch could take, we tested an Otterbox Defender handphone case. This has been advertised to perform up to 3x military standard, whatever that meant. The load went up to 60kN (~6000 kg), the case was flattened but not cracked. When we released the load, the hard plastic outer case was deformed, but the inner rubber layer sprang back to shape, looking good as new. I guess I know which brand of casing to get next.

Tension

We’ve always wondered how hard you can tug at your watch before the strap comes off. Would the strap snap before the spring bar bends out of shape? To answer that, we gripped and pulled the watch apart. The first time we pulled it, the strap was extremely elastic and was pulled to almost twice its length. We were forced to end the test as the machine’s crosshead has maxed out the movable length. The first test stretched the strap by some 12cm. We then gripped the straps very close to the lugs, so that we test the lug-to-strap connection instead of testing the straps.

Even then, you can see the small bit of exposed strap being stretched out before it gave way. It broke rather suddenly at about 119N (12kg) of load. The post-mortem implied that the spring bar was first bent out of shape and then pushed and sheared off bits of the lugs. It’s quite impressive how much weight these hollow spring bars can take.

Compression

We removed the watch straps, and set it up for the definitive test. Sapphire has Mohs Hardness 9. The compression platen has been specified to Rockwell Hardness C (HRC) 60. To provide some background, there are a few methods for measuring hardness of materials. We are most familiar with Mohs hardness, which is more like a ranking of hardness based on which material gets scratched/ worn out more easily. Other methods such as Brinell Hardness and Rockwell Hardness involve indenting the test materials and evaluating the indentation. Although different scales, there are online tools that estimate the equivalents across the scales, and HRC60 can be estimated to have Mohs hardness of 5.5. In order to protect the compression platen from getting scratched by the sapphire crystal, we used the watch strap to pad the crystal during the test. That would also help contain any sapphire debris that might have flew out of the test zone.

We first saw the rubber pads get compressed, and then we heard a snap at 20kN (2,000kg). We suspect that was the crystal. After that, we heard more muted cracks and could see the lugs flatten out, and the watch case cracking and expanding at 25kN (2,500kg). When we thought that the machine could go on, it couldn’t. We had maxed out the load capacity of 100kN! And even at the max pressure of 10,000 kg of force resting on the watch head, and it did not pancake. We can now be certain that the watch can sustain a lot more than our wrist.

We stopped the test, raised the platen, and took a close look at the scene. The sapphire crystal was smashed to smithereens, along with the light tubes. We carefully removed the sapphire debris and checked the carcass for other failures.

Conclusion and summary of damages

A summary of damages are listed below:

• Bezel – good as when we received it, but dislodged.
• Crystal – turned to powder
• Rehaut – dislodged and bent.
• Dial and hands – pressed together into a thin brass disc.
• No sign of light tubes in the rehaut, indices or hands, probably crushed into powder.
• Date wheel- good as new
• Movement- dented at the battery, stopped moving altogether
• Case – Cracked into a few pieces, revealing short chopped carbon fiber
• Case back – good as new.