Details of the Gronefeld One Hertz caliber G-02

Dutch watchmakers Tim and Bart Grönefeld are close to completing their new self developed watch, the Grönefeld One Hertz. For the movement they made some quality choices!

Recently I visited Tim and Bart Grönefeld to witness how they finished parts of the new caliber G-02. This movement has several extraordinary features and is designed to last a few lifetimes. The first thing that everyone will notice is the seconds hand that jumps with a speed of one hertz (hence the name) or one jump per second. Yes, it features a seconde morte or dead beat seconds, but no ‘ordinary’ dead beat seconds! This is the first wrist watch featuring an independent dead beat seconds. This means that one main spring drives the hour and minute hands and the other main spring drives the dead beat seconds hand.

Later I’ll post about how the Grönefelds constructed this beautiful complication. Another feature, which most of you will probably immediately like if you operate it, is that by simply pressing the crown you can switch between winding the watch and setting the time. So you don’t have to unscrew the crown and pull once or twice to do different things. Now you can simply push the crown to change it’s function and the indicator on the dial (W/S) shows the active function.

The new Grönefeld G-02 is extraordinary in more ways. The bridges are made of stainless steel. Usually bridges are made of brass or on more expensive watch they’re made of German silver. Stainless steel is a harder material and thus more scratch resistant. Besides that it also looks absolutely stunning when it’s finished.

Another unusual choice is the attachment of the bridges to the mainplate. Usually bridges have two feet and one screw to secure the bridge. All bridges of caliber G-02 have two screws, which are secured by two ‘pieds vis’ through the bridge. The pieds vis sit tight in a recessed part of the bridge. This is also not only done because it looks good, but this secures bridges much better to the mainplate.

Here’s why this attachment of the bridges makes a significant difference:

• Mainplates are often rhodinated; a process that adds roughly 0,003 mm to all sides of the mainplate. This means that 0,003 mm is also added to the inside of the holes drilled for the feet of bridges.
• Bridges are also often rhodinated, which again means an extra 0,003 mm to every side of the bridge including the feet.
• This means 0,012 mm extra metal, possibly causing friction when fitting bridge feet in the mainplate.
• If a watchmaker accidentally scratches the bridge or mainplate during the finishing, that part will be rhodinated again and additional millimeters are added.
• If a screw thread is busted, it has to be tapped again… something that will never happen with this construction. And if the screw thread is worn out, the watchmaker simply replaces the pieds vis.

When I visit the Grönefeld atelier next time I’ll try to make some photos.

And like mentioned before, the stainless steel bridges are not only much harder, they also look beautiful when finished. Just look at the photo below!

At The PuristS Pro I posted an extensive report about the finishing of a bridge. Bart Grönefeld showed me the whole process of how he finished a bridge of the new caliber G-02. Finishing a bridge takes more that 2 hours for an experienced watchmaker, from chamfering to the final polishing. There are 9 bridges in caliber G-02 and of course many other parts that need finishing.

The final result, including anglage, is absolutely stunning. To see the entire report about the finishing process, visit the ‘AHCI and Independent Haute Horlogerie‘ forum of The PuristS Pro.

Check the Grönefeld website and Facebook page for more information.