Finishing a bridge

Dec 05, 2010,06:15 AM

Finishing a movement is not only done to show it’s beauty, but it also positively affects the movement's rate and lifespan. Although I’ve been interested in watches for quite some time, I’ve never seen what it takes to finish a movement part to a very high degree.

Recently I visited Tim and Bart Grönefeld in their atelier. They had just picked up the unfinished bridges of their new movement, caliber G-02, which they developed themselves. Let’s take a look at the finishing of one bridge of the new Grönefeld One Hertz’s caliber G-02.

After a design process of many months, it’s an exiting moment now the first parts have arrived. It’s finally time to start working on the new One Hertz. I’m absolutely thrilled about the new Grönefeld One Hertz with its independent dead beat seconds complication.

Bart Grönefeld showed me every step in the process of finishing a bridge.

The photo above shows an unfinished bridge, the way it comes from the manufacturer. The Grönefelds have chosen for stainless steel bridges, which is quite unusual as far as I know. Usually bridges are made of brass or German silver.

After the CNC process the bridges are laser engraved. The heath of this process is responsible for the different colors of the unfinished bridges. After being treated with an acid, the discoloration disappears. Than the bridge is screwed on an unfinished mainplate to get a stable bridge to work on.

First the bridge is brushed, to eliminate small parts. The following step is removing burs around the holes.

This has to be done on both sides of the bridge.

After deburring the bridge looks like this.

Now it’s time for micro blasting, which smoothens the surface.

After the micro blasting the bridge is cleaned in an ultrasonic cleaner. Here’s the result of the front and backside.

Now the part start, that makes most of us really happy… the angling! Anglage truly makes the difference on a hand-finished movement.
The first step in angling is done by a very fine file or by wood. Which tool is used, depends on the shape of the edge and the material of which the bridge is made of.

Using the file on the round edges is impossible, so this is done by this tool (don’t know what it’s called) with a wooden pin.

And another part is done by a very fine, curved wooden file.

The next step in angling is to polish the angled sides to obtain the beautiful shiny anglage. This is done with felt.

Bart explains the angling he does makes the angles round, so the reflection of the light is more beautiful.

And after all edges have been polished, the holes also have to be polished.

Now the bridge is screwed on the unfinished mainplate that functions as a good bridge-keeper during the finishing process.

The flat parts also have to be polished…

Check, double check… This is done during the whole process, over and over again.

A bit more…

And Bart Grönefeld is done. At least with one of the bridges. The entire process took 3 hours and there are 9 bridges. If more bridges are finished this reduces the process to roughly 2 hours for each bridge. And this is just for the bridges!

Hand finishing a movement requires skills, a steady hand, knowledge and patience. Massive amounts of patience… But the result looks fabulous.

My sincerest thanks go to Tim and Bart Grönefeld for taking the time to show me how a bridge is finished. I'm absolutely looking forward to seeing more of this movement and of course the entire watch when it's ready.

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This gives us a small idea of the work going into a highly finished movement...

 By: DonCorson : December 5th, 2010-06:47
Thanks for the great report Frank! Don

you're right...

 By: monochrome : December 5th, 2010-06:58

simply impressive

 By: axisskin : December 5th, 2010-07:01
thank you for that

my pleasure

 By: monochrome : December 5th, 2010-07:16

Excellent report

 By: grigo : December 5th, 2010-07:03
These are the reports I like the most. I can't wait to see the finished product. I alos hope that there will be more reports updating us on the advancement of the watch manufacturing process. Best regards, George

there will be coming more...

 By: monochrome : December 5th, 2010-07:19


 By: chaser579 : December 5th, 2010-07:39

very cool, thanks! (nt)

 By: ei8htohms : December 5th, 2010-07:56

thanks for the indepth lesson in Anglage Frank.

 By: G99 : December 5th, 2010-08:37
its amazing to think that you can file and polish metal with wood. you learn something new every day. thanks again Graham

you're welcome Graham...

 By: monochrome : December 5th, 2010-08:52


 By: DonCorson : December 5th, 2010-12:03
Hi Graham, It sounds strange, but you always use something softer than what you want to polish as a substrate. The polishing medium itself, like diamantine, which is aluminum oxide, is quite hard. Imagine you want to polish steel. You take the diamantine ... 

With your permission I would like to post an image showing this

 By: aditya : December 7th, 2010-08:55
Here is the fourth wheel & it's bridge from an English fusee pocket watch that I have. The botched up bush & its effect on the steel pivot is clearly seen. Kind regards Aditya...  

Great post Frank

 By: Wimster8 : December 5th, 2010-08:42


 By: aldossari_faisal : December 5th, 2010-09:13

Thanks Frank

 By: Geo : December 5th, 2010-10:18
Cool to read finally some more about the One Hertz and see these interesting pictures Do you have any idea when and where the watch will be officially presented and we will see some life shots of the finished product? GEO

Ready in January...

 By: monochrome : December 5th, 2010-10:31

Thanks Frank ! May I add a few pics ?

 By: foversta : December 5th, 2010-12:54
Like you, I saw Tim and Bart at the Salon Belles Montres and I took these pics: A test of new hands to improve the readability of the Tourbillon & Minute Repeater (GTM-06) watch: Movement is based on a Claret ebauche: I told them that the One Hertz moveme...  

Thanx Fr.Xavier! [nt]

 By: monochrome : December 6th, 2010-04:41

Love the work!

 By: amerix : December 5th, 2010-13:17

a fantastic post Frank ...

 By: -=EHH=- : December 5th, 2010-14:45

Thanks Frank,

 By: papillonwatchman : December 6th, 2010-00:31
What a great report with great picture's , you really showed the hole proces in a good way! Best, Michel

Another report...

 By: monochrome : December 6th, 2010-04:35

thanks for sharing

 By: Tony A.H : December 6th, 2010-11:59

Many thanks for sharing this!

 By: Gary G : December 7th, 2010-03:29
Great job capturing the process -- a great series of photos, all of which seem to be well-lit and in focus! Somehow when I am in situations like this I end up with a bunch of fuzzy shots... Thanks for this enlightening series. Best, Gary G

My pleasure :-) [nt]

 By: monochrome : December 7th, 2010-03:55

Thanks for this detailed interesting post.

 By: RJW : December 7th, 2010-03:48
And thanks to the Gronefelds for allowing you to show us. Those are some rather amazing photos. Regards, Richard.

Thanx Richard [nt]

 By: monochrome : December 7th, 2010-04:38

very informative

 By: playtime : December 7th, 2010-06:28

Love it.

 By: big daddy : December 12th, 2010-15:37