I recently bought one of these Birkenstock (Beco Technic) dual head winders, mainly for testing automatic watches after servicing.
(picture from seller’s online store – Watch Tool Shop)
There is very little information available regarding suitable turns per day (TPD) settings for Seiko automatics so I had to do some experimenting.
A mechanical watch will use a percentage of it’s mainspring power over a 24 hour period, and depending on the TPD setting, a winder will either add more or less power to the mainspring than it uses during the day, on other words, increasing or decreasing the ‘state of wind’.
If the state of wind is increasing each day, eventually the mainspring will become fully wound and if the watch is left on the winder for a long period, it would cause excessive wear on the mainspring bridle and wall as it slips continuously around the mainspring barrel… not good.
If the state of wind is decreasing each day, eventually the mainspring will unwind to the point that the watch will stop. Of course, there is a chance that the winder will put exactly the same amount of power into the mainspring as it uses during the day, but that would be more of a coincidence than the norm.
I was interested in finding the lowest TPD setting at which the winder would increase the state of wind. I used a watch with an average calibre (a 21J 6119C) for the experiments…
… and before each test I removed the auto-winding mechanism, wound the mainspring half way, replaced the auto-winding mechanism and put it on the winder at the required TPD setting. After 24 hrs I checked the state of wind again.
I found the tipping point to be 950 TPD. More than this and the state of wind increased, at 950 TPD and below, the watch unwound. As the same ‘magic lever’ winding mechanism is used in all Seiko watches I’m presuming that the results for other models will be similar, but I’ll be verifying that as time goes on.
While performing the tests I put a fully wound Bell-Matic on the other winder head at the minimum setting of 650 TPD to see how long it would run. It stopped on the 10th day, so a setting of 950 TPD should keep a watch running for around a month, certainly longer than I’ll need for testing.
Overall, I’m very happy with the Beco winder, it’s solidly built and is virtually silent. It has 15 TPD settings ranging from 650 to 3600 and winds clockwise, anti-clockwise or bi-directionally. As winders go I think this one covers all the bases, and for sensible money too.
Rich.
