Kern Standard mainspring

antiekeradio

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Mar 1, 2010
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Hello

At the moment my repair bench is populated with parts from a Kern Standard movement, approx. 1949.

It is exactly the same movement as the one with diamond dial as pictured on Bill's website (clockinfo.com):
kern_standard_movement.jpg

I am slightly confused as to what to do with the mainspring.
I tried to take it out 'the right way', that is with a mainspring winder.

Unfortunately, I could only turn the winding arbor 4,5 complete turns, which resulted in the entire length of the spring wound up tight around the arbor. The outer diameter of the arbor + tied up spring was too big for the mainspring shell, and the next size did not fit into the barrel.

So I had to take it out the old fashioned way. (put in a cloth and pull the centre with a pair of needle nose pliers)

According to the Horolovar repair guide, this movement is supposed to house a 18x38 mainspring.

I have a leaflet from a parts supplier that lists these horolovar numbers with their actual sizes. the 18x38 spring is 18 mm wide, strength = 0,45 mm and total length is 1,12 meter.

The spring that came out has the same width and length, but has a strength of 0,55 mm!

I have read that the Schatz standard clocks have a mainspring barrel that revolves 4,77 times per 365 days, and alsmost 5 and a quarter revolutions for the entire 400 day run.

I expect the Schatz and Kern standard movements to be very similar with regard to the revolution count, so taking into account the maximum 4,5 revolutions of the mainspring arbor, this clock will never run 400 days.

Also, since the spring is now distorted and looks very 'tired' (it only expanded to just under 2,5 times the drum size) I want to replace it.

How many turns should the replacement spring allow??

I can buy springs with the correct width and thickness (assuming that the correct thickness is indeed 0,45 mm!) But according to the supplier (and my own experience with other clocks) new springs of the same thickness are quite a bit stronger than what is needed. The supplier advises to choose a 0,05 thinner version, which also allows more length to be fitted.

thanks for your opinion on the matter

antiekeradio


PS (edit) the spring that came out has a name stamped near the outer eye; FINIS
below to the left of the name is a small A in a different typesetting
 

antiekeradio

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Mar 1, 2010
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OK i'm sorry if i have posted a too complicated/ unclear question.

to make things clearer for myself, I counted all the wheels and put it in a table with the turns per year and turns per 400 days:

wheelcount_kern_standard.gif

So it seems the Kern Standard has a mainspring drum that revolves even less than the Schatz Standard movements!

In the meantime I tried to fit the 18x0,40x1m40 spring and failed because it is simply too long. I think I will just order the right strength and cut it to length... if somebody can confirm me that horolovar 18x38 equivalent SHOULD be 18x0,45x1,12m and not 0,50, or even something else.
 

NECCnut

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Dec 17, 2009
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Was there any resolution on this? I have a Kern standard I just got from eBay that has a broken mainspring, and it appears to be 18 x 38. I would like to buy a Horolovar spring to put in but I don't want a lot of hassle with that. Let me know what worked in this case. Thanks.
 

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