Crazy Timegrapher Results

[SwissSeiko]

do you have a photo of the new mainspring in the barrel? that way we can see if it looks like the right size.

[gpraceman]

6 minutes ago, SwissSeiko said:

do you have a photo of the new mainspring in the barrel? that way we can see if it looks like the right size.

Sorry, but no.  Old mainspring is in there right now.

[SwissSeiko]

Here is what the mainspring sizing should be in the barrel

[praezis]

Quote

After determining the mainspring thickness …

… which is the problem 

[gpraceman]

On 10/16/2024 at 10:31 AM, SwissSeiko said:

Here is what the mainspring sizing should be in the barrel

Thanks, that is helpful. 

My scenario is A = 2.86 mm and B = 9.1 mm

Assuming that I need a strength of 0.10 mm, I get a length of about 293 mm.

With a strength of 0.11 mm, length calculates to about 267 mm. 

The new mainspring I have is 0.11 mm X 300 mm.  Which seems too strong and too long.  Maybe less of a power reserve with that extra length?

Edited October 17, 2024 by gpraceman

[SwissSeiko]

14 minutes ago, gpraceman said:

Thanks, that is helpful. 

My scenario is A = 2.86 mm and B = 9.1 mm

Assuming that I need a strength of 0.10 mm, I get a length of about 293 mm.

With a strength of 0.11 mm, length calculates to about 267 mm. 

The new mainspring I have is 0.11 mm X 300 mm.  Which seems too strong and too long.  Maybe less of a power reserve with that extra length?

yeah it seems like with your math, its about 11% too long

[praezis]

18 minutes ago, SwissSeiko said:

yeah it seems like with your math, its about 11% too long …

… which means nearly nothing for length of power reserve. 

And many sizes of original mainsprings are about 10% longer than optimum per math

Frank

[SwissSeiko]

10 minutes ago, praezis said:

… which means nearly nothing for length of power reserve. 

And many sizes of original mainsprings are about 10% longer than optimum per math

Frank

if its too long, it will have too many coils, and limit the amount of rotations it can make, which will shorten the length of power reserve.

 

[praezis]

46 minutes ago, SwissSeiko said:

if its too long, it will have too many coils, and limit the amount of rotations it can make, which will shorten the length of power reserve.

If you know this, you can also tell us how much? The only interesting fact?

Frank

[SwissSeiko]

17 hours ago, praezis said:

If you know this, you can also tell us how much? The only interesting fact?

Frank

Unfortunately, I'm not sure how to determine how much is lost. The only way I know of is to compare results from a full wind with both springs

[spectre6000]

I saw a video a few years ago of a lecture about all the various mainspring calculations. It was really good. Lecture format; guy standing in front of/drawing on a dry erase board. I've tried to find it a few times since, but never successfully. Definitely seems like one of those things where if you know the formulae and how to use them, it's like seeing the matrix. I got what I needed at the time out of it, and moved on. Wish I had bookmarked it and/or really internalized it. 

[SwissSeiko]

Here is what JB says to use as a calculation for mainspring thickness

 

 

 

 

so from the dimensions you gave, you need a 0.09mm x 325mm x whatever the width you need for a mainspring

Edited October 18, 2024 by SwissSeiko

[JohnR725]

On 10/15/2024 at 4:30 PM, gpraceman said:

ere's what I ordered, based on what I measured from the old mainspring:

• 1.60 x 0.110 x 300

Here's what Emmy Watch lists:

• 1.55 x 0.105 x 280
• 1.50 x 0.110 x 300

Looking on eBay, I see a Benrus BA mainspring with a spec of 1.50 x 0.11 x 318 mm.

On 10/16/2024 at 12:13 AM, nevenbekriev said:

The movement is actually ETA900 I guess and from Ranft database, the spring should be 1.55/0.10/290

I do find it interesting various sources listing all sorts of differing dimensions for the exact same watch. Here's another link which lists a spring 1.50-.11-300.

http://cgi.julesborel.com/cgi-bin/matcgi2?ref=BEN_BA

oh and the calculations do not take into account that over time conceivably the lever escapement has changed slightly in other words how efficiently it functions has changed. yes manufacturers continuously are improving the lever escapement sufficiency.

then the calculations totally failed to take into account the shape of the mainspring or basically how well it was actually manufactured. Sometimes you get mainsprings with beautiful back curves like they're supposed to have another times they don't. or does it take into account the metallurgy of the various Springs blued steel spring is typically are stronger than modern white Springs.

So basically the calculations are a not an exact science.

oh and then your balance wheel pivots plus the jewels can wear out with time it's amazing what a fresh clean balance staff will do for things.

[gpraceman]

After trying a mainspring that has slightly less strength (0.10 vs 0.11), that rebanking issue went away.  I still get a healthy amplitude.  So, I was finally able to finish up my grandfather's watch.