Jump to content

Cause for regular variance of around 30 degrees in amplitude


patchwerk

Recommended Posts

I am working on a 18/0s Elgin 484 movement from the 30s. After cleaning, and doing a lot of work on the balance it runs but the amplitude varies in a regular pattern by about 30 degrees. Because of the regular pattern I figured it was a problem with the train, and replaced the train wheels from another movement just like it. The exact same pattern emerged. The x scale in the images below is in hours and the period of the pattern is around 6 minutes. Any ideas?

image.thumb.png.5a92845a2ec4877f733ac5cadf5da22e.png

 

Thanks!

Link to comment
Share on other sites

3 hours ago, praezis said:

Period of those waves is 6 seconds.

Escape wheel needs 6 seconds per revolution...

Frank

I presume from that, the culprit is likely to be a dirty, damaged, or worn tooth on the escape wheel.

My money is on a tiny spec of dirt, so small as to possibly require a microscope to see it, causing just sufficient drag to create that periodic "limp" in the motion of the escapement. 

I had a similar issue, I posted about here.

 

Edited by AndyHull
Link to comment
Share on other sites

Thanks for all the responses!

@praezisThe period is 6 minutes, not 6 seconds (the x axis is hours:minutes on that chart), so I do not believe it is the escape wheel. The six minutes makes me think it is the third wheel, but I have swapped it out for others twice with the same effect.

@Nutiborskoku,I have used different barrels and arbors with it but will check the barrel bridge and mainplate holes.

@Nucejoe, no endstones.

Link to comment
Share on other sites

3 hours ago, patchwerk said:

Thanks for all the responses!

@praezisThe period is 6 minutes, not 6 seconds (the x axis is hours:minutes on that chart), so I do not believe it is the escape wheel. The six minutes makes me think it is the third wheel, but I have swapped it out for others twice with the same effect.

@Nutiborskoku,I have used different barrels and arbors with it but will check the barrel bridge and mainplate holes.

@Nucejoe, no endstones.

Oh, you are right, thank you!

But the principle stays the same, you can find the source this way. 6 minutes can be

- the revolution of a wheel, or

- the passing time of two meshing teeth

Frank

Link to comment
Share on other sites

5 hours ago, praezis said:

Oh, you are right, thank you!

But the principle stays the same, you can find the source this way. 6 minutes can be

- the revolution of a wheel, or

- the passing time of two meshing teeth

Frank

The six minutes interval roughly correlates with the 3rd wheel in a standard 18000 movement (right?). How would I calculate which other wheel pinion and teeth interactions happen that regularly? I have more scrap movements of these types and can try replacing more of the train wheels but would love to learn how to approach this more surgically. 

Link to comment
Share on other sites

To calculate, you need teeth numbers of wheels and pinions and known revolution times (e.g. 2nd wheel, 4th wheel).

Once I calculated these times for a calibre that I often work on (18000, small second):
1 tooth of the barrel (=2nd wheel pinion tooth) = 5 minutes
1 revolution 3rd wheel = 7.5 minutes

I found that most often the tooth is to consider, less often the wheel.

Frank
 

Edited by praezis
  • Like 1
Link to comment
Share on other sites



×
×
  • Create New...