Movement accuracy differs - DU to DD

[Bonzer]

I have a movement that has very steady timekeeping when DD but the timing is constantly fluctuating when the DU. I've noticed that when DD (accurate), I cannot see any gap between the hairspring and the regulator pins but when it is DU (fluctuating), there is a small gap between the edge of the spring and the pin.

 

Could this be causing the fluctuation in timekeeping?

 

[Klassiker]

I think you need to quantify what you mean by steady and fluctuating. Some pictures of the timegrapher traces and the pins would help.

The short answer to your question is yes. The hairspring should oscillate between the pins identically DU and DD.

[jguitron]

I've found that tons of positional variations are HS dependent... meaning, a slight asymmetry may make the HS rub on the plate on certain positions, etc. Recall that the pins don't have effect on rate on the horizontal positions... only verticals.

If HS is fine, then I would look at the pivot on the affected down side (DU) as it can be worn or even deformed. This is assuming the jewel is clean and well oiled and such.

Just my 2 cents... 

[Bonzer]

Since posting this, I think I've discovered the problem - Where the end of the hair spring is secured by a screw and clamp, the spring it was not completely horizontal. I loosened the screw and levelled the spring and it is much much better now!

Thanks for your help and advice.

[JohnR725]

29 minutes ago, Bonzer said:

Where the end of the hair spring is secured by a screw and clamp, the spring it was not completely horizontal. I loosened the screw and levelled the spring and it is much much better now!

Yes they hairspring has to be flat definitely can not be touching the balance or the balance bridge. Then even if it's cone shaped that can be an issue because it's putting too much pressure on one pivot.

Then the other thing that affects this is the condition of the pivots of the balance wheel. If one pivot is not shaped to ride or trough or lacking lubrication or dirty lubrication that definitely has an effect also. Especially common on pocket watches that don't have shock protected balance jewels. Often times you can look through and see the end of the pivot winking at you because it has a  flat spot. The pivots have to be right and they hairspring has to be right amongst a whole bunch of other stuff.

Dial-up and dial down should basically always be identical or as close as possible.