Regulating Problem

[David Holk]

I am repairing an 8 day Sessions and having trouble regulating it (runs fast first of week,slow last half) The pivots and holes checked out fine. It was still running about two weeks after winding. I repalecd the time spring and this helped, but it gains and loses about 5 minutes. I have not been able to find guidance on setting up this style escapement, and could this be the problem?

Thanks,

David Holk

[David Holk]

I am repairing an 8 day Sessions and having trouble regulating it (runs fast first of week,slow last half) The pivots and holes checked out fine. It was still running about two weeks after winding. I repalecd the time spring and this helped, but it gains and loses about 5 minutes. I have not been able to find guidance on setting up this style escapement, and could this be the problem?

Thanks,

David Holk

[LaBounty]

David-

You are experiencing isochronal error. "Questions and Answers of and for the Clockmaking Profession", available from AWI's on-line store (http://www.awi-net.org/store/view_frm.asp?strCat_id=1), suggests a longer, thinner time mainspring as well as some escapement adjustments.

The formula for spring length can be found here...

old ref::Spring Length

I'd suggest something on the order of 0.016" for thickness instead of the normal 0.018". If that doesn't work you may want to try a thinner or thicker suspension spring. Other than that, there are some rather complicated pallet adjustments you could make.


I've found that an old, original mainspring will perform better for time-keeping than a new one. So in the case of a broken mainspring I'll move the original from the strike side to the time side, provided they are the same.

Honestly though, gaining or loosing 5 minutes a week due to isochronal error (error in amplitude of the swing of the pendulum) really isn't too bad in a spring driven American clock. I've seen some that have a 15 minute error!

Let us know what happens.

David.

[MikeP]

This is really fairly common. I think we expect more of old American clocks than they were designed to (or needed to) deliver. You might improve the timekeeping by trying different mainsprings but probably not by a dramatic amount.

But I agree that a spring with the original specs will do much better than the modern, generic "8 day spring for American Clocks."

[Len Lataille]

You have a Sessions that keeps time to 5 minutes per week and yor're not happy? Do yourself a favor and leave it alone. You're not dealing with a Howard wall regulator. Want better timekeeping, get a quartz.

Len
THE CLOCK CUCKOO

[lpbp]

First I hope you installed a quality mainspring, and not one from India. As has been mentioned a longer thinner mainspring could help. Like a 3/4X .017X120. And difference in weather, temperature, and even moving location can all affect timekeeping. In reality 5 mins. isn't too bad.

Larry Pearson, FNAWCC #35863 138
candidate for Director

[Carroll Hardin]

Maybe it's just me, but of all the clocks I repair, the Sessions is the worst timekeeper of them all(except maybe 400 day clocks).
I think every one has the same experience with Sessions-that is, about 5 minutes variation in a week is good enough for the original purpose of the clock.
But I would go with less than the 3/4 x 18x96.

Carroll