Koma Midget

[dennishoy]

Folks,

I've now acquired yet another slow running Koma midget (early version with weak spring) and don't really want to spend a fortune on a replacement 'later' wider springs and barrels.
Is there any reason why I can't adjust the weight (equally) of the three lead balls that fit inside the pendulum to speed up my clocks?
The worst case is the clock which loses 5 minutes per hour with the adjuster set to maximum ' + '.
The others are not so bad, but still out of the range of the adjuster.

I'm thinking of weighing the balls, then replacing them with fisherman's lead shot inside the pendulum.
I figuring that if I remove lead shot to adjust the weight of the pendulum, then the clock will speed up.

Once I'm happy with the time keeping, I would weigh the lead shot in the pendulum then shave off some lead from the orignal balls to match.
I would then replace 'x' amount of lead shot with altered lead balls also weighing 'x'.

Am I being stupid here or is it feasible?..... please, any thoughts?
Thanks in advance.

I would add that the time loss is constant and the clocks run with no other problems.

Dennis.

[MartinM]

Dennis. You're confusing a weak mainspring that causes a clock to not run, at all, with an undersized suspension spring that's causing it to run slow.
I don't have any KoMa midgets that have lead in the weights. they're all solid brass, IIRC.
You should just get a new suspension spring that's slightly thicker.
And... Be absolutely sure you're turning the adjuster the right direction. These are backwards from most.

[John Hubby]

Dennis, as Martin says the correct solution is to replace the suspension spring with one of the correct size. The one you have on the clock now is 0.0002 inches too thin, based on your observation that the clock is running 5 minutes per hour slow with the pendulum adjusted full fast. If the pendulum were at mid-point it would be running between 7 and 8 minutes per hour slow, and the rule of thumb is that each 0.0001 inches change in thickness will give you 4 minutes per hour change in rate. Thicker = faster, thinner = slower.

Do NOT mess with the pendulum!! That is the last thing anyone working on these clocks should do, since changing the suspension spring is easy and the right thing to do. Also, it will create problems for the next owner.

[dennishoy]

Martin/John,

Thank you very much for all your help and advice.

Sorry, but I'm still learning with these types. All the clocks I've overhauled run forever (i.e. they don't stop), but run SLOW!

I think I understand what you are saying....
According to Mervyn and Passmore, the suspension spring should be 0.0022" / 0.056mm.
John, you say that if I make up a spring that is 0.001 inches thicker, then the clock will run 4 minutes faster per hour.

Shall I proceed like this?
Wind the adjuster fully one way ( + ) and see how much the clock loses, then fully the other way ( - ) to see how much more the clock loses per hour.
Let's say it loses 12 minutes an hour at full ( - ) and only 4 minutes an hour at full ( + ) then I would expect it to lose 8 minutes per hour in the mid position.
Then leaving the adjuster in the mid position, I need to make up a spring that is 0.0002 inches thicker i.e. use 0.0024" / 0.061mm thickness material.
This spring will be 0.0002 inches thicker than the old one and will speed up the clock by 8 minutes per hour.

Sorry to appear thick, but this is my first encounter with something different from the norm.
I fully take onboard your point about not touching the pendulum. I will leave it alone.

Thanks for your patience - I'm listening and learning.

Dennis.

[John Hubby]

You've got it right. 0.0002 inches thicker will run 8 minutes per hour faster. Making the pendulum check you proposed is a good idea. That way you will know the adjusting range you can get with the pendulum from full slow to full fast, that will help after you change the spring to know the limits of your adjusting range.

[dennishoy]

John,
Thank you again for all your help.
I will give this a try over the coming weekend (I was looking for something interesting to do at home, if the weather is too hot to go out).

Dennis.

[dennishoy]

John,
Sorry for the delay in continuing with this interesting exercise. This is a good learning curve for me.

I've now got some test results....
With the adjuster set fully at '-', the clock loses (1) 85min over 742min and (2) 74min over 645min which I calculate to be a loss of 7 min/hour.
With the adjuster set fully at '+', the clock loses (3) 31min over 653min and (4) 33min over 660min which I calculate to be a loss of 3 min/hour.

Can I presume the clock would therefore lose 5 min/hour with the adjuster set at the mid point?
If so, I will make a new spring with thickness 0.0023" (0.0001" thicker) and the clock will run 4 min/hour faster which should enable the adjuster to be set around mid-range for correct time.
Please let me know if my thinking is flawed... I'm new to this.

Many thanks.
Dennis.

[MartinM]

With the new spring, I see you getting a number of ~.85 min/hr slow with the adjuster at midpoint.
I'd install the spring and set the adjuster about halfway to fully "+", where it should be just slightly fast, and back it down from there.

[John Hubby]

You've got it exactly correct, and by following Martin's instruction you should get the clock right to time. I notice with interest that the "range" of pendulum adjustment is 4 minutes per hour from full slow to full fast, confirming what you will find with most 4-Ball pendulums. That's also why the change of 0.0001" was designed to give a rate change of 4 minutes per hour at constant pendulum setting, so that you can get right in the correct adjustment range using that rule of thumb.