Pendelum Suspension Spring

[canthus]

Hi, I was asked to look at an old mantle clock with a basic English made pendulum movement.  The suspension spring for the pendelum was partly missing with only the top part left pinned.  Is there anyway of calculating the size of a replacement spring?  I can work out the possible mid-position for the pendulum and lever rod assembly but do not know what strength (ie thickness, width, length, number of leaves etc) the spring should be.  I have returned the clock now but wouldn't mind having another look at it if I can solve the spring issue.  Can anybody give some guidance.  Thanks

[clockboy]

I presume it is the spring at the top of the pendulum rod. The strength is not critical in fact I don't think they are supplied with different strengths just different shapes & sizes. The pic below is from Cousins & shows the measurements you need.

This is a common breakage caused by either clocks being moved or pendulums being adjusted without first removing the pendulum.

 

PS If I have got it wrong what you require post a picture

 

 

[canthus]

Thanks Clockboy,  I did go through these and others at the time and identified a few candidates.  However I could not find anything re strength/stiffness required so gave up on that project.  If as you say any strength will do, I may revisit and buy a selection (they are not expensive) to try out.  Thanks for your help.

[clockboy]

Providing it is one of the short springs such as I showed in my first post they all work. However there are long suspension springs that actually can form part of the pendulum. If it is one of these then things gets a bit more complicated as you will need to know the total length of the pendulum. Too short or too long & you will run out of adjustment when getting the clock in time.

To calculate the required pendulum length go to either of the following sites.

 

http://www.nawcc-index.net/CalcPendulumLength.php

 

http://www.abbeyclock.com/Pendulum.html

 

 

 

[canthus]

Thanks clockboy.  It was the shorter type as per your first post, with 2 springs and pin top & bottom I think.  Have bookmarked the links for when I have another go at this project, probably in the summer (if we get one!). It has been a long time since I had to do the maths like the ones indicated!!

[anilv]

Hi Canthus,

 

Witness marks on the pendulum rod will give you an idea of the total lenght of the pendulum..

 

Anil

[canthus]

Thanks for the tip Anil.  I did many measurements at the time to determine the range of spring length but didn't know how stiff it should be.  As I said, I will source a few different ones (bearing in mind your tip) when I get around to looking at it again.