Count wheel & backstop roller & Pendulum length to bob?


Richard Kemp
 

If you need to make an new bob its not too difficult. I recently restored an ECS master that was missing its bob. I made a replacement quite easily. I purchased a short length of cylindrical steel of the correct diameter from ebay and got a friend with a lathe to center drill it (with an extra long drill bit also purchased cheaply on ebay) and round the corners. The original bob on an ECS is cast iron, but given the density of cast iron and steel are very similar I  just duplicated the dimensions as close as I could. I spray painted the new bob in black crackle finish paint and it looks good and works perfectly. The clock is very stable (dare I say, better than my synchronome!) and is regulated with the nut about half way up the threaded rod - so I guess I got it about right. 
Richard


John Hubert
 

You will have to try it.  It is entirely possible the bob is a replacement, but the weight is not ‘critical’.  The rod itself is quite light, so the bob dominates the CoG.  You might have to extend the threaded section at the rating nut end if it has been snapped short, but that is easy.  I believe it is 4 BA threaded rod/stud/bar - widely available in longish lengths quite cheaply.  6 inch and 12 inch lengths of 4 BA threaded bar (note bar or stud is a better search term) are available on eBay for under £10.

John

On 23 Feb 2021, at 16:05, Chris Wollaston <chris@...> wrote:

Hi, well, I may be in a bit of a pickle here with this pendulum and bob. The facts are:
Bob weight = 9.25lbs, dimensions of bob: Ht = 15.4cm,  Dia = 6.2 cm
Invar steel rod length - w/o threaded adjuster, just rod to steel top clamp, not with suspension spring = 102cm
So, is it likely that the CofG is going to be very much different to a 16lb bob on a standard Invar rod of say 108cm that an acquaintance has on a Synchronome master and hence the time period for each swing way out of standardisation?
i.e. Is it likely that this pendulum and bob are for a different clock altogether?
If it isn't going to keep anywhere like correct time then how do I source the correct pendulum and bob?


Chris Wollaston
 

Hi, well, I may be in a bit of a pickle here with this pendulum and bob. The facts are:
Bob weight = 9.25lbs, dimensions of bob: Ht = 15.4cm,  Dia = 6.2 cm
Invar steel rod length - w/o threaded adjuster, just rod to steel top clamp, not with suspension spring = 102cm
So, is it likely that the CofG is going to be very much different to a 16lb bob on a standard Invar rod of say 108cm that an acquaintance has on a Synchronome master and hence the time period for each swing way out of standardisation?
i.e. Is it likely that this pendulum and bob are for a different clock altogether?
If it isn't going to keep anywhere like correct time then how do I source the correct pendulum and bob?


John Hubert
 

I have just had an (approximate) as they are running measure.

Clock No 1 - Lead bob about 16 lbs I believe - fitted with light early type weight tray.  Approx 90 cm from top of lower brass suspension block to top of bob
Clock No 2 -Steel bob - 16 lbs nominal - fitted with heavier pattern weight tray and seconds trip.  Again approx 90 cm from top of lower brass suspension block to top of bob

Both these clocks are running.

I can’t remember what the thread should be - but 8 BA is too small.  Mine is 4BA (about 3.5mm outside diameter) and the threaded section is approx 65mm with about 12mm unthreaded and reduced diameter unthreaded at the bottom.  These thread into the invar rod which has a female thread.  The bob should be nominally about 16 lbs.  On looking at a ’spare’ rod, there is no notch/mark.  

John

On 23 Feb 2021, at 14:43, Chris Wollaston <chris@...> wrote:

Hi John, Many tks for the info on various bobs and pendulum lengths. My pendulum doesn't have a weights tray and sadly, someone must have dropped the pendulum and snapped off a length of the 8BA? threaded end on which the brass rating nut travels. Thus, I've 41mm of thread sticking out the bottom of the rod but no record of how long it should be when intact?  The cylindrical brass bob weighs 4.4kg approx 9.25lbs and looks authentic so a very rough measurement guide from the top of the brass block above the suspension spring to the top of the bob would be a useful start? I'm suggesting 92cm, what do you reckon? Chris


Chris Wollaston
 

Correction, the bob weighs 4.2kg


Chris Wollaston
 

Hi John, Many tks for the info on various bobs and pendulum lengths. My pendulum doesn't have a weights tray and sadly, someone must have dropped the pendulum and snapped off a length of the 8BA? threaded end on which the brass rating nut travels. Thus, I've 41mm of thread sticking out the bottom of the rod but no record of how long it should be when intact?  The cylindrical brass bob weighs 4.4kg approx 9.25lbs and looks authentic so a very rough measurement guide from the top of the brass block above the suspension spring to the top of the bob would be a useful start? I'm suggesting 92cm, what do you reckon? Chris


John Hubert
 

The ‘notch’ is really a little file cut - and I don’t think it was always used, but I have seen it on some of my clocks.  It was not very accurate because things varied.  A variety of bob shapes and variations have been used; normal and shell type (at least two versions of shell type), iron/steel, lead, brass, possible other combinations (I have heard suggested brass case, lead fill).  In addition - various other ‘additions’ are occasionally used on the rod; weight trays are common, seconds switch ’trip’ is used on seconds clocks, synchroniser spring assembly is used on a few clocks etc, so it is only a very approximate mark for initial set up.  If you start by putting the rating nut about half way up the available thread, you will soon find you can work from there.  As you get close - you have to take more time, but the initial ‘coarse’ adjustment can be done simply by comparison with a seconds equipped radio controlled clock and typical can be got within a minute a day or so quite easily.  More patience is needed for the fine adjustment!  Very fine ’trimming’ can be achieved by a 4 or 6 BA washer (or two) on the bob top.

John

On 23 Feb 2021, at 13:36, Chris Wollaston <chris@...> wrote:

Hi, I've just fitted my backstop glass roller but it persisted in remaining in front of the Y-bracket thus not held in place and at risk of falling off and disappearing under the furniture (for a second time) so I've bent the backstop wire hopefully sufficiently to tuck one edge of the roller just behind the bracket. The next task is to get the count-wheel vane just a few thou from the latch as per the picture in Bob Miles' tome, p.238, because at the mo it's some way off.
Also, I read somewhere, either tvtesla or the manual that the pendulum's Invar steel rod is supposed to have a 'notch' showing where the top of the bob should be placed. Mine has no notch, just some oxidation roughly in the right place so can anyone give me a measurement from the top of the trunnion's upper brass block to top of bob please? Tks, Chris in E Sussex


Chris Wollaston
 

Hi, I've just fitted my backstop glass roller but it persisted in remaining in front of the Y-bracket thus not held in place and at risk of falling off and disappearing under the furniture (for a second time) so I've bent the backstop wire hopefully sufficiently to tuck one edge of the roller just behind the bracket. The next task is to get the count-wheel vane just a few thou from the latch as per the picture in Bob Miles' tome, p.238, because at the mo it's some way off.
Also, I read somewhere, either tvtesla or the manual that the pendulum's Invar steel rod is supposed to have a 'notch' showing where the top of the bob should be placed. Mine has no notch, just some oxidation roughly in the right place so can anyone give me a measurement from the top of the trunnion's upper brass block to top of bob please? Tks, Chris in E Sussex