Carbon dating results now in

Last year a license was granted for the removal of two samples of timber from the clock-frame, for carbon dating. As many of you will know, carbon dating is an analytical technique that uses the measured content of C14, a naturally occurring isotope of carbon, to estimate the age, post mortem, of once-living material.
The samples were taken from the underside of the clock frame, more specifically from the mortises of the two main upright frame members. These uprights would appear to be amongst the oldest parts of the frame; one of them bears the scars left by the early, foliot escapement, as I mentioned before in my post of 28th February 2012.
The C14 results are very interesting. The more recent of the two uprights is assigned a date of 1577 plus or minus twenty two years. This is entirely consistent with the legendary donation of the clock by Queen Elizabeth the First, for which, otherwise, no documentary evidence has been found. Further work in the Manx National Archive might be called for.... The other upright is assigned a date of 1421 +/- 22 years, which indicates that this is re-cycled timber. Plus

ça change....

Removing the main and great wheels

The great wheel and main wheel are mounted on arbors slotted through wooden drums around which the ropes are wound. As you can see from the photographs, each is made in two sections, one fitting inside the other. The drum arbors terminate in squared-off pins onto which the winding handle fits; there is a click(ratchet) to allow the drum to be wound up without turning the clock or striking mechanisms backward.



Castle Rushen Clock, main wheel, Sinister pivot; note new pinion




The pivot dismantled: note the turned section in the jaws of the pivot





Castle Rushen Clock: the main wheel removed. The polythene sheet is there to help maintain the correct level of humidity




Castle Rushen Clock main wheel and arbor separated, showing the click mechanism

 The pivots, clicks and wheels are very heavily encrusted with dirty, sticky, congealed grease, as well as modern paint. This needs to be removed and is best done with the components detached. When the cleaning has been completed the wheels and arbors will be reinstated. There is negligible wear in the pivots, which are 19th or 20th century; the photographs show how previous restorers turned down the arbors on a lathe to create smooth surfaces to fit in the remodelled pivots.

Extracting rusted fixings from the escapement frame

These photographas show one of the oak escapement frame uprights (late 17th century), with the original fixings extracted for conservation. The fixing will be re-instated in due course...

Work on the escapement frame



The clock viewed from behind, showing the escapement frame

 

The escapement frame detached

 
 

Specially made jig for removing the original fixings, prior to their conservation and reinstatement



Next phase of repair now underway

We have nearly completed the replacement of the defective, modern pinions, and this has freed me to turn my attention to the escapement.

When the clock escapement was converted from the original verge and foliot mechanism to the current, pendulum regulated one, the new escapement mechanism was assembled in a separate, upright frame that sits behind the clock. The mechanism is fixed to the frame by means of iron pins driven through the timber. Over time these have rusted and have split the wood.

Having taken the decision to to restore the clock to working order and return it to the castle, we have to accept that further corrosion is inevitable. To minimise this we are removing the iron fixings, cleaning them and reinstating them.

Further progress in the replacement of worn pinions and bushes.....

Geoff Mitchell is continuing to make progress with the replacement pinions and bushes.

Because we are integrating new components with original ones (so far as we are able to judge), we have to be absolutely certain that we have designed and fitted them as accurately as possible. The pinions in particular have a very difficult job to do - namely to mesh effectively with teeth that are substantially and eccentrically worn . If we don't get these details right, further wear will inevitably result. We have to assume this will be our last opportunity to take this approach because further wear will render the original wheels inoperable. At that point the clock will cease to run without either aggressive interventive work on the medieval wheels, or their replacement.

The new release wheel pinion, with reversible mount



The new countwheel pinion



The engineering workshop

Here are some images of work in progress. Geoff Mitchell, Technical Services Officer, has been hard at work designing and then making replacement pinions for the clock movement. The new parts are properly uniform, without any of the inaccuracy associated with those they are replacing (see below). They will mesh more effectively, making better use of the the original wheels and placing minimal stress on portions of the original teeth that are already badly worn.



Design notes for the new count wheel pinion



The original pinions were fastened to their respective arbors (see glossary) by peening, meaning the edges of the arbor were hammered to pinch the pinion tightly. As we do not want to reproduce this technique (which would further damage the original arbors) Geoff has designed the new pinions with retention screws which can be undone at any time.



The new countwheel pinion alongside the original, and the countwheel itself



We know that, given the advanced wear suffered by some of the original wheels during the last 50 years, our restoration work presents a final chance to retain the Castle Rushen Clock in working order. Any further pronounced wear in the original wheels would render them inoperable without very invasive treatment, such as re-profiling of the teeth with new metal. We will watch the clock movement very closely indeed for signs of such wear over the coming ten to twenty years.



The new fly pinion in situ. Note also the new pivot for the fly arbor. I am holding the old pinion



Reminder

Don't forget that at the Manx National Heritage iMuseum visitors can find and read newspaper articles on this and thousands of other topics dating back to the eitheenth century. If you haven't yet visited, you should! Open Wednesday to Saturday 10am - 5pm (open until 7pm on Thursday evenings).

Conservation underway

It has been some time since my last post on this blog, but we have not be idle! A great deal of background research has now been undertaken, and we have diagnosed in considerable detail the patterns of wear in the movement of the clock. Our findings include:

• none of the pinions are original; this empirical observation was confirmed by analysis of the composition of each metal part by x-ray fluorescence spectroscopy;
• the pinions are, for the most part, of very poor quality;
• their design is entirely consistent with that common to many other 15th and 16th century turret clocks, suggesting earlier replacement on a like-for-like basis;
• many of the components can be associated by metallic composition with a group we are currently assuming to be original;
• the clock very probably dates from the second half of the 16th century: we are awaiting the results of radio carbon dating which we hope will confirm this;
• the clock incorporates some eccentric and unique design features (c.f. English Church Clocks 1280-1850, C.F.C. Beeson, 1971);
 



The clock from behind for the first time


• scars now found on the frame are consistent with mountings for a verge escapement underneath.



The release wheel pinion: note poor design and advanced wear.



There's plenty more of course but it will wait for another post. Meanwhile we have obtained the necessary license for the replacement of the worn and faulty modern pinions, and the work is progressing well. The best news is that we believe we can restore the clock to working order without replacing, or otherwise altering, any of the early components.