Read a report about the clock repair

Stapleford Church Clock RestorationRichard WhiteCEng MIMechE MBHIDesigner and manufacturer of clock auto-wind andregulation equipment. Maintenance and repair ofchurch and tower clocks.www.richardwhiteclocks.co.uk63 Main Street Smeeton Westerby Leicestershire LE8 0QJ0116 240 4005 0781 396 2912 Richard@RTWhite.com

IntroductionThe clock is of a ‘chair frame’ construction by Whitehurst of Derby and is dated 1773. It waslast overhauled in 1971 but according to local information, has not been allowed to run for manyyears because it was a very erratic timekeeper.Automatic winding equipment was fitted after the restoration and the newly restored clockmounted on a custom made steel bench. Each side of the bench was fitted with specialsupports to hold the old winding barrels which had been removed in order to allow access forthe drive chains of the automatic winder.RestorationThe photograph left showsthe clock prior to the recentrestoration. The drivechains for the automaticwinder are visible and oneof the original windingbarrels can be seen on thelower left hand side of theclock resting on a speciallymade bracket.General ConditionThe overall condition of the clock was good considering the time for which it had beenunattended. Mechanically, it was probably as good as it was shortly after the 1971 restorationand there were no serious mechanical issues to deal with.The frame had been painted in a rather bright green colour which in my opinion was notappropriate for an eighteenth century clock. The winding barrels appeared to have beenuntouched during the last restoration and there are small fragments of what may be the originalpaint finish on them.The custom made steel bench was still very sound but in need of a thorough rubbing down andre-painting. There were no parts of the old auto wind system which could be used so this wasremoved.

Clock RebuildThe clock was removed from its supporting metal bench and taken to my workshop where it wascompletely dismantled. After jet cleaning, all the mechanism was reassembled and tested andthen dismantled again. All the painted components were then recoated with black paint which Iconsidered to be a more appropriate finish for this age of clock. The original green was notremoved as there may have been traces of the original finish beneath which would have beenlost by chemical stripping.The winding barrels were thoroughly cleaned and then coated with micro-crystalline wax. All theother metal components, both painted and unpainted, have been coated with the samepreparation.Automatic DrivesThe automatic clock drives that I manufacture drive the clock through the original drive train byfixing to the clock winding square. Torque is applied to the drive chassis by a cord attached toa spring. As the clock mechanism moves, the barrels rotate. When this rotation is greatenough, an angle sensor on the drive switches on the drive motor which repositions the driverchassis thus continuing to provide torque to the winding barrel through the winding square.The photograph above left shows the automatic drives attached to the two clock windingbarrels. Nylon cords are attached to each of the drives and these pass over pulleys at the endof the clock bench. Each cord is then fixed to a vertically mounted spring attached to the clockroom floor. The springs are shown in the photograph on the right.

Time RegulatorThe method of time regulation employed on this installation is a ‘pendulum capture’ system.The principle of this is that the clock is set to run permanently fast and then the time is checkedeach hour and the pendulum held for the appropriate time to correct it. Because the correctionis made each hour, the error is very small. Additionally, the pendulum stopping mechanism canbe used to make the biannual time changes for summertime and wintertime by stopping thependulum for a period of eleven hours or one hour.The equipment is controlled with a small microprocessor contained in the control box beneaththe clock table. The timing is controlled in accordance with the MSF radio time signal and this isreceived by a small box mounted on the wall in the clock room. This is separate from the controlbox in order that it can be positioned for the optimum signal reception.The photograph left shows theregulator’s articulated arm actuallyhold the pendulum to stop the clock.After the appropriate time, the armwithdraws and the pendulumcontinues to swing.The arm is mounted on the controlbox beneath the clock and this alsocontains the power supply for theautomatic clock drives.The photograph left shows themagnetic switch sensor whichdetects the moment at which theclock strikes the hour. The switch isattached to the clock frame with aspecial clamp to avoid any drilling orother defacement of the originalclock frame.A similar switch and arrangement isemployed to detect the position ofthe pendulum in order that thearticulated ‘capture’ arm will stopthe pendulum without any danger ofdamage to the clock mechanism.

Night Strike ControlThe system of night strike control chosen for this installation was one which stopped the actualstrike mechanism of the clock rather than interrupting the drive to the bell. Because the clockstrike mechanism is of a ‘count wheel’ type, it must be stopped for 12 complete hours in orderthat the clock does not lose its synchrony with the strike.This was achieved by fitting a small collar to the strike ‘fly’ shaft which has a small lug attachedto it. The strike is then disabled by an electromagnetically raised cam which engages with or isheld away from the lug thus preventing it from rotating.Pictured left is the electro-magneticallycontrolled fly shaft ‘brake’. This deviceis also fitted to the clock frame with aspecially made clamp to avoiddefacing the clock frame.The picture below shows thecompleted clock together with itsautomatic drives and renovatedsupporting bench.Richard White 22 nd January 2012