Clockmakers Aid Version 3.0
Users Manual

Copyright (c) T. Harrison-Smith FBHI 1988,1993,1994,1998

All rights reserved.

Tony Harrison-Smith. 150 Moreland Avenue, Benfleet, Essex. SS7 4JW. England.

Back to the program

Table of Contents

Gravity Settings
Calculate Pendulum Length
Change in length.
Pendulum beats from info on clock plates
Calculate Wheel diameter and depth of cut
Wheel Module:
Cutting speeds
Calculate how much to shorten an overlength mainspring.


Back to the program


The document 'clockaid.htm' and the accompanying help page 'caiddoc.htm' are supplied on an 'AS IS' basis without any warranty of any kind. The entire risk of the quality and accuracy rests with the user. Whilst ever effort has been made to ensure that the information on these pages is correct, should any part of the main page or help page   prove defective, the user will assume the entire cost of all necessary repair, servicing or correction.

Whilst the copyright of the program remains with the author, the pages may be freely copied and distributed, provided that you do not alter or remove either of the pages listed above. You may not make any charges for these pages what so ever.

Back to Table of Contents

Back to the program


These pages have been written so that should run on any browser that will run JavaScript. It has been tested on Microsoft Internet Explorer v4.01 and Netscape navigator V4.01.

Clockmakers Aid has been written to provide a quick and easy way of performing routine calculations needed in a clockmakers workshop. It is based on some of articles published in the British Horological  Institute's magazine 'Horological Journal' as well as the BHI's Correspondence Course. Modifications were made to the program based on  the suggestions of Mr I Thorpe, these suggestions were accepted with  great appreciation and have improved the usability of the program.

The program will perform calculations for gear cutting operations,  pendulum length calculations, cutting speeds, mainspring calculations  and will show approximate moon phases. It is strongly advised that you make a working copy of these pages for normal use, and store the masters in a safe place.

The pendulum calculations are based on an article and formulae published in the August 1988 edition of the 'Horological Journal' by Mr R.C. Barclay of the USA. Additional material was used from the British Horological Institute's Correspondence Course. The Wheel calculations used in these options are based on an article written by Eliot Isaacs FBHI and published in the October 1988 edition of the BHI's 'Horological Journal'. The cutting speeds were taken from the Presto ™  Cutting tools advisory booklet. The mainspring calculations formulae are from the British Horological Institute's Intermediate correspondence course.

The pages have been designed to be stand alone pages so that they can be saved in a convenient place, such as the desktop, and called at any time without having to log on to the Internet.

Back to Table of Contents

Back to the program

Gravity Settings

If you do not live in the UK, then you will need to change the gravity setting to your local setting. The table below gives suggested settings for various places in the world.

Town G in cm/sec/sec
London 981.2
Aberdeen 981.7
Belfast 981.5
Edinburgh 981.6
Manchester 981.4
Montreal 980.7
New York 980.7
Paris 980.9
Toronto 980.5
Washington 980.1

Back to Table of Contents

Back to the program

Calculate Pendulum Length

This option is used to calculate the theoretical length of a simple pendulum required to maintain timekeeping on a clock that has a known gear train. The length of the pendulum will then be given in cm

The formulae used are:-

Vibrations per minute

V =(CW x TW x EW x 2) / (TP x EP x 60)

where, V = Vibrations per minute
CW = Count of Centre wheel teeth
TW = Count of Third wheel teeth
EW = Count of Escape wheel teeth
TP = Count of Third pinion leaves
EP = Count of Escape pinion leaves.

Theoretical pendulum length

L =(T2 x G)/ (PI2)

where L = Theoretical length of the pendulum
T = Time of vibration (seconds)
G = Gravity in cm/sec/sec
PI = 3.1416

Back to Table of Contents

Back to the program

Change in length.

This option is used to calculate the change in a pendulum's length to correct its timekeeping error. It is used when a clock has been running for a known length of time with a test pendulum, and it has not kept