How to Make a Suspension Spring

Making Suspension Springs

Specialist technique

How to make a suspension spring

www.howtorepairpendulumclocks.co.uk

Making suspension springs

Introduction

Due to corrosion, damage or loss, replacing a pendulum suspension spring is a common task for the clockmaker. Although spring units consisting of a suspension spring already fitted with a block or blocks are available commercially, it usually desirable and often necessary to make a bespoke spring unit. Invariably this will fit, look and work better. Importantly, commercial replacements may not be available in a suitable or range of spring thicknesses.

Deciding on the thickness of a new suspension spring is important; see our chapter Suspension Spring General.

To make a suspension spring you will need a strip of steel suspension spring stock. This is available in lengths 6mm / ¼” wide, and in various thickness ranging typically from 0.08 to 0.15mm. As a rule of thumb, for longcase and fusee clocks, start with a spring of 0.12 mm thickness. For wider springs, feeler gauge stock can be a useful source of material.

If the suspension spring is missing, broken, or is not the correct length, it will be necessary to estimate the length of the new spring. Do this by first looking at the pendulum top block for wear marks from interaction with the crutch. Normally the crutch should rest half way along the block. If there is any doubt, this can be taken as a starting point. With a fusee clock, begin with the crutch pin half way along the slot in the pendulum rod.

Before making a new suspension spring, look at the position of the rating nut on the pendulum rating thread. If the nut is near either extreme end of the thread, it may be necessary to adjust the length or thickness of the new suspension spring accordingly.

This is particularly important in the case of a fusee clock where the rating nut has been let down to its lowest adjustment because a suspension spring has been fitted that is too thick. This can cause the clock to gain because of increased restoring force.

N.B. There can be other causes for the above scenario including too strong a mainspring being fitted.

fig. 1 wear mark on a pendulum top block indicates the length of a previous spring

To make a suspension spring it is necessary to punch neat holes in spring steel.

In the relatively thin material used for most domestic clocks, punch holes using a staking set. Use a flat-ended punch that is a good fit in a corresponding hole in the staking block. Place the spring centrally between the punch and the hole in the staking block and give a smart tap to the punch with a medium weight hammer. This should result in a clean hole in the spring. If the hammer blow is too heavy, the punch will jam in the hole or split the spring.

fig. 2 punching a hole in suspension spring material

This is a 17 page document. Pages 4 – 15 of this chapter sample are blank.

Making parallel sided pins

Take a normal long soft iron or mild steel taper pin and hold the wider end in a pin vice. Using a large, fine hand file and wooden filing block, file the exposed section of the pin parallel. File a bevel as a lead-in and leave the wider end larger diameter so the pin can easily inserted and removed. Use a fine needle or escapement file to draw-file the parallel section.

fig. 26

fig. 27

fig. 28