An 8-day clock – what does that mean?

What is an 8-day clock? The term refers to a clock with a mechanical movement or “works” that must be wound once per week with a key. However, it is not quite as simple as that; let me explain.

Double-side winding key

Mechanical clocks come in many varieties and may have different run times. A 30-hour clock is often called a 1-day clock. Most ogee weight-driven clocks and alarm clocks are 1 day running. Clocks such as those made with Chinese or Korean movements may have a run time of 31 days. There are 14-day clocks, 15 day clocks, 60 day clocks and even anniversary clocks called 400-day clocks. In each case the number of days refers to the period of time the clock will run until it requires winding.

Junghans 14-day time and strike mantel clock
Junghans 14-day time and strike mantel clock

Why is it important to wind a clock?

If you do not wind a clock near the end of its rated cycle the clock will eventually stop. It stops because the mainspring or weight can no longer supply the motive power for the clock to run. It may not stop immediately after its designed run time which means that a spring-driven 8-day clock that has been cleaned and serviced may run a day or two longer than its rated cycle.

An 8-day clock that will not complete its rated cycle is sending a strong message that it requires servicing.

The clock is either dirty or the movement is very worn and no amount of oil will make it run better. In fact applying oil may make it run better initially but the new oil combined with the old oil will accelerate wear on the pivots and bushings.

Servicing, according to professional clock repair people, means taking the movement out of its case, disassembling it, cleaning it, addressing wear issues, reassembly, oiling and testing.

Arthur Pequegnat Moncton
Arthur Pequegnat Moncton 15 day clock

Clocks in my collection

Of the 80+ clocks in my collection 30 clocks are running at any given point in time. Of that number three are 1-day ogee clocks, two run 14 days and the remainder are 8-day clocks. The majority of my clocks are 8-day clocks. Similarly, you will find many antique and vintage clocks that are found in antique shops and offered for sale online are week running clocks.

Seth Thomas round top
Seth Thomas round top 8-day clock

Speed variance and a clock’s cycle

You may notice that your 8-day spring-driven mechanical clock loses time near the end of its cycle. It is normal for an antique or vintage mechanical clock to lose a minute or so at the end of the week.

In a spring-driven movement, the spring is spiral shaped and releases its energy through a set of gears. Turning the key tightens the sturdy metal spring to store the energy. You are actually moving a force through a distance by compressing the spring. The energy is released through the week and towards the end of the cycle the spring releases less energy and the clock slows down.

Arrows showing Geneva stops or stop works

The variable release of energy is also a reason what some spring-driven mechanical clocks have what are called stop works or Geneva stops. Stop works are used as a compromise by utilizing only the middle portion of a long and powerful spring, which varies too much in the amount of its power in the fully wound and completely released positions to get a good rate on the clock if all the force of the spring were utilized in driving the movement.

Gustav Becker 8-day weight-driven wall clock
Gustav Becker 8-day weight-driven wall clock

Stick to a schedule

Your 8-day clock must be wound once per week and setting aside a time each week to wind the clock ensures that it continues to run. Check out this post on how to wind a mechanical clock. Part of my weekly ritual is to wind my clocks on Sunday morning, during which time I will make small adjustments, if necessary, should the clock run too slow or too fast.

In an 8-day weight-driven clock, the force of the weight is constant as the clock clock runs through its cycle. Weight-driven clocks are therefore inherently more accurate than spring driven clocks.

Like all machines, clocks will run happily for years if they are exercised, maintained, and serviced regularly.

And that is the reason it is called an 8-day clock.

Leave a comment or question below.

4 thoughts on “An 8-day clock – what does that mean?

  1. Thanks Ron, In this day of micro-second accuracy of satellite GPS controlled digital time, its a great homage to the minds who strove for accuracy with mechanical movements. There’s charm and respect for a mechanical clock that a quartz, or cyber space derived time check cannot live up to.

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    1. I am not that fastidious when it comes to my clocks. If they are accurate to within a minute or so a week, that’s fine by me.

      Liked by 1 person

  2. Just a reminder to wind your clock SLOWLEY . I made the mistake when I wound my clock fast “my fault” and the ratchet that clicks past the gear slipped and spring unwound and broke. Fortunately i have located a clock craftsman to repair my mantle clock ! He explained what i did wrong and agreed totally !

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    1. Did that once, the rachet slipped and I ended up with a bruised thumb. Now I wear cotton gloves and as you say, wind slowly.

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