Mechanical

The Internals of a Quartz Clock Mechanism

Introduction

Most of the world has seen and used a clock; but how many of you have actually opened up your clocks to see what is inside and how it works. In this guide inside clock mechanism I will attempt to discover as much as I can about how clocks work and how they are controlled internally; it’s going to be a bit of a journey of discovery and I hope you enjoy it as much as I will. For this video I bought a cheap clock from KMart for AUD$3 (you can see it on the right).

I must prefix this guide with the following statement: I know nothing about the construction of clocks, but I am going to attempt to reason about this one anyway. In this video I mention how the solenoid works and how it creates the clocks “tick” but I do not know if that information is accurate. Please feel free to correct me in the comments if I got it wrong.

Gear Ratios

After doing all of that work making the video I decided that it would also be a good idea to record the gear ratios that are present inside the clocks and discovered that they both have exactly the same gear ratios on every part. I am just going to write down the details for each gear and explain how it is connected to the next gear:

Gear Name Teeth on Top Half Teeth on Bottom Half Connection to Next Gear
Pinion / Motor Gear 12 Magnet Top to Top
Pinion To Seconds 48 8 Bottom to Bottom
Seconds 8 60 Top to Top
Seconds To Minutes 64 8 Bottom to Top
Minutes 60 16 Bottom to Top
Minutes To Hours 48 8 Bottom to Top
Minutes To Hours 32 NA NA – No Next Gear

Now that we know these gear ratios we can work out how long it will take each gear to make a complete revolution. We can do this because we know that the small pinion gear takes 2 seconds to make a complete revolution (because it makes half revolution per tick). Therefore we can work back the time it takes for each gear to perform a full revolution by starting with the pinion gear and working it forwards.

Gear Name Calculation Seconds per Full Rotation
Pinion / Motor Gear Given 2
Pinion to Seconds 2 * 48 / 12 8
Seconds 8 * 60 / 8 60 (One Minute)
Seconds to Minutes 60 * 64 / 8 480
Minutes 480 * 60 / 8 3600 (One Hour)
Minutes to Hours 3600 * 48 / 16 10800
Hours 10800 * 32 / 8 43200 (Twelve Hours)

Now the first thing that we should notice is that the seconds hand takes one minute to rotate once, the minutes hand takes an hour to rotate once and the hours hand takes twelve hours to rotate once: this is excellent. If that did not work correctly then this would not be a very accurate clock at all; it would be completely wrong.

The other thing that you should notice is that Minutes to Hours gear will rotate once every three hours (10800 seconds). But remember that this is also the gear that we indirectly spin by using the control on the back of the Quartz Clock Mechanism. This control gear has 16 teeth internally and it is connected to the top of the “Minutes to Hours” gear which has 48 teeth. This means that every full revolution of the control dial on the back of Quartz Clock will rotate the “Minutes to Hours” gear by one quarter. This means a quarter of three hours which is 45 minutes. That tells you exactly the granularity that you have with the control dial on the back of the device. You give it one full spin for 45 minutes worth of time. This means that it takes sixteen (12 * 60 / 45) complete revolutions of the control dial to rotate the full twelve hours around the clock. However, since you can go in both directions with the control dial, it will only take a maximum of 8 spins to set the clock to any time that you like.

For those of you that are wondering how I counted the number of teeth on each gear then the answer is simple. I took photos of each and every gear and marked the photos such that increments of five teeth were easy to see and thus the number of teeth on the entire gear was trivial to calculate. For example, on the gear above I can see 9 groups of 5 gears and an extra three spare, making 48 teeth in total. A much simpler task than individually counting each and every tooth; much more accurate too.

Concluding Words

Hopefully you have learned something fun from this video and you now understand fully how a Quartz Clock works on the inside. Please feel free to comment below. I will happily take any comments that you may have and would be more than interested in discussing anything about Quartz Clocks.