Tag: mainspring

Your Clock Has Stopped | Follow These First 5 Steps Before Calling A Clock Repairer

There are few things more frustrating for an antique or vintage clock owner than when a favorite clock suddenly stops. Mechanical clocks are intricate machines, but that doesn’t always mean the problem is complicated. In fact, many stoppages are caused by small, simple issues that can be corrected at home without tools or technical expertise.

Before you assume the worst or take your clock to a repair shop, here are 5 things you can do yourself to have your clock ticking again.

1. Is the Clock Wound?

It may sound obvious, but the most common reason a clock stops is simply that it has run down. Spring-driven clocks need their mainsprings wound fully with a key, while weight-driven clocks require the weights to be raised. All mechanical clocks require power to operate. Simply put, if the clock is not wound, it cannot run — so always begin here before moving on to more complex possibilities.

Winding arbors on a Seth Thomas mantel clock (arrows)
Winding arbors on a Seth Thomas mantel clock (arrows)

2. Is the Clock Level and in Beat?

Pendulum clocks must be in beat to function properly. Being “in beat” means that the tick and tock are evenly spaced in time. If the case is leaning or the crutch (the arm that drives the pendulum) is out of position, the pendulum will quickly stall. Place the clock on a level surface and listen carefully: if the tick and tock sound uneven, adjust the clock slightly to the left or right until the beat evens out. Sometimes, fine adjustments to the crutch are necessary, but often leveling the case is all it takes.

Unless your wall clock is anchored, simply moving the case very slightly left or right and listening for an even beat is all that’s required.

Is your clock level on the wall?

3. Is the Pendulum Free to Swing?

The pendulum is the heart of your clock, and it must swing freely without interference. Check that the suspension spring is straight and properly seated, not twisted or bent. Make sure the pendulum bob is not rubbing against the backboard, striking the chime rods, or touching the bottom of the case. Any sort of rubbing will affect the swing of the pendulum, thereby robbing the clock of power. The smallest obstruction can rob the pendulum of momentum and bring the clock to a halt.

Clocks with a floating balance or a hairspring escapement are popular with some collectors since they continue running even when the surface isn’t perfectly level.

A mantel clock movement showing the pendulum

4. Are the Hands Binding?

Sometimes the problem lies not with the movement but with the clock hands. If the hour and minute hands are rubbing against each other, or if the minute hand is scraping against the dial or the glass, the train can be stopped entirely. If the clock stops at a specific time every 12 hours, hands that are interfering with each other are likely the culprit. Inspect the hands carefully and make sure there is a little clearance between them. A gentle outward bend is usually all that’s needed to free them.

Any one of the four hands on this clock can cause interference

5. Is the Movement Dirty or Dry?

Mechanical clocks rely on clean pivots and fresh oil. Over time, old oil becomes gummy and collects dust, creating friction that will eventually stop the clock. If you notice dry or blackened pivot holes, sticky residue, or an overall grimy look to the movement, then lack of servicing is likely the culprit. Gummed-up oil in the mainspring coils can also cause the springs to appear as if they are glued together. Some people incorrectly refer to this condition as a clock that is “over-wound”.

When I first examine a newly purchased clock that does not run, I carefully release the mainspring’s power and then attempt to run the movement. If it runs, that tells me the mainsprings require servicing. At this point, the clock will need a complete cleaning and oiling by a qualified repairer.

Very dirty movement
A very dirty movement

Conclusion: When Simple Fixes Aren’t Enough

If you have checked these five areas and your clock still refuses to run, the cause is almost certainly deeper and more complex. Worn pivot holes, tired mainsprings, bent teeth, or other mechanical issues may be at fault — problems that cannot be corrected with quick at-home adjustments. A clock movement may appear clean, yet still be quite worn — something you can’t always detect without disassembly.

The good news is that your clock is very likely repairable, but it will require the attention of an experienced clockmaker. By ruling out these simple issues first, you’ll know with confidence when it’s time to seek professional help, and you may just save yourself a service call.

3

Common Reasons Your Clock Is Running Slow

There are four general categories of clocks: quartz, electro-mechanical, electric, and mechanical. Mechanical clocks—whether antique or vintage—are the focus of this discussion on why a clock might run slowly.

We’ve become accustomed to the accuracy of quartz clocks, which lose or gain only milliseconds per week. Contrast that with an era when people were content to accept that their mechanical clock might be a minute fast or slow over the course of a week. It was common practice to make small adjustments throughout the run cycle of a clock.

In fact, a typical American spring-driven clock in properly serviced condition may gain or lose a couple of minutes per week as a norm. Weight-driven mechanical clocks that gain or lose only a few seconds per week are considered to be much more accurate.

That said, how many mechanical devices do you know that still run (relatively speaking) perfectly after 120 years?

A clock can run slowly for a variety of reasons.

  • Environmental
  • Pendulum too low or too high
  • Pendulum of incorrect weight
  • Suspension spring length is incorrect
  • Suspension spring is not attached correctly
  • Lack of lubrication
  • Gummed-up lubrication (over-oiled)
  • Balance wheel needs adjustment
  • Weak mainspring
  • Changes or alterations during servicing
  • Clock cycle time variance
  • Slipping or binding
  • Bent gear teeth or arbors

Let’s explore each one of these factors:

Clock parts

Environmental Factors

Mechanical clocks are subject to environmental conditions that may cause them to gain or lose time over the year. These include heat, cold, and humidity. Warmer temperatures can slow down a clock due to the expansion and lengthening of the pendulum, unless it has a compensating pendulum with mercury or dissimilar metal rods. Denser air can also cause the pendulum to swing more slowly.

Even a change in elevation, such as moving a clock from sea level to a higher altitude, can affect the speed of the clock.

Pendulum Too Low or Too High

The lower the pendulum, the slower the clock will run. Many pendulum clocks have an adjustment screw at the bottom or on the bob itself. If not, there is often a regulator on the clock face. You can use the small end of a double-sided key to insert into the dial and adjust the speed.

Shortening the pendulum speeds up the clock. Anything that increases the pendulum’s effective length will slow it down.

Incorrect Pendulum Weight

A pendulum that is too heavy lowers the center of gravity, which causes the clock to run slowly. Using the correct weight for your clock ensures proper and reliable operation.

Incorrect Suspension Spring Length

When someone unfamiliar with the mechanics of a clock replaces a suspension spring with one of the wrong length or thickness, the result is a clock that may run too fast or too slow. Always ensure the spring matches your clock’s specifications.

Suspension Spring Not Attached Correctly or Kinked

The suspension spring connects the top post to the pendulum leader and allows the pendulum to swing. If it’s not installed securely, the pendulum may not swing properly or may wobble, reducing efficiency and affecting the clock’s accuracy.

A kinked or damaged suspension spring will impede the smooth action of the pendulum rod.

Lack of Lubrication

Dry pivot holes mean there is no lubricating barrier between the pivots and the bearing holes—even if the movement appears clean. Apply a small drop of clock oil to each dry pivot hole to ensure smooth running. Without oil, steel pivots will wear the brass holes, eventually causing gear misalignment and stopping the clock.

Note: Only a small drop of oil per bushing hole is needed—no more.

Gummed-Up Lubrication

When a clock runs slowly, the instinct may be to add more oil. But if there’s already old, dirty oil—often blackened or greenish—it will mix with new oil, forming an abrasive paste. Though this may offer a temporary improvement, the clock will soon begin running slowly again.

The only solution is proper servicing: disassembly, thorough cleaning, addressing wear, reassembly, and testing.

Balance Wheel Needs Adjustment

For those clocks that have a balance wheel instead of a conventional escapement arrangement.

The escapement is regulated by sliding the two small weights on the balance wheel. Slide them inward to speed up the clock, outward to slow it down. Use the adjustment “finger”—moving it to the right increases speed, to the left decreases it. One dot of adjustment usually changes the time by about 10 seconds per day.

Look for markings near the balance wheel: “S” for slow, and “F” for fast.

Weak Mainspring

Many antique clocks still have their original mainsprings. These springs were often made from high-quality steel, though they weaken over time—a condition known as becoming “set.” A set mainspring won’t run a full cycle (8 days for eight-day clocks or 30 hours for one-day clocks).

While repair shops often replace mainsprings as standard practice, most properly serviced original mainsprings still perform reliably. If replacement is necessary, use a correct-size, high-quality American or German mainspring for dependable performance. Avoid springs made in India at all costs!

Changes or Alterations During Servicing

Altering a mechanism—such as replacing a gear with one that has the wrong tooth count—can affect timekeeping. Even if parts look identical, manufacturers often made slight variations over the years. Using incorrect parts may lead to a slow or fast clock.

Clock Cycle Time Variance

American spring-driven eight-day clocks typically run a little faster at the beginning of their cycle (when the mainspring is fully wound) and slower as the power diminishes. This is considered normal and usually does not require adjustment.

Weight-driven clocks provide constant power, so any time variance from the beginning to the end of a cycle is more likely due to wear or other issues.

Slipping or Binding

If your clock is losing hours per day, something is slipping or binding inside the movement. If it’s losing minutes per day after all adjustments have been made, worn bushings or components may be the cause.

Clockmakers check for end shake—the slight lateral movement of gears between the movement plates. Without sufficient end shake, gears may bind, slowing the clock. Ensuring proper end shake is a standard part of any professional servicing.

Bent Gear Teeth or Arbours

Bent or slightly out-of-true arbors or gear teeth can cause intermittent resistance, slowing or halting the clock temporarily.

Final Thoughts

Your situation may be unique, and if your clock issue isn’t covered in this article, I recommend consulting a professional clock repairer. If you have limited experience, attempting your own repairs may lead to irreversible damage.

Working with mechanical clocks also involves risk. Mainsprings store a significant amount of energy and can cause serious injury if mishandled.

Understanding why your clock runs slowly is the first step. Addressing the problem is the next. Beyond that, periodic maintenance and the use of quality parts are key to a long and reliable life for your clock.

2

Mainsprings dilemma | To Replace or Not To Replace

Mainspring contained in a clamp

As a clock repairer, there are several compelling reasons to keep the original mainsprings if they are still in good condition.

Keeping the original mainsprings ensures that the clock remains as close to its original condition as possible. Collectors and enthusiasts often value clocks with original parts, as they maintain the authenticity and historical significance of the clock.

Brass mainsprings for Manross clock
Older brass mainsprings are not replaceable

Many older mainsprings were made with higher-quality steel and manufacturing techniques and modern replacements may not be of the same quality. Original springs, if well-preserved, may outperform modern equivalents in terms of durability and performance.

Consider the original design of the movement and how it is powered. The original mainspring is designed specifically for the clock’s movement, ensuring the proper balance of power delivery and running time. Replacements, even when sized correctly, may not deliver power consistently due to slight variations in material and design.

Modern mainsprings can sometimes deliver too much power, especially in delicate or vintage movements, leading to accelerated wear or damage to gears and pivots. Original springs are often “seasoned,” meaning they’ve been conditioned by years of use and may be gentler on the movement. Even replacements that have the same dimensions as the original are overpowered. Recommended replacement springs might overload the movement and lead to wear issues sooner rather than later.

Laurie Penman, who authors a regular feature in Clocks Magazine, stresses the importance of considering replacement springs in the September 2024 issue, stating “it bears repeating that if you fit a spring that approximates to the original nineteenth century the movement will be overloaded”.1

Cleaning an open mainspring

If the original mainspring is functional, reusing it can save the cost of purchasing a replacement. In fact, finding an exact replacement for some older or rare clocks can be very challenging for the repairer.

That said, we certainly do not need to send more items to landfill sites. Reusing parts when possible reduces waste and the environmental impact of manufacturing new components.

Inspect the mainsprings during every servicing

Part of servicing a clock movement includes inspecting and cleaning the mainsprings. While open mainsprings are easier to inspect and work with, some repairers may be tempted to skip cleaning those encased in barrels. It’s important to learn how to open mainspring barrels for proper maintenance.

Mainspring barrel
Mainspring barrel

Over time, the mainspring(s) can accumulate old oil, dirt, rust, and debris, which can impede its smooth operation. Removing the mainspring from the barrel or open springs from a movement allows for proper cleaning and lubrication, ensuring the clock runs efficiently.

Open mainsprings that have been serviced

Removing the spring also allows you to apply fresh mainspring oil evenly along the entire length of the spring. But that is not the only reason.

When Should You Replace the Mainsprings?

Removing the mainspring allows you to thoroughly inspect it for any signs of wear, fatigue, or damage that might require replacement. If the spring is in good condition but the hook end is cracked, it can be reused by cutting the spring and fashioning a new hook end. This will make the spring slightly shorter.

However, after a thorough cleaning, the movement will run more efficiently and require less power to run through its designed cycle, be it a day or a week, two weeks, and so, there may be little to no effect from a shortened mainspring. That said, the task of repairing a mainspring is best suited for an experienced clockmaker.

The most straightforward solution for the novice is simply to replace the spring.

Although they may appear set to some, this spring is perfectly usable

As a clock repairer, I rarely replace a mainspring. Even if a mainspring appears “set,” it often still has functionality. The important step is to return the spring to the movement and test it to ensure it meets the required standard by completing its designed cycle. If there is a significant loss, a running time of 2-3 days for an 8-day clock, and if there are no other obvious issues the mainspring must be replaced.

For some, ensuring a clock runs while preserving its original parts might take priority, even if the original mainspring cannot power the clock through its designed cycle. It is therefore essential to balance preservation with functionality.

Using a spring winder while working on a spring within a barrel

By carefully evaluating the mainspring’s condition and the specific needs of the movement, you can make an informed decision that respects both the clock’s history and its mechanical performance.

  1. Clocks magazine, September edition ↩︎

The Myth of Over-Winding: Clarifying a Common Misconception

Broken mainspring for barrel

In the fascinating world of horology, many terms and expressions are often misunderstood or misused. A classic example is the frequent confusion between the words “mantel” and “mantle” to describe certain types of clocks. While “mantel” refers to a shelf over a fireplace, “mantle” is something you wear, like a cloak.

Another pervasive myth is the notion of “over-winding” a clock. How many times have you heard, “It was running fine until I over-wound it”? This phrase is commonly found on clock forums, Facebook groups, and among enthusiasts. However, attributing clock malfunctions to over-winding is a misunderstanding of how clocks operate.

American time and strike clock movement

While it is technically possible for a mainspring to be damaged by excessive tightening—winding it until it’s tight and then continuing to wind it further—this is not the primary cause of most clock failures. The real issues often stem from different sources.

Consider the spring barrel, as shown in the photo below.

When the spring is wound, it coils tightly around the winding arbor, with the other end hooked to a small stud inside the barrel. This hook can become fatigued over time due to repeated excessive winding or the riveted stud can break free, but this is not the typical cause of a clock stopping.

In American open mainspring clocks, what appears to be “over-winding” is often a result of old oil, rust, and dirt accumulating in the mainspring coil. These contaminants can cause the coil to stick and seize somewhat like the action of an adhesive, making it “seem” as though the clock is “over-wound.”

This spring is re-useable

When I receive a clock that is said to be “overwound”, I use a let-down tool to release the mainspring partially or completely, apply mainspring oil generously, and then rewind the clock. This step will help in some cases, but it’s important to note that it doesn’t replace a thorough cleaning or address other potential issues that might be causing the clock to stop.

The letdown key
The letdown key

Disassembling the movement and removing the mainspring allows for a proper inspection. Dirt and old oil can be cleaned, light rust can be removed with emery paper or steel wool, and heavy rust necessitates the replacement of the mainspring. The spring should also be checked for cracks or breaks. Often, a mainspring in good condition can be salvaged with proper care even if there are minor problems with the connecting section of the spring.

I frequently reuse mainsprings in my clock repairs, as long as they are not “set.” A mainspring is considered “set” when it has developed permanent deformations or has lost its original flexibility and strength due to repeated use or overstressing. In such cases, reusing the mainspring compromises the clock’s reliability and shortens its operational cycle.

When a mainspring is “set,” I typically replace it to ensure the clock functions optimally and to avoid potential issues. If I were operating a clock repair business, I would replace the mainsprings as a standard practice and pass the cost onto the customer.

“C” clamps used to contain the power of the mainspring

Another potential issue is the click mechanism. In some clocks, such as those made by Sessions for example, the click rivets can become fatigued and fail. Inspecting and repairing/replacing this component is a common procedure in clock servicing.

Worn click on Sessions movement

When buying a new clock, do not assume it has been recently serviced unless the seller can confirm it. If there’s no assurance of recent servicing, plan to have the movement serviced as soon as possible either by yourself or a competent professional.

Regular maintenance is crucial for any mechanical clock to ensure its longevity and proper function.

“Over-winding” is a myth that often misguides clock enthusiasts. The real causes of clock issues are typically related to dirt, old oil, or mechanical wear, not the act of winding the clock. Understanding this can help in better troubleshooting and maintaining your cherished antique or vintage clock.

Wrapping up the servicing of a Seth Thomas type 89 movement

Seth Thomas is a well-known American clock manufacturer with a long history, and they produced a variety of clock movements over the years. The Type 89 movement is one of the many clock movements produced by Seth Thomas between 1900 and 1938.

Seth Thomas mantel clock from the 1930s
Seth Thomas mantel or shelf clock

The mantel clock in question features the Type 89 movement. Acquired in the summer of 2023, this clock boasts a simple and straightforward design.

In the first part of this two-part series, I discussed the disappointments I encountered with the clock’s case.

Seth Thomas type 89 movement showing dirt and rust
Seth Thomas type 89 movement, dirty and rusty

The focus then shifted to the disassembly process and my examination of the widely-used Seth Thomas Type 89 clock movement.

My observations highlighted a replaced mainspring on the strike side, the necessity for bushing work, and indications of rust, all of which posed challenges that I committed to addressing in subsequent stages such as cleaning, bushing, oiling, and reassembly.

The focus of this blog post is the completion of servicing of this type 89 clock movement.

The front plate of a type 89 Seth Thomas movement
Front of the type 89 movement before disassembly

Cleaning of the mainsprings

There is always the temptation to do nothing with the mainsprings if they look acceptable. However, cleaning the mainsprings is an essential part of clock servicing. Uncoiling and wiping the dirt and grime from the mainsprings with a cloth is the preferred method, but cleaning them with an ultrasonic cleaner is also an option.

In Part I, I cleaned the mainsprings in my ultrasonic cleaner and provided a rationale for this decision. Before I go any further, I’d like to emphasize a crucial point regarding the cleaning of mainsprings in an ultrasonic cleaner. This practice is not recommended and should only be considered as a last resort.

While cleaning mainsprings in an ultrasonic cleaner has little impact on the surfaces or mechanism of the cleaner itself the oil removed from the mainsprings generates a black liquid that contaminates the cleaning solution, rendering it ineffective for future use.

Seth Thomas type 89 mainsprings, note the replacement spring on the right
Seth Thomas type 89 mainsprings, note the replacement spring on the right

Clamps have been applied to secure the mainsprings after oiling, and they’ve been set aside. Now, we move on to the next step: the bushing phase.

The back plate is removed on a type 89 Seth Thomas movement
Backplate removed

Bushing the movement

As the movement is fully disassembled this is the stage where bushing work can be done.
I commend individuals who choose to bush by hand, but personally, It is not for me.

Various systems exist for bushing, with KWM and Bergeon being the two most widely adopted. It’s worth noting that neither system is inherently superior to the other, as preferences tend to vary among enthusiasts. When referring to a “system,” it’s important to understand that the bushings from one system are not interchangeable with those from the other.

That said I use the Bergeon system.

Bergeon 6200 Bushing Machine
Bergeon Bushing Machine

Before bushing, I identify all the locations requiring attention and mark them with a Sharpie. There is no permanent mark as rubbing alcohol will easily remove all traces of ink.

I have an excellent assortment of bushings and have all the required ones for this project.

An assortment of Bergeon bushings, assortment #5488
An assortment of Bergeon bushings, #5488

Using cutters each hole is drilled out and chamfered, that is, removing the sharp edges to allow the pushings to be pressed in smoothly. As I insert each new bushing I test the fit by assembling the wheels to check how freely they move. This allows me to make small adjustments in the event the pivot is too tight in the bushing hole.

Cutting into the bushing hole with Bergeon bushing machine
Cutting into a brass plate

Based on my initial assessment, the bushings for both the front and back plates of the escape wheel were the most worn. The next new bushing is the fourth wheel front plate, the one adjacent to the escape wheel. After three bushings everything looks good and the wear further down the train does not look too bad. A fourth bushing for the fourth wheel should be enough.

A cutting broach is used to enlarge any holes that are a tight fit for a pivot followed by a smoothing broach. To prepare for the wheels to go back in place all bushing holes are cleaned with pegs/toothpicks.

Test fitting the time-side wheels during the bushing process, type 89 Seth Thomas movement
Test fitting the time-side wheels during the bushing process

In the photo above, the plates and gears look shinier after a session with the ultrasonic cleaner. However, it’s important to note that the main goal in clock repair isn’t to make everything as shiny as possible. The focus is on reducing wear and tear. Some dirt and grime on the plates might not come off completely during the cleaning process in every case and it is not something the clock repairer should be overly concerned with.

Back to bushing. There is a little bit of play on the second and third wheels but it is tolerable so, I think I will stop at this point.

Punching a 3.5 mm Bergeon bushing into a clock plate
Punching a bushing into the plate

Were I in the clock repair business I would bush everything on the time train, or the entire movement for that matter, but since I usually inspect movements in my collection every 2-3 years I can address any additional wear at that time.

On to the strike train. In the first article, I mentioned that there was not much wear on the strike side which might be attributable to that side not being wound as often. The only hole that must be addressed is the cam wheel bushing on the front plate. Why this bushing hole is worn much worse than the others is a bit of a mystery.

Okay, all the work is done for a total of five new Bergeon bushings. The holes have been pegged, and the movement is now ready to be reassembled.

The one hiccup encountered during the bushing process was the malfunction of my caliper tool. Fortunately, this isn’t a major problem, as all the Bergeon bushings are uniform at 3.5mm outside diameter, with inside diameters of either 1.4mm or 1.5mm so I knew what size to grab first.

Reassembly

When dealing with American 8-day time and strike movements, there are challenges in configuring the strike mechanism accurately. Occasionally, luck is on my side, and I manage to place the paddle in the deep slot, position the lever in the lowest part of the cam wheel, and align the warning wheel just right on the first attempt.

A useful tip. If the lever is in the lower part of the cam wheel and the paddle is not in the deep slot, simply move the toothed count wheel sideways so that it does not engage the pinon and reposition the wheel till the paddle finds the deep slot.

No luck setting up the strike this time! If the strike train does not lock correctly it will simply keep on running and you will know that soon enough.

The plates can be partially pried open without the risk of all the wheels and levers springing out. Repositioning the warning wheel involves moving the fly aside, carefully extracting the 4th wheel from its pivot hole, and rotating it a quarter turn or so to ensure the warning pin aligns with the stop lever.

Seth Thomas movement on the test stand
Seth Thomas movement on the test stand

A minor issue with the hammer lever surfaced as it was not aligning correctly with the strike pins on the cam wheel. No disassembly of the movement is required for this adjustment. Simply loosen the bottom two nuts by the mainsprings, and the strike hammer can be removed to straighten it. After having been bent multiple times over the years, straightening it out resolved the issue.

Next, the movement is oiled with Keystone clock pivot oil and mounted on a test stand. After a week it is running and striking as it should.

And lastly, my new caliper arrived just as I was concluding the servicing on this clock.

Addendum

To properly configure the strike side, pay attention to the positioning of the levers as pointed out by the arrows.

Seth Thomas movement
ST movement

In the above photo, the lower arrow shows the paddle in the deep slot, and the upper arrow shows the drop lever in the indent of the cam.

Seth Thomas movement
Seth Thomas movement

The upper arrow shows the position of the stop pin on the stop wheel. The lower arrow shows the locking lever.

The Inner Workings of Mechanical Clocks: How They Keep Time

Every time I glance at one of the vintage clocks in my collection, I am struck by the exceptional level of craftsmanship and marvel at how a mechanical device crafted over a century ago can still maintain precise timekeeping.

Mechanical clocks are machines designed to measure, keep, and indicate time. Mechanical clocks rely on a combination of essential components to operate accurately, including a power source, gear train, escapement mechanism, regulating device, and display indicator. Each component plays a critical role in maintaining the clock’s accuracy and precision in timekeeping.

For simplicity, our discussion will be limited to mechanical clocks driven by a pendulum.

Let’s examine each function in detail.

Power:

The power source of a mechanical clock comes from winding the spring or lifting the weight.

Clock weights

Energy is transferred from the winder’s hand to the mainspring or weight, which stores the energy. When the clock is running, the energy is gradually released through the gears through the escapement, causing them to turn and power the clock’s movement. This movement, in turn, powers the clock’s hands and other features, such as the striking gears. Essentially, the mechanical energy from the winding mechanism is converted and transferred through various parts of the clock to keep time.

Clean and restrained mainspring
Mainspring for an American time and strike clock

Gears:

Gears, which are circular components with teeth, facilitate the transfer of energy through the gear train and turn each succeeding gear. In the case of the time-side gear train, it connects to the escape wheel, which rotates at a faster speed than the main wheel because of the interplay between the gears.

Reduction gears are commonly used in the striking or chiming mechanism of the clock, which sounds the hour or quarter-hour. The striking mechanism requires a slower and more prolonged release of energy, and reduction gears help to achieve this by slowing down the rate of rotation of the striking hammers.

Fusee

In some clock designs, the gear train may also incorporate a fusee, a cone-shaped pulley with a spiral groove, which compensates for the decreasing tension of the mainspring as it unwinds. The fusee acts as a mechanical amplifier, multiplying the force of the mainspring as it unwinds and compensating for the reduction in power over time. This allows the clock to maintain accurate timekeeping even as the mainspring unwinds.

Overall, the gear train and reduction gears are essential components of a clock’s mechanism, enabling the precise transfer and conversion of energy to power its movement and features.

Escapement:

The escapement allows the power to “escape” at a controlled rate. The tick-tock sound heard from a mechanical clock is caused by the verge catching and releasing the teeth of the escape wheel, transmitting an impulse to the pendulum to keep it swinging.

Bushing installed on escape wheel arbour
Escape wheel and pallets

Regulator:

The regulator controls the speed of the clock. Pendulums with longer rods oscillate more slowly, while those with shorter rods oscillate faster.

The rate of the escapement, which controls the release of energy from the gear train, can be adjusted by altering the effective length of the pendulum, which is the oscillating component of the clock’s regulating system. This can be done by adjusting the position of the pendulum weight or changing the length of the pendulum rod. By altering the length of the pendulum, the clock can be regulated and keep more accurate time.

Indicator:

The clock hands provide a visual reference of the current time, while the chimes or alarms provide an audible signal at specific intervals, such as the top of the hour or the quarter hour.

Synergy

Thus, the concept of synergy is essential in understanding how all the individual parts of a clock work together as a cohesive system to achieve the singular purpose of timekeeping. Each component has its specific function, but they all work together in harmony to create an accurate and reliable timekeeping tool.

The large hands of a gallery or dial clock

Mechanical clocks are a testament to the brilliance of their inventors, as many of these machines still run as well today as they did over a hundred years ago. The interaction of these five elements results in a synergy that allows these machines to do one thing: tell time.

Calibrating a typical American spring-driven mechanical clock

In our quest to have our antique mechanical clocks run accurately the immediate response is to regulate the clock, but have you thought about calibrating your mechanical clock? It is not as difficult as it sounds.

This is not the same as regulating your clock. A properly regulated Anerican-made spring-driven clock will show the correct time at the beginning of the week but will run fast through the week and may gain as much as 3 or 4 minutes mid-week and lose time at the end of the week.

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

Let’s use a spring-driven mantel clock with an 8-day cycle for our example.

Mainsprings release their peak power at the beginning of their cycle. As the mainspring winds down power is gradually released until the spring unwinds completely and the clock stops.

Gilbert spring driven wall clock

On some antique clocks, one might find “stop works” (otherwise called a Geneva stop) which is a clever star-shaped brass add-on to the main wheel that reduces the full release of power initially by flattening the mainspring’s power curve over its rated cycle (8-days) and thus maintain some level of accuracy through the week.

Geneva stops as indicated by the white arrows

But most clocks I have come across don’t have this ingenious device.

Weight-driven clocks are a different kettle of fish because the release of power is constant throughout the week. Once a weight-driven clock is regulated it should not require calibration.

Gustav Becker Vienna Regulator with weights

Calibration makes the assumption that your spring-driven clock will never accurately tell the time at any one given point in its cycle and essentially means setting your clock so that it loses no more than a couple of minutes at any given time through the week.

Sessions mainsprings, one for the time train and the other for the strike train

According to the Canadian Oxford dictionary to calibrate means “to correlate readings of an instrument with a standard”. If the standard is plus or minus two minutes per week, without the use of “stops” or other means to flatten the power curve, setting the clock two minutes slow at the beginning of the week will ensure that it is never off by more than a minute or two through the week.

According to noted horologist Robert H. Croswell, “If the clock is regulated such that it has a zero net gain or loss of time from the start to the end of the week, then take ½ the maximum fast error during the week and set the clock that many minutes “slow” when the clock is wound.” If the maximum is 6 minutes, then, half would be three minutes.

One could use a complex mathematical formula to determine the precise amount of time to set the clock at the beginning of the week but setting it two minutes slow for a clock that loses 4 minutes each week should suffice for most purposes.

What is this clock thing for? #5 – the mainspring clamp

Click replaced

The only way you can safely disassemble a clock with an open mainspring is by using mainspring restraining clamps. 4 piece sets, which will accommodate various mainsprings sizes are available from all clock suppliers.

Wind the mainsprings tightly enough so that you can work the clamps around the springs. Move the rachet click aside and allow the let-down key to release the mainspring slowly into the clamp.

Mainspring contained in a clamp
Mainspring  restrained within in a clamp

With the mainspring safely clamped you can proceed with cleaning and servicing a clock movement.

A soft steel wire becomes a clamp

When a clamp may not fit or you do not have clamps, a soft steel wire will suffice.

This clamp on a time side mainspring

Round and flat mainspring clamps are available from suppliers. The above shows a flat clamp on a mainspring

Olie Baker spring winder
Applying a round mainspring clamp while using an Olie Baker spring winder

If you can afford it, a spring winder is one of several essential tools of a clockmaker.

Removing lever with helper spring
Assembling a movement with a mainspring restrained in a clamp

Safety is paramount when working with a clock.  If you are going to buy just one set, I would purchase flat clamps. They are easier to maneuver around the mainspring than a round clamp. Mainsprings are not to be fooled with. They are very powerful and all that power can cause damage not only to clock components but to your limbs as well.

My antique clock runs slow – why?

Seth Thomas column and cornice "Empire" style time and strike shelf clock

There are four general categories of clocks; quartz, electro-mechanical, electric, and mechanical. Mechanical clocks, whether they are antique or vintage are the focus of our discussion on why a clock runs slow.

We are quite accustomed to the accuracy of quartz clocks which lose or gain mere milli-seconds per week. Contrast that with an era when folks were content to accept that their mechanical clock would be a minute fast or slow through the week and it was a common practice to make small adjustments over the run cycle of a clock.

In fact, a typical American spring-driven clock in properly serviced condition may gain or lose a couple of minutes per week as a norm. Weight-driven mechanical clocks that gain or lose several seconds per week are considered to be very accurate.

That said, how many mechanical devices do you know run perfectly (relatively speaking) after 120 years.

A clock runs slow for a variety of reasons.

Let’s look at some factors and examine each one.

  • Environmental
  • Pendulum too low or too high
  • The pendulum is the incorrect weight
  • Suspension spring length is incorrect
  • The suspension spring is not attached correctly
  • Lack of lubrication
  • Gummed-up lubrication (over-oiled)
  • The balance wheel needs adjusting
  • A weak mainspring
  • Changes or alterations when servicing
  • Clock cycle time variance
  • Slipping or binding
one-weight Vienna wall clock
One-weight wall clock with large pendulum bob and rate adjustment on the bottom
Ogee clock showing replacement pendulum bob
Ogee clock showing replacement 1 oz rate adjusting pendulum bob

Environmental 

Mechanical clocks are subject to a number of environmental factors which may cause them to gain or lose speed over the course of a year. These factors include heat, cold, and humidity. Increasing the ambient temperature of a clock will slow it down from the expansion and lengthening of the pendulum unless the pendulum is a compensating type using Mercury or dissimilar metal rods. Denser air also causes the pendulum to move more slowly.

Moving a clock from sea level to a higher elevation will affect the speed of the clock.

Numbers on bob correspond with the movement
Pendulum bob with inset rate adjustment

Pendulum too low or too high: The lower the pendulum the slower the clock will run. Many pendulum clocks can be adjusted either by a set screw at the bottom of the pendulum or by an inset screw on the pendulum. In the absence of an adjustment on the pendulum, there is a regulator on the clock face. Use the small end of a double side key and insert it into the dial face of the clock to speed or slow down the clock.

Shortening the pendulum will speed up the clock. Anything that increases the length of the pendulum will reduce the rate of the pendulum and result in a clock that will run slower.

Parts of the clock related to the pendulum
Parts of the clock related to the pendulum

The pendulum is the incorrect weight: If the pendulum is too heavy it causes the centre of gravity to be too low, consequently the clock will run slower. Having the correct weight pendulum for your clock ensures smooth running.

Suspension spring length: Often, when a clock is repaired by a person who has limited knowledge of the effect a replacement spring will have on the running of a clock they will occasionally install an incorrect length or thickness of suspension spring. Choose the suspension spring that is correct for your clock.

Rate adjustment under the 12. Use the small end of the double-sided key to make the adjustment

Suspension spring not attached correctly: A suspension spring is located at the top of the pendulum rod and is the flexible part that allows the pendulum to swing. It is the connection between the top post and the pendulum leader. If it is not installed securely the pendulum may not swing at all or will wobble, robbing the movement of its energy.

Lack of lubrication: Pivot holes that have dried up means that there is no lubricating barrier between the pivots and their bearing holes although the movement may otherwise be very clean. Small drops of clock oil applied to the dry pivot holes will ensure the clock runs well and will have a long life. Without oil, the steel pivots will wear the brass pivot holes resulting in wheels that will not mesh properly eventually stopping the clock.

Note: a small drop of oil in each bushing hole is all that is required.

Gummed-up lubrication: When a clock runs slowly the first instinct is to apply more oil. Old blackened or greenish oil in the pivot holes is a sure sign the clock has been over-oiled. Although there is an almost immediate improvement in the running of the clock it will not be long-lasting. In no time at all the clock will begin to run slowly again as the new oil mixes with the dirt and grime in the old oil. When this occurs the oil becomes an abrasive paste resulting in exacerbated wear. The only solution is servicing which includes disassembly, cleaning of the movement, addressing wear issues, reassembly, and testing.

Balance wheel needs adjusting: Regulation of the escapement consists of sliding the two-small weights attached to the center of the balance wheel. Inwards for fast and outwards for slow. Hold the wheel and push the small adjustment “finger”. Moving the finger toward your right will be faster and vice versa. Moving the finger one dot represents a change of about 10 seconds per day. The movement will have a directional indicator with an”S” for slow and “F” for fast on the sides adjacent to the balance wheel.

Balance wheel escapement

A weak mainspring: Often the mainspring you will find in your antique clock is the original one(s). The steel used at the time the clock was made was generally of higher quality than the steel used today with some exceptions. By their very nature mainsprings become weak over time.

Weak mainspring are called “set” mainsprings. If “set”, your clock will not run a full cycle, 8 days for eight-day clocks, a full 30 hours for one-day clocks, or the designed cycle. When a spring-driven clock is brought in for a professional repair the mainsprings are often replaced.

Most properly serviced clocks with their original mainsprings will run their full cycle. Should your clock require a mainspring replacement a correct size quality American or German-made mainspring should provide years of reliable service.

Changes or alterations: Changing or altering the mechanism such as replacing a gear with an incorrect teeth count may speed up or slow down a clock. Although movement parts may appear to be similar, manufacturers often made small changes resulting in parts that may not be interchangeable with the exact movement over the years.

Clock cycle time variance: American spring-driven eight-day clocks will run slightly faster at the beginning of their cycle by providing most of their power and run more slowly through the week as the power of the mainspring unloads. A spring-driven clock that is one or two minutes fast at the beginning of the week is often a minute or two slower at the end of its cycle. This is considered normal and no adjustment is necessary. The power on a weight-driven clock, on the other hand, is constant and the loss or gain in time at the beginning of the cycle will be the same at the end assuming no wear issues are slowing it down.

Slipping or binding: If your clock is losing hours per day something in the mechanism is slipping or binding. If your clock is losing minutes per day after all adjustments are made, it is likely bushing wear or some other worn component is causing the problem. Clock repairers have a term called end shake. End shake allows freedom of lateral movement for each of the wheels between the movement plates. If the plates are tight and there is no end shake, too much resistance will slow a clock. It is why clock repairers always check for sufficient end-shake when servicing the wheels on a movement.

Final thoughts

Your situation may be unique and if it is not a clock issue covered by this article I suggest consulting an expert in clock repair. If you have little experience and choose to do your own work on an antique or vintage clock, the mistakes you make may be irreversible.

There is also a certain element of risk working with mechanical clocks as the power contained in the mainsprings may cause serious injury if not handled properly.

Knowing why your clock runs slowly is the first step in diagnosing the problem. Addressing the issue is the next step. Beyond that, periodic maintenance and servicing with quality parts is the key to a long life for your clock.

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