The Seth Thomas Office Calendar No. 2 is a large weight driven double dial calendar clock. They were made from about 1863 – 1890 and stand 44″ tall. Time is displayed on the top 14″ dial, and the day of the week, date, and month are shown on the lower dial of the same size.

The Seth Thomas Office Calendar No. 2 is a perpetual calendar. In short, this means the clock knows how many days each month has – February has 28, December has 31, etc. This clock goes one step further – it actually compensates for leap year.

 

Calendar Mechanism Walkthrough

Seth Thomas used 3rd party calendar mechanisms in many of their clocks; the mechanism in my Office No 2 is the Mix Brothers variant which has a kidney-shaped cam driving the calendar mechanism. The Mix Brothers calendar movement was used on the early Office Calendars from 1863 to sometime in the 1870’s. After that, Seth Thomas migrated to using the Andrews mechanism which uses a snail-shaped cam.

Lifting System

The calendar mechanism is driven from the time train by a wheel that rotates once per day. This wheel drives a kidney-shaped cam that in turn raises the main lifting lever. This lever raises two rods that drive the left and right sides of the calendar mechanism.

The left rod is connected to a ratchet mechanism that drives the day of the week drum. The right rod is connected to another rachet mechanism that drives the date of the month mechanism, which in turn drives the month drum.

Day of Week

The day of week drum is relatively simple. The wheel on the right side of the drum has 14 teeth, one for each day. The wheel takes two weeks to rotate fully. The two pawls at the top of the wheel lock the wheel into position so that it only advances one day at a time. The rear pawl prevents the wheel from going forward other than when lifted by the mechanism, the front prevents the wheel from reversing.

The day wheel is driven by a ratchet mounted on the drum side of the lever connected to the main lifting arm.

Date of Month

The date hand is driven by the right lifting rod from the main lifting arm behind the time movement. The date hand shaft has 31 teeth at the back of the mechanism – one for each date of the month, and at the front of the mechanism is the ratchet mechanism that prevents the date hand from moving backwards. The 31-tooth date wheel is advanced by a ratchet pawl on the back side of the next lever in the lifting linkage in a similar manner to the day of week wheel,  and the date wheel is arrested after advancing one day by the stopping lever coming from the right side of the mechanism.

Month

The month drum is driven off the date wheel shaft by a lifting cam that raises the month lifting lever. The month lifting lever drives a ratchet that advances the month wheel. The month drum is regulated by two pawls in the same manner used on the day of the week drum.

 

Perpetual Calendar Components

The perpetual calendar mechanism needs to advance the movement based on the variable number of days in each month. To do this, it needs to know how many days a given month has, and it then needs a mechanism to move forward the appropriate number of days – skipping the 31st for 30 day months like June, skipping the 29th, 30th, and 31st for a normal February, and skipping the 30th and 31st for a leap year February.

There are three components to the Mix Brothers perpetual calendar mechanism, the 30/31 cam plate, the 28/29 cam plate, and the date wheel itself, plus the perpetual calendar lifting lever.

Date Wheel

The date wheel has 31 teeth. 28 of these are identical, and the other three are shorter – decreasing in height with the 29th tooth being slightly shorter, the 30th tooth shorter yet, and the 31st tooth being the shortest.

30/31 Day Cam Wheel

On the left side of the month drum is a thin brass cam disk with two levels. The lower position correlates with 31-day months and the upper position correlates with 30-day months. Note that the cam is read at the top of the drum, but the month is actually read on the front of the drum, so the cam positions are 90˚ off from the label positions.

28/29 Day February Wheel

Slightly left of the 30/31 day wheel is the February wheel. This wheel has four teeth – three are shorter, and one is slightly longer. The longer tooth is marked with two dots – this is the February 29th Leap Year tooth.

Perpetual Calendar Lifting Lever

The perpetual calendar lifting lever reads the position of the 30/31 day cam wheel and the 28/29 day February wheel. The position of these two wheels determines how far the day wheel stop lever advances.

 

Perpetual Calendar Operation

If the calendar is on a 31-day month, the 30/31 day cam wheel is in its low position and the February wheel is not engaged. The date wheel pawl drops all the way down to the bottom of the teeth of the date wheel and the calendar advances only one day for every day of the month, stopping at the 28th, 29th, 30th, and 31st days.

If the calendar is on a 30-day month, the 30/31 day cam wheel is lifted slightly. This causes the date wheel pawl to drop slightly less than all the way, and the pawl will stop the calendar normally on days 1-30 of the month, however the 31st tooth of the date wheel will pass under the date wheel pawl and skip directly from the 30th to the 1st.

If the calendar is on a Leap Year February, the lifting cam is raised slightly higher than the 30 day position and the calendar operates normally on days 1-29, but this lifting position is high enough so that both the 30th and 31st teeth pass under the date wheel pawl, and the clock jumps from the 29th to the 1st.

If the calendar is on a non-Leap Year February, the lifting cam is raised to it’s highest resting position and the 29th, 30th, and 31st teeth all pass beneath the date wheel pawl and the mechanism will advance all the way from the 28th to the 1st.

Adjusting the Calendar Mechanism

The principal means of adjusting the calendar mechanism is by lengthening or shortening the lifting rods by rotating the adjustment nut. Figuring out how the clock should be set requires removing both the time and calendar dials.

IMPORTANT NOTE: The calendar mechanism is a low speed device. It takes 18 hours to build up energy to fire, and it takes about 3 hours to actually fire the mechanism. When manually advancing the calendar mechanism, do it slowly or else very wrong things will happen. Lift the lever slowly, and lower it slowly to mimic the actual operation of the calendar mechanism.

IMPORTANT NOTE 2: The calendar mechanism is not intended to be lubricated. Do not oil it. Since the mechanism only activates once per day rather than tens of thousands of times per day like the time movement does, no lubrication is required.

IMPORTANT NOTE 3: The paper on the day of week and month drums are very fragile. Do not touch it. Touch the sides of the drums instead.

I have also done a video walkthrough of this content that may be helpful. This article goes into more depth, but seeing the mechanism in video may increase your understanding.

Step 1 – Remove the hands and dials

Carefully note the position of the calendar date hand and the time hands. Remove both the time and calendar dials. Reinstall the calendar date hand and the two time hands in their positions.

Step 2 – Understand how to adjust the lifting linkages

Both the day of week and date/month lifting linkages use eccentric nuts for adjustment. These are held in place by a locking nut underneath the eccentric nut that is tightened against the eccentric nut to prevent the eccentric nut from turning when you don’t want it to.

To adjust the length, loosen the locking nut and spin it down the lower shaft slightly. Then you can carefully rotate the eccentric nut to raise or lower the linkage. Turn the eccentric nut clockwise to shorten the linkage (causes the calendar levers to be pulled farther up), or counter-clockwise to lengthen the linkage (causes the calendar levers to be pulled less).

After making the adjustment, tighten the locking nut against the eccentric nut.

Step 3 – Make sure all gravity levers are in place.

The calendar mechanism needs gravity to be pointing down to operate. The clock will need to be standing for adjustment and a number of levers need to be flipped down in their operational position for the mechanism to work correctly.

There are two levers on the right side of the day of week drum, one in the front and center of the mechanism near the date hand, and two on the right side of the month drum that may become stuck after laying the clock down and must be flipped back into position.

Step 4 – Establish the Maximum Lifting Height of the Main Lifting Lever

Before attempting to adjust the calendar lifting levers, it is important to know how high the movement lifts the main lifting lever. On the left side of the time movement where the main lifting lever passes into the compartment with the movement, a metal plate defines the travel path and maximum height of the main lifting lever. This isn’t necessarily how high the time movement lifts the levers; it is a mechanical maximum for the clock.

To determine how high the calendar mechanism actually lifts the main lifting lever, wind the time movement forward until the kidney-shaped cam lifts the main lifting lever to its highest point. Unlike some movements where running the movement backwards can damage things, it should be OK to run this backwards a bit as the kidney cam doesn’t have a sharp drop off.

When the main lifting lever is in its highest position, note the position of the main lifting lever in the metal slot left of the time movement. Use a piece of tape or some other means of marking it. This is our lifting reference. Now wind the clock ahead to about 6:00AM or so – the position where the lifting arm is at the lowest point on the kidney cam (this may happen at a different time

Step 5 – Day of Week Adjustment

The left lifting rod powers the day of week drum. Slowly lift the main lifting lever to the position you marked in step 3 and observe the wheel and ratchet mechanism to the right of the day of week drum. The ratchet mechanism should advance with a faint click sound. If you do not see the ratchet advancing, you probably need to shorten the lifting linkage (see Step 2).

Note also the position of the pin that raises the rear locking pawl. If the lifting rod causes the  pin to bind against the pawl, your linkage is set too short and should be lengthened.

Step 6 – Month Drum Adjustment

The paper with months printed on it needs to be correctly oriented to the 30/31 day cam disk. Because the cam disk is read at the top of the drum but the month printing is read from the front portion of the drum, the high cam positions do not line up with 30 day months. Instead, the month roll needs to be 90˚ ahead of the cam positions.

If your clock has original paper, this should be already correct, but if your clock has replacement paper, you may need to check this.  The easiest way to align the paper on the drum is to look for the longest distance around the cam drum between 30-day bumps. The bump before the long low section should correlate to August, and the bump after the low section should correlate to January.

Step 7 – February Wheel Adjustment

The February wheel is driven off the Month drum with a couple gears and a friction clutch. When the month drum shows February, one of the teeth of the February wheel needs to be under the cam following lever. Note in the picture above the February disk is out of alignment – February is to the front of the drum, but the February tooth is not under the cam following lever.

You can advance the month drum for testing by simultaneously lifting the cam following lever and the month advancing lever (the one that rides on the snail cam on the date hand shaft). It will be difficult to do fine testing this way as the end of the month day skipping mechanism is sensitive to how high the cam following lever is lifted, but you can advance this way to get close and then fire the calendar mechanism one day at a time by lifting the main lifting lever at the top of the clock by the time movement.

If the February tooth is not under the cam following lever when the drum displays February, you can carefully hold the edges of the month drum (don’t touch the paper!) and turn the February wheel with your fingers until the tooth is in position.

Step 8 – Day Skipping Mechanism Adjustment

The number of days to be skipped at the end of short months is determined by the cam following lever resting above the length of one or more of the shorter than normal date teeth. The cam following lever is directly connected to the date of month stopping pawl.

Make sure the date hand is on the shaft correctly – there are four potential positions the square hole in the hand can fit on the shaft. The correct one is where the hand points approximately toward the short teeth of the date wheel.

Set the month drum to a 31-day month. You can rotate the month drum if you lift both the cam following lever and the month advancing lever (the one that rides on the snail cam on the date hand shaft). Verify that the date of month stopping pawl goes to the bottom of the teeth on date wheel. Look at the 30/31 day cam disk on the left side of the month drum to make sure that the cam following lever is touching the cam disk.

If this needs adjustment, the best way to do it is to torsionally bend the cam following lever/date wheel stopping pawl slightly, which will adjust the relative position of the date wheel stopping pawl and the cam follower.

Carefully advance the calendar movement by lifting the main lifting lever (top of the clock by the time movement) to the position you marked to verify that the date wheel ratchet engages and the date wheel advances. If the ratchet doesn’t engage, you need to shorten the linkage (see Step 2).

Set the month drum to a 30-day month and observe the position of the date wheel stopping pawl. It should be raised slightly off the gullet since the cam following lever is now resting on the raised cam position of the 30/31 day cam disk.

Carefully advance the calendar movement by lifting the main lifting lever (top of the clock by the time movement) to the position you marked until you reach the end of the month. Go slow and verify that the shortest 31st tooth passes under the date wheel stopping pawl but the pawl reaches low enough to stop the 30th tooth. Make small torsional adjustments to the cam following lever if necessary.

Repeat this process for the 29 and 28 day months. The tooth with the two dots punched in it on the February wheel is the leap year tooth. Test this as well as a regular 28-day February.

If the date wheel doesn’t skip all the way from the 28th to the 1st, this could be because of a date wheel stopping pawl depth issue, or it could be that the lifting linkage is too short and the date lever is not being allowed to drop low enough to skip enough days. Lengthen the linkage following the procedure in Step 2.

Step 9 – Setting the calendar and reassembly

I recommend this order for setting and reassembly:

  • If possible, locate the clock to where it is permanently going to live.
  • Figure out leap year (see below)
  • Quickly advance the month wheel so that you are in the correct year relative to leap year but about 1 1/2 months behind today’s date
  • Put the calendar dial back on and reinstall the date hand
  • Raise the main lifting lever carefully to the marked position and lower it repeatedly to advance the mechanism one day at a time until the calendar is one day behind today’s date
  • Set the day of week drum to match the date hand by lifting and releasing the left lifting linkage to advance the day drum.
  • Bring the calendar mechanism forward to today by winding the time movement through a cycle, stopping wen the kidney cam is at its lowest point.
  • Reinstall the time dial and position the hands at 6:00 AM, roughly corresponding with the correct position of the kidney cam
  • Set the time forward to the correct time.

If you have followed this entire guide, you should be familiar with how to quickly advance the month drum by lifting the month advance lever and the cam following/date stopping lever and then turning the month drum. Note that in normal operation the month drum rotates upward from the perspective of the viewing window. The February wheel rotates downward in operation, as it is geared off the month drum.

To set the clock correctly for leap year, observe the tooth of the February wheel that is shorter than the other three and marked with two dots. This article was written in July 2020, with 2020 being a leap year. Setting the clock correctly for July 2020 would have the marked February tooth at about the 1:30 position when looking at the side of the February wheel – the leap year tooth should have just passed the cam reading position at the top of the wheel, and then come forward slightly as the calendar is advanced from February until July. For July of 2021, the month drum would need to be rotated until the leap year tooth is at about the 4:30 position, etc.

Note: The easiest positions of the kidney cam to reference are when the main lifting lever is at its maximum and minimum positions. The maximum position should correspond roughly with midnight, which means the lowest position corresponds at about 6:00AM. As the calendar mechanism fires gradually on the falling stroke of the main lifting arm, that means the date change happens somewhere around maybe 3:00AM. I find this is acceptable for my taste, but if you want the date change to happen closer to midnight, you can rotate the hour hand backward a couple of hours so the maximum position of the lifting lever happens at maybe 10:00PM, and the minimum would therefore be about 4:00AM.

Also note that the calendar mechanism can’t be manually advanced when the time movement is high in its lifting cycle. If your clock stops or you need to make an adjustment for some other reason, it needs to be done in the morning or perhaps early afternoon – especially if you are in the month of February where the calendar mechanism needs a long stroke to skip days. Adjusting  the calendar mechanism to fire closer to midnight may make your adjustment window shorter.

 

If you’ve made it this far, congratulations! Hopefully you have a working calendar mechanism. If you’re still having trouble with something, take your time and narrow down the problem and observe the mechanism carefully. Look for bent stuff, overly loose things, etc. You can also compare your clock mechanism to mine in the walkthrough video I did. Good luck!

 


Most of my repair work has been on smaller pieces, but I’ve done a few full-sized clocks lately, and have needed something more convenient to rig and test movements in process. Previously I set them back up in the case, which creates challenges accessing the back of the movement.

I got some ideas from looking at other commercially available stands and then hit the scrap bin.  These aren’t rocket science, and I have a substantial pile of odds and ends from previous projects to make use of. We’re still under Coronavirus lockdown, so I wanted to see how little extra I had to procure to make this happen.

The frame is pretty simple –  2 x 4 verticals and 1/2″ plywood cross members on the top and bottom. The width of the stand is pretty arbitrary – I settled on 20″ wide which should cover pretty much everything. The depth is more critical – it needs to be narrow enough to not get in the way of the hands in front and the pendulum in back. I cut down the sides of the 2 x 4 verticals to 2″, giving a 2″ gap between the cross members and about 3″ total depth.

I cut the legs out on my CNC router and added a couple of leveling feet.

I have been learning many things in my horological pursuits these last few years. I’m not new to building things, and I’m blessed to have a fairly well-equipped, if small, shop. One thing I wasn’t expecting to learn was to navigate the challenge of having good mess-free photography of shop projects in a working shop that is, well, a bit messy. I don’t think my shop is any messier than the typical shop, but the normal workings of making things – tools and project bits – tend to stay out on surfaces while the project is underway. This isn’t a huge problem for pictures of small items – it’s easy to frame the camera shot around the sawdust or tools, but larger projects like the stand require a shot with a wider field of view, which in the case of the center photo below, includes the open door on one of my benches revealing my high-tech cardboard box holding my shop rags. Conveniently cropped out of the frame on top of the bench is the half-reassembled remote control car I was epoxying back together for my son.

While the basic stand is straightforward,  the movement mount took a little more thought. It needs to be able to accommodate a wide range of sizes. Back to the CNC router, I cut a couple dog bones that can slide to handle whatever size movement I’m working on.

I made a couple long J bolts by threading a piece of 3/16″ zinc plated steel rod. Please excuse the crudity of the J bend – I don’t own a metal bending jig and made them with a vise and a couple pairs of pliers. I threaded the rod by putting the rod in a drill chuck in my mill and holding the thread die. The machine did the turning, I just held on.

The J hooks attach to the stand dog bones with a pair of angle pieces. I milled a slot in the top piece to allow for some positional adjustment, as some movement pillars have decoration or other obstructions that wouldn’t be able to be worked around with a straight up and down clamp arrangement.

The rods are long enough so the clamps can be tightened at the bottom of the dog bones which is easier to access than trying to reach between the stand cross members. 

I left the dog bones a little bit taller than they needed to be to clear the cross members. My original plan was to attach T nuts to the bottoms of the dog bones where hand screws would come up through the bottom leg of the dog bone, through the T nut, and then press on the cross member to clamp it in place. I may still do that eventually, but due to the magic of tight-tolerance machines (CNC routers are amazing), the dog bones have almost the perfect amount of friction against the cross members that they are plenty secure.

On the stand is a tall case movement from the first half of the 18th century – possibly 1725 or so. The open design of the stand allows the free end of the weight cord to be moved around for clearance. 

It’s a bit hard to tell from the picture, but the weight cords on this movement come off the left side of both the time and strike winding drums. The time drum (right side of movement) works out well with the free end of the weight cord to the right of the movement, and the time weight hangs almost directly below the time drum. Since the strike drum (left side of movement) winds in the same direction and therefore the cord comes off the same left side of the drum as the time side, the strike weight actually runs to the left of the movement drum, and the free end of the strike cord is a few inches on the left side of the movement. For clearance, I actually rotated one of the dog bones so the metal brackets wouldn’t be in the weight path.

The free ends of the weight cords were tied around a couple dowels. This movement mounts to a seat board and the weight holes are in the seat board. This stand should accommodate putting the seat board on with the movement, but I wanted to get a bit more clearance on the movement, and so improvised a bit. The thickness of the movement stand was calculated so the pendulum is outside the stand to the back, the weights fall through the middle of the stand, and the hands can rotate unobstructed in front of the stand.

This is an interesting and very old movement. In addition to the usual counting of the hours on the bell, this clock strikes the half hour as well. The date is shown through an aperture on the dial, driven by the gear at the bottom front of the movement with a metal flag sticking out. More on this fascinating clock soon!

 

Clocks are most useful when they keep accurate time. While very few mechanical clocks are as accurate as modern quartz movements and certainly will never match the absolute accuracy of your cell phone or computer’s USNO Master Clock-synched time, even fairly low-grade mechanical clocks are more than good enough for regular household use if you take a little time to adjust them.  Check out this article for basic care and operation of your clock.

The rate of a clock is determined mostly by the length of its pendulum.  Several other factors affect the timing of a clock to a smaller degree including the power curve of the clock’s mainspring (fully-wound springs are much stronger than nearly wound-down springs) and environmental factors like temperature and humidity.

It’s relatively straightforward to adjust a clock to correct rate keeping if you have a reference like a cell phone clock to compare against, however this can be very time consuming – especially if you are setting up a new clock that hasn’t been run in a while. You will have to watch the clock over days or weeks to fine-tune its rate. Technology has come to the rescue! The Adams Brown TimeTrax 185 timer is a relatively low cost device that listens to the escapement of the clock and reads the clock’s beat rate on a display. With nearly immediate feedback, you can make repeated rate adjustments and see their effect in minutes rather than days.

How it Works

 

Electronic timing machines like the TimeTrax or the more expensive but more sophisticated Microset use a piezo electric microphone very similar to a guitar pickup to detect the tick/tock of the escapement. The time between the ticks is counted against an internal quartz oscillator and the resulting BPH – beats per hour – is displayed on the screen.

Knowing the beat rate your clock is currently running at is only half the battle. What rate should it run at? That depends on the design of the clock. Large clocks like tall case/grandfather clocks often run at 3600 BPH which correlates to one tick per second. Smaller clocks can’t have a meter-long pendulum and therefore are geared to run at a faster beat rate. This article will help you determine the correct beat rate for your clock.

Setup

 

The TimeTrax’s pickup needs to be clamped onto something metal attached to the movement. For clocks without a center second hand, a winding arbor is generally the easiest place. For clocks with a center second hand, a winding arbor may still be the best place if the second hand is removable. If the center second hand is integral to the operation of the clock as it is on some pinwheel regulators, you will need to find something else to clamp to – a movement post or possibly the dial pan (as an alternative, the Microset timer offers an optical sensor that can be set behind the pendulum).

Using the TimeTrax

 

Once you’ve successfully attached the sensor, turn the TimeTrax on. The TimeTrax includes a beat amplifier that amplifies the sound of the ticks which can be helpful in adjusting the clock to be in beat, but for timing, move the switch to the far right position. After a moment, the device should start counting beats. The red light on the right side of the unit should be flashing with each tick. If the light does not light consistently for each tick or if the light blinks rapidly, the sensitivity needs to be adjusted. Increase sensitivity by turning the gain knob up if the sensor is missing ticks, or turn the gain knob down if the sensor is registering noise as ticks. The sensor is very sensitive to mechanical vibration. Set the TimeTrax down on a stable surface and try not to disturb the sensor cable during measurement.

 

Hit the Beats/Cycle plus key several times to increase the averaging to around 10 beats. The BPH reading should stabilize significantly. 

There is a trade off with averaging. A small sample size means the display updates frequently, however the reading jumps around. A larger sample size means the display more truly reflects the rate of the clock, however this significantly slows the display update rate as the TimeTrax only updates the display twice per sample set. At high sample rates, this means it may take you a minute to get a new reading.

If your clock is running significantly fast or slow, I find that an averaging setting around 10 to 16 beats produces reasonable results with fairly frequent display updates. After I make a couple rounds of pendulum adjustment and get the rate closer to the target, I increase the sample size to around 30 to continue to fine tune.

If you know how many teeth your escape wheel has, setting the sample size to twice the number of teeth on the escape wheel (each tooth is touched twice per revolution – one tick and one tock) will give you the best balance of accuracy and fast display uptime. A sample size different than twice the number of escape wheel teeth will double-count or under-count errors in the escape wheel, whereas a sample size of twice the number of teeth of the escape wheel will correctly average the whole wheel. Many escape wheels turn once per minute – typically larger clocks. For these clocks the number of teeth on the escape wheel is 1/2 of the BPM rate of the clock. For example, a 4800 BPH/80 BPM clock will normally have a 40 tooth escape wheel, so a setting of 80 beats/cycle fully represents the escape wheel. That’s a good place to start, but your clock may be different. Most smaller clocks with beat rates higher than 80 BPM perform more than one rotation per minute, so the above rule doesn’t apply.

Final Rate Adjustment

 

Getting your clock to show its rated BPM on the TimeTrax isn’t quite the whole story. The TimeTrax has a resolution of one beat. That gets you to 99.99% of the correct rate, however the TimeTrax will not tell you if your clock is running at 3600.4 BPM or 3599.5 BPM. Over the course of a week this can accumulate to an error of more than 2 minutes.

There is a second factor that can be significant- the state of wind of your clock when you timed it. While weight-driven clocks always have a constant force and therefore a constant rate as the clock winds down, spring-driven clocks run fast when first wound and gradually slow down near the end of their wind. This error can be a couple of minutes as well. The TimeTrax will get you close, but you will need to fine-tune your clock’s rate over a few weeks by comparing it to an accurate reference like your cell phone clock.

 


 

Balance Function

 

The TimeTrax has a secondary function to help put the clock in beat. To access the balance function, turn the timer on, wait a second for it to initialize, and then press the minus button until the display shows “bal” to indicate it is in balance mode.  

 

The reading will change with every tick of the clock. A perfectly in-beat clock with a perfect escape wheel will display zero for both the tick and the tock. This is not a realistic situation, as every movement has imperfections causing slight errors. A clock that is reasonably in beat will have numbers in the range of +/- 40 or less. If you’re seeing larger numbers, then your clock is not in beat.

Some clocks have imperfections in their escape wheel such that the clock sounds in beat some of the time and out of beat some of the time. Correcting this requires disassembling the clock and working on the escape wheel – either straightening the arbor or straightening the teeth of the escape wheel.

 


 

Putting Your Clock In Beat

 

A clock that is “in beat” will have evenly-spaced ticks and tocks. Clocks that are significantly out of beat will have a galloping sound. Correcting this depends on the type of clock you have.

The first place to start is to make sure your clock is level. Some wall clocks have beat indicators – a scale at the bottom of the pendulum swing. Tilt your clock until the pendulum (stop the clock) point to the center mark of the scale. For mantle or shelf clocks, you may need to shim one side to make the clock level.

If you are lucky, making the clock level will correct the beat issue, however sometimes further adjustment is necessary. Some clocks such as Vienna Regulators have an adjustment near the top of the pendulum – turn the screw to move the pendulum bob relative to the upper pendulum suspension. Make small adjustments and see if the clock is improving. If it is getting worse, turn the nut in the opposite direction.

Some clocks have a verge that is friction-fit onto the shaft so pulling the pendulum slightly farther than its normal travel in the direction of the short tick can help correct the issue. On other clocks, the crutch wire that connects the verge to the pendulum rod needs to be slightly bent. This may require partial disassembly of your clock and is best done by someone with some experience.

If your clock is slightly out of beat, adjusting the clock’s orientation so it is in beat but not level may be a reasonable compromise and won’t harm the clock.  On some clocks that may have lived a bit of a hard life, it might be hard to judge which of the non-parallel sides to use as your level reference anyway.

 

Rate calculation

The rate of a clock is determined by two things – the length of the pendulum and the total gear ratio of the time train of the clock. The length of the pendulum determines its natural oscillation rate, and it requires a fairly significant force to overcome its natural rate, which makes them ideal for regulating clocks. The gear train determines how many ticks are required to move the clock hands a certain distance.  While length of the pendulum and gear train are related, they are separate factors. The pendulum’s rate is determined by the laws of physics, while the gear train translates that into the human construct of the minute hand going around once per hour. 

Knowing how to regulate your clock requires either empirical testing over a period of time – comparing your clock to an accurate time source and making corrections, or using a timing device, which requires knowing the target beat rate for the clock.

If you have access to the movement and a careful eye, you can count the teeth in the time train and calculate the correct beat rate for your clock. This page includes instructions and an online calculator if you wish to try this method.

The table below is a list of rates of some clocks expressed in beats per hour (BPH) and beats per minute (BPM). This is far from an exhaustive list as there are a large number of different BPH combinations used over the years. Others have published much longer listsof clock BPH rates.

It is theoretically possible to work the other direction – to start with the length of the pendulum and calculate the BPH rate it would need to swing at to keep time, however in practice this is difficult, as the critical dimension is from the top of the suspension spring to the center of mass of the pendulum. Measuring the center of mass of a pendulum is difficult as it depends on the type and design of the pendulum. For lyre pendulums, the center of mass is above the center of the bob. For stick pendulums, the center of mass is usually slightly below the center of mass.

This is a work in progress and the list will grow over time. Please Contact Us if you have any beat rates to add to the list.

Clock Beat Rates

Clock ManufacturerClock ModelBeats Per Hour (BPH)Beats Per Minute (BPM)Tick Time (Seconds)Escape Wheel TeethComments
AnsoniaCabinet Antique12500208.330.28830
AnsoniaPrompt4440740.811
AnsoniaSymbol Crystal Regulator9068.6151.140.397
E HowardNo 70 Regulator5084.784.7450.708
EN WelchPatti No 2 (Baby Patti)10495.6174.9270.343
EN WelchPatti V.P.7523.27125.3870.47832
GilbertNo 8 Regulator360060130
GilbertNo 16 Regulator360060130
GilbertNo 20 Regulator360060130
IngramKitchen Clock8489.8141.500.424
IthacaNo 2 Bank405067.50.88930
Killam & Co Banjo470478.40.765
LeCoultreAtmos120230
Lockwood & Almquist90-Day4800800.7540
National Time RecorderTime Clock577396.220624
SessionsStore Regulator552592.0830.65234This is the box version with two square pieces of glass on the front. Clocks often advertised for Calumet baking powder
Seth ThomasAdamantine9777.9162.970.368
Seth ThomasElipse8372139.530.43
Seth ThomasNo 1 Regulator4800800.7540
Seth ThomasNo 2 Regulator4800800.7540
Seth ThomasOffice Calendar No 25760960.625This is a beat rate of the Office Calendar No 2 reported by others
Seth ThomasOffice Calendar No 25880980.61242This is the beat rate of my Office No 2. Apparently a second movement was also used with a slightly different beat rate.
Seth ThomasOffice Calendar No 68372139.530.43
Seth ThomasOffice No 11 30-day64
Seth ThomasSelf-winding No 172001200.560
Seth ThomasShips Clock180003000.2
Seth ThomasSummit9100151.670.395
VariousEnglish Dial9050150.830.398
VariousGrandfather/Tallcase clocks360060130
WaterburyEaton552592.0830.65234
WaterburyLibrary36
WaterburyNo 8 mini school house8181.55136.360.4432
WaterburyRegulator No 34800800.7540
WaterburySchool House, "Siam"6825113.750.527428 day time/strike, 12" dial
WillardBanjo clock470478.40.765

 

Clocks are most useful when they keep accurate time. While very few mechanical clocks are as accurate as modern quartz movements and no mechanical clock will ever match the absolute accuracy of your cell phone or computer’s US Naval Observatory Master Clock-synched time, even fairly low-grade mechanical clocks are more than good enough for regular household use if you take a little time to adjust them.

 

The rate of a clock is determined mostly by the length of its pendulum.  Several other factors affect the timing of a clock to a smaller degree including the power curve of the clock’s mainspring (fully-wound springs are much stronger than nearly wound-down springs) and environmental factors like temperature and humidity.


The Impressive Escapement

I’ve been fascinated by mechanical timekeeping devices my whole life. Though my career is in Information Technology and I spend 40 hours a week on the cutting (and sometimes bleeding) edge of technology, there is something I find impressive about a relatively simple, hundreds of years old mechanical device.

 

Most clocks run 8 days on a wind and were intended to be wound weekly. A ubiquitous “kitchen clock” has a beat rate around 9300 beats per hour, which multiplied by 168 hours in a week, means the clock ticks 1,562,400 times per week. With a pendulum swing of around an inch, that means the pendulum runs a marathon – 26 miles – each week!

 

Mechanical clocks are also incredibly energy-efficient. Our example kitchen clock’s mainspring drives a gear ratio of nearly 3000:1 with a force of only a couple foot-pounds of energy.


Reasonable Expectations

Because of the sheer number of ticks a clock must make over the course of a week and the sensitivity of the mechanism, some errors are inevitable. A clock that gains or loses one minute per week – something that should be attainable by pretty much any antique clock if it’s in good condition – is 99.99% accurate. Weight-driven clocks often do even better than this as their driving force is constant, while spring-driven clocks tend to run a bit fast at the beginning of the week when the spring is strongest and then slow down slightly later in the week.

 

I true up my clocks when I wind them. The clock on your cell phone is a great tool for this, as its clock is always perfectly correct since it is synchronized with international time standards. You can carry around this perfectly accurate time reference as you wind your clocks and easily make slight time adjustments. Your phone clock will also reveal any clocks that are significantly out of whack.


Setting The Time

Most clocks are adjusted by carefully moving the minute hand. There are a few things to watch out for.

 

Advancing The Clock

Time-only clocks can usually be adjusted either forward or backward, and as long as you are gentle, you are unlikely to cause any harm. Clocks that chime or strike require more care. If you need to set the clock ahead, you may do that slowly as long as you stop to allow the striking or chiming sequence to fully complete before you move the hand.

 

Setting The Clock Back

Once again, time-only clocks can be adjusted forward or backward. Setting a chiming or striking clock backward requires extra care, as the chiming or striking mechanisms interact with the time train and can be damaged if adjusted incorrectly.

 

The safest way to set a chiming or striking clock backward is to stop the pendulum and wait until time catches up with the clock’s setting.

 

 With care, you can in some circumstances set a chiming or striking clock back. As a general rule, you can set a clock a few minutes backwards if it’s in the first quarter hour – between 12:00 and 3:00, or the third quarter hour – between 6:00 and 9:00.  These are the periods where the chiming or striking sequence has finished and some motion is possible. Do not try to move the minute hand backward across the 12, 3, 6, or 9 as you will likely damage something. If you feel resistance, then stop moving the hands! Stop the pendulum and restart it when time catches up with what the clock displays.


Adjusting The Rate Of The Clock

 
If my clocks are running within 2 minutes per week of the correct time, I will normally just move the hands to the correct time and not try to do further regulation, as often times due to changes in temperature or humidity, the clock will run at a slightly different rate the next week, and I may end up chasing my tail. If a clock is consistently running fast or slow, then I will try to adjust the rate of the clock.

The rate of a clock is usually adjusted in one of several ways – either by a nut mounted near the bottom of the pendulum, a small square shaft through the dial adjusted with a small key, or a lever on the rear of the clock. Adjustments that make the pendulum shorter cause the clock to run faster, and adjustments that make the pendulum longer cause the clock to run slower. 

 

Small changes in pendulum length can make big changes in timekeeping. For clocks with adjustable pendulum bobs, a quarter-turn is a good starting point for an error of a couple minutes per week. Through-dial adjustment shafts are similar – start with 1/4 turn or so. For clocks with a lever adjustment, make a small change of only a few degrees at a time.

 

I find that I adjust the rate of my clocks mostly in the spring and in the fall, when seasonal temperature and humidity adjustments are greatest.


Winding Schedule

Mechanical clocks require maintenance – at a minimum they need to be regularly wound. Some clocks need to be wound every day. It requires dedication to use a 30-hour clock regularly, but if you’re willing to put the time in to wind every day, go for it. Most clocks run for 8 days on a wind (assuming they are in reasonable operating condition – a clock that runs less than a week needs to be serviced), and they were intended to be wound weekly. Choose a day and time when you will normally be home to wind your clocks, and add it to the routine. I wind my clocks Sunday evenings while I wait for my children to get ready for bed. This works for me logistically as well as mentally – winding my clocks becomes part of my routine to get ready for the week.

 

I have a couple clocks that will run longer than a week, but I still wind them weekly so I don’t forget. I find it’s harder to manage a 30-day wind schedule than a 7-day schedule.


Service and Repair

Antique clocks are mechanical devices and, like your car, need periodic maintenance. With modern high-tech oils, clocks should be able to run for 5-10 years after being serviced. If you purchased a clock with an unknown service history or if it’s been more than 10 years since you’ve had your clock serviced, it’s time to schedule an appointment with your favorite clock repair person. Clocks that are overdue for service will likely be poor timekeepers and are at risk of damage as they are wearing at an accelerated rate.

 

A full service will include taking the movement completely apart, thoroughly cleaning it, addressing worn or broken items, and then reassembling and testing. This is a time-consuming process, and therefore the cost can be significant depending on what’s needed. With more common clocks that are purchased inexpensively, the service cost can equal or even exceed what you paid for the clock. This seems to be a common conundrum at the moment as clock prices are severely depressed right now. It’s up to you to decide if the cost is worthwhile, but I would suggest that you not look at this through the eyes of an accountant; rather look at this as an opportunity to restore a beautiful object that you purchased at a significant discount.

 

Once you have a clock fully serviced including taking care of all of the worn or broken items from decades of neglect, which is the normal state for antique clocks, future maintenance will be less expensive as all that will be required is cleaning and oiling.


Is It Worth It?

Many people don’t think the effort and cost of maintaining an antique clock is worth the work, but if you’ve read this far, that’s probably not you. With a bit of care and a few dollars a year saved for an overhaul every decade, antique clocks can bring interest to your home and satisfaction of maintaining a piece of history.