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)Comments
AnsoniaCabinet Antique12500208.330.288
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.7523.27125.3870.478
GilbertNo 8 Regulator3600601
GilbertNo 16 Regulator3600601
GilbertNo 20 Regulator3600601
IngramKitchen Clock8489.8141.500.424
IthacaNo 2 Bank405067.50.889
Killam & Co Banjo470478.40.765
Lockwood & Almquist90-Day4800800.75
Seth ThomasAdamantine9777.9162.970.368
Seth ThomasElipse8372139.530.43
Seth ThomasNo 1 Regulator4800800.75
Seth ThomasNo 2 Regulator4800800.75
Seth ThomasOffice Calendar No 25760960.625This is a beat rate of the Office Calendar No 2 reported by others
Seth ThomasOffice Calendar No 25880980.612This 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 ThomasSelf-winding No 172001200.5
Seth ThomasShips Clock180003000.2
Seth ThomasSummit9100151.670.395
VariousEnglish Dial9050150.830.398
VariousGrandfather/Tallcase clocks3600601
WaterburyRegulator No 34800800.75
WillardBanjo clock470278.40.765

 

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.

 

We had a great time at the Little Log House Antique Power Show in Hastings, MN this past weekend. Ashland Hollow Clock Repair organized a building to show clocks and watches and we joined to help promote the local chapter of the NAWCC.

 

The Little Log House Pioneer Village is a great venue with a number of historic buildings that were moved onsite, sometimes brick by brick, to be preserved and enjoyed. The Antique Power Show is a significant event with historical reenactments of pioneer life, a huge amount of working antique machinery including an antique tractor parade, and a flea market/swap meet. The food is good – some of the vendors from the Minnesota State Fair come to serve this event, and in many ways it feels like a more relaxed mini-State Fair, though not that mini – there is more than enough to do for a whole day and thousands of people attend.

 


The Machine Shed

We particularly enjoyed the machine shed. One room had antique engines – from small hit-and-miss style portable ones to larger permanent ones. One of these engines was connected to the whole shop drive shaft mounted on the ceiling.

 

This drive shaft provided power to the machines in the next room. The machines on display included a band saw, a sawmill blade grinder, a reciprocating saw, an implement grinder, an automatic forge, and several drill presses.

 

 


Saw Mill

We also enjoyed the live sawmill demonstration. The sawmill was being powered by belt drive from a tractor outside the shed.

 

The saw is a large circular saw, and logs are fed into the blade on a cable-driven carriage. Chips are removed by an auger system.

 

 


Clocks And Watches

Our contribution to the show was bringing a selection of watches to display. We brought a number of pocket watches ranging in age from 1827 to 1950. On the older end is a pair-cased verge fusee watch made in York, England (upper left in the picture). The middle of the pack included a number of railroad and non-railroad watches from 1870 – 1920, and the youngest items on display included a Hamilton 992b from 1947 and an Elgin BW Raymond from 1950. My son contributed his Elgin (center of the photo with chain) to the exhibit.

Ashland Hollow brought several dozen clocks for display, but sadly I forgot to take a picture! If you’re looking for something in particular, contact Fred to see if he may have what you’re looking for.

I hope to see you at the show next year!