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!

 

I have been working on a very old clock – an English tall case clock from somewhere around 1725. This clock was last serviced about ten years ago by a respected repairer. I went through the movement doing the usual pivot polishing/bushing work. After reassembly, the strike train had a couple issues, one of which is wear on the gathering pallet.

The gathering pallet is sort of like a one tooth gear that advances the strike rack so the clock stops striking after the right number of strikes. The gathering pallet has two components – the tooth that advances the rack, and the flag on the other end that contacts the stop pin to stop striking.

When the clock was made in 1725, the industrial revolution was in progress, but early on. The gears were probably machine-made, but the clock plates and other components were largely handmade, including our gathering pallet. It’s a pretty complicated part including a square hole, and a moderately tight tolerance on the other dimensions. I suspect it probably took the clock maker several hours. If I had to make one from scratch, it might take me an entire day, and that’s assuming I didn’t screw something up and had to start over. For the sake of maintaining originality and also to avoid exposing my marginal craftsmanship, I wanted to see if I could repair the wear rather than trying to replace the part.

The wear on the gathering pallet is on the tooth that advances the rack. It works marginally, but some of the time the tooth doesn’t quite engage enough with the rack to advance the rack, meaning the clock may strike too many times. The solution to this is to fill in the missing metal somehow.

There are several ways to potentially do this – silver soldering, or perhaps some kind of epoxy or modern material. The problem with these is wear resistance. Any material that could be applied cold would likely not last long rubbing on the steel rack. The best solution would be welding the part to build it up with the original material – more steel. 

The challenge to welding is the microscopic size of the part. Welding melts both the original part and the filler material. The benefit of this is a welded repair is likely as strong as the original part was. The challenge is that welding – particularly on a part this small, may warp or crack the part. Thankfully, I know a great welder – my father spent his career in metal fabrication and had a few tricks up his sleeve.

There are a lot of kinds of welding. One of the most refined is TIG welding – tungsten inert gas. TIG welding uses electricity passing from a tungsten electrode to the part to create an arc, and then filler material is melted into the arc to build up the part. With care and experience, it is possible to scale TIG welding down far enough to work on parts this small. The electrical power of the welder can be adjusted to vary the amount of heat. Normally TIG welding is done at around 150 amps or more; for this job my dad used a setting of 15 amps.

Here is the pallet after welding – a blob of steel has filled in the missing metal.

Grinding the weld back to the right form required some care. I carefully used a belt sander to remove most of the extra material, then I moved to a very fine file to match the original profile. I left a little extra material to compensate for any wear on the rack.

 

After a bit of polish to remove the discoloration from welding it went on the clock and is working great. Thanks to my dad for a great job that should last another couple centuries.

Here is the new pallet in action.

 


I have been working on an early American tall case clock. The click spring on the strike drum is pretty shot – the finger that makes contact with the click  is worn down and the spring is bent. Winding the clock causes the click to jump behind the spring, breaking the ratchet action.

Clocks this old were largely hand-made. Gears were cut with a machine, but much of the other work was done by hand. This click spring was filed out of a sheet of brass and riveted onto the gear. I think the spring was poorly designed – it is fairly tall which gives it its pushing force, but it is also very thin, meaning it bends easily in a direction I don’t want it to bend. For the replacement spring I wanted to make it out of a thicker sheet of brass.

My interests run the gamut of technology – from clocks built before the industrial revolution to modern manufacturing techniques. I wanted to see if I could make the replacement part using my CNC router.

I measured the gear and made a crude model in my CAD software. The outer circle is the outside of the teeth, the next two rings are the solid ring of the gear, and the inner circle is an approximation of where the contact point between the click and the click spring needs to be. I drew the spring profile with a couple Bezier curves.

My CNC router is primarily a wood-cutting machine, but it can also cut soft metals like aluminum and brass. This was my first attempt at brass.

There is quite a bit to the math of feeds and speeds and cutting geometry. This matters to varying degrees depending on what you’re trying to do. A feed rate that is too fast can break bits. Too slow and the heat of the cut isn’t evacuated in the chips and the bit overheats and dulls. If I was making a thousand of these, this stuff would matter (and I probably wouldn’t be making them on a woodworking CNC router), but for a one-off experiment, taking shallow passes and going slow is the path to success.

The prescribed bit for cutting brass and aluminum is called an “o-flute” bit. This is a one flute bit with a curved gullet that is designed to remove material without the chips sticking to the cutter.

I started with a 1/4″ bit, thinking that would likely be more forgiving than starting with something smaller and more fragile. In larger work, I think I can probably take passes up to 0.200″ thick, but since these bits cost about 30 bucks, I decided I had more time than money and  took 0.006″ passes. When I ran the job it was almost comically slow – it took about 6 minutes to shave off 30 thousandths on a 1″ x 3″ area, but I didn’t break my bit! Part of the slowness was the stepover parameter – how far the bit moves over for each pass. The tool default was 10%, meaning that on a 0.250″ diameter tool, the tool only moved over 25 thousandths per pass.

The profile passes were similarly shallow, but unlike the clearance path, the bit has to cut full width to go around the part. This went fine for the most part, but it did leave a little nub of brass on the click spring because the bit broke the part away from the stock.

The finished click spring is a little rough looking, but it’s the shape and size it is supposed to be. I clamped it onto a piece of metal to get a feel for how strong the spring was. Since I wanted to change the design of the click spring, I needed to determine experimentally the right width of the spring. The first attempt was pretty stiff.

Back in the CAD software, a minute change to one of the Bezier curves made the spring slightly thinner in width. Small changes can make big differences in spring strength, so I wanted to go easy for the second attempt. Buoyed by my relative success the first time around, I decided to shift down to a 1/8″ bit so I wouldn’t waste as much material. With new toolpaths in hand, I headed back to the router.

The 1/8″ diameter bit is a better choice for the profile cut – a smaller cutter means less cutting force on the part, so in theory the chances of me firing it across the shop would be lower. However, a 1/8″ bit removes a lot less material than a 1/4″ bit, so the pocketing operation would take longer this second try.

The difference between the first and second parts is hard to see without them being side by side. I clamped up the new spring to test the spring force and this time it felt about right.

The click spring is pinned to the gear. The old spring was pretty easy to remove – the pins had worked themselves loose in the 170 years this clock has operated. After removing the original click spring, I mocked up new spring to see if this was going to work. Normally Murphy’s Law would assume that it would take three guesses to answer a yes or no question, but Murphy must have been busy – spring #2 was almost perfect.

I probably spend too much time agonizing about non-performance-affecting elements of clock work. I have no problem putting the work in to make a clock mechanically sound, however the tedious stuff like polishing wheels is not a source of joy for me. Out of the router, the surface finish of the new click spring was pretty rough. I sanded it with 120-grit sandpaper and then hit it with some Simichrome polish with a wheel in my rotary tool, and I think it looks good enough to be worthy of the clock.

With the spring and wheel still held in the vise, I scratched the outline of the click spring onto the wheel.  I re-clamped the spring and wheel in the vise to allow access to the holes. I wanted to reuse the original holes in the wheel, so I used them as a reference and drilled through the new click. I reamed the holes to size using a cutting broach. I made the holes in the click slightly larger than the holes in the wheel because I wanted to mount these with taper pins, with the wide side of the pin coming into the click spring. After a few minutes of fussing around, I had a good product.

I  cut the pins to size using a cutoff wheel in my rotary tool. The picture below shows the original click spring (top), my first router-cut part (middle), and the second spring riveted onto the wheel.

I have no doubt this was the long way to solve this problem. I could probably have traced the old click spring, cut it out with my scroll saw and been done in 1/2 the time, but I learned a lot doing it this way, and any project where you get to use a power tool is a good project. That and if I ever work on another identical tall case movement needing exactly this geometry of a click spring, I’ll be ready to go.

 

 

I last worked on Lockwood & Almquist back in November. That’s also when I last photographed the clock as well – please forgive the reprint complete with Christmas lights. I promise they’re not still up. It’s an interesting clock with an industrial strength movement. The last month or so I’ve noticed the clock running a bit slower than before and also needing to be wound tighter than before to stay running. It was time to take another look.

The Movement

I pulled the movement out to see how 5 months of runtime played out. I should say that it is unusual that a clock will develop issues after only months of running. A well-serviced clock should run at least 5-10 years. Something clearly wasn’t right when I first serviced the movement.

This movement is unusual in a couple ways. First, it is designed to run for 90 days on a wind. To achieve such a long run time, the clock is powered by two massive springs. The winding arbor drives both springs and is geared down to only require a reasonable amount of force. The consequence of this is that fully winding the clock requires over 250 turns of the winding crank.

Another way the clock is unusual is the back plate – it is thick cast iron rather than brass. Most clocks use brass for the movement plates and steel for the pivots. In addition to looking pretty, this is done for a reason – brass and steel are chemically compatible for wear. Steel on steel can be problematic. This is mitigated to a large degree with oil, and this clock obviously worked fine for the first hundred years of operation, so clearly it can work just fine, but it’s an unusual setup.

When I originally serviced this clock I approached it the way I approach any clock. The basic steps are to ultrasonically clean, polish the pivots, repair any wear with bushings, reassemble, and oil. Bushings get polished as well with a smoothing broach. If a pivot hole isn’t sufficiently worn to require a bushing, I normally just scrape out any leftover gunk the ultrasonic cycle missed with some peg wood.

At first glance the oil on the winding gear pivots was a little dirty. This surprised me. Also, the pivots in the back side of the movement looked dry. There was a bit of oil there, but not as much as I expected.

I disassembled the movement to check the condition of the pivots. They looked fine. I checked the verge pallets, and there were a couple minor marks. I don’t believe I polished the verge the first time around, so I did it this time.

Before reassembling the movement, I tried to address the pivot holes in the cast iron back plate.   I’m not entirely sure what the best way to approach this would be, but I took some time with some peg wood and got some more junk out. I did this the first time too, but apparently not adequately. I reassembled the movement and added a bit more oil to the rear plate pivots.

The Pendulum

The other thing I wanted to readdress this time around was to add even more weight (!) to the top of the pendulum rod. A quick refresher (more detail in my first post) – with the bob in the center of the adjustment range, the clock ran 5 minutes per hour too slow. Somewhere along the way the movement got altered or replaced, and the pendulum as I found the clock was too long for accurate timekeeping. For aesthetic reasons I didn’t want to just cut the pendulum rod shorter – it already seemed too short for the case, so I opted to add a bunch of weight to the top of the pendulum rod, which increases the speed of the pendulum, allowing me to move the bob down to a reasonable location on the rod.

The clock kept time with the added weight I settled on last time, but just barely – the bob was all the way at the top of the adjustment range. I wanted to drop the bob to the middle of the adjustment range if possible.

Space behind the movement is limited, so the weight needed to go mostly to the side of the rod. Last time I used multiple layers of 1/8″ thick 1 1/2″ wide steel bar. This time I used a piece of 3/8″ thick by 2″ wide bar.

The pendulum rod is just under 3/4″ wide. A 3/4″ end mill was almost a perfect fit. I cut the slot in two depth passes, leaving the slot just shallower than the thickness of the pendulum rod.

Here you can see the original weight arrangement the clock ran with for the last 5 months and the larger machined block.

I didn’t want to do anything to irreversibly alter the pendulum, so I decided to clamp the weight to the pendulum rod with a piece of the same 1/8″ thick 1 1/2″ wide bar I used previously.

I drilled and tapped holes (including one broken tap) for screws to clamp the pieces together. Other than the broken tap, it turned out great. Even the casual eye may notice something strange about my drilling setup in the photo above. A real machinist would have measured offsets from the edges of the parts and calculated the hole positions for drilling. As I am not a real machinist I am free from those constraints, so I took the “close enough” expedient alignment method of eyeballing it and using a C-clamp to hold the parts in position while I drilled the pilot holes. The parts were just long enough for me to be able to flip the part around to drill the second side without having to reclamp the C-clamp position.

 
 

This is a really strange situation – the top end of the pendulum weighs more than the bob.

Pendulums need to be plumb to run correctly. This means the suspension point needs to be directly over the center of mass, otherwise the pendulum will do funny things. When I reassembled the clock, the pendulum was arcing in the horizontal direction – the leading edge arced toward the back of the case. I bent the hanger slightly backward to better align the center of mass under the suspension spring and it started running normally.

I timed the clock and put the dial and hands back on. Amplitude seems to be better than it was, so hopefully I’ve addressed whatever issue I didn’t handle adequately on my first go at the movement. It’s a little unsatisfying to not find a smoking gun, but much of success or failure in clock repair comes down to little problems adding up. Hopefully my second look will give this guy another decade of good service before I need to look at it again.

 

 


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!