Wooden clocks, kinetic sculptures, celestial instruments and sawdust.
If your accuracy at the scroll saw happens to be a bit lacking, here are four steps to help you create a wheel with a high degree of accuracy.
I chose the escape wheel for this demonstration because the escape wheel has the most exacting requirements of any of the clock's train of wheels. However, these four steps can also be successfully applied when creating any of the clock's other wheels.
The parts shown in green on each picture are the parts to be cut or sanded at that particular step.
Steve asks Clayton:
I've noticed on the Swing Time plans the notation "AH", which I hadn't seen on other plans I bought before.
FOR A CLOCK THAT RUNS TOO SLOW...(but also be sure to read over the section below on "For a clock that runs too fast").
If you have recently finished your clock and put it into beat and it's running too slowly - I recommend you do nothing for four to six weeks.
Some time ago I got an email from a builder whose Simplicity ran too slowly at first, he cut off the pendulum...only it was too soon. When his clock eventually found its beat, it then ran too fast. I recommend waiting a few weeks before shortening a pendulum shaft because it is much easier to cut off a pendulum than to add to it.
Some clocks need to run a while before they find their "beat". It is best to simply watch a new clock for a few weeks. Stand back and enjoy viewing its motion, and congratulate yourself for getting a chunk of wood to move. Just enjoy the movement.
If your clock still runs too slowly after it has run for a few weeks, then you can begin to shorten the pendulum's shaft a little at a time, until you get your clock running at the perfect beat.
But even before cutting off the pendulum, I would recommend that you read over the "Depthing" procedure in my Troubleshooting Blog posts and in my FAQ's, and follow those instructions. Depthing will help to free up any residual internal friction in your clock and possibly make it run more freely. The links to my Blog and FAQ's is at the bottom of my main page.
You can also add just a slight bit of paraffin to the tooth contact surfaces where the pinion and wheel teeth touch. Add just a very slight amount - because too much paraffin can clog the dedendum and make the clock stop. Candle wax works okay, but I like to use a color coordinated Crayon. Crayon paraffin is softer than candle wax, and that sharp point makes getting between the teeth much simpler.
You can also remove the pallets, wind your clock, and let the gears run free. When the wheels stop, rewind the clock and let it run free again a few times. Things get spinning pretty fast! But sometimes this helps to "break in" the mechanism more quickly.
If/when you have done all of the above suggestions and your clock is still running too slowly with the bob all the way up as high as it will go on the pendulum; to determine how much of the pendulum to cut off you can measure the threaded rod sticking out the bottom of the bob, and remove about half that length from the pendulum's shaft...but be sure to wait a few weeks before cutting the pendulum to give your clock time to 'break in' and find its beat.
FOR A CLOCK THAT RUNS TOO FAST...(but also read "For a clock that runs too slow" above.)
If you have just put your clock into beat, leave all alone and just enjoy the movement for four to six weeks. Some clocks run fast, others too slowly when first put into beat and they require a "break in" period to find their beat. I recommend during this time to just stand proudly in front of your clock and pat yourself on the back for doing such a good job of getting a chunk of wood to move.
After the break in period if your clock is still running too fast (and it depends upon how fast) two things may be happening. If your clock is gaining minutes a day, you can try to simply make the bob heavier, and/or lengthen the pendulum by a few inches. If your clock is gaining hours a day, something is probably slipping inside the clock's train and you'll need to investigate further to find the broken, unglued, or unrestrained part.
Certain escapements, like the Graham, are not very sensitive to drive weight, but others, like the grasshoppers and the "walking" on the HO, and the verge and foliot on the Wee Willie and Horologium are quite sensitive to drive weight. If your clock is running fast, try to decrease the amount of drive weight. Also read the section on "Depthing" on my site in my FAQ's and the four informative Troubleshooting posts in my Blog. The links to these can be found at the bottom of my main page.
As I mentioned, if you just put your clock into beat, it is best to not do anything for a few weeks except enjoy the movement. After that time you'll want to check the bob weight by adding fish weights evenly on each side of the bob, and/or increase the pendulum's length depending upon how fast the clock is running.
Take a look at my Attempt for an easy way to add length to a pendulum.
Also, you'll want to do all of this where the clock will actually be permanently mounted. It's weird, but sometimes just moving the clock from the shop to the house can cause the clock to run faster or slower (I have no explanation as to why, but it has happened a few times to my own clocks).
Enjoy!
Aloha. Clayton
Question from reader: How accurate is your Number Six Clock?
My Number Six clock is quite accurate. It is usually nearly spot on, but sometimes can run within about a minute or two a day depending on ambient atmospheric changes.
If you maintain a constant heat and humidity in your home, a pendulum clock will maintain better accuracy. If your home has huge heat and cooling swings, or huge changes from humid to dry air, then any pendulum clock will also show less accuracy, this even includes clocks with metal pendulums.
The pendulum is the timing unit of any clock. A clock's accuracy is determined by the pendulum, and not by the gears. However, the stability of the material used for the pendulum can affect the clocks accuracy.
A very stable wood used for a pendulum shaft is going to be a more accurate pendulum than a wood that changes a lot with changes in the ambient heat and humidity. So if accuracy is top of mind, we would like to know the "Relative Seasonal Stability" of the woods we choose for our pendulum.
The way the wood is cut from the tree also has an effect on the stability of the final pendulum.
There are three ways wood is cut from a log; 1) Flatsawn (AKA Plain Sawn), 2) Riftsawn & 3) Quartersawn. The stability of the final product from those cuts is also in that same order.
Flatsawn (the kind of wood that most of us have readily available) has the least stability to changes in heat and humidity. Riftsawn is quite stable and can give better results when used as a pendulum, but the very most stable cut of wood is the Quartersawn. Here is a picture that describes the three different ways wood is cut from a log.
With that being said, even Flat or Plain Sawn wood make excellent pendulums because the grain of the wood is almost assuredly going vertically throughout the entire length of the pendulum. Flat or Plain Sawn wood has about the same stability to atmospheric changes as a solid metal rod.
Flat or Plain Sawn wood make excellent pendulums, and except for some plywood pendulums, Flat Sawn wood is generally the only type that I ever use on any of my clocks.
Here is a chart that shows the relative stability of wood by species and cut. Since most of use can only get (or afford) Plain/Flat Sawn wood, compare the examples of White Oak (9.1) and and Honduras Mahogany (4.1). The Flatsawn Mahogany has more than twice the Relative Seasonal Stability of the Oak.
So according to this chart if you had a choice of Oak or Mahogany, and you were shooting for the best accuracy from your pendulum, you would absolutely prefer your pendulum being made from a close grained wood such as Mahogany.
Builder Joe has a question about Graham escapements:
I have another question regarding my pendulum slowly stopping. In your FAQ (on our website):
"Now when you get to the escape wheel, put the wheel in with the pallet arbor. When the pallets are in proper position, gently restrain the pallets with your finger on the arbor. Now turn the escape wheel. It should first push one of the pallets out of the way, and this will cause the other pallet to come into contact with another escape wheel tooth. Keep turning the escape wheel and the pallets should gently rock back and forth."
Should the pendulum be on it? I have tried without the pendulum, but I can’t get the pallets to keep rocking.
Thanks again, Joe
Clayton answers:
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Clayton,
In your written instructions for the Mantis clock you say to slow the time adjust the Bob up and to speed the clock turn the Bob down. Isn’t this backwards?
I thought to slow the clock you make the pendulum longer and shorter to speed it up.
Thanks, Cal
Cal, your query got me thinking that I should create a blog post explaining about the various types of pendulums and hopefully make their action simpler to understand.
There are basically three pendulum arrangements used in modern clockmaking. These are shown in the Pendulums jpg below. It is important to notice first that "0" is the pivot point.
Fig 31 shows a standard straight hanging "simple" pendulum with the pivot at the top. Most of my clock designs use this type of pendulum. It's fairly simple to understand. If we raise the bob, it speeds the clock. If we lower the bob, it slows the clock. The longer the pendulum shaft, and the lower the bob, the slower this type of pendulum will oscillate. We can also slow the oscillation of the clock by increasing the mass of the bob. With this style of pendulum, a very short pendulum shaft, or very light bob, will oscillate much faster.
Fig 32 shows a compound balance pendulum. This is the style of pendulum used on the Mantis, Celebration, Balance, Organic and SwingTime and others. Compound balance pendulums have the most variation, and are the most difficult to understand...but are pretty cool, because of their versatility. For example, we could create a compound balance pendulum that is very short, say only 15 inches (38cm) tall, to take the place of a standard "simple" pendulum (Fig 31) that would need to be 42 inches (107cm) long. Of course, we can make our compound balance pendulum shorter than 15", but the shorter we make them, the touchier, and more difficult to adjust it would become. I saw one metal clock with a compound balance pendulum that was only three inches (7.5cm). However, that's a bit unrealistic for our wooden mechanisms.
Fig 33 shows the pendulum arrangement used on the Toucan and Arts&Crafts clocks. There is a stationary bob at the bottom of the pendulum shaft, and an adjustable bob between the stationary bob and the pivot. Although it is a variant of the compound pendulum, this type pendulum works much like the pendulum in Fig 31. Raise the bob (or lighten it) to speed the beat, and lower the bob (or add more bob weight) to slow the clock's beat.
This morning I was sitting on the couch reading a book and it hit me how to answer your question and explain a compound balance pendulum's action. It all has to to with what is called "Restoring Force". The force exerted on the pendulum by gravity.
With a heavier bob on the bottom of the pendulum shaft, there is more restoring force on the bottom. That's simple to imagine. (we will not be concerned here with oscillations - only the effects that gravity has on the restoring force of the pendulum)
Think about a pendulum that pivots in the center, like the pendulum example that is shown in Fig 32. But in our example here, instead of the pendulum being vertical, think of it horizontally. (if you want a visual, simply turn the Pendulums jpg 90 degrees and look at Fig 32)
With the pendulum shaft being held horizontally, add a stationary, immovable weight at the very end of one side of the shaft, and then add a heavier, adjustable weight to the other side. Don't let go of it yet. Keep holding it horizontally. If you move that heavier bob inwardly toward the pivot until it balances with the lighter, stationary bob at the other end, the pendulum has no restoring force. You can let it go and the pendulum stays at rest horizontally.
With that same horizontal pendulum arrangement in mind, move the heavier bob down the shaft away from the pivot just a fraction of the distance so that the pendulum is no longer perfectly balanced. Let it go and the pendulum will begin to move. The heavier side moves down toward the floor, and the lighter side moves up toward the ceiling. You can imagine that if the imbalance is very slight that the movement of the heavier side toward vertical is quite slow.
In a second experiment, holding the pendulum at balance horizontally, move the heavier bob all the way out to the extreme end of the pendulum shaft, and let the pendulum go. The pendulum will now move quite fast to the vertical position (and overshoot vertical, thus the pendulum will oscillate a while. But we are not concerned with oscillations here. We are only concerned with the speed at which restoration takes place.)
In the first example with the heavier, adjustable bob essentially raised up (in) toward the pivot, the pendulum has little restoring force and moves slowly to a vertical position. (thus, when lower adjustable bob is raised it causes slower restoration)
In the second example with the bob lowered toward the bottom end of the shaft, the pendulum quickly moves under the influence of gravity to the vertical position. (thus, when we lower the adjustable bob further from the pivot it causes faster restoration).
Since Mantis has a compound balance pendulum, as shown in Fig. 32, by raising the bob up toward the pivot the motion of the pendulum is slowed.
We can also slow the Mantis pendulum another way; by lightening the lower bob. A lighter lower adjustable bob has less restoring force.
SwingTime and Organic have compound balance pendulums also, however unlike the adjustable lower bob of the Mantis, their lower bob mass is not adjustable and stays constant. On these clocks the upper bob is the bob used to adjust the beat. Fortunately, the same "Restoring Force" physics apply whether you are adjusting the upper bob or the lower bob. On a pendulum with a constant weight below the pivot, if we raise the bob that is above the pivot we slow the beat of the clock...alternatively, we could simply make the upper bob heavier. In this case of an upper adjustable bob, both a heavier bob or raising the upper bob have the same effect on the restoring force of the pendulum.
One more, just for fun. I created a clock that is yet another variation of Fig 33. This clock is ALL pendulum. The only part that is not pendulum is the wall mount. Everything else is contained in or on the pendulum. I call this clock "Minimalist."
Since the clockworks is integrated into the pendulum we have a compound balance pendulum that is similar to the Toucan or Arts&Crafts, except that in this case the center bob (the clockworks) is stationary, and the lower bob is the adjustment for the beat.
Because of the clock being integrated into the pendulum, the mass of the pendulum has increased and thus we need lower the bob with a longer pendulum shaft than would normally be the case. Most of my "Simple" seconds pendulums are around 42" (107cm) from pivot to center of the bob. The Minimalist pendulum requires about 63" (160cm) to give a seconds beat. My purpose for this clock was to stretch out and thin down the overall appearance of the mechanism. Integrating the clockworks into the pendulum allowed me to do just that.
Thin, slim and streamlined, Minimalist is a lovely clockworks with a unique pendulum.
