Introduction

As teachers, we were looking for a clock kit that an uninitiated student could build as part of a class project. We wanted a kit based on easy to obtain materials, using only basic power tools, like a drill and a band or scroll saw (at most).

We couldn't find anything out there that suited our needs, so we developed our own "clock kit," that is presented here. At this time it's just an escapement, that "ticks and tocks" with a swinging pendulum, but adding a time indicator is straightforward (see below). Here is the outcome of the directions you'll find here:

So, this site describes how to build a simple, mechanical, wooden clock-escapement mechanism out of parts that can mostly be found at a hardware store. We have had success in assigning the construction of this escapement as a "do it all yourself" project in a science-oriented, college-level, general education class that has a timekeeping unit. We have also developed this into a "ready to assemble" kit that students were able to build and complete in a 3-hour lab-period.

As far as teaching goes, building a clock is full of geometrical considerations and engineering challenges that involve many scientific principles (pendulums, friction, gears, torque, etc.). It is also incredibly satisfying when the clock suddently starts working, ticking and tocking all on its own. We always get many shrieks and smiles from our students when this happens.

Your input

We are interested in hearing your thoughts, and most particularly seeing your results if you happen to build this escapement. Here are a few who have successfully built this escapement (please tell us if you do, and we'd be happy to add a link to your work). We have a Google Group going here, which you can use to communicate with us or others in the group. You can also email us directly: t...@gmail.com

The Instructions

I. Parts

To build this mechanism, you’ll need the following 23 parts. See the table below for a description and recommended source.

QuantityDiagramDescriptionSource
2A 1.5" long 10-24 thread nylon pan head machine screw. You might be able to get away with a metal screw here, but we found nylon to reduce friction a bit more. McMaster.com, Part #93135A115
2B 1" long 4-40 thread nylon pan head screw. These are used as set screws for wood. Nylon is really needed as metal screws tend to chew up the wooden parts they are to secure. McMaster.com, Part #97263A251
2C Skateboard bearings, Outer diameter of the casing is 7/8", and the inner diameter of the hole is 5/16" (these are pretty standard bearings and sizes for skateboards). Amazon.com #B004UOM4YM or (here)
1D Nylon 10-24 Acorn Nut. You might be able to get away with a metal nut here, but we found nylon to reduce friction. McMaster.com, Part #93135A115
4E #8 (or #6) 1/2" long wood screws Any hardware store
2F 3" lengths of a 5/16" diameter wooden dowel (should fit snugly into skateboard bearings) Any hardware or craft store
2G Flat washers, 1/2" on the inner diameter, 1 7/16" outer diameter. Plastic or nylon washers would also work, but they are hard to find in this size and very expensive. Any hardware store
1H 3 1/2" section of 3/4"x3/4" wooden stock Any hardware store
1I 7" section of 3/4"x2 1/2" pine wood stock (likely sold as "1 by 2 pine"). This will be the base support of your clock. Any hardware store
1J Wooden yardstick Painting section of hardware store
1K Empty wooden sewing-thread spool with 5/16” hole (dowels above should fit snugly into central hole) Craft store
1L String, weight (anything will do) and a paperclip Various
1M 12-tooth escape wheel, approximately 3 1/2" diameter. You’ll need to make this yourself. Starts as 1/4" thick "Alder" or "Poplar" Hobby wood. Any wood will do, but we had good luck with these types of 1/4”-thick woods. Home Depot or craft store

II. Tools Needed

  1. A drill (we used this).
  2. 11/64", 5/64", 3/32" and 5/16" drill bits
  3. 7/8" and 5/8" wood boring drill bits (Forstner-style bits are recommended)
  4. Scroll saw or band saw to cut escape wheel. We used this but this would work too.
  5. Other saw to cut wood as per the dimensions in the table above
  6. Slotted and Phillips style screw-driver.
  7. Ability to tap 10-24 and 4-40 holes (can be done with tap and dye set or metal 10-24/4-40 screws).
  8. Protractor (for measuring angles)
  9. Compass (for drawing circles, not for navigation)
  10. Some kind of sander. We used this one.

III. Instructions

Constructing the escapement is done in five sections, constructing the escape wheel, the clock base, the pallet holder/mechanism, the pendulum, then final escapement assembly.

A. Escape wheel

Cutting a working escape wheel is very difficult. If the wheel isn't almost perfect, the clock won't tick and tock at all, or it will run for a few seconds, then stop. Our design here is for a 12-tooth escape wheel. We have a couple of plans for this.

The Original Plans

First, using the compass draw two circles on your 1/4" Alder/Poplar wood sheet. The outer circle should be 3 1/2" in diameter, the inner one should be 2 1/2" in diameter, like this (be sure the center-mark is obvious and clear for later):

Next, mark off lines with your protractor at every 30 degrees around the circle. Work carefully, and be sure your marks are actually at 30 degrees. Each line should pass through the center of the circle:

Connect the intersection points between a given line and the inner circle, and the next line over and the larger circle, to mark off your the teeth of the escape wheel, like this:

With the scroll saw, cut out the wheel, tooth by tooth, like this (you can try using a coping saw but it’ll be hard). We start by doing all of the radial cuts (those along the diameters of the circles) first. It is helpful to cut away excess wood exterior to the outer circle.

Keep cutting until you’re done. Work carefully so that the tips of each teeth are all on the line of the outer circle. Read the last sentence again. It is critical that your teeth are all the same size. The escapement may not function properly if the teeth reach differing diameters (even slightly). Here’s our final product:

Using the center indentation your compass made, drill a 5/16” hole through the center of the gear, and insert one of the 3” dowel sections like this. Do not glue the dowel in the gear (yet).

You can set this part aside for now.

B. Clock base

Mark a center line along the long dimension of the 1"x4" pine block. Mark two position on the center line, 6 cm apart near the upper third of the piece. Here is an example:

Next, with the 7/8" Forstner bit, cut a hole just at each mark, deep enough to hold accommodate the depth of the skateboard bearing. DO NOT DRILL THIS HOLE ALL THE WAY THROUGH! Here is an example:

Each hole should accommodate a bearing, so that the surface of the bearing is flush with the surface of the wood like this:

Remove the bearings, and using the 5/8” Forstner drill bit, drill all the way through the wood using the same center as for the original 7/8” hole. Each hold should look like this when done:

Next, take the two metal washers, and drill two 5/32” holes along a diameter and near the edge of each washer like this (it is helpful to mark each hole with a center punch before drilling).

Replace the bearing into the hole and center the washer over the bearing. Mark the wood with the position of each hole is the washers, as shown here:

With the holes marked, remove the washers and bearings and drill 4, 5/64" holes, one for each hole in the washer. Replace the bearing and washer, and screw the washers into the wood using the #6 or #8, 1/2" wood screws. Your final result should look like this, with the washers snugly holding the bearings in the wood.

The 3" dowel segment should fit snugly into each bearing and turn freely, without touching the nearby washer or the wooden base.

C. Escapement Pallet (or the anchor)

Next, we’ll prepare the pallet holder and mechanism. Take the 3 1/2" section of 3/4"x3/4" wooden stock (part H in the parts photo above), and draw a line down the center of its long length. Put a small tick mark at its center. Draw two more tick marks, one 2 cm to the left, and the other 2 cm to the right of the central tick mark, as shown here:

Next, on an adjacent side, mark the center as shown here:

Drill this center hole with a 5/16” drill bit, as shown here:

Next, drill 3 holes on the original face. The center hole should be drilled with a 3/32" drill bit, all the way through to the larger 5/16” hole you just drilled. The two outer holes should be drilled with a 11/64” drill bit, all the way through the material.

Next, get a 10-24 tap and thread two outer holes. The idea is that you want the outer holes to be threaded, so you can screw a 10-24 nylon screw into it. If you don’t have a 10-24 tap, you can thread the hole by screwing (carefully, yet with force) a metal 10-24 screw into the hole. The metal screw will likely have enough cutting ability to make the threads (but you’ll have to work it). Here’s a hole being threaded with a 10-24 tap:

The center hole should be threaded with a 4-40 tap, like this. Again, if you don’t have a tap, it’s possible to read this hole with a metal 4-40 screw, by forcing the 4-40 screw to “screw into” the hole.

When the threading is complete, you should be able to screw two nylon 10-24 screws into the outer holes, and a 4-40 screw into the center hole like this:

This completes the assembly of the pallet holder. The outer 10-24 screws, inserted as shown, seem to engage the escape wheel in a manner that will keep the clock running. The smaller 4-40 screw is a set screw, that allows you to clamp this pallet holder onto a 5/16” dowel segment. Here are the assembled pallet holder and escape wheel:

D. Pendulum

Get the yardstick and drill a 5/16" hole near one end. On the thin face, drill a 3/32" hole through to the 5/16" hole you just drilled. Tap the 5/16" hole for a 4-40 screw. The final pendulum end should look like this:

E. Final assembly

Assemble all parts as shown here. If the dowels form too loose of a fit, either in the skateboard bearings, or in the pallet holder or escape wheel, then tightly wrap the dowel with a small piece of masking tape, to build up the diameter of the dowel just a little but (or as needed to make the fit snug).

We found the acorn nut on the right of the escape wheel, and the inverted pan head screw on the left of it to be the optimal orientation, for their interaction with the escape wheel. Note the orientation of the escape wheel’s teeth. Adjust the two black screws until you can turn the escape wheel counterclockwise (by hand) and see the pallets ticking and tocking against the teeth without seizing up.

Next, find a suitable mount for the whole assembly, and attach the pendulum to the rear of the pallet holder’s axis, as shown here:

Push the sewing thread spool onto the front axis of the escape wheel (you might have to adjust the size of the hole in the spool), and wrap some string around the spool.

IV. Running the Escapement

We found a small amount of weight runs the clock, on the order of about 20 g or so. The thread spool may not be needed, as string can be wrapped around the escape wheel’s axis directly, but the larger diameter of the spool provides a bit more torque, as provided by the weight on the end of the spring.

With the clock wound up, give the pendulum a swing. Hopefully it’ll start ticking away. Watch the pallet engagement to the escape wheel carefully, and adjust either the left or right 10-24 screws as needed, if the clock stops.

The pallet should not engage the escape wheel teeth more than 2-3 mm into the depth of the teeth. We found that the angle of the inverted pan-head screw more-or-less matches the angle of the tooth it engages. The screw on the left should just barely allow a given tooth to pass under it, when not engaged.

More weight may be needed if the escapement still won’t run. The angle of the pendulum on its axis is also a variable that might need adjusting. We found the top flat edge of the yardstick is often not parallel to the top flat edge of the pallet holder.

If you cannot get the clock to run without stopping (or skipping teeth), then you might have to reassess your escape wheel. Likely, you have some teeth that are different sizes. You may have to go back and (more carefully) cut another escape wheel. It is not uncommon to cut several escape wheels before you get one that works. This is without a doubt, the hardest part of the any clock "to get right." Here are our escape wheels that simply wouldn't work: