As part of the thingiverse MakerEd2 Challenge I decided to design a 3D printable clock.
I chose to design a clock which included a wide range of educational functions ranging from teaching children the time, to concepts of stored energy, inertia, gearing, leverage and many of the concepts in Newtonian physics.
As such this clock provides a visual and hands-on demonstration of a wide range of engineering and physics concepts that would be useful in the classroom.
The clock has been designed with ease of construction and cost in mind, as such specialized parts have been kept to a minimum, with the few specialized parts required being easily and cheaply obtainable.
Refer to the project text for specific printing settings
After printing it is essential to clean the gears and bearing surfaces with a file or sandpaper. Often when printing the first layers will flatten out creating a lip. If this occurs the clock will not run freely, so all gear teeth should be cleaned and checked for consistency after printing.
Olde-worlde Weight Clock
Overview & Background:
This project explores how a mechanical weight powered, pendulum regulated clock operates.
The clock design demonstrates a wide range of physics and mechanical concepts ranging from gear ratios, stored kinetic energy, momentum, inertia as well as clock design and escapement mechanisms, in this case the verge-and-foliot system.
This clock is a fun and safe way to engage students while also teaching them valuable skills and concepts. The clock will also prove useful as learning aid for teaching younger students the time, so has a wide classroom application.
The objective is for students to get hands on experience building a clockwork mechanism and in the process build an understanding of all of the concepts and forces at play behind its operation.
Students should develop an understanding of newtons principals and the three laws of motion throughout this project.
Early secondary school and late primary school students are the target audience for this project. This clock is designed to help students conceptualize Newtons laws of motion through hands on interaction and experimentation with the mechanism.
An approximate class range would be from year levels 6 to 8.
This project would be applicable to physics as well as general science classes in primary and secondary schools.
The ability to follow instructions.
Fine motor skills.
3D printing and slicing.
Understanding of the laws of motion.
This mechanical weight clock has been designed with ease of printing and construction in mind. The design uses a minimum of specialized parts, requiring just 2x paper clips, 4x 12mm countersunk head timber screws, some epoxy glue, 4x M20 stuctural nuts and 9x M14 nuts. All other parts are printed.
All the gear and mechanical components can be printed on the same platter with supports turned on and about 25% infill.
The chassis components can be printed without supports and should for aesthetic reasons be printed in a complimentary colour to the gears. If your printer is not long enough to print the back chassis panel, it can simply be printed in two parts and glued together.
Once the mechanical and chassis components have finished printing it is important to remove the burrs from the gear teeth and bearing surfaces. The easiest way to do this is with a nail file or jewelers file, making sure to clean every tooth on every gear.
Construction starts by assembling the main shaft. The main shaft consists of a 56 tooth gear, three ratchet arms and a 4 toothed gear at the very end. The cord pulley with its ratcheting teeth fits over this shaft and is kept in position by the 26 tooth minute drive gear which slides over the square collar on the main shaft. The raised collar on the minute drive gear should face outward.
The next part to construct is the escapement mechanism. The escapement wheel has 17 lugs and is driven by an 26 toothed gear. To assemble, this press the square end of the escapement shaft into the square cutaway in the escapement wheel, be careful not to break any of the escapement teeth in this process.
The escapement contacts the cams on the escapement shaft which then drives the two horizontal pendulums from side to side. It is the duration of the pendulums to move from side to side that sets the time taken for the escapement to advance one tooth.
The next step is hour hand onto the hour gear, it might be necessary to file the inside of the hand a little in order to make it all fit nicely.
To begin assembly of the main clock start by fitting the minute hand gear through the hole in the front chassis plate and securing it in place with the minute gear carrier. be sure to fit the carrier the right way up as the escapement shaft rides in the hole at the top.
At this stage secure the escapement carrier, if this does not fit in tightly, a little glue can be used to secure it.
Mount the face plate onto the chassis, then fit the hour gear with hand over the bearing collar.
This is a good opportunity to mount the minute hand, as it is easier to apply downward pressure on the shaft in this position.
The next part to assemble into the chassis is the idler shaft. This is a single piece comprised of a 48 tooth gear on one end and 7 teeth on the other. The idler shaft runs off the 56 toothed gear on the main shaft and in turn drives the escapement wheel which is connected to the 48 toothed gear.
Once the idler shaft is fitted into the chassis the main shaft and escapement gear can be mounted onto/into their bearing points.
Mount the top of the chassis onto the chassis back taking care to align all the bearing surfaces. Everything should fit snugly with very little force. Once everything is mounted make sure that everything spins freely, if there is any tightness in the mechanism find which part is the culprit and file/sand it smooth.
Once everything runs freely screw the front down using four 12mm countersunk head timber screws.
Fit the escapement shaft, this slides in on an angle making sure not to damage any of the teeth on the escapement wheel.
Once the escapement shaft is fitted add the pendulum arm.
Now that the clock body is assembled it's time to build the pendulums. The two pendulums consist of two half hemispheres glued together with an M14 nut inside and paperclip loops. These should be printed with supports.
Once the supports have been cut away, unfold and cut two paperclips off at 30mm.
Fit the paperclip loop through the two holes in the top of the pendulum housing and bend the ends over.
Push the bent over ends of the paperclips into the grove, splash some epoxy around and glue both haves of the pendulum over the M14 nut.
Building the counterweight is straightforward, simply scale the STL file to fit your nut diameter, then add 7 M14 nuts and glue the lid on.
Building the main weight is the same process, simply scale the STL file to fit your nut diameters, add the nuts and epoxy the lid on
Before finalizing the clock decided that the clock face looked a little bare, so I printed out some numbers 0.3mm in thickness and stuck to the face. You can design your own using any typeface you like be they numbers or roman numerals, you could even write your numbers on by hand with a marker.
The clock is completed by refitting the face, attaching the pendulums to the pendulum arm and mounting the weights and counterweights using a piece of standard blind cord. The escapement shaft should be suspended by a length of cotton so as to reduce any points of friction.
The main weight should sit to the left, with the counterweight to the right. To rewind the clock simply pull the counterweight down, the ratchet will prevent the clock mechanism from running backward or being damaged.
To calibrate the time simply move the pendulum weights along the arm until you find a position that keeps reasonable time. Obviously this won't keep perfect time, but with proper calibration it can come close.
The project will take about 40 hours to print at 50mm/s. and will need to be printed in 3 to 4 batches.
Filing, cleaning and inspecting the gears and bearing surface will take about an hour to complete, but is essential for the smooth running of the clock
Construction should take no more than 2 hours with most of that time being spent gluing the numbers to the clock face as well as assembling the weights and pendulums.
After the parts have been printed they should be carefully cleaned with a sharp hobby knife and a file so as to ensure that there are no lips or excess plastic on any of the gear teeth or bearing surfaces.
The list of printed parts is:
- Chassis front.
- Chassis back.
- Minute gear carrier.
- Escapement wheel carrier.
- Clock face.
- Main shaft.
- Main shaft ratchet pulley.
- Main shaft minute gear.
- Minute hand gear.
- Hour hand gear.
- Escapement wheel shaft
- Escapement wheel
- Escapement shaft
- Pendulum arm.
- 2X Pendulum tops
- 2X pendulum bottom
- Main weight.
- Main weight top.
- Counterweight top.
- Minute hand.
- Hour hand.
The non printed parts are:
- 2x paper clips.
- 4x 12mm countersunk head timber screws.
- 5 Minute epoxy glue.
- 4x M20 stuctural nuts
- 9x M14 nuts
Rubric & Assessment:
By the end of the project:
Did the student successfully print all clock components for the model?
Did the student assembled the project according to instructions resulting in a working clock?
Did the student experiment and calibrate the clock by changing the pendulum positions?
Did the student develop an understanding of the principals at work within the clock?
Did the student develop an understanding of Newton's laws of motion?
Did the student understand the concept of kinetic and stored kinetic energy?
- Does the student understand how to read the time?
Handouts & Assets: