Introduction: Wooden Gear Clock
I've added video of the clock. I will be working on carving out windows in the face of the clock. I will upload pictures and/or a video of that when I am done.
I've been into woodworking for a few years now. I love the idea of being able to make things that I can use. A few years ago I came across a clock that was made out of wood. The face, arms, frame, and gears were all wood. It really impressed me, and I kept it in mind for a future project.
I've decided to take on the wooden clock in this Instructable, and hopefully share what I have learned to help others with similar interests.
One of my goals with this was to use common tools that are more widely available to most people. I didn't use any expensive hard to find wood working machines, or costly software packages when designing this. The software used is either open source, or free, and the machines used are some of the common ones that most woodworkers would have.
Step 1: What You Will Need
Here is a list of things you will need
OpenOffice Calc - For calculating the Gear ratios
free2Design - For designing the gears
Gimp- Modifying and editing images
Blender - For rough modeling gears to make sure there aren't any interferences between gears and axles.
*note - You probably can use Blender to do all the designing, but my Blender skills aren't up to speed. It was easier to draw them dimensionally accurate in a 2D package and import that into blender.
Miter Saw (Table or Band saw will also work)
Spray Adhesive (3M Super77)
Step 2: How Does It Work?
The clock I have designed is a basic pendulum clock. These have been in existance since the mid 1600's. It uses a weight as the energy source, and a pendulum to regulate how fast this energy escapes.
The weight is wound around one of the axles. As it pulls down, it rotates the gears causing the minute and hour hands to rotate. If this was just the weight and gears, when the weight was released, the gears would spin for a few seconds and the weight would hit the floor. This isn't very practical unless you want to pretend you are in a time machine. Placement of the weight and cord is a little critical. You want it farther down the gear train so you aren't winding the clock every 4 hours. Once or twice a day isn't bad. The farther down on the gear train, the slower it will unwind. If it is placed on the hour hand, you can easily get by with winding once a day.
We need some way to allow this energy to escape slowly. This is where the "Escapment " comes in. From the word escape, it allows the energy of the weight to escape in a slow manner, as to not use up the energy at once. This escape mechanism also creates the "Tick Tock" that you hear from clocks. The escapement is built out of the escape gear, escape lever, and the pendulum. The pendulum swings back and forth moving the escapement lever in and out of the escape gear, causing the gear to stop spinning. This allows the energy of the weight to be spread over a period of time so you are not winding the clock every 2 minutes.
Step 3: The Pendulum
Pendulums are an interesting mechanism. They are a weight at the end of a string or pole, with a pivot at the opposite end of the weight. The period of a pendulum is the time it takes to go from one side to the other and back again. The neat thing about pendulums is that this time, or period, is not dependent on the amount of weight or length of arc, it's dependent on the length of the pendulum. So, if you had a 2 foot long pendulum with a 5 pound weight, pulled to the right at 90 degrees, it would take the same amount of time to swing across and back as a 2 foot long pendulum with 2 pounds of weight pulled to the right at 30 degrees. The weight at the end of the pendulum does affect how many times the pendulum will swing. So the pendulum with the 5 pound weight will swing for a longer amount of time, than the 2 pound weight. This is helpful because we want to keep the pendulum swinging. You can, however, have too much weight. As we will see next, the escapement helps give the pendulum a push. If you have too heavy of a weight, you will not have enough energy to keep it swinging.
For our clock, we want to have a period of 2 seconds. That way, it will take the pendulum 1 second to swing to one side. With each swing the escapement will allow the escape gear to turn one tooth at a time. If the period is 2 seconds, this will basically make the escape gear our second hand since it is rotating one tooth every second. For a period of 2 seconds we need it to have a length of 1 meter. Since our escape lever will have 2 teeth, one to stop the escape gear at each end of the pendulum swing, our pendulum will need to have 30 teeth. It will make one rotation every 60 seconds. Many pendulum clocks have the escape gear on the second hand axle. That is what we are going to do.
As the pendulum swings back and forth, it rotates the escape lever in and out of the escape gear. This causes the clock gears to stop and start rotating every second. The lever is designed so that as it is moving out of the escape gear, the gear gives it a little push. This push is enough to keep the pendulum swinging.
Step 4: The Gear Train
Since the escapement gear rotates once every 60 seconds, we can make another axle rotate once every 3,600 seconds. This will be our minute hand. Then we can make another axle rotate once every 43,200 seconds (12 hours). This will be our hour hand. When we calculate this we will have a functioning clock on paper.
The spreadsheet shows the calculations of the gear ratios needed. I started with a 3 axle minute hand, but moved to a 4 axle to keep the size of the gears down.
To make a minute hand, you need a gear ratio of 60 between the Escapement axle and the Minute Hand axle. For an hour hand, you will need a gear ratio of 12 from the Minute hand to the hour hand.
The spreadsheet shows the formula and the calculations to get the number of teeth for each gear. By using the spreadsheet I was able to plug in different number of teeth for each gear and pinion to try to get the Gear Ratio needed.
Step 5: Designing the Gears
When designing gears, there are many parameters that can affect the size. I took some of the standard values for the variables when making the calculations. I used a pressure angle of 20 degrees, and a Diametral Pitch of 8. These combined with the number of teeth of each gear, I was able to calculate the Pitch Diameter, Root Diameter, Outside Diameter, and Base Circle Diameter.
Now that I have the Diameters of the gears, I can start drawing them. I found instructions on drawing gears with CAD and followed them to draw these gears. It was written by Nick Carter. A link to his page is in the last step in the References Section.
The free2Design file has the Gears and Pinions with a layer that shows the lines drawn to create the teeth. While researching clocks, I came across Gary's Clocks. He mentioned that there is a big difference in what you can draw with CAD and what you can actually cut using a scroll saw. I learned this the hard way. Cutting the gullet between the teeth is a bit tedious. To try to speed things up I decided to add circles between each teeth to be drilled out with the drill press. That saved time trying to round out the valley between the teeth, but I think it caused some problems with the teeth meshing with each other.
Along with the gears are the Escapement and the Ratchet Mechanism. As stated earlier the Escapement is a mechanism that allows the energy to escape slowly. This is done using a gear, lever and pendulum. What hasn't been talked about yet is the Ratchet. We said that a weight is wrapped around an axle with string, and it slowly lets out to drive the clock. We need a way to re-set this, or wind the clock. The Ratchet will allow us to do that. It fits loosely over the axle of one of the gears, and pushes against the gear with a pin and lever. When the clock needs to be wound, the Ratchet can be turned counter-clockwise without moving the gear. Then when the weight pulls it clockwise again, it catches on to the pin fixed to the gear, and continues to power the clock.
Step 6: Cutting the Gears
Now comes time to put the hard design process to the test. Cutting the gears. After printing out the full size drawings, I cut them out and glued them to the wood. A spray adhesive works great. I use 3M Super77, and it dries fairly quick. At least within a few minutes after gluing, I'm ready to start cutting without it peeling off.
I drill all the holes first. It's easier to handle a full size board with the drill press than trying to clamp a gear blank that's only 1.5 inches in diameter without splitting it. Also, if something goes wrong, you haven't wasted all that time cutting it out just to have the board split.
After drilling the holes, I cut the gears out around the outside diameter, then I start cutting the teeth.
Step 7: Gear Placement
I drew rough gears in Blender with the Outer Diameter and Pitch Diameter to figure out placement in the frame. This told me if I will have interference between a gear and an axle, and give me a rough idea where my axles will be placed. After creating a 'template' on where to drill the holes, I drilled the first one starting with the Escapement Axle. Once that was drilled, I slid the gear on an axle, placed it in the hole, placed the mating gear on an axle, and held it in the approximate location. I then modified the placement of the next gear, marked it, and drilled the hole. Then I would re-check the fit with both gears on an axle fit in the hole. If it fit, I was on to do this again with the next gear. This continued until all the holes were cut, and the gears fit.
Three axles will go all the way through the frame, and three axles will have blind holes. I now have one side of the frame drilled, but I need a matching frame. In order to get a mirror image of the holes, I cut a half inch length of 1/2" dowel to place in each hole. I drove a brad nail into the center of each piece of dowel and cliped off the end of the nail with a pair of snippers. I placed the mating board on top of the nails and pressed firmly. This left an indentation where each of the centers of the holes should be drilled.
After the holes were drilled, it was time to assemble the clock.
Step 8: Assembling and Finishing the Clock
I slide the gears on the axles and place them in their slots. Place the face over the axles and secure it with the 1/4" dowels. The Escape Gear and Levers go on the back with the Pendulum. I created 2 square bars across the back to hang it on the wall. These are raised away from the back of the clock using 1/4" dowels and allow a place to attach the pendulum.
Well, here are some pictures of the assembled clock. I need to do a little sanding here and there, and add a finish as well as numbers, but it is finished for the most part.
Being that this was my first clock, I didn't get too complicated and left the hour and minute hand on separate axis. To combine them, as on most clocks, there would be more gearing, and axles that slip over one and other.
There are a few things that I plan on improving. First is the look. I know it's not the most appealing clock, but I was more focused on function. Replacing the front board with Plexiglas is one idea. The gears look great, and I'd like to show them off more. The other thing I'd like to improve is my scroll saw skills. I cut a LOT of gears that made it into the kindling box.
Step 9: Final Thoughts and References
I always like starting projects that require me to do research, and learn new or improve my skills and abilities. I hit several areas with this projects. When I saw my first wooden clock years ago. I never realized that when I started to create one, I would learn so much about how they work. I now look at clocks and watches from a new perspective. I now start to look for the escapement, and follow the gears through.
As I said I learned a lot, and I wanted to share the sites where I got some ideas. I figure they helped me, and they might be able to help others.
Gary's Wooden Clocks - a very helpful site with several cool designs submitted by various people.
How Stuff Works - a decent overview of the parts of a Pendulum Clock
Nick Carter - a detailed instruction on how to draw gears in a CAD program. The nice thing is it isn't specific to any one program. It's generic enough that any CAD program will work
And finally, working with gears wouldn't be complete without using the handy dandy Machinery's Handbook 24th edition. This is the source for my formulas and calculations.