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
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 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
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
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
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
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
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
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
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.