If a horologist were to only marginally err, even as much as being off a fraction of a centimeter, the entire timepiece would not function properly. Because of this incredible learning curve in custom geared clocks, we're going to use a pre-constructed gear box, and incorporate it into a unique clock of your own design. Prefabricated gearboxes and hands can typically be found at any crafts store.
Step 1- Measure and Mark the Plywood
Measuring and marking your wood is an important step in most woodworking projects, but when building a clock it is absolutely imperative to ensure your marks are precise, otherwise your clock will not keep time accurately. Start by finding the center point of your plywood and mark it. Once you have found this center point, use your compass to create a circular outline on the plywood. This outline will be the size of your clock. The size of your clock should be determined by the torque of your gearbox and hand size it can turn. The average hand size gives you a clock face of about 6 to 18 inches, and the high torque hands will allow for a clock face of about 24 to 36 inches.
Next make the "12," "3," "6," and "9" positions. Do this by marking the vertical and horizontal diameters of the clock face, essentially dividing the face into equal quarters. At this point if you'd like to create a unique look to the clockface you should mark your plywood accordingly.
Step 2 - Cut the Clock Face from the Plywood
Using the jigsaw, cut along the circumference of the clock face. In place of a jigsaw, you could use a bandsaw if you feel more comfortable and accurate with that. If you have created any designs in the outlying look of the clock you should use the saw to cut these designs as well.
Step 3 - Drill the Center Shaft Hole
Once the clock face has been cut out, you need to drill the hole for the clock's shaft to transverse. The exact size and shape of the shaft can vary from gearbox to gearbox, so you need to find the right drill bit for yours. Additionally, many shafts include a mounting nut to help support the shafts position.
Start with the smallest possible drill bit, which will typically be the same size as your clock's shaft, and drill through the center point of the plywood. Drill from the front of the clock face into the back of the clock to avoid any splintered wood showing. Once you've drilled this center hole, continue to increase the size of your drill bit and hole until the shaft pushes through the hole with light to little resistance. If you don't want to have the shaft's holding nut showing, use the drill to create a larger opening in the clock face so that the nut will fit securely inside. Remember not to drill all the way through to the back of the clock or your shaft will not stay in place.
Step 4 - Mark the Numbers
Adding number to the clock face is the most difficult part of building the clock. Each number needs to line up perfectly with the corresponding hour and minute hands. The easiest method of ensuring that the clock keeps accurate time is by inserting the gearboxes shaft through the back of the clock, and attaching both the hour and minute hands to the shaft. Start by drawing out a rough of the "12," "3," "6," and "9," as these will be the top, left, right, and bottom numbers on the clock face.
Once you've roughed out the numbers, turn the minute hand until it reads "12:00," "3:00," "6:00," and "9:00," ensuring that the minute hand lines up with the "12" and the hour hand lines up with the corresponding number. Once you've ensured these number are equal, turn the minute to each remaining number's hour ("1:00," "2:00," "3:00," etc.) and rough out the number of that hour. Additionally if you want each number to be flush with it's counterpart and parallels (i.e "2" would be counterpart to "8" and parallel to "10" and "4") you can use a straightedge to outline the position of a number to match the others. Just be sure to check and make sure the hands match up.
Step 5 - Burn the Numbers In
Once you've finished creating roughs of the numbers, engrave or burning your number designs into the wood. Use an electric woodburning tool to draw the numbers and permanently etch and darken the wood. It's a simple tool, and as long as you follow the markings you made in the last step it's hard to make a mistake.
An engraver is also a simple tool, but the spinning head can get away from you if you're not careful, and drag a mark where you don't want one. With either tool, you can't erase your mistakes, so practice on a piece of scrap before you do the final work.
Additionally you can use typical prefabricated numbers that adhere to the wood after you've finished it, if you do not want to engrave or burn the wood.
Step 6 - Finish the Wood
After engraving or burning the numbers into the wood, you need to finish it to ensure your clock's look and longevity. The method you use to finish your clock depends on the look you want. Make sure to remove the hands and gearbox before you start to finish the clock.
Start by sanding the edges of the wood down until you have a smooth circumference, then move onto the clock face. Ensure that you sand within the engraved numbers and the center shaft's hole. If you like you can also sand the back of the clock, especially if you don't plan on wall mounting it.
Once you've sanded, stain and seal the wood. If you want your engraved numbers to have a darker finish than the clock face, allow the stain to gather in the numbers and settle for longer than the rest of the clock face. When the stain is dry, apply a wood sealer. Once your finish has been completed reinstall the gearbox and the hands and set them to the appropriate time.