I spend a lot of time in the summer swimming and floating with friends and family in the lake down the hill from my house. It is easy to lose track of time while relaxing, and I don’t bring a phone with me into the lake. To solve this problem, I want to put a large clock on the wall of the dock so everyone can see the time from the water.
Design Goals
The primary requirement for this clock is that it is large. I want to be able to see the clock from at least 50 feet away. I have an entire empty wall to hang the clock from, so there isn’t much of a limit imposed by the size of the mounting surface. The availability of off-the-shelf clock hardware is likely the limiting factor on size.
I want to avoid having to penetrate the vinyl siding of the wall the clock will mount to if at all possible. Metal clips that mount things to vinyl siding without penetrating the siding are widely available, and can usually hold about 10 pounds. To keep the clock from rotating, I would probably want to use two of these clips, so that puts an upper limit of about 20 pounds on the whole clock.
The clock will live outdoors by freshwater for the warm half of the year, and be kept in storage during the winter (although potentially not in a climate controlled storage space). This has some impact on potential materials that can be used for the project, and at the very least requires that any wood used is properly protected from the elements.
I have AC power available in the little ‘attic’ space above the wall so I could run the clock on grid power instead of a battery. However, the breaker to the dock trips every month or two (I have no idea why) and it would be extremely frustrating for the clock to lose its time. Automatically synchronizing the time based on the atomic clock radio signal or an internet time server would solve that problem, but modern batteries and quartz timekeeping crystals are so good that I could potentially get an entire season out of a C-cell battery, setting the time just once, manually, in the Spring.
Clock Parts
It is tempting to grab an ESP-32 and a stepper motor, then start searching GitHub for Arduino clock software. However, clock movement modules are extremely cheap on the internet, follow a bunch of longtime standards, and are very easy to implement. At the heart, most modern clock movement modules are a quartz timekeeping circuit connected to a motor and a bunch of gears that output rotating coaxial shafts indicating hours, minute, and seconds.
There are plenty of optional features to consider in addition to the basic functionality, although most of them do not change the form factor or cost appreciably:
- AA battery? C-Cell? Wall power?
- Pendulum connection? Chime output?
- Radio atomic clock input?
- Daylight savings time switch or manual reset?
- Time zone selector switch with permanent backup battery and DST adjustment?
- Sweeping or stepping movement?
- Standard or high-torque motor?
- Shaft Length (threaded portion)?
I chose a AA battery option because I found that I can always use a ‘Battery Eliminator’ (AC/DC power supply in a battery form factor) to run the device off of AC power anyway. I had never heard of a battery eliminator before, but it is obviously such a smart concept! The clock building world in particular seems to use battery eliminators with a built in back up battery (oh the irony!) to keep the clock going in case of power failure. Some battery eliminators run from 5V USB power which could make them a good pairing with a simple USB solar cell, like I used in the GPS Base Station Project.
I am not using a pendulum because it seems like a huge waste of space and a large increase in complexity for my application. The one-hour chime is a tempting addition, but I think over time I would find the chime more annoying than helpful.
The radio atomic clock input seems like it would be a good idea on the surface. However, quartz timekeeping has gotten so good at low price points that it isn’t really necessary if you are willing to set your clock once yourself. Because atomic time does not adjust for daylight savings you don’t even get that feature automatically.
The daylight savings time switch to toggle the clock forward/backward one hour seems way easier than resetting the clock entirely, but because I will probably have the clock stored away during daylight savings time I don’t need the feature. The automatic time keeping and daylight savings correction models (using an internal backup battery) are an interesting option. My biggest concern is that daylight savings time is hardcoded into the firmware, and if the government changes daylight savings time rules again (which I hope they do) the entire clock module would need to be replaced.
To me, the classic ‘tick’ noise of a clock (specifically the seconds hand) is distracting and annoying. ‘Sweep’ style movements replace this with a continuous, smooth movement of all of the hands. I am not planning on using a second hand on this clock (because the timing precision is not required for this use case) so I don’t care if my module is ticking or sweeping.
The one feature I definitely need my clock module to have is a ‘high torque’ movement. Even though hour and minute hands are typically ‘balanced’ around their center, the extra inertia is a burden for the internals. It appears that most ‘large’ clock hands (which are measured by the distance from the point of rotation to the tip of the minute hand) top out at about 18 inches of length. This puts a reasonable upper limit on my clock face diameter at around 3.5 feet.
Finally, the length of the threaded portion of the shaft (5/16″ diameter) needs to line up with the thickness of the clock face you intend on using so it can bolt around it. A typical thickness is under 1/4″ and it is very difficult to find thicknesses over 1/2″, so if the clock face is any thicker than that you need to router away a section of the back to make room for the boxy plastic body of the clock module. Designing around a thickness of 1/4″ should keep this design simple.
Clock Face Design
This is a clock meant exclusively to help people currently swimming in the lake to tell what time it is, so I wanted the design to go all in on the lake theme. I opted for an outline of the major section of Smith Mountain Lake itself as the centerpiece of the face, with the clock arms coming out of the main peninsula of the lake. The body of the clock face is a wooden circle, with numbers around the outside.
There are a few ways to approach the lake outline feature. One way would be to carve out a negative of the lake and fill it with epoxy (I have big dreams to eventually make a topographic wooden carving of the area, with accurate contours above and below a water line marked by an epoxy pour). Another would be to simply cut an acrylic profile of the lake on a laser cutter and glue it to the wood (this is possibly the easiest, and has some cool opportunities for backlighting!). The hardest option might be to do a wooden inlay out of a separate material for the lake, but that seems to ambitious for my first inlay project. The approach I settled on was to do a simple V-carve of the profile of the lake to a constant depth (while masking the wooden substrate), then paint the exposed, carved lake area blue.
The numbers around the outside could be either Arabic numerals or Roman numerals. I opted for Roman numerals because I like how they can all face towards the center of the clock, while Arabic numerals typically all face ‘upright’ when arranged on a clock. For simplicity’s sake, I will use the same mask, v-carve, and paint process on the letters and the border feature.
To get the geographic data for the lake I used Snazzy Maps. It is extremely easy to turn off all of the typical google maps features (roads, parks, labels, location markers) and just get a simple image of the water feature. The website lets you export the result as an image, which can be imported to Inkscape and converted to a vector (“trace bitmap” tool). Cleaning up some of the small tributaries with a pixel brush before tracing the bitmap can make the resulting profile much simpler.
The vector profile can be exported to a DXF file which is easy to import to a CAD package (in my case Solidworks) and extrude as a cut feature. I have found that scaling and rotating the profile is significantly easier in Inkscape than in CAD software because the DXF can import so many lines and arcs that it makes the CAD software run super slow. In the end I rotated the lake by about 5 degrees so I could scale it up and sneak the Roanoke River between the 11 and 12 markers on the dial.
Clock Face Material
Wood is my preferred material for an aesthetic build, and its high stiffness to weight ratio make it a good structural material choice as well. I briefly considered a very simple plasma cut piece of sheet metal (with the lake and numbers as a negative feature) but thought it wouldn’t have enough contrast on the dock to be useful, and the weight limit might make hanging it impractical.
To match the 18″ minute hand reach I’ve settled on a 3’8″ diameter clock face (this lets the minute hand overlap the numbers, but prevents the hour hand from overlapping). Unfortunately my CNC Router only has a work area of about 4′ x 2’4″, and it is hard to get solid pieces of really nice hardwood at almost 4 feet in diameter! (although I briefly looked into large live-edge ‘cookie’ cuts in my area). Therefore I either need to use a nice veneered hardwood plywood or make the clock face out of several individual pieces of solid hardwood (or plywood).
One option to fit all of the carving onto my CNC is to cut each of the twelve ‘wedges’ of the clock individually and reassemble them afterwards. This could work with either plywood or hardwood, and it makes an interesting pattern with the grain of the wood, but I’m not sure if I could hold the tight tolerances necessary to align the pieces and not make the lake cutout look funny.
Another option is to cut the clock in multiple setups out of a single piece of plywood. I think the lake could be cut in a single setup if it were oriented properly on the router, and any misalignment caused by cutting the numbers in two setups probably wouldn’t be very noticeable. However, cutting the border and profile into the clock face would be very difficult to align with two setups or do well by hand.
By far the easiest option is for me to go to my local makerspace and use their 4×4 router to make the clock face in a single setup! Using a single piece of 1/4″ plywood (red oak?) will be significantly cheaper than buying up a bunch of hardwood lumber anyway. Maybe in the future I will make a scaled down version of the clock for indoor use and I can use my own CNC, or I can retrofit my router into the 4×4 configuration I designed.