The Clock Face
Arguably the most important part of the “clock” is the timepiece itself. I wanted this to be as close as possible to the original Guinness clock in terms of colours, fonts, hands etc. However, I decided to use a modern quartz clock mechanism of high torque to carry the large home-made hands. The original Guinness clock face is shown here. Interestingly, various pictures on the internet show the pictures of the moon phases in different positions. I suspect the cover gets removed and replaced in a rotated orientation!
Essentially, the clock face is installed behind a frame and protected by 4mm UV-resistant acrylic sheet. From the low resolution picture above of the original, I sketched out the shape of the hands at the correct size to use as a template. I transferred this template to some thin sheet aluminium. Originally I cut up a lager can using scissors and made hands from that, but the material was too thin and became slightly wrinkled and rather crude looking, so “quality control” (Penny) rejected them. I bought some 0.5mm thick aluminium sheet and made the hands from that using a band saw and file to cut them accurately – much more robust. They were sprayed with a metallic gold paint and fixed to the clock mechanism which was mounted behind the clock face.
Incidentally, the clock mechanism ran off a single AA cell. I decided to replace this with a much larger D cell mounted in the controller cabinet. Wires from this run to the back of the clock and are soldered to the battery holder contacts. It is now much easier to change the cell which should also last much longer.
Original clock face.
Clock face front.
In order to set the clock activities in motion up to once every 15 minutes, I needed to detect when the minute hand reaches 3, 6, 9 and 12. For this I arranged the end of the minute hand to be extended and bent back at a right angle to hold a small reflector extended behind the edge of the numbers ring. On the rear of the ring I positioned four small opto-sensors at the relevant positions. These transmitted a beam of infrared light which was then reflected back from the reflector on the end of the hand, back to a photo-detector. This in turn sent a signal to the controller. Using the switches on the controller panel, one can select to trigger the clock events every hour, every half hour or every quart hour. A multi-way plug and socket allows the clock face to be removed.
The clock face is comprised of a Foamex disc painted yellow with black lines and glued behind a larger white Foamex ring containing self-adhesive printed numerals. I could not find a font identical to the original and Guinness had no record of it, so I picked the closest I could find and customised the digits in Photoshop. My local printer then printed them on self-adhesive vinyl which I then stuck to the ring observing that, like the original, the number 8 was actually upside-down compared with the number 4 on the other side. 8 usually has the small circle on the top.
Clock face rear showing sensors and wiring.
Unfortunately, in practice, these optical sensors were found to be activated by strong sunlight. Experimenting with shielding never really solved the problem. In the end I changed the sensors to a more advanced type that used 38kHz modulated light. Along with software debouncing, this was found to be much more reliable.
You can see from the photo of the rear of the clock face, four standoff pillars. These are used to attach the clock face to the base board which is set back from the front of the clock tower. The clock mechanism (shown here) is also attached to the base board by a bracket and the threaded shaft on the front of the mechanism is screwed to the front of the clock face.
Close-up view of original minute hand sensor.
Quartz clock movement.
Around the outside of the complete clock face is the Arthur Ransome ring containing images of the book covers of the 12 books in the Swallows and Amazons series, written between 1929 and 1947. As mentioned earlier, these books gave me great pleasure when I was a youngster and have been with me all the rest of my life. I have a collection of largely first editions. I wanted good covers for them, and some years ago I painstakingly recreated covers identical to the originals, again using good old Photoshop. I printed “Reproduction Cover” on the front so the books would never be sold as having mint-condition dust jackets! Using the original artworks, I created the artwork for the ring and my local printer, Kevin Rose of V-Signs kindly printed it and laminated it onto 5mm Foamex board. I carefully cut this into a ring shape. The pictures between the book covers are significant images from the adjacent book of the same colour.
The original Guinness clock featured a similar ring that rotated once every minute. This featured various characters and animals used in their advertising. The mechanism for driving this is shown below.
"Arthur Ransome" clock outer ring.
Original clock face and mechanism*
I have used a very similar mechanism utilising five rimmed bearings used in 3D printers to hold the ring away from the baseboard slightly and positioned just behind the clock face so as not to interfere with the opto-sensors. In the lower right there is a geared motor attached to a rubber toy car wheel which is pressed up against the rim of the ring. This is sufficient to rotate the ring. I could not get a motor of exactly the right gear ratio to turn the ring once every 60 seconds, so I got a slightly faster one and slowed the motor by adding a small resistor in series with its supply. I later changed some of the bearings for large “mudguard washers” and spacers as the ring occasionally lifted and jammed on the rather small rims of the pulleys. The picture here is taken before the numbers were applied to the clock face. It also shows my first attempt at the hands. A little bit of jiggling was required to get the clock to sit exactly centrally in the rotating ring. Another tweak requested by Quality Control! In the end I painted the baseboard black.
To frame it all, I made three square frames from wooden mouldings. The first is an inner frame glued and screwed to the baseboard and painted black. This fills the gap between the baseboard and the inside of the Foamex skin. The other two are of the same size and sandwich a sheet of 4mm UV-resistant acrylic between them. This is then screwed through the large square cut-out in the Foamex skin onto the inner frame. The rear of the acrylic I painted with the phases of the moon and similar effects to the original Guinness clock. The outer frame I painted in gloss white paint. The brass screw heads are painted white also. To access the front of the clock these screws, 12 in all, need to be removed. Then the outer frame and acrylic can be removed from the front.
My clock ring mechanism.
The picture here shows a cross section of the upper half of the clock face as if viewed from the number “3”. Once assembled, I realised that some of the clock ring mechanism could be seen from the front. I later added a baffle ring made from worktop edging and painted black. This material was flexible enough to be curved but ridged enough to form a smooth circle. This I fixed to the inside of the outer frame with blocks of wood glued and pinned all around.
Ignoring some reflections on the acrylic, I am quite pleased with the result.
Finished Clock Face and ring.
Cross-section of clock.
Unfortunately, when I painted the back of the acrylic, I used adhesive masks to create the shapes, but in places the paint crept under the mask edges and gave a rather rough edge. This was rejected by "Quality Control". We decided that, as this was a key feature of the whole clock, quality could not be sacrificed. So, I created an artwork and sent it off to a professional acrylic printing company in Germany who created a perfect version. The image of the Finished Clock Face and ring shows the original version, however.
Play the video below to see it working!
As a footnote, after I completed the rear panels for the main tower, I realised I could no longer adjust the clock time for when the clocks change by an hour, without removing the rear panel. I decided to fabricate an extension to the adjustment knurled knob on the rear of the clock mechanism and extend it through the rear panel. I fitted an old Meccano gear to the outside end of the extension shaft to act as an adjustment knob!