MAKE A CLOCK THAT ROCKS
BUILD A CLOCK THAT EVERYONE WILL WANT TO WATCH
Edge-lit acrylic signs have been around for years. These days, most consist of a base containing the light source with a slot in the top. The bottom edge of the etched or engraved acrylic is inserted into the slot. Light then travels through the acrylic and refracts when it encounters the etched or engraved areas.
This type of sign is most effective when placed against a dark background or in a darkened room. Imagine if all the
I already had some 14mm thick oaklined floor panels and a sheet of 6mm MDF. I purchased a sheet of 3mm clear acrylic; a clock mechanism, complete with hands; and the LED strip with a controller. The total spend at this point was around $23 per clock. With screws, material for a stand, blackboard paint (I used a test pot) and the AA battery of the clock mechanism still to get, I was on target with the budget.
The key
The overall diameter of the clock was determined by the length of the clock hands, the number of flooring planks I was willing to use, and the font size I needed for the numerals/characters to be clearly formed with a 2mm end mill. The answer was a 290mm diameter clock using two floor panels and a 20mm high font.
This design can be modified to suit whatever wood you choose to use for the front and back plates. However, one of these plates must be a minimum of 12mm in thickness to accommodate the 10mm wide LED strip.
The length of the clock mechanism shaft also comes into play. With my design, the total thickness of the clock came to 17mm. The clock shaft was only 12mm long. I milled a pocket into the front and back plates, so the clock mechanism was flush at the back while allowing the clock shaft to protrude through the front with room for the washer and locking nut.
The key design aspect is to align the centre of the acrylic edge to the lens on the LEDs. I allowed a gap of 2mm between the acrylic and the LED lens.
Manufacturing the components
Dimensions for the front plate, back plate, and acrylic ring are shown on page 26.
Making the acrylic ring was a bit of a challenge as it was the first time I had used this material. The 3mm acrylic sheet I used is very flexible and is prone to ride up the mill or drill bit. After I had mangled my first sheet, I made a simple clamping frame to hold down the sheet to the CNC spoil board. The frame was made from 6mm MDF. I fixed another screw in the centre of the acrylic for good measure.
The acrylic comes with a protective film on each side. This is left on until the ring has been completely milled. Engraved numerals or characters do not have to be deep — 0.5mm works well.
Milling the front and back plates was straightforward. I painted the back plate where the acrylic sits with blackboard paint to accentuate the illuminated acrylic.