Metric Clock (Analog)

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Metric Clock (Analog)
The Metric Clock[1] was invented by the French after their Revolution of 1789[2]. It divides the day into 10 hours, not 24 hours, with 100 minutes per hour and 100 seconds per minute. This project is about creating an analog Metric Wall Clock with a real 10 hour day single day cycle. Metric clocks sold today have a metric face but a 12-hour mechanism. This project is for naught without a real 10-hour a day clock mechanism. But how to accomplish that? A 12-hour clock completes two cycles in a day. A metric clock completes one cycle in a day. Modify a 12-hour clock mechanism to move the hands at half-speed and we have a metric clock mechanism! Now all I have to do is figure that out how.

Phase 1. Converting a 12-hour analog clock mechanism to run at half-speed

Purchased an ArtMinds mechanism for inspection. See Figure 1 below. The mechanism itself is a Sheng Bang Model HD-1688[3]. Which HD-1688? Take your pick.

Removing the back cover, Figure 4, revealed gears. Removing the gear chassis, Figure 5, revealed more gears and fully exposed the circuit board with the electric motor.

The choices are changing the gears to make them run a half-speed or making the circuit board run at half-speed. Changing the gears means calculating new gear ratios, finding suitable gears, hoping it all fits, then that it runs continuously without jamming. Too many possibilities for failure in that approach. Looking at the circuit board we find it is controlled by one quartz crystal oscillator.Replace that with one half the frequency and the hands should move at half-speed. But what is the frequency? There is nothing printed on the oscillator and Sheng Bang technical support is useless. Never can find a frequency counter around when you need one.

Table 1: Sheng Bang Model HD-1688 Mechanism Figures
Figure 1.
ArtMinds clock mechanism.
Figure 2.
Figure 3.
Figure 4.
Back, cover removed.
Figure 5.
Back, gear chassis removed.
Figure 6.
Circuit board.

The typical quartz clock[4] uses a 32.768 MHz Quartz Crystal Resonator.[5] Assuming the HD-1688 uses a commodity 32.768 MHz Quartz Oscillator try replacing it with a 16.384 MHz Quartz Oscillator and hope it runs at half the speed.

Phase 2. Converting a 12-hour analog clock face to a 10-hour analog clock face

Clock Numbers

This requires an analog wall clock with numbers that can be replaced or rearranged. After looking over wall clocks online, replacing the numbers is the best option. But with what? Hand drawn, stickers and house numbers are the only ready options. What size house numbers? That will determine everything. Six inch high numbers seen too large, even on a 33" clock. The four inch numbers are too small for a wall clock. Settle on 5 inches. That calls for a 31" diameter clock. The Gatehouse 5" numbers from Lowe's Hardware[6] look better on that size. They look too small on a larger face and cramped on a smaller one. These numbers were chosen because I find them visually appealing. Then Lowe's discontinued the line and I had to scramble to acquire them all. Went through three suppliers before finding that stubborn #2.

*Model numbers were changed, causing more confusion.
Table 2: Gatehouse Numbers Used for the Clock Face
Item 178709 Model 27040PKBLG 5"x2 5/8"
Item 178308 Model 27041PKBLG 5"x1 5/8"
Item 178311 Model 27042PKBLG 5"x3"
Item 178332 Model 27043PKBLG 5"x3 1/8"
Item 178358 Model 27044PKBLG 5"x3 2/8"
Item 178403 Model 27045PKBLG 5"x3"
Item 178527 Model 27046PKBLG 5"x3 1/8"
Item 178531 Model 27047PKBLG 5"x2 6/8"
Item 178583 Model 27048PKBLG 5"x3 5/8"
Item 178611 Model 27049PKBLG 5"x3 1/8"

The numbers six and nine had issues. Some paint came off six while opening the package and both were painted in flat-black, see Figure 11. The other numbers were painted in a matte-black. Took number four and matched it to Rust-oleum Matte-Finish, 263422 BLACK, hoping it would work. Looking at Figure 12 the match was dead-on.

Figure 7.
Figure 8.

Clock Face

  • Any attempt to erase a mark on the face, with anything, will take the finish off with it. So don't make any mark you don't intend to cover with paint.

For the clock I chose the "Floral Medallion Wood Wall Clock" from Hobby Lobby, see Figure 9[7]. The clock is the right size, 30.5" or 80cm, the numbers are easily removable, and the wood back plane can hold screws from the new numbers. The floral disk is tin and measures 13" or 33cm across. That's the upside. The downside is the weight, 10.4 pounds, is heavy. Most customers complain the hands don't work or fall off. After examining its truly crappy mechanism I understand why. But that will be replaced anyway.

After the numbers are removed divide the face into 10 even segments, drill pilot holes for the number and paint a white circle just where the number will be, as shown in Figure 10. The "10" at the top and "5" at the bottom. Some contemporary metric clocks have a "0" but the vintage French metric clocks always had a "10" at the top. Figure 11 shows the actual clock.

Figure 9.
Flora Wall Clock.
Figure 10.
Planned Clock Face Design
Figure 11.
The actual clock.

To place the numbers on the Clock Face without guide marks use a cardboard circle as a template. Then place the template over the clock and drill the holes.

Removing the Old Roman Numbers

The real clock is shown in Figure 9, above. The first idea was to use a solvent to dissolve the glue holding the numbers to the face without staining or damaging the wood face. This proved infeasible as no liquid could get to all the glue. The second idea is to insert a blade between the number and clock face then tap it until it cuts through the glue. First secure the clock to the work table with a C-clamp in Figure 13. Notice the rag around the clock and table so the clamp won't leave any marks. Then insert the putty knife between the number and face. Use very light hammer taps to cut the glue and separate them as in Figure 14. But as we see in Figure 15 it took the glue and wood up leaving marks. Multiply that by 11 more numbers and the face might be unusable.

Figure 13.
Figure 14.
Putty knife between the face and number.
Figure 15.
Putty knife alone.

Going to need something sharper for this job with a much wider blade. Seems DeWALT makes a wide snap-off blade, Figure 16. The blade is thin enough to work between the number and face and also wide enough for a whole number. See Figure 17. Place the blade. Use the putty knife to push the blade and a few hammer taps. Looking at Figure 18 there are few marks at all. Figure 19 shows the face with all the numbers removed and in the same position as in Figure 11. Notice how the marks at number one stand out.

Figure 16.
DeWALT blade.
Figure 17.
Blade and putty knife.
Figure 18.
Number 2 removed.
Figure 19.

Arranging the New Arab Numbers

On a 12-hour clock face each number occupies 30° as shown in Figure 9. On a 10-hour clock face each number occupies 36° as shown in Figure 20. This puts four numbers on horizontal axis, 2,3,7,8. The result groups the numbers into three sets. The Green Set with 1,4,6, and 9, as shown in Figure 21. The Blue Set with 2,3,7, and 8, as shown in Figure 22. The Red Set with 5 and 10, as shown in Figure 23.

Figure 20.
Ten numbers with 36° arcs.
Figure 21.
Green group 1, 4, 6, and 9.
Figure 22.
Blue group 2, 3, 7, and 8.
Figure 23.
Red group 5 and 10.

Now to apply this to the real face. Removing the tin-foil center earlier leaves too large a hole for drawing the radial lines. The solution was to bolt three cardboard sheets to the face and use the tin-foil center to locate the exact center. Using the center groove to align the horizontal axis and the hole to align the vertical axis for the 10-segment compass, as shown in Figure 24. Marking the radials and vertical axes with white paint places the radial spacing on the actual clock-face. That describes the radial spacing.

The polar spacing is described by the distance between the tin-foil center and outer edge which measures 9 1/8" exactly, as shown in Figure 26. This leaves 2 1/16" above and below the Red Set numbers. Spacing with the other groups will vary, especially at the corners.

Figure 27 shows the grooves made by joining the four boards together to form the face. They are 8" or 20cm apart and will make good references for arranging the numbers.

Figure 24.
Blank clock face with 36° compass in the center.
Figure 25.
Clock face with the 36° radial lines painted on.
Figure 26.
The distance between the floral tin center and the edge is 9 1/8".
Figure 27.
Four planks 20cm wide make up the face.

To place the Red Set I drew a white line between the radial lines top and bottom. Then cut a cardboard block 2 1/16" wide. The 9 1/8" space minus the 5" letter is 4 1/8" divided by two is 2 1/16". Using the block the numbers are always centered along the polar axis and the radial axis, as shown in Figure 28. Marked the drill points through the number screw-holes with a green marker, which looks black on the wood, then drilled pilot holes, as shown in Figure 29. Number Ten is a composite with the first step being how much space to put between the One and Zero. Separating them with the One's shaft width, 7/8", looked the best, as shown in Figure 30. The drill holes for Number Ten are shown in Figure 31.

Figure 28.
Number Five centered.
Figure 29.
Drill holes for number Five in white circles.
Figure 30.
Number Ten centered.
Figure 31.
Drill holes for number 10 in white circles.

The Blue Set is actually two sets aligned along separate vertical axes and the equatorial horizontal axis, as shown in Figure 22. The Two and Three group are shown in Figure 33 aligned along the equatorial groove and half way between the outer edge and the tin-foil center's left side. The Seven and Eight Group are aligned the same way on the tin-foil center's right side. Aligning Two and Three relative to each other was done by placing the yard stick to their right and at a right-angle to the equatorial groove. Pressed the yard stick to the numbers and, alignment! Aligning the Seven and Eight to each other was more difficult. The Seven has a flat vertical profile on the left side side while the Eight has a flat vertical profile on the right side. Fortunately, the top drill hole for the Seven is right in the middle. Placing that on the vertical axis and leveling its top gave the perfect position. The Eight has no flat sides and looks good at different angles relative to the vertical axis. Hmm. Looking at its picture in Table 2 both lobs line up along the vertical axis on the right side. Press the yard stick against Eight's right side and push it until the yard stick touches the Seven. The whole Blue Set arrangement is shown in Figure 35.

Figure 32.
The Red Set arrangement.
Figure 33.
Two and Three with their drill holes in white circles.
Figure 34.
Seven and Eight with their drill holes in white.
Figure 35.
The Blue Set arrangement.

The Green Set numbers occupy the corners between the Blue Set and Red Set, as shown in Figure 21. To align the numbers center each in its radian. This is done just as in the Red Set by drawing a center-line down the radian and marking it at half the polar distance, then putting a cross on that spot true to the horizontal and vertical axes, as shown in Figure 36. The next problem is centering the number on that spot and at the right angle. For this I again referred to Table 2. The numbers One and Four were easy since their center shaft is exactly vertical. The numbers Six and Nine are identical so the alignment for one is the inverse for the other. The whole Green Set arrangement is shown in Figure 37. The complete number arrangement is shown in Figure 38.

Figure 36.
Number Six by its center with white drill holes.
Figure 37.
The Green Set arrangement.
Figure 38.
All the numbers arranged.

Painting the Clock Face

There are two paint scheme options. Paint a white circle under the numbers, or, paint the whole clock face white. Try for a circle and if that fails paint the face white. This will require two cardboard cut outs to mask the clock face. The numbers are 5" tall so make the circle 6" wide. Subtract 6 from the 9 1/8" wide surface leaves 3 1/8". Divide that by two for the inner and outer edges leaves the cardboard cut outs at 1 9/16" wide each. This is illustrated in Figure 39. First a test. Layout paper and the mask on the garage floor, as shown in Figure 40. Use Personal Protective Equipment and ventilate the garage. Figures 41 and 42. Apply black spray paint produces a pretty good shape in Figures 43 and 44.

Figure 39.
Clock face with cardboard masking.
Figure 40.
Mask test.
Figure 41.
Personal Protective Equipment (PPE).
Figure 42.
Open garage.
Figure 43.
Figure 44.

Time to paint the clock face. Use four C-clamps, painters tape and whole lot more paper, as shown in Figure 45. Figure 46 shows the clock with one coat. Decided to leave it at that. Put the numbers on and the floral disk and it is finished in Figure 47.

Figure 45.
Clock face read to paint.
Figure 46.
Clock face with one coat white paint
Figure 47.
Final clock face.

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