Introduction: Hand in Hand Clock
I recently moved (and out of my parents home) and among the huge amount of stuff missing, is a clock. Now I like quirky stuff, so a bought normal clock simply won't do. There are already a ton of DIY led clocks out there, but I wanted something mechanical.
The thing I wanted is a hand in hand clock. This clock type has the minute hand attached to the end of the hour hand (and optionally, the second hand to the end of the minute hand). It is a fairly unknown clock type, but I was introduced with it 5 years ago by an old classmate and have been thinking about building one for 3 years now. Finally, with a clock missing, it was time to build one. The clock is 3D printable and requires no support. It does require a printer 200x200mm for the minute hand, but otherwise, 150x150 will also work.
This clock is (or will be) entered in the 3D Printing Contest, Move It Contest and Mind For Design contest. A vote would be great, but only if you think this clock has deserved it. Thanks in advance.
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Step 1: Parts and Tools
To make this clock you will need several things.For some of the screws, amounts may vary by a bit.
- 200-300g of 3D printing filament in a colour of your choice.
- 2x 608 bearing
- 3x 624 bearing
- 3x 683 bearing
- 3x 684 bearing
- 6x M3 washer
- 3x M3 nut
- 3x M3 screw, 6mm
- 6x M3 screw, 10mm
- 6x M3 washer, drilled to 4mm
- 7x M4 washer
- 7x M4 nut
- 2x M4 screw, 20mm
- 2x M4 screw, 40mm
- 1x M4 thread, 75mm
- 1x M8 nut
- 1x M8 thread, 25mm
- 1x Nema17 short stepper motor
- Any arduino compatibel microcontroller with at least 5 I/O's
- Stepper motor driver
- 9V or 12V power supply, 250mA+
- 16V 100uF electrolytic capacitor
- 2x switches
- 3x 10k resistor
- Piece of prototype board
- Thin cable or white wire
- A 3D printer
- A drill with 2mm, 2.5, 3mm, 4mm and 4.5mm metal drill bits
- Super glue
- Basic screwdivers, pliers and wrenches
Step 2: 3D Printing
The most laborious tast of the clock is 3D printing it. It is one of my smaller projects, but it will still take around 10 hours to print, depending on your printer and settings. I printed it at 40% infill, at 0.4mm layer thickness. I don´t want to hide the fact that it is 3D printed.
Download files here: http://ytec3d.com/hand-in-hand-clock/
A full list of the 3D printed parts:
- HIHC face minute bracket 1
- HIHC face minute bracket 2
- HIHC face plate
- HIHC hour hand holder
- HIHC hour hand
- HIHC HTM1 z48 m1.25
- HIHC HTM2 z45-12 m1.25
- HIHC HTM3 z48-15 m1.25
- HIHC minute bearing holder
- HIHC Minute end gear z12 M1.5 a25
- HIHC minute hand
- HIHC minute inbetween gear 1 z13 M1.5 a25
- HIHC minute inbetween gear 2 z15 M1.5 a25
- HIHC minute inbetween gear 3 z25 M1.5 a25
- HIHC minute Receiver gear z12 M1.5 a25
- HIHC motor gear z12 m1.25
Step 3: Hand Assembly
When the printing is finally done, you can start assembly. The starting point is the hands.
- Press fit an M4 nut in the minute hand. When you are statisfied it is perpendicular, use super glue to secure it. Also get as much weight as possible in the back of the minute hand, to balance it out. (this step can also be used for the hour hand)
- The Hour hand requires some work before it can be used. Drill the 6 holes with a 2.5mm drill, so the M3 screws will thread themselves in. Also carefully file the 2 bearing holes so the bearings will not destroy the hour hand.
- Press fit 2 684 bearing in the hour hand. Also press fit the 3 M3 nuts in the hour hand. The small holder needs a 684 bearing, the large holder a 624 bearing and the 3 gears need 683 bearings. The remaining 2 gears need M4 nuts, which need to be glued in place.
- Mount the 3 idling gears in the hour hand. The bearing needs to be down, and the 25 tooth gear (the largest gear) need to be placed first. After that, there is only one way it will fit properly.
- Mount the minute hand to the hour hand with the assembly of nuts and washers shown in the pictures. Use locktite on the minute hand when it fits right.
- Drill a hole through the 25mm M8 thread. Start of small (2mm) and work your way up to at least 4.5mm. Try to stay as much in the center as possible.
- Tap an M8 thread in the hour hand holder. Then, screw the hollow M8 thread in the hour hand holder, and when it is in the middle, glue it in place.
- Attach the M4 thread to the receiver gear. Use good thread locking glue on this, to secure it. It will receive the most strain of any part in the clock.
- Mount the hour hand holder assembly on the end, using the pictures as guide. Try and spin the minute hand to see how smooth it goes. If needed, you can sand some of the gears to make them run smoother.
- When you are satisfied that the hand assembly is running well, disassemble and use thread locking glue and super glue to properly secure everything in place.
Step 4: House Assembly
The housing holds all the gears and the motor.
- Press fit the bearings into the right components. The Housing needs 2x 608 bearing, on top of each other. The 2 brackets both need a 624 bearing. The HTM1 gear needs an M8 nut glued in place, and the smaller, HTM3 gear needs an M4 nut, but that does not have to be glued in place.
- if possible, try to use a 3.5mm drill to drill the 4 holes in the housing to make the M4 screws catch the plastic. Also use a 4mm drill on the HTM2 gear to get a clean 4mm hole.
- mount hand assembly in the housing, and secure it in place with the HTM1 gear.
- Mount the first bracket over the hands M4 thread. Do not yet secure it, but do align it.
- Mount the HTM2 gear, with a 20mm M4 screw. Do not over tighten it, or it will cause friction.
- mount the HTM3 gear over the M4 thread. Rotate it in place. At some point, it will engage in the gears of the hour hand, but this is no problem. Keep going until you reach the bearing.
- Set the clock to 12:00 by rotating the gears.
- secure the third gear with an M4 nut. Test the rotation to check if everything is running smooth.
- Press fit fourth gear to motor. You may need to file the gears and hole a bit first, then using a vice, press the gear over the shaft. You do need to have something on the other end of the shaft, so you are not breaking the bearings.
- Mount the motor, test rotation again.
- If everything is running smooth, Disassemble, then reassemble the entire housing with locktite and glue.
Step 5: Electronics
For the clock's microcontroller you will need something that has 5 I/O's and a built in power regulator. I used a trinket, which I stole from my bicycle rim lights (no front wheel anymore :( ) It has 5 I/O's, but does require some careful planning, because not all I/O's respond the same. 3 and 4 cannot be safely used as inputs. To run the stepper motor, I use a stepstick A4988 stepper motor driver. There are 2 buttons on the clock to make the time go up and down.
I made my circuit on a piece of prototype board. I do not plan on making more of them, and it is quicker than making a PCB. I cannot really share a design, because there wasn't one, but if you follow the schematic, it should be fairly easy to replicate. The input voltage (9-12V) needs to go to the Vin or VBat pin of you microcontroller. The 5V comes from the microcontroller.
To get the power to the clock, you can pick one of two approaches. First, you can try to hide the fact that there are wires running to the clock, secondly, you can make it pretty. I tried to hide the wires by using very thin white wires to feed the clock. The current to these wires on average will be only around 50mA, so there will be no problems.
Step 6: Firmware
The code will run this clock. It does not actually keep track of the time, it simply triggers a step on a constant interval. The length of the interval will depend on the electronics. I have a 1:4 reduction to the minute hand, and 200 steps per rotation. I also have 1/4 microstepping on the motor driver (the smallest amount before the steps will skip). Totaling this, I needed 3200 steps per hour. This means that the clock will step once every 1.125 seconds. This is odd, a clock that doesn't step every second, but it works.
The 2 switches on the back will make the time go up and down. holding both at the same time for 3-5 seconds will toggle the mode between normal running mode and fast running mode. Under normal circumstances, you should not need the fast mode, but I did need it, and it isn't in the way.
If the clock is running the wrong way, disconnect the power and rotate the stepper motor cable 180 degrees. Now the motor should be running the right way around.
The code is universal enough that it should run on any Arduino compatible microcontroller by simply changing the pin numbers.
Step 7: Final Thoughts
Before I end of this instructable, there are always improvements, and this clock is no exception.
- Normal clocks can run of a battery for years, this one needs a power supply. It will cut of power to the steppers after each step, but it still uses orders of magnitude more power than a conventional clock. I do not know if it is possible to make a clock like this, that can run for at least a month on some sort of battery, but it would require more efficient electronics and lighter motors.
- There is no second hand. This had to be, and it wasn't a wrong choice, but somewhere, it would have been nice. The problem is that the clock becomes more than twice as complicated with an added second hand. Maybe the next one?
- Noise. While it is not the end of the world noisy (it is about as noisy as most battery powered mechanical clocks) it still make a noticeable noise. Since my living room is my bedroom, I might look for a better alternative at some point. maybe something DC gearmotor with encoders. For living rooms it is fine, but for my bedroom, I might revisit.
- The hand are not balanced. This is not the end of the world, but for any future version that runs smoother and lighter, this will need to be fixed.
- The 3D printed gears are far from optimal. Sometimes they have friction, sometimes backlash, and sometimes both at the same time. Using a better printer would already help, but using cast gears would improve this clock immensely (but reduce the maker friendliness).