Hollow Clock 3

Hollow Clock 3 - The hour hand is no longer connected to the surrounding circle.

• Stepper motor 28BYJ-48 and driver board comes with
• Micro computer (Arduino nano, etc.) to control the stepper motor
• 2mm x 10mm tapping screw * 8
• grease (high viscous)

This clock is printable with most common 200 x 200mm printers, except decoration part (index.stl, 203 x 203mm). Smaller version (85%) would be added afterwords.

• Print parts with supplied posture.
• Some parts need supports.
• Deburr well. Especially, very small gears (worm and pinion gears at the center of the clock) should be very clean.

• Plastic welding with soldering iron is useful to connect gear.stl, axis.stl and worm-gear.stl each other.
• You can also use some secure glue such as two-component epoxy adhesive.
• Fill central gearbox with viscous grease. It will not only decrease friction but also backlash.
• Backlash of central gearbox much affects to the preciseness of the clock. Select better pinion gear from two candidates. h-gear1.1x.stl is a bit larger than original h-gear.stl to suppress backlash.

• If the head of 2mm tapping screw is smaller than the holes of stepper motor, use washers or larger screws.

• To avoid the gears drop out, flip body side (green part in the figure above), then engage the hook at top.
• Attach minute-cover with three tapping screws.

• Attach hour hand using a tapping screw with moderate force. It should slip when you adjust the clock.
• Attach hoot and index. It also holds the rotor.

• Connect port 4, 5, 6 and 7 to the stepper motor driver.
• Connect VCC (+5V) and GND.

If you want to enclose the circuitry, print following parts. It can be also assembled with two 2mm tapping screws.

Flash the code to the Arduino.

If your motor runs to the wrong direction, please change the order of the numbers in code as

int port[4] = {4, 5, 6, 7};

to

int port[4] = {7, 6, 5, 4};

where the numbers are related to the pins of Arduino nano (D4 - D7).

• Since the gear train has some backlash, the position of the hour hand deviates at left and right. To suppress such problem, insert soft material such as felt or sponge there to give weak friction.
• Paint the hands for better visibility. Pigment based paint is better than dye based ink which would spread by capillary action.

You can find some useful info in the comments at https://www.thingiverse.com/thing:5142739

• One minute advance with reset button of micro computer
• Fine position adjustment with reset button while the motor is rotating
• Hour hand can be adjusted by your hand (against the friction)

For smaller 3D printer (such as Prusa mini, 180x180cm), I prepared 85% scaled version.