GearHeads Forum

I know this is an old post, but I did some calculations a while back that might be interesting.

Google says that the lunar cycle is 29.5305888531 days.  A standard lunar dial turns half a rotation per lunar cycles or once per 59.0611777061 days.  The hour hand rotates twice per day, so the gear train should divide by 2 times 59.06... = 118.1223554124.

A gear train can be built using an 8 tooth pinion on the hour hand driving an 84 tooth wheel with another 8 tooth pinion driving a 90 tooth wheel.  This would have a ratio of 84/8 * 90/8 = 118.125 which is extremely close to the target of 118.1223554124.  The error would be less than 1 day per 120 years.

Steve

Hi Donovan,

Good looking clock - congratulations, I hope you have as much fun an challenge as I do with these projects.

I approached the moon dial from a slightly different angle.  I have only one moon  but with two "shadows" on opposite sides of the shadowing wheel, since one would be waxing for half the rotation and the other waning for the other half.  In this way I was able to only have 59 cogs (I used a pin driving a ratchet design)

Donovan;

Your clock is awesome, great job..


Cheers
Bob

Thanks for the complement.  It is indeed laser cut. 

To clarify,  I want to create the typical Moon Dial as seen on many grandfather clocks. 

I need a wheel which will rotate once every 59 days.  59 days is the length of two lunar cycles.  On this wheel,  I will place two pictures of the moon at opposite ends of the wheel.  Only one picture of the moon will be visible at a time.  As it rotates, the moon will slowly be covered up by a circle making it a crescent shape.  Once the Moon is fully covered up, the second Moon will start the cycle. 

Since there is such a huge gear ratio involved,  I will attach a gear with only one tooth to the hour hand.  This gear will rotate twice a day moving the "Moon Wheel" which has 59 X 2 teeth.  Since it advances two teeth per day, it will take 59 days to rotate.   

Donovan,
Read it twice and still not sure what you are saying  ;D mostly dutch to me.

But I do like your clock.
Laser cut?

Really need to get back on my laser to try and get it going.

Here's my latest.  It has a two second pendulum that ticks once per second. A hand is attached to the escape wheel to indicate the seconds.  It has a running time of about 18 hours.

For my next clock, I will try to get the running time to be about 30 hours and to include a moon dial. 

The lunar cycle occurs over a period of 29.5 days. The "Moon Wheel" will have two moons at opposite ends of the wheel, and will revolve once every 59 days!  The easiest way to accomplish this  (I believe) would be to have a "Moon Wheel" with 59*2 = 118 teeth and a pinion attached to the hour hand with only one leaf.  This one leaf pinion would advance the moon wheel two teeth per day.  Since there is no torque on the moon wheel, I don't need to worry about any slipping.    Although it can be done with one pinion and one wheel,  I will probably implement it as a train of wheels and pinions. 

Any thoughts?

~Donovan