Tuesday, July 21, 2015

Building the planetary clock

20150723_112153One of the things I love best from my profession and my hobby is when I can see in real life what I created in my mind. Technology is great for me because I don’t have the skills to draw by hand in paper so computers and CAD programs helped me to develop my creativity.

Combining technical knowledge with creativity has been the most important tool for my work and now my hobby.

The planetary clock was a challenge. The diameter ratio of the sun pinion to the planet wheels for 12:1 reduction and 8 teeth pinion is at the critical point. Too much play in the teeth can make the system to block as two planet gears can touch each other. Any eccentricity  of the ring will block the system and if the teeth spacing is too tight the system will eventually lock itself.

I had to mill more than three times all the parts making small design adjustments to adapt everything to the tolerances for wood. It is almost impossible to obtain tolerances in the range 0 .1 mm with wood so I worked with .5 mm tolerances to allow space for the natural expansion/contraction of the wood temperature and humidity. I also made tests with hot and cool room temperature.


The picture below shows the three planet wheels, the sun pinion, the ring gear, the two ring covers


Below is a detail of the ring covers and the mill down of the sprocket area of .5 mm to allow some play of the planets in the axial direction. This also reduces the friction caused by expansion.


Next picture is detail of the planet gears support, all made form a single piece of wood milled and carved with the CNC to obtain the shape and exact position of the arbor holes.


Here a video of the the testing of the planetary gear: It works nice

Next was to make in the lathe the two circular bases, one is like a cup to hold the motor. The wood I used was so hard that I burned the small motor of the lathe. This is when a full replacement warranty is valuable!


Next finish the wood assemble and glue together everything and pray that it will work as before wood finish. I have found that the best finish for wooden clocks is to use Danish Oil. it is not sticky dries relatively fast it is very easy to apply.

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The numbers and the seconds and minutes dashes are engraved in the dial ring:


Here us the clock finished (front view):

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Here the back view of the finished clock:


Everything moves very slow in the clock so here are a couple of fast motion videos compressing 3 minutes to few seconds  to show how it works:


I love this clock!

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