### Parametric OpenSCAD Clock Gear Train (Hours, Minutes & Seconds)

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Published on April 16, 2011
This thing was Featured on April 18, 2011

#### Description

Extended the previous Proof of Concept for the printable clock to include the entire gear train.

I had to use a total of eight pinion wheels, four to gear down from the escapement/seconds wheel to the minutes wheel, and another four for the hour wheel (5,3,2,2). Two would make for high gear ratios (10,6 or 8,7.5 typically) which are hard to print, and three would make the minute hand run counter-clockwise.

I wrote the OpenSCAD script so that all the wheels are equidistant (by adjusting the tooth size pair by pair) and so that the gear train can be bent at each wheel in order to stack the second, minute and hour hands on top of each other (e.g. with four wheels between hands, you need to fold by 90 degrees between each wheel).

It is all fully parametric for that distance, the fold angle, the gear ratios, and number of teeth for each wheel... and you can animate the gear train, they will all rotate at the correct speed and mesh.

The only thing I was not able to do is to make the code recursive, because OpenSCAD does not support that. Booh!

#### Instructions

Feel free to play with the OpenSCAD script and try different configurations:

Set the fold angle to zero to lay out the gear train for a looooong clock.

Remove the first two gears, adjust the remaining six gear ratios to something like 5,4 & 3, and make the fold angle 120 degrees for a triangular clock with retrograde minute hand.

Remove the first four gears, adjust the remaining four gear ratios to something like 8 & 7.5, and make the fold angle 180 degrees for a more typical two-arbor clock.

(EDIT: I've added a OpenSCAD script, some JPEGs and an STL of a two-arbor clock with gear rations 10-6-10-6, and open-face gears. Just because.)

Last friendly warning: on my two year old Thinkpad, the eight wheel gear train takes 12 minutes to process in OpenSCAD. :-)
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Is there anything you'd like the greater Thingiverse community to do to help you on this project? I just thing this is so awesome and can't wait to print out a grandfather style clock!

Thank you! I think multiple heads are better than one, so anyone with an interest in clocks is certainly welcome to grab the escapement library and play with it... ad majorem thingiversi gloriam.

The one thing I definitely need help on is tuning the escapement itself so that it works. They can be finicky beasts and I don't have a way to test the design myself... but people should work on whichever part they find interesting!

Did you use the formulas for involute gears in OpenSCAD?

The teeth look much like triangles on the photos.

Yup, I used the module from the MCAD library.

In an effort to have roughly the same tooth size everywhere, I tried to keep the product of the gear ratio and the number of teeth on the pinion roughly the same. In order to be easily printable, I also tried to use the smallest number of teeth possible.

The combined result is: for the 2:1 ratio,
the corresponding pinion has 9 teeth, for 3:1 it has 7 teeth and for 5:1 it is has 5.

You can clearly see on the two top wheels that they have a 5-tooth pinion with very undercut teeth, which naturally meshes with rather triangular-looking teeth. Undercut teeth are hard to manufacture traditionall
y, and more fragile. The first problem is not pertinent in a 3D printer, and the second is obviated by the fact that the pinion is supported by the larger gear it is 'glued' to.

We could bump all the pinions up a grade to have teeth that look more like what you would expect, but that would mean sma
ller teeth.

The nice thing about OpenSCAD and parametric design being, of course, that it only takes some trivial changes to the parameter section of the script to try that out!

:-)

now all we need is a case and some hands and we're (excuse the pun) ticking!

Well, we still need a power source, and some kind of nesting axis system for the hands, and we need to make sure the escapement actually works... but we're making progress! :-)