Sunday, October 7, 2012

Printing a clock...

I've always had an interest in clocks. They can be hypnotic and fascinating, masterpieces of mechanical engineering, and things of beauty. But could a clock be printed on a home 3d printer? Would it work? I was delighted to see a clock published to Thingiverse (The Makerbot clock) but was disappointed to learn that the hardware kit was no longer available. That didn't deter me.

The finished item is a simple and pleasing open style, weight driven, wall clock with a 9" face and 3ft pendulum.

It was a printing challenge and will test the accuracy of any printer. For the most part the gears came out cleanly and meshed well with each other when the clock was mocked-up. Some test assembly and hand turning highlighted a few sticky points. They where easily sorted with a needle file. I printed using my .5mm nozzle but in hindsight a .35mm nozzle would have resulted is better meshing gears and post print tuning/filing.

The range of parts can be seen in the above photo. If you study the MakerBot assembly instructions you can get an idea of the hardware required, but I had to deviate from the original bill of materials in a number of items. I could only source the tubes that drive the hands in metric dimensions so I had to alter the hole sizes in some of the printed parts to match my brass tubes. I sourced the little bearings on ebay. They were inexpensive and came in a packet of 10. The pendulum shaft and second-hand shaft are welding rods. The weights are filled with 2 Cent coins (Euro). The original design suggested a 1 Cent US coin. They are the same size.


To give added strength and enable wall-mounting I cut a circular backing board from some 15mm chipboard, and mounted the clock base plate to that. I used longer bolts than specified and allowed them to travel right into the backing board for extra rigidity in the assembly. The upper frames were quite light and didn't hold the gears quite as well as I would have liked.



Modifying the mechanism
When I first started the clock it was running too fast. The published escapement wheel has 15 teeth. That results is the second hand advancing by two second increments for each pendulum swing. But combined with a 1 meter pendulum, the second hand completes a full revolution in only 30 seconds. That said, I expect this clock was only ever published as a printing show piece and for it to tick/tock away in any fashion could be considered a success!

On examination of the SketchUp file included in the Thingiverse publication I found an alternative escapement wheel which had 30 teeth, allowing a more refined movement of the second hand. The escapement paddles also need adjustment to fit this wheel. (For anyone that really want's to get into the detail I found a good publication on excapement mechanics here: www.abbeyclock.com/EscMechanics.pdf )
That article is a bit over involved for this purpose but does show you how to draw paddles that are a good fit for the escapement wheel.



I exported my newly shaped paddles to .stl, then printed and fitted the two new parts.

The finished clock
The clock is probably as good as I'm going to get it now, for a home printed plastic clock it's pretty amazing! It will only run for a few hours on a single wind so don't expect it to replace your kitchen clock any time soon. I've provided a little video clip below so you can see and hear it in action!


Thanks for viewing!
NumberSix

2 comments:

  1. i have been trying to fix the minute wheel due to it being not a manifold. however netfabb has failed me, i was wondering how you managed to print the minute wheel and would appreciate it if you can provide the fixed STL file. also if you can provide the escapement wheel as well it would be great!

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  2. Hi Fai,
    I had no problem with the published minute wheel, but I'll happily send you on my local copy if you like. If it's the one-minute escapement wheel you are looking for then it's contained within the Sketchup file, and can be exported from there. (Can send you that also if you want it).
    Drop me a PM via the Forum.RepRap.org site and I'll mail the files to you via there.
    NumberSix

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