Some History And Background
I've written in the past about 3D printing tourbillons. These are, in essence, the timing core of certain clock and watch mechanisms. They regulate the rate of the overall mechanism by means of an arrangement of a spring, an escapement wheel and a shaped piece called a fork. You can think of a clock as consisting of a power source (like a weight or mainspring) and a gear train which provides the right ratio between the movement of the hour, minute and seconds hands. The tourbillon alternately locks and then releases the entire mechanism so that the timing of this gear train is regulated. It requires precision, to get the timing right, and strength, as it has to slam into place to halt the whole mechanism and then hold back the power source until it is time for the next tick
As such, 3D printing from plastic doesn't seem like a good design choice. Plastic deforms (bad for holding back the mechanism), is springy (bad for exact timing) and is weak (bad for resisting the forces when it has to halt the mechanism). Nevertheless, there have been some remarkable successes in printed designs for clockwork mechanisms based on tourbillons. Here are some examples:
- Mechanical watch by TheGoofy (design, video), driven by a plastic spring.
- Clockwerk deep space tourbillon (design, video), driven by a weight.
- NOP21's Gyrotourbillon (design, video), driven by a metal spring.
- Cabestan triaxial design by mcmaven (design, video), driven by a stepper motor.
- Astronomia triaxial tourbillon, based on a watch design by Jacob and Co. This has been through multiple versions:
- the original design by A26 (design, video). It used a weight as a power source.
- mcmaven's improved version (design, video), also using a weight.
- a variant in which the overall motion and the tourbillon are driven mechanically with a weight as the power source, but the timepiece is replaced by an off-the-shelf quartz clock (design, video).
- a further modification in which the weight is replaced by a pair of stepper motors (design, video 1, video 2). This is called the Triaxial Motorized design, and it's what I'll mostly be talking about here.
- Escape wheel: needed special slicer configuration to set the perimeter width to 0.35mm. Otherwise the PrusaSlicer discards part of the model.
- Fork frame back: slightly changed the dimensions of the hex "plugs" so they fit more easily into the fork frame.
- 40T fork frame gear: added a MR52 bearing
- Crown gear: dispensed with the bearing spacer and instead added set screws for the bearings. . More on this and the 40T gear below.
- Base Gear 2: split into two parts.
- Base Frame 2: split into two parts.
- Carrier shaft: added 1mm pins for aligning the halves and scaled by 0.98.
- Stepper pinions: slightly scaled the interior hole so it fits more easily on the stepper shaft, after breaking them several times.
- Counter weight and cover: added screws to hold them together. Slightly scaled down the length so it fits in the crown gear more easily.
- 8T gear: scaled the interior hole for a closer fit.
- Base bottom: added a rim to get extra depth for the wiring. This would have been better as a change to the base, but by then I had already printed it.
- Globe shafts: merged the half models and then split them perpendicular to the axis. This gives a nicer appearance in the printed result. Used a 1mm pin to align the parts.
- Globes: I replaced these.
- T Frame Middle B: slightly reduced the size of the top cylindrical element. See below.
- Fork: made the fork pin slightly thinner. See below.