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SP12 (Crazy Gear) Gear Weights

Hello! I am about to embark on my first printing of the SP12 Crazy Gear clock. This will be my first experience clock building! In addition, I was interested in making some modifications to the larger gears so that they have a more classic gear appearance. For example, my modified gear2-36-8:

The tooth profile remains the same. However, this will add weight to these gears, on the order of an additional 65% to 70% increase on average. These are the gears I plan to modify, along with the weights reported by my slicer:

gear2-36-8 - From 26g to 44g.

gear3-36-8 - From 32g to 51g.

gear4-36-8 - From 27g to 48g.

gear5-36-12 - From 31g to 50g.

gear6-32 - From 16g to 32g.

gear7-36-ratchet - From 43g to 68g.

gear8-36-8days - From 77g to 125g.

The total weight change (based on the slicer info) is going from ~252 grams for the normal gears to ~418 grams for all the modified gears, for a total of ~166 grams of additional weight. I would note that I did not modify the escapment gear.

My question is: will this increase in weight prevent the clock from running, or from remaining accurate? I intend to run it at the 8-day limit. Would I simply need to increase the drop weight to compensate? Or do these gear weights have any bearing on the clock at all?

Thanks!

Tim

3 comments

3 Comments

rushl

Sep 18, 2023

I will do so, thank you! I do see what you mean about the filament flows. I'm planning on printing the gears with a wall count of 10, using a 0.36mm line width (and a 0.6 nozzle). Sliced, the gears are looking like:

My plan is to print outside-in for the walls, with the intent of getting the highest dimensional accuracy. The small internal gaps are left to act as a buffer to handle any overextrusion. Of course, they'll get covered over on the top and bottom layers. I'm happy to share my modified gears if you like! Although they've yet to be tested. You might already have a similar set, but if not it could save you some time if you're intrested.

Thanks for your help, and the very cool clock design!

Tim

Steve

Sep 18, 2023

Replying to

The outer gear profile is the only part that actually does any work. In a clock, only one side of each tooth actually touches, since the clock only runs in one direction. The rest of the gear is mostly cosmetic. Printing outer profiles first seems like a good idea. These gear teeth have fairly loose tolerances, so it might not matter.

These gear tooth profiles originated from a plan to convert to wood gears for cutting with a 1/8" or 3mm router bit. Different media can use different cutouts. Mine are optimized for 3D printing. Yours are closer to what would be used for wood gears, although the spokes would need to be wider. I like to design them with inner corners to fit an oscillating spindle sander. Brass gears often have sharp inside corners. It is perfectly acceptable to deviate from these values, with one downside being the extra weight, as you have already noticed.

Steve

Sep 18, 2023

The extra weight should have some effect since the gear train needs to start and stop with each pendulum swing. You are correct that the solution is likely only a small increase in drive weight. It is probably minor, since the rotational inertia should be a small portion of the overall power requirements.

The main reason I used the gear profiles is to create smooth filament flows during printing. The printer produces this:

Instead of this:

The secome picture has a lot more tiny movements, more retractions, and it will result in additional stringing. The extra stringing won't be an issue with the large gear profiles in these clocks, but it could be significant with smaller gear teeth.

Also, I think the narrow rim merged with the gear teeth looks great. It's cool to have a different opinion and it will create a different look. Please post picture of the final product if you get a chance.

Steve