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Author Topic: fancy gears  (Read 225 times)
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steve323
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« on: June 22, 2019, 09:28:37 PM »

Gary's Wooden Clocks has a web site at http://garysclocks.sawdustcorner.com/fancy-gears.html with a descripti on of what he calls fancy gears for clocks.  The concept is that clocks only rotate in one direction, so the back side flank of each gear tooth can be cut away to provide additiona l clearance .

This is good for a wooden gear clock, but the teeth might become weak.  I applied the concept to a 3D printed clock with amazing results.  The biggest benefit was made by optimizin g each gear by observing the slicer output.  I started with 20DP gears at 14.5 degree PA.  The active tooth surface was drawn and the tooth was made 0.060" wide.  This prints with 2 inner and 3 outer passes.  The rim and spokes were made 0.090" thick to print with 6 passes.

The pictures below show the sliced output of fancy gears and normal gears.  Notice all the tiny infill segments  on the normal gears (marked in green).  Each one has a retractio n and the possibili ty of creating a string or a small blob.  These small imperfect ions add slightly to the surface roughness .  The fancy gears print about 25% faster and are amazingly smooth. 

It looks like involute gears could be made with as few as 8 teeth or possibly even 6 teeth using this method.  One downside is that the gears become direction al so you have to be careful to always use the active side of each tooth.

I changed out the gear train in my clock (https://www.thingiverse.com/thing:3524448) and it works great.  The gear train without the escapemen t starts moving with 7 ounces of weight compared to 8.5 ounces for the normal gears.  This design uses 12 tooth pinions, but I may try a smaller design with 6 or 8 tooth pinions. 

Steve


* fancy_gears_sliced.jpg (65.2 KB, 855x686 - viewed 32 times.)

* normal_gears_sliced.jpg (65.16 KB, 728x491 - viewed 33 times.)
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ArtF
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« Reply #1 on: June 23, 2019, 06:45:28 AM »

Steve:

  I hadn't really considere d unidirect ional gears allowing that..

  'Preciate the thoughts. . nice work..

Art
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John T
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« Reply #2 on: June 23, 2019, 11:38:15 AM »

I have also made a clock using Gary’s concept and was very happy with it - no major “debugging” necessary .  Mine was made using CNC and Baltic Birch.
Would love to see your finished project.
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steve323
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« Reply #3 on: June 23, 2019, 02:18:22 PM »

Here is a picture of the completed clock and a stack of test gears in various sizes.  The clock looks a lot like the normal version because the large gears have somewhat normal shaped teeth.  The pinions look a lot different, but they are mostly hidden from view.

I was a bit worried about the tooth strength because of the narrow root.  However, they are quite strong because the print path is a continuou s length of filament.  The rim flexes well before the tooth bends.

Steve


* IMG_20190623_115126555b.jpg (113.24 KB, 586x816 - viewed 29 times.)

* IMG_20190623_115220975b.jpg (94.54 KB, 613x847 - viewed 30 times.)
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Mooselake
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« Reply #4 on: June 24, 2019, 10:54:33 AM »

That's an impressiv e pile-o-gears!

The latest PrusaSlic er (formerly slic3r PE) claims to have added wipe into infill, wonder if it might help with the infill related roughness on the gear teeth.  I'd suggest you try a really fine nozzle diameter, during a tiny tree frog competiti on a long time ago I made nozzles down to 0.2mm on a Unimat SL, but I suspect it's easier to buy them these days.

My temporari ly enforced post-knee surgery idleness is causing way too much spare time to think about expanding the essential ly tool less southern mooseshop and picking up the very long project wish list

Kirk
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steve323
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« Reply #5 on: June 24, 2019, 12:30:28 PM »

Wipe before infill looks like a good option.  I am using PrusaSlic er, but it might have a different name.  I will search for it.

The biggest advantage s with fancy gears is additiona l clearance with low tooth count pinions.  My last clock uses 12 tooth pinions.  This increases the size of everythin g else and the total print time is around 90 hours.  Fancy gears should allow the use of 8 tooth pinions and a much smaller clock.

Steve
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Mooselake
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« Reply #6 on: June 24, 2019, 01:44:30 PM »

90 hours!  I think my longest single print was more like 24.  Despite advising people (mod on a couple 3d printer forums...) to continuou sly monitor their prints due to potential fire danger, even at 24 it's just not possible.  Hopefully the smoke detectors catch it.

Hmm, already using PrusaSlic er.  Do you have a Prusa i3 and if so what do you think of it?  My Printrbot and Thingybot delta, plus all the supplies, are a couple thousand miles away and I'm getting the 3D printer itch again.  An i3 mk3s and the mmu2s upgrade (5 filament feeder, extracts one filament and feeds another) looks more attractiv e every day.  I've seen a i3 mk2 running (another printrbot talk mod) and was suitably impressed with it


Kirk
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steve323
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« Reply #7 on: June 24, 2019, 03:22:05 PM »

90 hours is the total print time.  The largest component is the weight shell at 17 hours.  Each half of the frame is around 12 hours.  Most of the rest are under 2 hours unless grouping multiple items.  I trust the Prusa enough to start a job in the evening that will run unattende d all night.  It is inside the house and we are well protected with smoke detectors .

I have a Prusa i3 MK3 and really like it.  I considere d the multi-material upgrade, but wasn't sure about the reliabili ty.  Every color change needs to cut, retract, reload, and purge the filament.  There are too many possible failure points.  Manual color changes by layer have been working just fine for my clocks.

Steve
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