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DIY Moon Phase Dial


Gina

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Found this :-

Quote

Sometimes used in clocks, the cage gear should always be driven by a gearwheel, not used as the driver.

Oh dear :(  Looks like a rethink required.

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Two thoughts :-

  1. Use two extra axles and gears (two needed to get the correct direction of rotation)
  2. Change to a lower mod to get more teeth on the pinion

For option 1. the gears could go in the space below the main axle.  Option 2. needs more precision or much larger gears.


 

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This clock differs from "normal" clocks in that the drive is on the fast end of the gear train whereas most clocks drive the slow end and other clocks use precision metal gears rather than rough and ready 3D printed plastic gears.  Both these factors make things more difficult in some respects.  Having a sweep seconds hand also complicates matters a bit but I'm not giving that up.  I think I'll stick with the stepper motor drive to the seconds as well since I have a pendulum clock on the books already.  Plus I've put a lot of time and effort into getting that sorted out.

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I'm looking at printing mod 1 gears and have designed a pair to try - just waiting for the printer to warm up.  I've printed mod 1 gears before when the printer was working well.  This would be simpler if it works but I think extra gears might be a better option so I'm looking into both approaches.

For a 60:1 ratio and an even number of gear pairs to get the right direction of rotation we need either 2 as before or 4.  2 pairs means 10:1 and 6:1 and 4 pairs will be 5:1, 3:1, 2:1 and 2:1.  Apart from less precision needed in production, I think this might make for a more interesting appearance by separating the gears.

Edited by Gina
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Finished printing the mod 1 gears and the section of large gear printed fine but the pinion didn't.  I might be possible to clean it up but being only 10mm diameter it's almost a microscope jobby :(  Unless I were to make a bigger clock and use bigger gears, 10:1 is not really on with 3D printing with what I have.  So it's extra gears then as I suspected.

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Using an axle spacing of 60mm makes calculations easy as it divides by all the ratios required in whole millimetres.

  1. 1:5  10t & 50t  10mm & 50mm radius mod 2
  2. 1:3  15t & 45t  15mm & 45mm radius mod 2
  3. 1:2  20t & 40t  20mm & 40mm radius mod 2
  4. 1:2  20t & 40t  20mm & 40mm radius mod 2

Now to the layout...  Here is a diagram of how the gears might be laid out.  Now that's a lot of gears :D  But they will be visibly moving when the clock is running.  This shows the vertical layout - next will be to see how they fit together horizontally.

New SM Gears 01.JPG

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This diagram gives an idea of how all the gears (except ratchet and moon drive) would look in the clock with the frame.  Spreading the gears out means I can keep the same spacing for the back of the main visible part and makes the gears easier to see separately which I think will improve the appearance.

New Gears and Frame 01.JPG

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I've now designed a 3D diagram in SketchUp of the gear train from seconds wheel to minutes wheel.  Here are some screenshots.  Side view, top and bottom.  The second intermediate gear needs a narrower cylinder between the small and large gears and will be printed in two parts.

New SM Gears 02.JPGNew SM Gears 03.JPGNew SM Gears 04.JPG

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More printing - intermediate seconds to minutes gear train with minutes wheel.  IM Gear 2a and 2b (to be glued together), 3 amd minutes.

New Intermediate SM Gear 2a 01.JPG

New Intermediate SM Gear 2b 01.JPGNew Intermediate SM Gear 3 01.JPGNew Minutes Wheel 01.JPG

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I think I have now printed all the new gears and a bracket to hold the two ball bearings for the main axle :)  Next job will be to arrange bolts to hold the gear bearings fastened to the back panel.
 

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Well, the UP Plus 2 3D printer is certainly working better but it has one annoying fault - the first layer is out of register with the rest and needs filing off from the sides and top of some of the teeth. :(

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Now :D

All the new gaears laid out in the clock case and the main axle bracket half with bearings in slots - the two halves fit together to hold the bearings and are then bolted onto the clock back.

New Gears 01.jpgNew Main Axle Bearing Support 01.jpg

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With such a "mess" of gears I'm wondering it they would be better in all different colours as I've done with my pendulum clock.  That will have to wait until I've got my Pilot 3D printer working again though as the UP is too fussy about which filament it will accept.

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Now have all the gears mounted and have run the clock in fast forward mode and it all seems to work fine except that the main shaft is still wiggling around so I can only conclude that the shaft is bent.  The shaft is run through two ball bearings and there is no plastic other than the support bracket and that's good and solid.

Here are some photos.  Firstly the gear train from stepper motor through the seconds wheel and all the intermediate gears to the minute wheel.  Secondly, the gear train in motion with the consequent blurring and finally with the intermediate wheel and hour wheel plus cam follower lever and pawl lever to ratchet wheel for the moon drive.

New SM Gears 05.JPGNew SM Gears 06.jpgNew SM Gears 07.jpg

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On continuous running test, the stepper motor is getting hot and causing the ABS motor gear hub to expand and loose grip on the motor shaft.  I don't think it's very hot by stepper motor limits but it wants cooling to maintain drive.  Previously the motor was mounted on an ali plate but now it's just mounted directly to the wooden back panel (with a small gap).  I have several spare CPU heatsinks so could attach one of these to the back of the motor.

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Adding a CPU heatsink certainly reduced the resultant temperature of the motor down to just warm but the thermal expansion was still enough for the gear to lose drive so I'm going for a 12mm OD steel sleeve with tapped hole for a grub screw with the hub of the gear going on the outside of this.  The grub screw can go through the plastic hub and stop slipping.

3D printing with the UP seems to have improved with much less offset of the first layer - no idea why.  These photos show the print before any cleaning up - first two still on the perf board.  A few tiny blobs but little first layer offset.  I wonder why you always seem to get these little blobs in 3D printing - tiny inclusions in the filament maybe?  Damp?  Filament kept indoors in dry conditions so I wouldn't have thought it was damp.

The pips in the last are where the print has gone into the holes in the perf board (not using raft).

New Motor Gear 01.jpgNew Motor Gear 02.jpgNew Motor Gear 03.jpg

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Turned a piece of mild steel round stock to 12mm OD, 5mm ID and 17mm long with a chamfer on one end.  I find mild steel much better to turn than aluminium - less tendency to chatter or dig in.  Then put it in the little vice and attached that to the micro mill.  Milled a flat for the grub screw with a flat ended cutter followed by twist drill bits to make hole.  Tapped hole for grub screw by hand.

Motor Shaft Collar 01.jpgMotor Shaft Collar 02.jpgMotor Shaft Collar 03.jpgMotor Shaft Collar 04.jpg

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