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Longcase Pendulum Clock


Gina

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Traditional longcase (grandfather) clock but using 3D printed gears etc.  Also transparent acrylic clockface and mechanism front and back plates to show all the works.  The case is made of wood and pretty much traditional shape.  In addition to the usual hour and minute hands and dial this clock will have a moon globe above the main clock face similar to my moon dial clock.  I may add a small seconds dial if this proves viable.  There will also be an auto-winding mechanism driven from a stepper motor.   I'm hoping to add a striking mechanism once I have the main clock working.

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Gina

Posted (edited)

However hard I try, including some "thinking outside the box" there seems to be no way to have the striking mechanism on the right and that includes the rack lever with peg, without complicating it (more levers and pivots).  The probe (whatever sort) cannot clear the 1 o'clock part of the cam from the 12 o'clock position.  I even tried cutting back the cam but then the 1 o'clock wouldn't work.  Oh well, I've had a lot more CAD practice! ?

Edited by Gina
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These diagrams show the rack and small snail cam that lifts it plus how the lug on the end of the rack stops the action when the required number of strikes has be achieved.  The small snail cam shown in the second diagram rotates until it contacts the lug on the end of the rack and striking stops.

131016240_Screenshotfrom2018-10-0118-20-01.png.02b979b061f5b8aee2d9b31c811d7fd7.png1619453501_Screenshotfrom2018-10-0118-39-44.png.98b0ffbc1d87590136bd10175e6ca8fc.png

 

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Gina

Posted (edited)

This diagram shows the dimensions of the 3 shafts relevant to the getready/start which is controlled from the minutes shaft.

195443310_Screenshotfrom2018-10-0119-31-47.png.4894f29d5fc1ec4634cf5d831b446531.png

Edited by Gina
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Just before the hour, a cam on the minutes shaft applies a stop to the striking main shaft and then the rack pawl is lifted releasing the rack which falls until the probe hits the large snail cam.  On the hour the cam on the minutes shaft releases the pawl and striking shaft stop and the striking mechanism springs into motion.  With each revolution of the striking shaft the rack is raised one notch and the gong or bell is struck by a hammer.  As mentioned above, striking continues until stopped by the lug on the rack engaging with the small snail cam.  The process then repeats around the next hour.

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Gina

Posted (edited)

Reversed the main gear train to accommodate the striking mechanism on the left.  To make use of gravity on the pawls the auto-winding motor will now go in the middle.  This has one advantage that it can auto-wind both the main clock drive and the striking mechanism, if I can work out the gear ratio suitably.

672107090_GearTrain06.thumb.png.cd96c3f0f3c25f26587a07528fbc4d75.png

Edited by Gina
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Gina

Posted (edited)

CAD model of the getready/start striking control shown coming up to the hour and just about to start the striking sequence.  In this position the striking is held stopped and the rack pawl pushed away from the rack.  Next the triangle will drop on the minute shaft cam (bottom right) and stop and pawl released, letting the striking start.

1207846539_Screenshotfrom2018-10-0210-24-54.thumb.png.3c9684bc3a7b9972d753c79f0d0ff706.png648471700_Screenshotfrom2018-10-0210-37-34.png.5a6c122eb135363deda4f8959df5ac87.png

Edited by Gina
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Been testing the clock as far as I've got with it.  Bearings pressed into all their holes in the acrylic plates, gear train assembled including escape anchor, plus back and front plates attached to the two wooden side members with wood screws.  It is not quite free.  It will move by pushing the gears round but I think the pallets are just touching the teeth on the escape wheel where they should just clear.  I can either adjust the pallets or reprint the escape wheel with slightly lower teeth - it's only a few tenths of a millimetre.

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Gina

Posted (edited)

I examined the anchor and found I could adjust one of the pallets to provide the clearance required, put everything back together and the escapement now works.  The acrylic sheets still have their protective layers so are not fully transparent yet.  I'm leaving the protection on until I've finished drilling holes etc.  Second photo shows the position of the minutes to hours gear train, very roughly drawn in on the protective covering, with a felt tip pen..

1433560612_GearTrain07.thumb.png.719a062a4d32fa592bdbc78bb135749a.png637409716_GearTrain08.thumb.png.51060333fb18bbf0b60a870321a57499.png

Edited by Gina
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Gina

Posted (edited)

In sorting out how it will all fit together and how it will look, the striking rack needs lowering a bit.  As shown in the diagram in green below, the rack rests in its highest position and would cover the escape wheel, which though possible, wouldn't look right.  This means the release parts will also need changing as the main shaft and pawl will need to be lower.  The overall design is beginning to come together though there is still plenty to sort out.

1619453501_Screenshotfrom2018-10-0118-39-44.png.98b0ffbc1d87590136bd10175e6ca8fc.png

Edited by Gina
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The striking rack will just fit in covering the space between 8 o'clock and 11 o'clock with resting position with its top at 11 o'clock.  The bottom will only drop as far as the 8 o'clock position when striking 12.  The simplest way of doing this is simply to rotate the whole striking works around the clock centre by about 30°.

1208052339_Screenshotfrom2018-10-0221-04-10.thumb.png.6260227fb1f3f094345e83dfc99719ee.png

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Here are photos with a thin test print of the rack placed on the clock.  It is quite apparent that the rack is too big.

941251240_StrikingRack01.thumb.png.c2b9d6e7e9dee57d39d291b537f80801.png722704840_StrikingRack02.thumb.png.0c8d6f12fb7a7247b9fc6ffa4857f50b.png

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Gina

Posted (edited)

Scaled rack and large snail cam to 85% which seems not too far off.  Maybe just a little smaller.  The small nut roughly shows the position of the small snail cam.

1. Lowest position about to start 12 strikes - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  2. Highest and resting position.

2114731568_StrikingRack03.thumb.png.4d81c4e826e400888f37dd4e3781cb93.png433553413_StrikingRack04.thumb.png.b7232f5c0d91870c47845dd7b4243b99.png

Edited by Gina
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Gina

Posted (edited)

Repositioned the pivot for the rack.  Slight improvement in position of small snail cam (represented by small nut).  OTOH a smaller rack and large snail cam seems the way to go.  Fitting everything in whilst avoiding parts clashes and axles is not easy.

1156065021_StrikingRack05.thumb.png.75e745edcaed5d56d7cbee3606b34274.png315113409_StrikingRack06.thumb.png.49955238fdfdf09a89d550eb63d929ba.png

Edited by Gina
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Changed to 60% and trimmed the top of the rack with side cutters to reduce its width and took photos of the lower and upper positions of the rack.  This seems a lot better - the lower end of the rack can go behind on the minutes to hours intermediate pinion.

409906448_StrikingRack09.png.fdf676dacb0ff0dbbd485c855d3599d0.png720389553_StrikingRack10.png.8147986d91df333009987cb2be39d927.png

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Gina

Posted (edited)

Modified rack design.  The top of the rack needs very little strength as it only has to hold the weight of the rack whereas the bottom takes the force of stopping the striking action.

937597467_Screenshotfrom2018-10-0314-48-27.png.aa171847f9ab5053fd934391da5d3d38.png

 

Edited by Gina
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Rough cross-section diagram of parts associated with minutes and hours.  Top of diagram will be front of clock and the hands will fit on the axle and tube (minute and hour hands respectively).  Starting bottom on minutes shaft, spring, great wheel and driven pinion (which also provides one plate of clutch), clutch plate combined with pinion to drive hours gear train.  Other side of front (top) acrylic sheet is cam to start striking mechanism, large snail cam to control number of strikes attached to hour wheel which has tube to hour hand (not shown).  On the right is a shaft with spur gear and pinion to drive the hour wheel from the minutes shaft pinion.

1236975467_Screenshotfrom2018-10-0323-36-09.png.ac0fa1da05ac99cd001fcce1b2c1c3d2.png

  • Like 1
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Part of pendulum suspension and the crutch.  Top part of crutch is a vane that interrupts a light beam in an optical sensor to measure the pendulum timing for the auto-regulator.  A lever will raise or lower the actual pendulum suspension to change the length below the tiny gap shown where the suspension spring fits.

1870817592_Screenshotfrom2018-10-0611-23-36.png.d12841f23e65df3ee9c12f3f705a5697.png414169471_Screenshotfrom2018-10-0611-17-31.thumb.png.6a56eae35061dbceaa615fcca76b8b30.png

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Fitting everything in is mighty difficult.  The gears that drive the hour wheel have to be on the left as there is no room on the right.  This causes conflict with the striking gear chain and chain sprocket.  Both chains have to go between the two acrylic plates for the weights to fit in the trunk and not collide with the pendulum.

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This photo shows a possible arrangement for the hour drive gears and rack & cam for the striking mechanism.  The hour and strike parts are test pieces using some cheap ABS filament.  Only the first pair of hour train gears are shown and only part of the striking mechanism - there's also the gear train and the parts that start the striking controlled by the minutes (so that it strikes exactly on the hour).

1722392538_GearTrainStrikingParts01.png.a86b615b2d9b94655cc9a5f2f10b0ddb.png1944049013_GearTrainStrikingParts02.png.bee5e5ce313b9ced84f764b3ae17e7ad.png

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Gina

Posted (edited)

I think I might just have managed to fit all the clock and striking system parts in, provided I change to a different auto-wind for the striking system.  I thinking of using a single chain or maybe cord and winding up on a ratchet every so often with a motor.  Not as nice as a continuously running auto-winding (like the clock) but if needs must...

1900478943_Screenshotfrom2018-10-0814-41-39.png.c91383a0c4a8040c3c522dbc3367d126.png

Some calculations :-

  1. Gear ratio - main strike shaft to gear on MH axle = 180:30 = 6:1. 
  2. Next is 160:80 = 2:1 and the ratio of gear to drum is the same giving another 2:1.  Total ratio is 24:1. 
  3. Over a 12 hour period there are 78 strikes and 78 revolutions of the main striking axle.  78/24 = 3.25. 
  4. Circumference of drum = 80xPi = 251mm approx. 
  5. Drop in 12 hours would be 3.25x251 = 817 approx. 
  6. Without a doubling up pulley the drop is 1.5m which would be adequate for winding twice a day.  If winding were limited to once a day a pulley would be required.
Edited by Gina
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