Gina

Here is a more detailed diagram showing the gears that drive the layshaft on which gears drive the drums. 

The cams are on the left and show the main date drive cam in it's fully pushed position and the months wheel drive cam in the fully retracted position.  A ball bearing cam follower on the date drive cam is fitted to a lever (curved) pivoted above it.  Then a straight bar with pivot for the two main date drive cams is supported at the right hand end on another lever pivoted between the date and months wheels.  This latter lever extends below into a curved probe that will drop into the slots when the cam turns to let the bar move leftwards under the action of a spring (not shown).

The other cam drives the months wheel when the date is on day one on the month.  A lever pivoted between cams and date wheel rests on either the date wheel (day other than one) or on the cam if the probe on the other (lower) end finds the slot in the date wheel, on the cam.  On day one of the month the second bar ending in a pawl resting on the months ratchet wheel will be pushed to the right and advance the month wheel.  On other days the bar and pawl is held back by the lever probe resting on the date wheel (no slot).

I have an idea for reducing the height.  Another rearrangement of parts.

A couple of main lever parts redesigned and printed.  I would like to try to reduce the height if I can.  ATM the cams come further down than I was hoping.  I have a space on the wall where this could go but it would be better if it wasn't as high.

I'm not satisfied with the above explanation and I'll see if I can improve it.  Meanwhile, I'll continue to post my ideas for the separate calendar.  These posts will help with the explanation.

Here is another photo of the parts, rearranged.  I have moved the drum drive back to the right as that seems easiest.  I might even be able to use some of the parts without modification.  Of course, the main drive lever needs rearranging so I have split up the various parts.  The green cam follower with ball bearing roller, runs on and is operated by the green cam.  The lever moves the probe out of the slot and also operates the pawls on the main date wheel (orange).

Advancing the month slotted wheel relies on the red cam for drive and the blue probe lever to determine when, in conjunction with a slot in the date wheel.  The cam allows the probe to move towards the date wheel and either contacts it, in which case nothing happens, or finds the slot and pulls a pawl back on the yellow ratchet wheel attached to the slotted months wheel.  As the cam rotates it lifts the probe out of the slot and pushes the pawl advancing the month wheel.  This will be clearer when I've redesigned and printed the cam followers and main drive lever.

The next problem is that the date wants advancing on a different day for each month with a different number of days.  For instance, for February in a non-leap year, we want to advance the date by 4 days on the 28th, for a leap year a 3 day advance must occur on the 29th etc.  I studied a number of clock mechanisms before I managed to work out how the perpetual calendar part worked - I can't claim credit for the invention, much as I would like to

The diagram below gives a rough idea of how it works.  A lever with probe part is dropped into the slot and then at midnight it is moved out of the slot at the same time turning the date ratchet wheel with a pawl.  The crux of the matter is preventing the pawl on the ratchet wheel from advancing the day by the advance number at each midnight.  This is achieved by means of the "guard" which lifts the pawl away from the ratchet wheel except for the last bit when the pawl pushes the tooth and advances the date by one day.  This can be seen in the photo as the orange pointed piece just above the ratchet wheel.  The orange pawl runs up onto this and back down to turn the wheel one notch.  The yellow pawl rests on a plain cylinder with a peg which will be pushed by the yellow pawl when the wheel is in the right place.

When the date wheel has turned to the point where the days advance is wanted, a second pawl engages with a step and turns the wheel by the required number of days.  This is shown as the orange pawl and green cam in the diagram.

I think It's time for an explanation.  The main feature of the perpetual calendar is that the date is advanced by a number of days at the end of each month depending on the number of days in the month, in addition to the date being advanced by one at midnight every day.  Months have 31, 30, 29 or 28 days depending on the month and whether it's a leap year for February.  Basically the cycle repeats every four years though the century is different for some centuries but I'm not going to concern myself with what happens at the end of the century

To determine how many days advance are required at the end of the month a notched wheel is used with the depth of notch depending on the amount of advance required.  This is shown in the photo below.  The deep notches are February.  At the beginning of the next month the wheel is moved on one notch ready for the end of the month.  This is just part of it - more to follow...

This photo shows the parts laid out on the table.  To make things work various parts will need redesigning, such as reversing some of the ratchets and changing the levers.  The original had the drums driven from the LHS this will have the drive on the right.

One of the problems with the perpetual calendar mechanism in the longcase clock was that the cams and gears were on top of each other and some of the workings were obscured.  This can be seen in the photos below.  In the separate calendar unit I plan to spread things out so that everything can be seen.

Printed a new third gear on the Titan with 0.4mm nozzle and it's much better - can't see anything wrong with it   Might try the Nylon escape wheel or I might wait until I have a smaller nozzle available as the escape wheel needs to be very accurate.  It might be a good idea to use Nylon for the third wheel to reduce friction and maybe even go over to PTFE bearings.  Ball bearings are considered unsuitable for applications involving change of motion direction as with an anchor escapement though if I can get sufficient accuracy I might go over to a dead-beat escapement as that is reckoned to be more accurate.

Printed a calibration frame and measured it and the printer has gone out of calibration again already   0.5% loss of Y axis and 1.5mm difference in diagonals.  Enough to make the gear prints significantly oval!!  Evidently the problem must lie with the Y axis - movement of the print bed as the Y motion is obtained by moving the print bed.  I'm not going to get reliable printing until I get the new mini printer built.  I have ordered the parts needed for the new printer.  Meanwhile, I think I'll try my Titan printer with the smaller 0.4mm nozzle - that seems to keep its calibration.

Reprinted the auto-winding sprocket gear and the Nylon escape wheel, set up PTFE bearings for the escape wheel shaft and driven the shaft through the boss of the escape wheel, then set up the frame and acrylic plates to hold all the gears and escape wheel in position.  The friction is nice and low - I can spin the escape wheel with slight pressure with one finger on the chain drive gear.  However, the escape wheel is still far from right - the teeth deviate from a circle centred on the axle by a mm or more.  I shall check the calibration of the printer again.  If I can get decent prints I think this version of the clock might work.

Reprinted the chain gear drive as the first go was out of round.  The new one is better but not perfect.  I estimate it has about a half millimetre run-out which surprised me considering how carefully I calibrated the printer.  The centre gear printed on my Titan printer shows no discernible run-out.  The gear works well enough so I'll leave it at that.  I may try the escape wheel in Nylon.

Going for a footprint of 350mm x 400mm and the overall height will be 500mm. 

List of parts required :-

1. V-Slot Linear Rail - 20x20x500mm -- 4 off
2. V-Slot Linear Rail - 20x20mm - Cut To Size 310mm --- 4 off
3. V-Slot Linear Rail - 20x20mm - Cut To Size 360mm -- 4 off
4. V-Slot Linear Rail - 20x20mm - Cut To Size 350mm with tapped holes  -- 1 off
5. Inside Hidden Corner  -- 16 off

There might be more but I can order anything else later.

I've found out why the original escape wheel and the newer ones were out of shape.  The Pilot printer was significantly out of calibration.  X axis was fine at 100.04mm but the Y axis was short st 99.53mm so firstly I adjusted the Y calibration and put that right.  Then I checked the orthogonality of the XY axes - all of 2mm out in the diagonals.  That meant undoing the frame brackets and adjusting before tightening back up.  I needed to do this several times before I got it within a tenth of a mm.  This printer just won't hold calibration, hence the need for a new one.

Found some 350mm x 500 mm acrylic sheets, cost more than the 400mm x 500mm but if that's the size I want sobeit.  Anyway, I'll design the whole printer before committing.

Preparing for ordering the frame parts - I think I already have most of the working parts..  Been looking into which sizes of clear acrylic sheet are available to complete the box as the frame parts can can be ordered cut to length.  Ideally the depth would be 350mm but so far I've only found 300mm or 400mm.  The width works out fine at 400mm.

Looking at the possibility of 300mm depth, this would make the Y rails 260mm long (300mm - 2x20mm for the uprights).  Y range required is 200mm less a margin round the edges of the pr int bed that doesn't get heated.  This gives about 190 as the minimum Y axis range and the maximum width of the Y carriages as 260 - 190 = 70mm.  That might be alright if the Y carriage wheels could go right up to the ends of the Y rails.  The back is alright with the pulleys but the front requires space for the drum on the motor shaft making the minimum overall width 80mm without adding extra pulleys.  Can't be done!

I designed a perpetual calendar mechanism to go into my longcase clock and had it installed and working.  Unfortunately, I couldn't get the clock working so the calendar had no trigger at midnight.  I decided that the clock was far too crowded, so I dumped the calendar section from the clock.  I really want a decent sized and clear to read calendar as the digital clock/calendar I have is almost unreadable, particularly in the evening.

The perpetual calendar has thus bean moved into another project, and this is it.  The whole mechanism has been 3D printed and all the parts are there but they need a new host.  The original calendar mechanism was weight driven with a fly fan to regulate it.  It was triggered from the main clock at midnight from a 2:1 gearing down from the hour shaft and a snail cam.

Chain drive gear designed - 56 teeth and 70mm pitch radius.  That means a ratio of 10:7 compared with the centre gear.  1.4x compared with 3x on the original giving roughly a 2:1drive weight advantage.  Of course the auto-winding ratios will need re-calculating.  I want a smaller gear on the auto-winding sprocket anyway as the original is too big for my liking.  I could use the same size gear as on the clock drive which would avoid awkward ratios when sorting out the auto-winding.

The photo below shows the chain drive sprocket and also the escape wheel and anchor.  Below that are a couple of diagrams showing the the main drive chain arrangement and the auto-winding sprocket with its attached drive gear.  This shows that there is more at the bottom of the clock than at the top so it makes sense to move the centre 50mm further up the case (ie. the frame lower with respect to the works).  The main thing at the top is the moon globe but I plan to use the same design as for my moon dial clock, so it isn't included within the main frame.

I plan to use the space on the RHS of the case for the striking mechanism and its auto-winding system.  The drive for the moon globe will also be derived from the hour drive to the striking mechanism.  That will stop the drive lever from obscuring the main clock.

My brain snapped into gear   And...  Inspiration...  I can use the sprocket from the original clock and attach it to a suitable sized gear.  The original won't do because it's mod 3 and the centre gear is mod 2.5 but just simple job   I can also use the smaller sprocket that is driven by the auto-winding drive.

Been thinking about the chain drive and alternative options.  Since the clock is being auto-wound continuously the reduction gearing from the sprocket to the minutes wheel does not need to be so great.  First I thought of putting the drive sprocket directly on the minutes wheel but I couldn't work out where the chain would go to provide a viable auto-winding system.  Next I looked into a separate gear for the sprocket but driving the minutes wheel on its main teeth rather than a separate smaller gear.  I'll continue looking at it...

I have a shorter piece of 3mm SS rod that I might use for the anchor shaft to produce less friction than 5mm SS rod though I suspect the air friction on the bob and rod may be greater than a polished SS shaft in PTFE bearings.

Yes, I've found a piece just under 100mm long.  I think that will be long enough to take a seconds hand on the end.  I have tried it in a couple of bits of PTFE and it's ultra smooth.  I had thought of having a larger escape wheel than the original but on thinking about it, this would increase the friction from the pallets so I think I shall stick with the 100mm OD.  The problem with the original was poor production - I need to get a 3D printer to accurately print Nylon, which has a lot lower friction than any other thermoplastic but is a lot more difficult to print.

I have taken a file to the teeth on the main chain sprocket and managed to get the chain to run on it.  Not perfect but it may let me test the clock  - I can re-print it later if required.

Finished mounting the gears into the frame and tried it for friction.  There's too much for my liking, virtually all in the escape wheel bearings.  I don't think ball bearings are good enough, even 5x10x5 little ones, so I think it's PTFE as I had on the original.  I used 5mm polished stainless steel but I think I'll go for a smaller shaft.  I think I have some 3mm SS rod.

Produced the sprocket but the chain didn't quite fit well enough - the sprocket pitch was just a bit too long.  First photo below.  The other two show the gear arrangement with the gears roughly positioned in the original clock frame