Gina

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 :- V-Slot Linear Rail - 20x20x500mm -- 4 off V-Slot Linear Rail - 20x20mm - Cut To Size 310mm --- 4 off V-Slot Linear Rail - 20x20mm - Cut To Size 360mm -- 4 off V-Slot Linear Rail - 20x20mm - Cut To Size 350mm with tapped holes -- 1 off 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.

This is basically a mechanical perpetual calendar with 3D printed plastic parts but whether I drive it from a clock with hands etc. or simply from a stepper motor remains to be decided. The display consists of drums with numbers and letters stuck on. Each drum is driven from specialised gears and levers. The mechanism is designed to be visible and show the workings.

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

Calculation for the main drive chain sprocket which will be attached to the green gear in the photo above :- Radius of the gear = 84mm Pitch radius if sprocket teeth wants to be less say 75mm Link pitch = 20mm Circumference of new sprocket at tooth pitch = 471mm. Maybe 480mm which is 24 teeth. New diameter of tooth pitch = 152.8mm so radius = 76.4mm Angle per tooth= 15°

The chain drive gear was too big so I've made a new one.

Been designing the chain drive gear. The first photo shows the gears laid out on the new acrylic panels and in the second, I have removed almost all the parts from the Mark 1 clock to make use of the panels and framework to test the gearing. Once I have finalised the layout I shall transfer it to the new panels with the clock face further up the space.

I have been experimenting with printed gears to test the feasibility of fewer gears and I'm going to try it. In the attached photo, the yellow gear is the centre/minutes wheel and drives the orange gear with a 10:1 ratio. This in turn drives the escape wheel (light grey) with a 6:1 ratio giving an overall ratio of 60:1 as required. The position of the escape wheel makes its shaft ideal for a seconds hand with dial just below the 12 o'clock mark. The smaller gear on the main centre wheel is for the chain drive.

I did another net search to to see if I could get any ideas for alternative clock mechanisms and found one with a reduced number of gears as shown below. Fewer gears might help to reduce friction and would unclutter the clock a bit. The doubt was whether the higher gear ratios would work but with a bit of testing I think they may. One advantage of one less gear pair is that the escape wheel turns clockwise which would allow a seconds hand to be attached to the shaft.

I couldn't get the original (Mark 1) clock to work properly and also decided I was trying to cram far too much into it and it was very cluttered. These points together made me decide to start again with just the main clock mechanism and get that working first then add other bits. So I've dumped the perpetual calendar and that will go into a separate project. I'm keeping the auto-winding mechanism as I'm too lazy to wind it, and the moon globe as that is no problem (much the same as the Moon Dial Clock).

This blog continues from my threads in The Lounge, in particular DIY Grandfather (Longcase) Clock Mark 2

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.

The box makes use of 500mm square x 4mm acrylic sheets providing right-angle corners. The build volume is about 300mm (1ft) cube. The printer has been designed to be capable of printing with any sort of filament of 1.75mm diameter with an extrusion temperature up to 300°C and bed temperature up to 150°C, though I have only tried with 280°C and 110°C. I am currently using a 0.8mm nozzle though other sizes are available (0.4mm, 0.6mm, 1mm and 1.2mm). Printing surface is borosilicate glass 300mm square which is heated with a 24v 300W heating pad. The electronics uses the RepRap standard Arduino Mega 2560 microprocessor board and the RAMPS interface board, powered by a PC style ATX PSU with +5v and +12v power rails and providing the power for the stepper motors and hotend heater etc. Power for the print bed heater is provided separately by a 24v PSU. Heating is quite fast taking about 4 mins to get from 20°C to 100°C. I had originally designed this printer to use Bowden filament feed but this proved so troublesome that I made the decision to use direct feed with a small, lightweight extruder and stepper motor mounted on the X carriage. This is the E3D Titan Extruder (the name is a coincidence - I named my printer before their extruder came out) and is not only small and light but is reckoned to have a superior hobbed shaft. I am also using their Volcano hotend with better filament heating and flat ended nozzles.