Longcase (Grandfather) clock with 3D printed gears etc.

[Gina]

This is a project that has been going for some time without a great deal of success as yet.  There are a large number of posts on that other forum - StarGazers Lounge - but I thought a precis of the project would be of interest here.

I have been down a number of blind alleys with this project which I shall discuss only briefly here.  I guess the upshot of all this is that I was trying to be far too ambitious in trying to make a complicated pendulum clock with weights and chains and all the "bells and whistles".  I am now aiming at a much simpler clock but still with interesting mechanisms.

In this thread I plan to start by going over the principles then proceed with my construction.

[Gina]

An example.

[Gina]

Like my other clocks, this one will also show the "works" with a clear acrylic clock face and "window" door on the trunk to show pendulum and weights.

This is a drawing of how I imagined my clock at first, with a moon phase dial like my moon dial clock, perpetual calendar etc.  Now I have decided I don't need two moon dials in the same room.  The space would be better used by a gong and striking mechanism.  Never made one of those before.  As I'll explain later, the perpetual calendar proved too much to cram in the available space and looked far too complicated.

https://stargazerslounge.com/uploads/monthly_2017_03/58c1f11623963_ClockCase05.JPG.73dd6104fd69be77d1d94d37a2f9b509.JPG

[Gina]

Exploded view of longcase clock mechanism.  This is just the "time" train.  I'm planning to add a striking mechanism.

[Gina]

Anyone that knows me will know I wouldn't be content with a clock that needed winding up by hand so my clock has auto-winding.  A stepper motor that continuously winds the clock.

This diagram shows the principle of an auto-winding system for weight driven clocks.  The green sprocket drives the clock from the weight (black triangle).  Meanwhile, the red sprocket is driven at just the right speed to lift the weight at the same rate as the clock lowers it, resulting in the weight staying at the same height.  This principle has been used with tower clocks as in churches etc. to save manual winding.

[AstronomyUkraine]

@Gina Your example looks very impressive. Are you making the case, as well as the mechanism? Building a clock mechanism, is well beyond anything I am capable of, but working with wood is a different matter. I make furniture in my spare time, and love working with wood.

Brian

[Gina]

Latest.

[Gina]

These photos show the perpetual calendar version.  Very cluttered!!

[Gina]

I could explain the workings of the perpetual calendar mechanism if anyone is interested - just ask.  Otherwise I'll say very little,  The calendar would show day-of-week, date and month on 4 drums.  Calendar would be right for the whole century with leap years catered for.  Complicated cams provided this.

This version was continued with the auto-winding mechanism on the right hand side.

[Gina]

Bit of a shame to abandon the perpetual calendar as I put a lot of time and effort into designing that and it worked but the clock looked so cluttered with several layers of gears that it was just OTT!!  I might copy over some of the main parts of the construction as another thread later on if there is any interest.

[Gina]

That covers a rough history of this project - now to some details of the construction and to the latest incarnation.  To recap, no perpetual calendar and no moon dial.  Instead I plan to have a striking mechanism.  Unlike a traditional longcase clock this one will have auto-winding.

Now to the construction.  This was the start of the wooden case using floorboards that I had left over from another project.  Later I widened the trunk.  (Middle part.)

https://stargazerslounge.com/uploads/monthly_2017_03/58c295ed9176b_ClockCase06.thumb.JPG.afacca550409771d36e703f6139c9e41.JPG

[Gina]

Hands and dial.

[Gina]

Windows to show the works - clock face and pendulum/weights/chains.

https://stargazerslounge.com/uploads/monthly_2017_04/58f2644aaccfd_Clock14.thumb.JPG.9379bdab5a73d32a5382273b32513afb.JPG

[Gina]

Current state of the project.  The white lever and adjustment screw allows fine adjustment of the escapement. 

This is a starting point. To date I haven't managed to print an accurate enough escape wheel but I have made improvements to my 3D printer recently so I'm ready to have another go.

[Gina]

Posted by: @AstronomyUkraine

@Gina Your example looks very impressive. Are you making the case, as well as the mechanism? Building a clock mechanism, is well beyond anything I am capable of, but working with wood is a different matter. I make furniture in my spare time, and love working with wood.

Brian

Sorry I missed your question as I was posting stuff.  I think I have answered it though and yes, I like working with wood too.  Built my own wooden observatory several years ago.  There's a thread about it in the Observatories forum.

 

[Gina]

Escape wheel.

[Gina]

Printing the escape wheel.

[Gina]

I have further tested and adjusted the 3D printer and changed the centre hole in the escape wheel for better fit on the shaft and things do seem to be better.

The escape wheel has printed pretty well but when spinning it on it's shaft there is some variation in the points of the teeth but I think this is due to the difference in filament laying angle around the wheel rather than the accuracy of printing.  A Cartesian printing system is not the best for a polar form of object.

[Gina]

I've looked into the various escapements to see which would be best for 3D printing but most were superseded by later ones on account of accuracy. I've mainly been trying the Anchor Escapement but have tried the Deatbeat as well. It is said that the Anchor escapement is less bothered by tolerances than the Deadbeat so the Anchor seemed best.  I have tried some of the less popular ones too.

However, even the Anchor escapement is critical of any variation in the radius of the escape wheel teeth and this is what has been the problem so far.  Either the pendulum stops or it skips teeth, depending on the torque driving the escape wheel and the Anchor to wheel spacing.

It has occurred to me to "fudge" the issue by driving the pendulum separately from the escape mechanism in the style of a Slave Clock.

[Gina]

I may have another go at the Deadbeat escapement particularly if I decide to "push" the pendulum separately.

[Gina]

Been designing the deadbeat escapement.

[Gina]

Now printing the parts to see how the fit together.  I'll make up a test rig.

[Gina]

         

Deadbeat escapement, showing: (a) escape wheel, (b) pallets showing concentric locking faces, © crutch.

[Gina]

Another interesting escapement used in tower clocks. c/o Wikipedia.

Gravity escapement

A gravity escapement uses a small weight or a weak spring to give an impulse directly to the pendulum. The earliest form consisted of two arms which were pivoted very close to the suspension spring of the pendulum with one arm on each side of the pendulum. Each arm carried a small dead beat pallet with an angled plane leading to it. When the pendulum lifted one arm far enough its pallet would release the escape wheel. Almost immediately another tooth on the escape wheel would start to slide up the angle face on the other arm thereby lifting the arm. It would reach the pallet and stop. The other arm meanwhile was still in contact with pendulum and coming down again to a point lower than it had started from. This lowering of the arm provides the impulse to the pendulum. The design was developed steadily from the middle of the 18th century to the middle of the 19th century. It eventually became the escapement of choice for turret clocks, because their wheel trains are subjected to large variations in drive force caused by the large exterior hands, with their varying wind, snow, and ice loads. Since in a gravity escapement the drive force from the wheel train does not itself impel the pendulum but merely resets the weights that provide the impulse, the escapement is not affected by variations in drive force.

The 'Double Three-legged Gravity Escapement' shown here is a form of escapement first devised by a barrister named Bloxam and later improved by Lord Grimthorpe. It is the standard for all really accurate 'Tower' clocks.

In the animation shown here the two "gravity arms" are coloured blue and red. The two three-legged escape wheels are also coloured blue and red. They work in two parallel planes so that the blue wheel only impacts the locking block on the blue arm and the red wheel only impacts the red arm. In a real escapement these impacts give rise to loud audible "ticks" and these are indicated by the appearance of a * beside the locking blocks. The three black lifting pins are key to the operation of the escapement. They cause the weighted gravity arms to be raised by an amount indicated by the pair of parallel lines on each side of the escapement. This gain in potential energy is the energy given to the pendulum on each cycle. For the Trinity College Cambridge Clock a mass of around 50 grams is lifted through 3 mm each 1.5 seconds - which works out to 1 mW of power. The driving power from the falling weight is about 12 mW, so there is a substantial excess of power used to drive the escapement. Much of this energy is dissipated in the acceleration and deceleration of the frictional "fly" attached to the escape wheels.

The great clock at Westminster that rings London's Big Ben uses a double three-legged gravity escapement.

[Gina]

I think the deadbeat escapement stands a good chance of working if I can get my printer to behave. Otherwise, it would seem that the Gravity Escapement has little to go wrong. It would need a serious redesign of the whole clock though. It would certainly be different and that makes it appeal to me.