Function Clock build from scratch

[Bill Spence]

I have just built a mechanical clock pendulum from scratch, and I am interested in building another one. I am looking for suggestions for improvements to my current design.

The clock is all aluminum (6061 alloy), except the pivots are SS shafts in clock brass bushings, there is lead in the pendulum, the weight is steel and the hands and face markers are yellow brass. The wheels are cut on a home made CNC router mill with a 1/8 carbide bit. The arbors are 3/8 aluminum tube with 5/64 centered SS shafting, the bushings are drilled 5/64. The pendulum and pallet are assembled into one piece and pivot on SS pins located in the socket heads of 2.5mm SS machine screws, so there is no pendulum spring or crutch. The pendulum is a thin wall 1" diameter aluminum tube with about 1.4 lbs of lead in the bottom, with no temperature compensation (although I have a plan to add this, based on steel/plastic differential thermal expansion). The escape wheel is Graham, 56 tooth, 7.4" diameter, with a pendulum length for 1 revolution per 100 seconds. The gear train is epicyclic with 6.6667" diametral pitch Wheels 2 and 3 using 8 x 48 gearing, so wheel 3 is at minute hand speed. Wheel 4 is reduced 8:16 from wheel 3, and includes a 1.66" diameter drum connected to the shaft with a hex nut and socket clutch, to allow winding. The cord is two part, and the weight about 18 lbs. Wheel 4 runs on 3/8 nylon ball bearings. Wheel 5 drives the hands, through 36:18 (with 6.4286 diametral pitch) and 8:48 gearing. I had to adjust the clock a good bit to get it to run consistently, so I think the friction on it at times is near the maximum. I have not run it long enough to learn how well it keeps time.

For my next clock, I am considering a lighter 30 tooth escape wheel 2" diameter, smaller gears (maybe 12.5" diametral pitch, which means a smaller router bit), an improved frame structure and a lower windage pendulum . I am concerned about wear on the pendulum pin pivots and the aluminum pallet, and I need more efficiency. I am considering nylatron for the pallet, the escape pinion and bushings, a lower windage, heavier pendulum bob (with temperature compensation) with knife edge pivots. I am a retired engineer but i lack any much experience with clocks. I am looking for suggestions and comments.

 

[Danwatts2005]

You lost me WAY back up there, but I think this looks awesome. I've wondered if one could be made on a digital printer.

 

[Bill Spence]

You lost me WAY back up there, but I think this looks awesome. I've wondered if one could be made on a digital printer.

You lost me WAY back up there, but I think this looks awesome. I've wondered if one could be made on a digital printer.

Thanks for your awesome comment. You could make this (more accurately) on a powdered metal laser sintering 3D printer, but those machines cost upwards of $100,000. There is a nylon/aluminum powder composite product called Alumide that you can print on much lower cost 3D printers, but it only has strength about a third of that of aluminum metal. You can build a CNC router machine that will cut clock parts out of aluminum sheet for maybe $600, which works better for retirees with limited budgets but plenty of time.

I was hoping for help on the items in my second paragraph, but so far you are the only reply I have gotten.

You lost me WAY back up there, but I think this looks awesome. I've wondered if one could be made on a digital printer.

Thanks for your awesome comment. You could make this (more accurately) on a powdered metal laser sintering 3D printer, but those machines cost upwards of $100,000. There is a nylon/aluminum powder composite product called Alumide that you can print on much lower cost 3D printers, but it only has strength about a third of that of aluminum metal. You can build a CNC router machine that will cut clock parts out of aluminum sheet for maybe $600, which works better for retirees with limited budgets but plenty of time.

I was hoping for help on the items in my second paragraph, but so far you are the only reply I have gotten.

 

[Burkhard Rasch]

Bill , wellcome to this clock forum! You´ve made an interesting clock, congrats!
You asked for suggestions : I´d consider hanging the pendulum on a short flat spring suspended from a post attached to the movement frame , a so called suspension spring , to avoid wear in the pendulum pivots . A more delicat and elegant way is having it supported on knive edges like in precision vienna regulators , one in front and one in the back. That would go nicely with Your design of the upside-down dead beat anchor.
Just an idea from a clock fan , not an engineer...
Burkhard

 

[Steven Thornberry]

I moved this to the Clock Construction forum to see if more input is forthcoming.

 

[Bill Spence]

Bill , wellcome to this clock forum! You´ve made an interesting clock, congrats!
You asked for suggestions : I´d consider hanging the pendulum on a short flat spring suspended from a post attached to the movement frame , a so called suspension spring , to avoid wear in the pendulum pivots . A more delicat and elegant way is having it supported on knive edges like in precision vienna regulators , one in front and one in the back. That would go nicely with Your design of the upside-down dead beat anchor.
Just an idea from a clock fan , not an engineer...
Burkhard

There is a lot to be said for the knife edge pivots. They should lose less energy than pallet arbor pivots plus some losses in the crutch and very small losses in the suspension spring. I like just being able to lift the pendulum out.

 

[tok-tokkie]

I am confused by your description.
You write that the gearing is epicyclic. It appears to be a conventional gear train.
Epicyclic Epicyclic gearing - Wikipedia
The tooth profile looks conventional involute but it may be cycloidal Cycloid gear - Wikipedia Did you write epicyclic where you intended cycloidal?
To reduce the friction consider small ball bearings. Best is stainless steel races with ceramic balls. Wash all the grease out - easiest done with engine degreaser & running water. Stainless races with stainless balls & no grease has given fretting issues. Boca Bearings in California have a good on line catalogue with prices.
Windage of the pendulum can be much reduced by using a thin rod & heavy bob. Carbon fibre rod is an option. If you can source used tungsten carbide machining inserts that would be a nice filling for the bob as its density is 50% greater than lead. So less windage. Could make 'concrete' of tc bits in lead.
Suspension springs are very elegant frictionless pivots. They can be lift out. But the slot needs to be a nice sliding fit to support the 'fixed' side-to-side.

 

[Bill Spence]

I am confused by your description.
You write that the gearing is epicyclic. It appears to be a conventional gear train.
Epicyclic Epicyclic gearing - Wikipedia
The tooth profile looks conventional involute but it may be cycloidal Cycloid gear - Wikipedia Did you write epicyclic where you intended cycloidal?
To reduce the friction consider small ball bearings. Best is stainless steel races with ceramic balls. Wash all the grease out - easiest done with engine degreaser & running water. Stainless races with stainless balls & no grease has given fretting issues. Boca Bearings in California have a good on line catalogue with prices.
Windage of the pendulum can be much reduced by using a thin rod & heavy bob. Carbon fibre rod is an option. If you can source used tungsten carbide machining inserts that would be a nice filling for the bob as its density is 50% greater than lead. So less windage. Could make 'concrete' of tc bits in lead.
Suspension springs are very elegant frictionless pivots. They can be lift out. But the slot needs to be a nice sliding fit to support the 'fixed' side-to-side.

Thanks for your comments. You are right, I said epicyclic but I meant involute. I just looked briefly at Boca's website- it looks interesting , with quite reasonable prices. The bearings I used on the drum shaft of my clock were acetal with SS balls from McMaster Carr. I also tried some 5/64 SS bearings for lower load pivots, but when I got them I found there was significant resistance and roughness on them. So I went back to SS shafts directly on brass. I will look some more at BOCA's bearings. I will also look at carbon fibre pendulum rods- apparently you can get them with near zero thermal expansion.

I could connect the pendulum rigidly to the pallet, and hang the pallet from 0.003 SS shimstock (which would allow short springs) both sides of the escape wheel, but it seems the flexibility of even a short spring would mess up the deadbeat. I don't see how I could stabilise the pallet on a knife edge without a rigidly connected pendulum, so a lift out pendulum seems to require a pallet arbor and bearings of some sort. I could make a lift out pendulum/spring/mount clamp setup, with the pallet on an arbor, but then I would need a crutch to drive the pendulum. I have not been able to envisage a setup as simple and low friction as a rigid pallet/pendulum on a knife edge. I am thinking of 4140 steel for the knife edge (something like 1/16 x 1/2", ground to a chisel point) and plate. Or possibly ceramic, although I have never worked with that material.

What do you think about nylatron for the pallet and the small gears at the high speed end of the drivetrain. It is a low friction, wear resistant nylon.

 

[gmorse]

Hi Bill,

I could connect the pendulum rigidly to the pallet, and hang the pallet from 0.003 SS shimstock (which would allow short springs) both sides of the escape wheel, but it seems the flexibility of even a short spring would mess up the deadbeat.

You're quite correct in this observation, the relationship between the pallets and the escape wheel must be perfectly immovable. The escape wheel teeth are exerting forces on the pallets during impulse and locking; if the pallet arbor were to be flexibly mounted, it would result in loss of impulse at the very least, if it worked at all.

The concept of a crutch fixed to the pallets and connected to the pendulum in some way, with the pendulum suspended from a steel spring attached to a rigid fitting on the movement or the case, is a combination that has been tried and tested over hundreds of years. Have you considered an asymmetric crutch or one of the gravity escapements? In the latter, side arms are lifted by the escape wheel and when unlocked fall under gravity to impulse the pendulum. An example is the Great Clock at Westminster, (popularly but incorrectly known as 'Big Ben').

Regards,

Graham

 

[tok-tokkie]

As gmorse says using a suspension spring would not work if the pallets are mounted directly on the pendulum.

For a dead beat escape the pallets must be precisely constrained in relation to the axis of the escape wheel. You have made one so must appreciate how fine the tolerances are for the escape to function correctly. A suspension spring does not have a constrained pivot point. Even worse the pivot point changes depending on the direction from where the applied force is coming from.

There is a really exceptional clock that has the pallet mounted directly on the pendulum. Do a search on Tekippe. Here is one result https://mb.nawcc.org/threads/tekippe-precision-regulator.79463/

Nylatron is not sufficiently rigid to give crisp action when used as a pallet. The optimum material is jewels. Harrison somehow made his of diamond. I used tungsten carbide.

gmorse suggests a gravity escape as used on Big Ben. I have made a variation on the gravity escape which, with great modesty, I claim addresses the failings in the original design! I wrote it up here on NAWCC.

https://mb.nawcc.org/threads/30-legged-gravity-escape-clock.148968/

In particular I draw your attention to reply #15 where the world authority on gravity escapes states that it is "a clear improvement".
I would be delighted if you made a version of my escape. I have given details of how to lay it out for cnc cutting & would be pleased to answer any queries.
(Please not I was being ironic when stating that opinion on my version.)

 

[Bill Spence]

As gmorse says using a suspension spring would not work if the pallets are mounted directly on the pendulum.

For a dead beat escape the pallets must be precisely constrained in relation to the axis of the escape wheel. You have made one so must appreciate how fine the tolerances are for the escape to function correctly. A suspension spring does not have a constrained pivot point. Even worse the pivot point changes depending on the direction from where the applied force is coming from.

There is a really exceptional clock that has the pallet mounted directly on the pendulum. Do a search on Tekippe. Here is one result https://mb.nawcc.org/threads/tekippe-precision-regulator.79463/

Nylatron is not sufficiently rigid to give crisp action when used as a pallet. The optimum material is jewels. Harrison somehow made his of diamond. I used tungsten carbide.

gmorse suggests a gravity escape as used on Big Ben. I have made a variation on the gravity escape which, with great modesty, I claim addresses the failings in the original design! I wrote it up here on NAWCC.

https://mb.nawcc.org/threads/30-legged-gravity-escape-clock.148968/

In particular I draw your attention to reply #15 where the world authority on gravity escapes states that it is "a clear improvement".
I would be delighted if you made a version of my escape. I have given details of how to lay it out for cnc cutting & would be pleased to answer any queries.
(Please not I was being ironic when stating that opinion on my version.)

Thanks Graham and Tok-tokkie for your helpful suggestions. I am going on a trip tomorrow, and won't be back till the 2nd week of June, so no more clock building for me until then. I will study the 30 leg gravity escapement clock. From a quick look at the NAWCC post, it is evidentially a beautiful machine.