Riefler Pendulum Bob turning

[dandydude]

Hello,

Has anyone here turned a riefler style pendulum bob. How do you turn something this heavy without a hole in the centre and an arbor? Also cross drilling the hole across. My concern is to make sure the cross hole is dead centre.

Thanks
Dandy

 

[Phil Burman]

I put a hole in the centre, cross drilled from both ends to the centre with an undersized drill then drilled right through with the finish size drill. I used the centre hole to insert a half segment support for the temperature compensation.

The Riefler bob has one major disadvantage clearly seen with Microset, with the temperature compensation inside the bob it reacts very slowly to environmental temperature changes whereas the pendulum rod reacts relatively quickly.



Phil

 

[dandydude]

D

I put a hole in the centre, cross drilled from both ends to the centre with an undersized drill then drilled right through with the finish size drill. I used the centre hole to insert a half segment support for the temperature compensation.

The Riefler bob has one major disadvantage clearly seen with Microset, with the temperature compensation inside the bob it reacts very slowly to environmental temperature changes whereas the pendulum rod reacts relatively quickly.

View attachment 495910

Phil

Dear Phil,

Thanks a lot for your email. How do people turn the bob without a hole in the middle? Its too heavy for a wax chuck isn't it?

Thats a great insight you provided regarding temperature compensation... It has to be true as the bob is so thick in the mid section, it could take a while before the compensator reacts. It had never crossed my mind, that this could happen... I am currently using a single cylindrical bob with a compensator. I guess the cylindrical bob also should have a similar problem.

I guess the strasser pendulum (two cylinders) might be the best option considering the problem you mentioned. Then again the riefler bob shape supposedly has less drag according to 'accurate clock pendulums' by RJ Matthys . Looks like i really have to weight in a lot more factors to decide on a bob shape.

regards
Dandy

 

[Phil Burman]

Take a piece of bar of the necessary diameter with extra length, machine a sacrificial stub arbor on each end. Use the stub arbors in the chuck to machine the main profile front and back. Mount the bob in the chuck on its' outer diameter and machine off one stub arbor, reverse it and machine off the other stub arbor.

Later on Riefler introduced a secondary temperature compensation half way up the rod, supposedly to compensate for temperature stratification within the case. I wonder if this was actually to solve the problem with the temperature compensation in the bob.I think a lot of 19th century precision pendulum clock design was as much about form as it was about function.

I made a Strasser type two cylinder bob but was not happy with its stability sitting on the temperature compensator, hence I ended up with my three pillar/compensator shown in my "1-second-regulator-state-of-play" thread.

Phil

 

[Hessel Oosten]

Is this of help ?

Scroll down on the page in the link below (and after that.., admire the pics in the whole thread !)

Here on Uhrforum

Hessel

 

[dandydude]

Hello Hessel,

Thanks a lot for the link. Lovely pics. Really clarified my question.
I have one question though... The hole through the Bob has to have different radii until the centre... how is that one? Especially for heavy bobs?

Thanks Hessel

 

[Hessel Oosten]

Hi Dandydude (sorry, I don't know your name),

I'm not able to help on this question. Lack of experience on my side alas.

Probably you can ask on the link in the "Uhrforum", mentioned above.
Although it's German, they really speak/write English if necessary.

Hessel

 

[jhe.1973]

Hi dandydude,

Every now and then I have had to turn a disk and do so by applying pressure to it with a live center in the tailstock pushing a pad with just a blind center hole. A piece of single ply cardboard such as from a cereal box placed on either side will increase the friction against the part and keep from marking it. Just push all of this against a faceplate or a faced part in the lathe chuck. The flat on each face of the bob should work well.

Of course light cuts are necessary and always making sure that nothing is slipping such as the tailstock! If you do use a part in the chuck I recommend that it has a shoulder up against the jaws so it cannot move into the chuck.

As far as the mention of the bob not reacting as fast as the rest of the pendulum, the same criticism was made of mercury pendulums ages ago and it is my understanding that this was the reason that Riefler used a thinner column of mercury so that it would respond quicker. IIRC, this is also what led him to use aluminum as a compensator and move away from mercury altogether.

 

[John MacArthur]

Hi dandydude,

snip

As far as the mention of the bob not reacting as fast as the rest of the pendulum, the same criticism was made of mercury pendulums ages ago and it is my understanding that this was the reason that Riefler used a thinner column of mercury so that it would respond quicker. IIRC, this is also what led him to use aluminum as a compensator and move away from mercury altogether.

The same is true for grid-iron pendulums - the different metals are virtually identical in section, and so gain or lose temperature at equal rates. They do have a "stick-slip" problem that make them somewhat jerky in effect. Mercury filled jars only really "shine" in the field of elegance.
Johnny

 

[jhe.1973]

As luck would have it I had to turn a 5 inch diameter disk today from a square. After bandsawing the corners off I held it as shown just pushing it against the chuck jaws. Because it was to have a center bore when finished I just drilled a small center hole right into the brass and didn't bother with a push pad.

 

[John MacArthur]

Hi Jim - I thought Dandy was asking about drilling a hole from edge to edge of the bob, with half of it being a larger diameter, to accommodate the compensating sleeve of a Rieffler pendulum? That would be a little more challenging.
Johnny

 

[teslak]

Hello, dandy,
The bores depend on the diameter of the pendulum rod. I have on my watch a diameter of 12mm for the pendulum rod and 14mm for the compensation sleeves. The smaller hole goes up to the middle of the pendulum lens, important is a straight or right-angled support for the compensation tubes.

Since my English is unfortunately very bad, I need a program to translate it. I apologize for any inaccuracies.

I hope that my answer will help you.

Greetings,
Dieter

 

[John MacArthur]

I have recently become interested in making a pendulum with a Rieffler style bob, as in this thread. In all the threads and other info about this, I haven't read or seen how the bob is kept from turning on the rod when adjusting the rating nut. I assume there should be some sort of pin-in-slot arrangement, but this doesn't show up on the drawings. I can't imagine that the bob would just turn free, and need to be held by hand while adjusting, although this may be the case. Does anyone have any info on this?
Thanks,
Johnny

 

[Hessel Oosten]

Hi John,

As far as I can see here in this bob there are 2 nuts in the middle, which can probably adjusted by small pins (?) in them, just as is the case in small lathe chucks.

I can also imagine that after the adjusting by hand (and polishing/cleaning thereafter) the bob is never touched again, because the fine adjustment is done later on, only in the upper part of the pendulum.


Hessel

 

[John MacArthur]

Thank you Hessel. I had not noticed that the ones with the rating nut in the middle had the two nuts, and with the little holes for locking together. Many of them have the nut at the bottom, under a sleeve that rests on a ledge at the center of mass. I am beginning to wonder if it is possible that these do not actually have anything to keep them aligned with the axis of swing. It seems improbable, but possible. I still wonder if there couldn't be a little pin, as in the aligning pin for a collet in a lathe. Anyone else??
Johnny

 

[John MacArthur]

Hessel - in looking at this pendulum more closely, it might appear that the nuts in the middle of the bob only adjust the amount of compensation sleeve acting on the pendulum, and not the actual rating of it, which might occur somewhere else. This is apparently a hybrid mercury pendulum, and it's not at all obvious how it works. The only books I have on Riefler are in German, and the diagrams don't show everything.
Johnny

 

[Hessel Oosten]

John,

A friend of mine, is building a Riefler.
He possesses the book from Dieter Riefler about his grandfather: Sigmund Riefler.
Do you know the contents of this book ?
If the answer is "no" than I can ask him if... there is information in it.

Hessel

 

[John MacArthur]

Thank you Hessel - I do have that book. The diagrams on pp. 39-44 do not show any method of securing the bob from turning during regulation, but they are generally schematic, and not detailed. If your friend is aware of any such method, I would appreciate knowing of it. I found in another book on German precision clocks a picture of a pendulum by another maker that appears to have screw in the middle, which might be a pin-in-a-slot arrangement. However, none of the pictures of Riefler type J pendulums show (at least on the front) any such thing. I assume it would have been on the back of the bob, and thus almost never photographed. I appreciate your interest in this.
Johnny

 

[Hessel Oosten]

Well, last resort here....

I presume you also know the fabulous book-series: Präzisionspendeluhren (PPU) von Juergen Ermert.
Website: HERE

I saw there that the author (above) can be reached easily:Juergen.Ermert@PPU-Buch.de
I should think, that he should …. know the answer.

Hessel

 

[John MacArthur]

Thank you very much Hessel. I have volume 3 of that series, which deals largely with Strasser and Rohde, and very little with Riefler. At the time I ordered it, that was the only one available. I will reach out to Ermert about this question, and also see if the Vol 5, which is shown on the site, is the one that covers Riefler. I was just talking to a friend who has successfully machined an invar pendulum rod and bob, and who said that it cuts moderately easily, enough to mill a slot in it. I seems to be the "free machining" variety, with selenium, which has roughly twice the coefficient of expansion as regular invar. Thanks again for your interest.

 

[Hessel Oosten]

About the "free machining" INVAR.
.
Interesting information (even about cutter geometry!) HERE.

H.

 

[John MacArthur]

Thank you Hessel - I have been a little worried about threading and slotting invar. I contacted Juergen Ermert of the Prazisionspendeluhren no. 5, and he was very responsive. It is in fact the one about the Rieflers with 600 pages about them. It's pretty expensive, so I'll have to think on it.
Johnny

 

[Hessel Oosten]

John,

I have asked my friend, building a Riefler F type.
Here his answer, may be this can help another little bit ?

Hessel

/////

So I quote his answer:

It was quite a search, but I think I now know what it is. And then I concentrate entirely on the bob that John is talking about: the "pendulum" with the "two nuts in the middle of the bob".
This is a Riefler mercury compensation shuttle (Quecksilberkompensations shuttle Type H from 1891 to 1900 applied)

# 1 Steel pipe around 16 mm, inside around 14 mm. (Air-tight closed at both ends)
# 2 Tube is filled with mercury over +/- 2/3 length.
# 3 A "compensation weight" has been added under the bob. A whole story about this in volume 5. Interesting, but too extensive to describe it here.
# 4 Bob mounting: The lower part of the pendulum has a fine thread. Acme type. The pendulum is inserted into the bob. Up to the 2 "nuts". (Insert both nuts into the center of the pendulum by inserting them into the rectangular hole of the bob).
Swing down by turning both nuts. As far as necessary. Fix the lens by turning the upper nut upwards (fixed against the lens) and turning the lower nut downwards (fixed against the lens) .... Ready.
Small deviation in height compared to pendulum does not play such an important role !
# 5 Furthermore, a whole story about expansion of the steel tube in particular, Riefler's calculation of the quotient = moment of inertia / static moment. I too still need to dive into it.

# 6.End-adjustment by completing the following sequentially:

1. ROUGH adjustment by raising / lowering the lens using the "nuts".
2.FINE adjustment by moving the compensation weight under the bob up / down.
3.FINEST adjustment by using weights that are placed on a “cup” that is attached to the pendulum in a certain place (with 497mm second pendulum bend under the pendulum bending axis).

This pendulum is very accurate. Compensation error of 0.005 sec / day per 1 degree Celsius temperature change. Improvement compared to van Graham's mercury compensation pndulum
Graham performed corrections by adjusting the mercury level. Big disadvantage compared to H type from Riefler.

 

[John MacArthur]

Thank you Hessel, and thank your friend too, though the type H is not what I'm really interested in. I am interested in making a type J pendulum, with invar rod and bob shaped as in the OP's project. I find in your post #5 a reference to a posting in "uhrforum" which includes this drawing:

Notice the tiny slot above the bottom sleeve opening, on the back side only. I only recently noticed this, and am now convinced that a small pin protruding from the pendulum rod and riding in this slot is what keeps the bob from rotating while turning the regulating nut/sleeve.
I do look forward to getting a copy of Ermert's Vol 5, but it will have to wait a while.
Johnny

 

[Phil Burman]

Hi John, a pin at the lower entry point would have to pass though the compensating sleeve in order to locate the bob relative to the pendulum rod, so the compensating sleeve would also require slotting. Initially it looked like a more logical location for the pin would be at the top entry point. In either case the amount of available adjustment would appear to be limited. However if the length of the compensating tube required adjustment during calibration a pin located at the top would limit the amount of adjustment possible. Even with the pin a the lower entry point it seems that it would be necessary to calibrate the system before concluding on the location for the pin hole in the rod.

Phil

 

[John MacArthur]

Thank you for that insight Phil. I had already seen the need for slotting the compensation tube, but hadn't made the jump to a pin at the top being as effective. I also saw that the amount of adjustment as shown in the diagram is very small, but that a slot could obviously be rather longer, though slightly altering the center of mass. I have just received the Mathys book on accurate clock pendulums, and haven't digested it all. I have also been in contact with Juergen Ermert regarding the book on Reifler (per Hessel's suggestion), and may spring for it eventually. But I am tempted to just "jump in" with the info I have and see what happens. "Construction and Design, in *that* order.." seems to be my motto.
Johnny