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
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
D 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
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
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
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
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
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.
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
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.
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
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
