Vibrating pendulum rod

[JME]

Hi all, I have read and learned a lot from these fora, but this is my first post. In order to figure out how a clock work, I decided to try making one, using my 3d printer. My hope was to get it running, to help me understand the mechanics behind a clock. I understand that this could never be as accurate or efficient as a proper hand-made metal clock, but it is working.

I have a question that I hope someone here might help me with. The pendulum rod is shaking / oscillating when on extreme positions, this also makes a vibrating sound, which my wife finds highly irritating. The vibration is also seen in the escapement anchor. Her are some details, pictures and links to videos.

The escapement is a Graham escapement.
The pendulum is hung 5 cm (0.8 ") from a thread. The bar that holds the tread can be turned to adjust the beat ( the crutch is plastic and cannot be bent) The bar is currently adjusted 90 degrees cw.
The pendulum rod is a 3 mm (0.12"), 1m (39.4 ") long galvanized threaded rod. The crutch is positioned 5 cm (0.8 ") from were the rod is attached to the tread. The threads has been sanded off where the rod meets the crutch in order to reduce friction.
The pendulum bob is 220 g (0.49 pounds)
The mass of the weight is 1100 g ( 2.4 punds) with a drop of 50 cm (20")/ 24 hour

I am thinking that the vibration could be caused by:
Pendulum rod not stiff enough, if so what material and dimensions?
Wrong crutch placement
To heavy pendulum bob ( to much inertia)
Overpowered clock ( I have reduced mass from 1300 g to 110 gram, and will go down until clock stops)

Any suggestions?

 

[Jevan]

I don't say this is the answer to your problem but in my opinion a good starting point is the escapement which doesn't look correctly adjusted.

The instant a tooth drops onto the left pallet a slight recoil can be seen which means the pendulum is receiving an unexpected kick against its travel direction which may be sufficient to induce some shake, it is not easy to see the action of the right pallet.

With a Graham deadbeat the escapewheel tooth must drop onto the "dead" curved surface of the pallet which should be concentric with the pallet arbor pivots, if it miss-locks and falls onto the impulse face it will be abruptly pushed backwards as it runs back up the impulse face and onto the locking dead face due to the momentum of the pendulum, for the brief period this action is taking place the crutch will be imparting a force or recoil against the pendulum rod.

I think the beat adjustment and suspension arrangement might have the potential to cause an issue but I am not sure they are directly contributing to the main problem, does the thread vibrate or shudder as the clock ticks as this may indicate some adjustment may be needed.

My computer has low quality sound and the clock is very difficult to hear the in the video, I think a correctly adjusted escapement would be slightly quieter but I don't think by much.

I think your clock is a fine achievement and I hope you find a satisfactory solution, although I don't do any I have always found 3d printing fascinating.

 

[bruce linde]

- i don't see the escape wheel teeth recoiling, but i do see what looks like an excessive amount of EW teeth sliding on the locking pallets of the verge... and the verge vibrating when it shouldn't. i wonder if the pivot holes are too loose? if it were mine, i would want to raise the verge slightly... but it looks like the EW teeth are just barely hitting the locking faces. can we get a closeup of those locking faces? what is the verge/anchor made of? overall i think it's very impressive... but there's something a little off w/ the verge... better closeup photos and more info?

- the pendulum rod and crutch slot should both be a polished as possible.... not sure 'threaded rod with the threads sanded' is enough

- your videos are mp4 movies hosted on a google drive... which do not work for mac/ipad/iphone users when viewing the message board. the best way to embed videos is to upload them to youtube and then copy and paste video urls into posts here.... youtube handles making sure videos are cross-platform and cross-browser compatible. mac/iphone/ipad users like myself should click the little arrow icon in the upper right of your videos to see them on the google drive

 

[JME]

I don't say this is the answer to your problem but in my opinion a good starting point is the escapement which doesn't look correctly adjusted.

The instant a tooth drops onto the left pallet a slight recoil can be seen which means the pendulum is receiving an unexpected kick against its travel direction which may be sufficient to induce some shake, it is not easy to see the action of the right pallet.

With a Graham deadbeat the escapewheel tooth must drop onto the "dead" curved surface of the pallet which should be concentric with the pallet arbor pivots, if it miss-locks and falls onto the impulse face it will be abruptly pushed backwards as it runs back up the impulse face and onto the locking dead face due to the momentum of the pendulum, for the brief period this action is taking place the crutch will be imparting a force or recoil against the pendulum rod.

I think the beat adjustment and suspension arrangement might have the potential to cause an issue but I am not sure they are directly contributing to the main problem, does the thread vibrate or shudder as the clock ticks as this may indicate some adjustment may be needed.

My computer has low quality sound and the clock is very difficult to hear the in the video, I think a correctly adjusted escapement would be slightly quieter but I don't think by much.

I think your clock is a fine achievement and I hope you find a satisfactory solution, although I don't do any I have always found 3d printing fascinating.

Thanks for your input Jevan. The anchor arbor is fixed towords the back of the clock, but can be adjusted in front up or down on the right and left side. I have adjusted in order to remove the recoil movement, but its a difficult task. After your comment I took a slow motion video of the pallets, and it looks like you are right, the tooth might fall on the impulce face, at least some time.

movment at 30% speed:

 

[JME]

Thanks for your comment Bruce, I have uploaded escapment slow mo to you tube as suggested slow . The anchor is made of the same material as the clock, PETG. Its not printed solid (30% infill) so it could be more rigid, but its a trade off with weight. The anchor is compression fitted onto a 3mm steel arbor that is set in ball bearings on both side with a ca. 1 mm end shake

 

[Richard Cedar]

JME, (My response was written before seeing the other's responses)

Welcome to the Forum. I love your clock - 3D printing has opened the world of clock design/ construction to a new group of enthusiasts worldwide. I have been amazed at some of the very innovative and creative 3D-printed clocks that people are sharing on the web. I am hopeful that the cost of metal 3D printing will eventually come down to the point that it is affordable for the amateur horologist and open up the possibility of printing metal clocks and, potentially, watches.

If I understand your question correctly, the pendulum rod on your clock is oscillating in a similar manner to the vibration of a tuning fork on each swing. I had this problem with one of my clocks (also with a ~39" length pendulum). Effectively, with every beat of the escapement, the crutch was exciting a natural frequency of the pendulum rod (just like tapping a tuning fork). In your case, the natural frequency being excited is particularly annoying to your wife.

One potential solution is to modify the pendulum to change its natural frequency being excited to one less annoying or even outside the audible range. If you are into the engineering mathematics of the situation, try searching for "natural frequency of a beam," and you will find that the frequency depends on a long list of parameters, including:

• The material properties of the pendulum rod (Young's Modulus and density).
• The Moment of Inertia of the cross-section of the pendulum rod (If it is circular, the rod diameter)
• The length of the rod and the mass distribution along the pendulum
• The mechanical details of how it is allowed to move at the top of the pendulum.

Effectively, any change to the pendulum design with change the natural frequency. Looking at the equations for my clocks, I decided that changing the diameter of the pendulum rod that I was using would probably be the most effective. If I remember correctly, I changed the diameter of the wooden pendulum rod from 3/16" to 1/4", and that greatly improved the problem. If this is difficult for you to do, try changing things that are easily modified and see what works.

You may also find that reducing the weight you are using to power your clock to the minimum required to keep the clock running will result in a reduction of the impulse the crutch is imparting to the pendulum each beat and therefore lowering the amplitude of the vibration to the point the sound is not noticeable. Changing the length of the crutch will also change how it excites the pendulum.

I hope this helps.

Richard Cedar
Cedar Clocks (www.CedarClocks.com)

 

[gmorse]

Hi JME,

Since the recoil only appears to be evident on the entry pallet, is the arc of its locking face centred on the pivot as it should be, and as the exit pallet appears to be? If it isn't, that could account for the unwanted recoil.

Regards,

Graham

 

[bruce linde]

Thanks for your comment Bruce, I have uploaded escapment slow mo to you tube as suggested slow . The anchor is made of the same material as the clock, PETG. Its not printed solid (30% infill) so it could be more rigid, but its a trade off with weight. The anchor is compression fitted onto a 3mm steel arbor that is set in ball bearings on both side with a ca. 1 mm end shake

how smooth is the material? Pallet faces want to be hard and highly polished

 

[Jevan]

Hopefully of interest.

I had occasion to install many brand-new pendulums on some eighteenth century English longcase clocks, all were anchor escapement.
The majority had brass rods and it was not unusual to find the earlier clocks had thinner brass rods.

The nearest sizes I could commercially source were 3.2mm and 2.4mm diameter rod.

Although there was no accompanying noise I had the same very obvious tremor issue with one of the thinner rods, I changed the rod to the thicker 3.2mm diameter and although I believe the underlying issue probably still remained it was so much reduced that it was visually unnoticeable.

I didn't give a great deal of thought to the problem but at the time assumed the tremor was created by a steep impulse angle being presented to the pallet face on each vibration, in changing the rod the issue seemed solved so I gave it no more thought.

In some later longcases it is not unusual to see flat pendulum rods, I have never really understood the primary reason for these flat rods was but I imagine they would be almost immune to escapement induced vibration.

 

[JME]

Thank you all for tips and information. I really appreciate it.
I will order a 4 mm untreaded steel rod for a new pendulum rod, hopefully this will help.
The pallet faces on my anchor is pretty smooth, but a steel face will be much harder and smoother.
Regarding the symmetry of the pallets. I cant claim to fully understand escapement design theory, I have followed this design. According to this you have to choose between having the stopping faces equidistant from the arbour center or the impulse faces equidistance from the arbor center, I choose the latter, as indicated on the figure. The curve of both stopping faces are centered on the pivot, but the distance to the pivot (radii) are different.

Best regards Jørn

 

[John MacArthur]

You don't have enough safe "lock" on the dead face, what you call "stopping face". It appears that the corner between the dead face and the impulse face is somewhat rounded, and the scape teeth sometimes land on the rounded part. It is crucial that this point be a sharp as possible. In a normally made escapement these faces are ground accurately, and you can achieve greater precision of action. See #5 Regulator progress
Johnny

 

[gmorse]

Hi JME,

This extract from WJ Gazeley's 'Clock and Watch Escapements', covering the design and drawing of the Graham escapement may be useful.

Regards,

Graham

 

[JME]

Again I have to thank you all for the geerous way you are sharing your knowledge, with a complete newbie. I would definitely read through the pages you sent me Graham, I see its available on Amazon, I will probably order a copy.
When I started this project I knew that the pallet position was important, so I build in the possibility to move the anchor, as seen in the picture, but i didn't appreciate how the precise this need to be. In my next clock (this is just too interesting...) I will focus more on this.

Jørn

 

[bruce linde]

keep in mind the anchor math is important, but in realtionship to the escape wheel...

you have the relevant pages from gazeley.... a nice book to have, but not necessary at this point.

 

[JME]

To wrap up this thread I started: I had issues with vibrations in the pendulum rod, and noise from the escapement. As pointed out by several in this forum, the cause was probably due to recoil in the "supposed" deadbeat escapement.

The clock still have a slight recoil, but the sound problems has been mitigated by changing the pendulum rod from 3mm threaded rod to a 4 mm smooth rod. In addition the mass of the weight have been reduced from 1100 g to 450 g. ( power reduction from 63uW to 26 uW). These changes have made the clock much more silent and with no visible rod vibration.