yet another Shortt question.

[John Robinson]

Howdy,
On the Shortt mechanism, there is a weight on the impulse lever. According to the information I have been able to find, there are two different weights for this lever, one for running in vacuum, and one for running in the atmosphere. I am looking for the size or the mass of the weight used in atmosphere. thanks
johnrobinson

 

[Tinker Dwight]

I'm guessing they were tuned to each clock.
This based on the swing.
Tinker Dwight

 

[eskmill]

I suspect Robinson is seeking the characteristics of a compensating weight likely placed on the small gravity lever G1 in the diagram of the Shortt system shown in the sketch below.

To my knowledge, the Shortt clocks (less than 100 made) never had "fine-tune" weight tray on the pendulum rod.

The sketch taken from Hope-Jones "Electrical Timekeeping" does not show the small weight.

Apparently Robinson is fabricating a "Shortt Clone" and seeking some of the minute details of their fabrication. I am not aware of any remaining Shortt clocks in operation today. A few are privately owned and some reside in museums.

 

[John Robinson]

howdy,
My understanding is that the weight I am asking about (the weight is on the jeweled end of the impulse lever, just before the bend at the jewel. In the attached picture, I am pointing a mechanical pencil at the weight) This is one of the methods of slowing the action of the impulse and the resetting. The different weights are used so the clock can be adjusted in normal atmosphere, and then the heavy weight is changed to a light one, so the clock can be run in vacuum. I'm looking for the size and weight of the heavier atmosphere weight.
At a guess, the "normal" style weight tray cannot be used in a vacuum, due to the method of starting the pendulum while under vacuum, by introducing a little air to push the pendulum, which would probably cause the light weights on the tray to be blown off.
johnrobinson

 

[Tinker Dwight]

I assume the picture you have is from the vacuum system.
Your best luck might be to look at pictures and try to
get an estimate of size and weight that way.
Just locating one of these is a tough job.
I notice that Les' picture doesn't even show this weight.
Tinker Dwight

 

[John Robinson]

Howdy,
I am editing my reply from yesterday. I misspoke and this is the correction.

Yesterday I had several long conversations going on with my brothers and both sons, about my Synchronome clock and the proposed Shortt I want to build. I then logged onto this site and in my replying to a reply, I confused myself (easily done) and misspoke.
The weight I show in the picture is the correct weight for use in a vacuum, but that weight is used for giving the impulse to the pendulum (not to time the escapement as I stated incorrectly). Late last night I realized that I misspoke, and also! that I think I know how to find the answer to my question about the size of the atmospheric weight for the Shortt.

I am now looking for the article Mr. Hope-Jones (or was it Mr Shortt?) published showing the difference of the amount of work the Shortt clock does when compared to a standard Synchronome Master clock. The article shows a bar chart and that shows the Shortt clock using 30? ergs of power (I'm easily confused again me thinks).
I think I can "back out" calculate the approximate size of the Shortt atmospheric weight from those figures, providing I can find it in the piles of paper and books I have...

The weight for running the Shortt clock in normal atmosphere is only important to someone that is setting up a Shortt clock, it saves him a lot of time, rather than closing up the clock and drawing a vacuum to adjust and test the mechanism, you insert the heavier impulse weight used in air and just run the clock in air. Of all the pictures I've seen of a Shortt, they all seem to have only the smaller weight, which makes sense, if the clock is/was running back when it was set aside/stored/dismantled, there would be no reason to install a specialty adjustment part. So finding a picture of one is I think, almost impossible.

thanks, and drive carefully.

 

[Tinker Dwight]

I see the dilemma. Do you know the difference in ergs between
the two amounts of energy? If so, the weights should just be the
ratio of the two amounts of energy needed.
If not, you'll need to know the driven distance.
Tinker Dwight

 

[eskmill]

Hope-Jones's chapters on the free pendulum and more specifically, the Shortt clock reads like a physics classroom lecture on the forces needed to restore the pendulum motion and the amount of force needed to overcome the resistance of the suspension.

About ten or more years of experiment and trials by Shortt, Hope-Jones, Rudd and others are described in making the free pendulum.

What's not provided is the mass of the weighted lever that propels the pendulum via the jewel angle against the pendulum wheel; but the ratios in partial vacuum and atmosphere are derived.