Barograph ‘stiction’

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Barograph ‘stiction’

This topic has 29 replies, 14 voices, and was last updated 19 November 2022 at 19:18 by old mart.

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12 May 2022 at 11:58 #597949
modeng2000
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@modeng2000
My barograph mechanism has a fair amount of 'stiction' in the pen movement and so I wonder if replacing the simple sleve bearings for point bearings as used for escapement wheels would be worth doing.
I realise that the friction between pen and paper is one source of stiction but feel that the simple holes through the two posts is probably another.
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12 May 2022 at 11:58 #3969
modeng2000
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@modeng2000
12 May 2022 at 12:08 #597951
Brian Wood
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@brianwood45127
You may well be right

Brian
12 May 2022 at 12:31 #597952
modeng2000
Participant
@modeng2000
Brian, it would be fairly easy to make the change and to revert if no improvement.

So I think if it might help I should try. Just wasn't sure it would help.

John
12 May 2022 at 13:51 #597959
Brian Wood
Participant
@brianwood45127
John,

I don't think you have anything to lose by trying your ideas out.

It might be instructive to look at other instruments of this type to see how they have dealt with suspension matters; the forces acting on the device that is trying to trace the changes in barometric pressure will not be high and plain sleeve bearings will demand some of that as you suspect.

You might be pleasantly surprised at the result

Brian
12 May 2022 at 13:51 #597960
John Haine
Participant
@johnhaine32865
I think you mean "balance wheels" (sorry, inner pedant at work!). It might help just to dismantle, clean and oil the bearings.
12 May 2022 at 14:18 #597962
modeng2000
Participant
@modeng2000
Joohn,

Yes of course I mean balance wheels, sorry. I have tried to upload a photo but alas failed miserably.

The linkage is very basic, just pins through holes. So I think where a 2.5mm dia brass rod passes through two clearence holes in a pair of uprght posts is possibly where some of the sticking is taking place.

(I did manage to place a picture on the Home Model Engine Machinist site)

John
12 May 2022 at 14:32 #597963
gerry madden
Participant
@gerrymadden53711
One of the interesting characteristics of PTFE is that its static friction is the same as its dynamic. This helps avoid 'stiction' issues. Not sure if you would be able to work this in to your application… it might make things too big and therefore might increase friction to above what you already have, so perhaps the balance wheel pivot is better.

Gerry
12 May 2022 at 14:46 #597964
Dave Halford
Participant
@davehalford22513
The chart recorders at BT used a simple balanced pen similar in construction to a Lenco record player arm suspension. A vee shaped cutout balanced on knife edge. No pen arm sleeve bearings at all.
12 May 2022 at 14:47 #597965
David Jupp
Participant
@davidjupp51506
I seem to recall from University materials classes that for PTFE friction increases when direction of movement changes, so it isn't as good as you'd expect in oscillating systems. If movement is always in same direction friction remains low – almost as if there is a 'nap' on the surface that has to brushed into place by initial movement.
12 May 2022 at 17:02 #597971
Swarf, Mostly!
Participant
@swarfmostly
Long, long ago, someone told me that instruments for motor car dashboards used crude pivots for the sake of ruggedness and longevity but relied on the vibration when the engine was running to vercome the friction.

If you can bear it, strap a buzzer to your barograph!

Best regards,

Swarf, Mostly!

PS: OK, OK, I know that opening sentence is too long, sorry.
12 May 2022 at 17:32 #597975
gerry madden
Participant
@gerrymadden53711
David, I didn't know that about oscillating movements. Interesting. I had planned to use in a clock escapement, perhaps I wont now .

There is another material with similar CoF, called Vespel. Do you have any experience of this ?

Apologies if this is a thread hijack.

Gerry
12 May 2022 at 17:33 #597976
modeng2000
Participant
@modeng2000
"If you can bear it, strap a buzzer to your barograph! "

This is something I had considered but it would have to be clockwork!!
12 May 2022 at 17:48 #597978
David Jupp
Participant
@davidjupp51506
Gerry – I've heard of Vespel, but have zero experience of it.

I also seem to recall that PTFE gives lower friction if there is at least some moisture (humidity) around – strange given that it was allegedly developed for the space programme…
12 May 2022 at 19:35 #597993
Andy Stopford
Participant
@andystopford50521
Posted by David Jupp on 12/05/2022 17:48:42:

I also seem to recall that PTFE gives lower friction if there is at least some moisture (humidity) around – strange given that it was allegedly developed for the space programme…

The space programme thing is a myth – PTFE was discovered (more or less by accident) in the thirties. Its first notable use was in the Manhattan Project to protect the plumbing of the Oak Ridge Gaseous Diffusion Plant from the corrosive effects of Uranium Hexafluoride.

Interesting about the poorer performance for oscillating systems. I wonder if its the same for other slippery plastics like nylon and acetal.
12 May 2022 at 21:06 #598010
bernard towers
Participant
@bernardtowers37738
And the countries last Barograph and Barometer maker is closing for good next month after something like 175years!!!
12 May 2022 at 21:57 #598017
Robert Atkinson 2
Participant
@robertatkinson2
Swarf's comment on a buzzer is spot on. Many aircraft altimeters (basically aneroid barometers) have internal buzzers to overcome stiction. Altimeters have very good bearings but stiction is still an issue.

Robert G8RPI.
13 May 2022 at 07:15 #598065
modeng2000
Participant
@modeng2000
So I suppose Bernard, these will now be made abroad like a lot of other things these days. Which company is about to stop trading?

Robert, so this is why folk tap the barometer as they pass by watching it settle to the current reading.

A barometer really indicates the pressure when requested by giiving it a tap however the barograph normally sits on its own most of the time so stiction becomes a problem. I have started the modification so hopefully I'll find an improvement. An electronic device is the answer but finding one with a printed chart output is another matter and it would need an electric supply not just a spring.

Thanks for the suggestions to my question.

John
13 May 2022 at 07:31 #598070
Michael Gilligan
Participant
@michaelgilligan61133
Posted by modeng2000 on 13/05/2022 07:15:15:

So I suppose Bernard, these will now be made abroad like a lot of other things these days. Which company is about to stop trading?

.

… which reminds me to ask you, John: What barograph are you using ?

MichaelG.

.

P.S. __ a recent eMail from Jeffrey Formby Antiques mentioned this book, which might be of interest:

https://www.formby-clocks.co.uk/cgi-bin/sh000001.pl?WD=collins&PN=c-e-p5.htm&utm_source=BenchmarkEmail&utm_campaign=May_03_2022_Email&utm_medium=email#aN5082

http://www.barosbooks.co.uk/b.html

Edited By Michael Gilligan on 13/05/2022 07:50:15
13 May 2022 at 09:10 #598083
modeng2000
Participant
@modeng2000
Michael, it is a dome barograph by Russel Scientific. Quite compact and I believe this has compromised the design by being enclosed in a 4"dia by 6" tall glass dome.

The Philip Collins book looks really interesting, thanks for the link.

John
13 May 2022 at 10:16 #598093
modeng2000
Participant
@modeng2000
There is another possible reason for the pen sticking, as this is a small barograph the chart length is shorter than for a normal barograph therefor the distance the pen moves across the chart is also shorter so giving less chance to unstick as compared to a full size barograph..

John
13 May 2022 at 12:49 #598117
bernard towers
Participant
@bernardtowers37738
Its Russell scientific in east dereham norfolk that is closing, so if you want any bits get in now.
13 May 2022 at 13:40 #598128
noel shelley
Participant
@noelshelley55608
Russel scientific close any time now, sad after so many years, mercury ban and electronics have done for them ! I have a modern Russel, a simple linkage but never seems to stick.. Noel.
13 May 2022 at 15:52 #598150
old mart
Participant
@oldmart
Little vibrators were clamped on some aircraft instruments such as ASI's and alitmeters if the instrument panels did not have enough engine produced vibrations. With a slow moving instrument like a barograph, something timed to give a little tap every few minutes would be more suitable.
13 May 2022 at 17:52 #598171
modeng2000
Participant
@modeng2000
Thanks for the Russel Scientific information.

John
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