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Old 9th Sep 2021, 11:45 pm   #1
marrold
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Default Spring slipping on Dial No 12

Hello,

I recently acquired a GPO 332 with a No 12 Dial that was slow and sticking in places. I've stripped it down, cleaned it, and rebuilt it, but occasionally the spring slips out of the slot in the back of the dial.

As far as I can tell the spring and slot are in good condition, and I'm correctly fitting the spring into the slot (See pictures)

Does anyone have any suggestions on how to fix this?

Thanks
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Old 10th Sep 2021, 9:28 am   #2
ThePillenwerfer
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Default Re: Spring slipping on Dial No 12

I'd say the shaping of the inner end is wrong.
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Old 10th Sep 2021, 10:44 am   #3
ThePillenwerfer
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Default Re: Spring slipping on Dial No 12

Just a warning to anybody reading this: in the photographs above the spring is in the wrong way 'round. It should look like this:—
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Old 10th Sep 2021, 11:14 am   #4
marrold
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Default Re: Spring slipping on Dial No 12

Thanks for the photos, I can see the difference. I'll try a spring out another dial.

I wonder what the story is there. As far as I can tell the telephone / dial is otherwise original.
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Old 10th Sep 2021, 12:15 pm   #5
pip5678
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Default Re: Spring slipping on Dial No 12

I concur, the shape looks different to these two also. The spring end can be reshaped by heating in a gas hob flame for example and rebent with pliers so that it fits in the slot more precisely.
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Old 10th Sep 2021, 5:07 pm   #6
ajgriff
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Default Re: Spring slipping on Dial No 12

Once the misshapen spring end has been sorted you need to fit, tension and lubricate the spring in its holder as described here:

https://www.britishtelephones.com/te...20b5125.htm#14

This extract summarises the procedure:

Fitting and adjusting the main spring
The main spring should be wound in the spring box, starting from the outer edge (the arrow on the spring box indicates the direction of winding). The main spring should then be tensioned, by rotating the finger-plate in a clockwise direction, until the spring is felt to tighten; the finger-plate should then be allowed to return through one complete revolution and the stop screwed down. The dial should then return through not less than one half of a complete revolution to its normal position.

Main Spring - Lubrication
A main spring which is fit for re-use should be dipped in Oil, Bearing, No. 16 and drained before assembly. Further lubricant should not be applied. Spare main springs should be stored in a bath of Oil, Bearing, No. 16.

Alan
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Old 12th Sep 2021, 8:36 am   #7
dagskarlsen
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Default Re: Spring slipping on Dial No 12

Quote:
Originally Posted by ajgriff View Post
Once the misshapen spring end has been sorted you need to fit, tension and lubricate the spring in its holder as described here:

https://www.britishtelephones.com/te...20b5125.htm#14

This extract summarises the procedure....

Alan
Thank you! this was a good explanation and a good link, and it helps understanding and adjusting other dials too.

The most of equipment that understand rotary dials are not to tough on the make/break ratio, but some are. UK usually use 2/3 break (67.6%) and many other countries has 60%. By my experience tuning to 63-65% works well on all my equipment.

Sometimes I is impossible to come there , then I go so close I can, and usually it works with something. E.g. I have some old Ericsson dials that seems to be 50%, those has not been possible to tune to more than 58? without modifying, but works on some of my equipment.
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Old 12th Sep 2021, 9:45 am   #8
ajgriff
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Default Re: Spring slipping on Dial No 12

I agree that exact timing is not too critical. The important thing is to tension the spring correctly. The lubrication (light machine oil) is about rust protection and therefore longevity I suspect.

Alan

Last edited by ajgriff; 12th Sep 2021 at 10:14 am.
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