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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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25th Sep 2022, 9:34 pm | #1 |
Dekatron
Join Date: Apr 2009
Location: Oxfordshire, UK.
Posts: 4,935
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Removing Meter Face-Plates
Something like 50 years ago, the Edwards Company was the leading supplier of all things to do with vacuum equipment. One of their products was a Pirani gauge, which measured vacuum, and displayed its reading on a standard moving coil meter with a log scale in calibrated in Torr: not too much use for radio work.
The FSD of the meters was 1mA and I think they were made by Sangamo Weston. I have a couple of these meters from old discarded gauges. Attempting to take off the front cover to paste on a 0-1 scale, I found it impossible to get the cover off and ended up breaking the brittle plastic. I could not see any screws, fixings or adhesives that needed dealing with. The outcome was pretty poor, needed sticky taping and it is now at the bottom of the junk box (see attached). Has anyone any experience with working with Sangamo meters? Thanks B
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25th Sep 2022, 10:52 pm | #2 |
Heptode
Join Date: Apr 2016
Location: Cheltenham, Gloucestershire, UK.
Posts: 875
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Re: Removing Meter Face-Plates
I have no experience in this particular area/endeavour .... but - have you tried a little judicious heat?
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26th Sep 2022, 8:44 am | #3 |
Dekatron
Join Date: Jun 2013
Location: East Sussex, UK.
Posts: 3,326
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Re: Removing Meter Face-Plates
Most plastic fronts that I've encountered just clip on around the edge. Look from the back and see if you can see the join.
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26th Sep 2022, 12:40 pm | #4 |
Octode
Join Date: Mar 2015
Location: Yorkshire, England.
Posts: 1,301
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Re: Removing Meter Face-Plates
They may be welded by ultrasonics. In my thirties l worked in a factory that used this process to prevent tampering.
When l first started lt was painful to walk past the machine when it was operating, but when I left nine years later l couldn't hear it at all!
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26th Sep 2022, 1:01 pm | #5 |
Dekatron
Join Date: Apr 2009
Location: Oxfordshire, UK.
Posts: 4,935
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Re: Removing Meter Face-Plates
Thanks for the suggestions. Over the years, I've successfully removed the front covers off quite a lot of meters; as often as not you can see 2 or more little mouldings which just need gracefully sliding over the edge of the main body.
But this was distinctly different; I could not see any feature which retains the cover and which would be a starting point. Even with warming, the plastic seems to "super brittle" (perhaps not surprising given the age). With the first one, I effectively wrecked the cover getting it off and the annoying thing is that no matter how hard I look at what's left, I don't understand what held what, and learned nothing in process. Ultrasonic welding is a possibility. All I can conclude at this stage is that Sangamo did not want intruders to get inside their meters, and putting a new scale on them seems to be impossible? B
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Saturn V had 6 million pounds of fuel. It would take thirty thousand strong men to lift it an inch. |