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From: email@example.com (Gibbo)
Date: 02 Nov 2002 12:59:51 GMT
Organization: AOL, http://www.aol.co.uk
Subject: Re: Side effects of potting compound !
firstname.lastname@example.org (Bob Wilson) wrote:
>In article <email@example.com>,
>>"Tom Del Rosso" firstname.lastname@example.org wrote:
>>>"Gibbo" wrote in
>>>> The square ones with a circular element and worm drive. Beats me how
>>>> it's doing it. All three have moved by roughly the same amount (within
>>>> Can't leave it exposed as it'd buried really deep next to some high
>>>If you did the conformal coating after gluing it with nail polish, then
>>>you could be really confident of it.
>>>It would be neat to have a trimmer remain exposed through a tunnel,
>>>especially if the screw is on top. I'm thinking of a piece of tubing
>>>wide enough to surround the whole trimmer, a little silicone squirted on
>>>the board around the base of the trimmer, and the tube placed over the
>>>trimmer before potting. Just a thought since you don't need it exposed.
>>Yeah that would be the ideal but the time meddling with it kinda kills the
>>Tomorrow is truth day. I did 2 more today. Calibrated them then covered the
>>entire preset with 2 part silicon sealer. Then potted them in polyeurethane
>>(instead of epoxy). If that fails then they're having them unpotted. I'm
>>starting to get bored of it now !
>This may be somewhat pointless. Silicone is completely incompressible. While
>it may SEEM soft and rubbery to the touch, this is only because it DISPLACES
>when you compress one part of it. While this may be great for locally
>applied pressure when unpotted, once it is entirely encapsulated by a
>rock-hard potting compound, there is nowhere for the material to displace
>when presure is applied. Thus, once potted, silicone is effectively as hard
>as a rock.
I must say that what you wrote above makes perfect sense and in theory I agree
with you. However this combination was the only one that was successful ie it
didn't alter the preset setting.
I have no idea why. I suspect it may be something to do with the preset having
open space on one side and large components close by on the other. Perhaps the
curing process twisted it or pressed unevenly on one side. Perhaps the silicon
rubber allowed some flexibility to prevent this.
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