[SML] S4 bench focus...

[Dale Farmer]

On 6/24/2015 6:21 PM, Steven Hood via Stagecraft wrote:
> Lighting folks,
>
> Have any of you had an issue with the outer (XY) knob/nut seizing the
> aluminum hub casting? We have... I've had to drill out 3 of them this
> year - all from units that had been assigned 36 degree lenses. It seems
> like that hub casting is heating up more from having to pull the Z
> adjustment so far into the reflector and seizing on the outer nut as a
> result. Is there some way to prevent that deformation?
>
> TIA,
> Steven R. Hood
>
>
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It happens.  The only way to prevent it is to go in and unscrew the 
thing a couple of turns and retighten it every so often.  I've 
experimented with various high temp lube compounds, but haven't really 
gotten results yet.   My confidence is not high there is a reasonable 
solution.  It's bimetal corrosion between a steel nut and an aluminum (I 
think) casting.  So short of putting a magnesium sacrifical anode 
someplace on the light, that's not something you can stop.  (By the way, 
if anyone has a source of magnesium that is in the form of standard 
sized washers or nuts, I do have some gear that I do want to provide 
some sacrifical anodes on, but the only thing I have found is boat 
propeller nuts, which are way too large.  )

If you have one that is seized up, and you have a couple of days, you 
can take a q-tip and apply some penetrating oil to the threads and let 
it sit and soak in, giving it a good hard attempt to unscrew it twice a 
day, and adding more penetrating oil after each failure.    Don't forget 
to degrease it well once you have it apart, or you are gonna get some 
nasty smells from it the first time it is used.

   Or you can buy the replacement casting and a replacement plastic 
ring, because the plastic ring around the outside of the nut also gets 
broken when you put the big pliers on to unscrew it.  Which one depends 
on how much you are paying for parts and labor and how many spare lamp 
caps you have on hand.

--Dale