[Elecraft] Phillips Screws

[G3VVT at aol.com]

Will reply to the topic of corrosion with chassis screws on this  thread.
 
The reply from John, G4BOU on the subject of lubricating chassis  screws to 
help prevent corrosion was:
 
< 'petroleum jelly' despite being a very good insulator has a  lubrication  
factor of 1 
and any pressure (via the screw threads) will  break through the skin  and 
make 
good contact. It will of course also  cover the joint and limit corrosion.>
 
It sticks in my mind there was some controversy with the use of petroleum  
jelly for use in preventing corrosion on lead acid battery terminals as it was  
reputed to be hygroscopic, i.e. attracts water. This may not be a good 
property  for preventing corrosion on screw threads as it may even make the effect  
worse.
 
Perhaps somebody on the list who is more expert on the chemistry could  
comment.
 
Must admit however to filling the high gain UHF 8 stack antenna  connection 
boxes on a Cable TV head end to the brim with the same petroleum  jelly to 
prevent moisture entry in 1971 and that never ever suffered over many  years in 
what is reputed to be the wettest area in England. (the true rainfall  figure 
may have been inflated by small boys assisting in the collection  data by adding 
a certain yellow colored liquid)
 
Really all of this is academic as the biggest cause of non conductivity  with 
the chassis screws must be the coating on the outside of the case panels.  
This must be quite a good insulator and no way would I for one want to try  
removing it to ensure a good metallic contact. The inside of the case is a  
different matter and consequently with case bonding the connectivity must  rely on 
pressure between the inner of the case and the chassis 2D fastener,  not the 
screw thread directly.
 
The problems that come up with trashing the Phillips screw head is usually  
made worse by using the wrong type of Phillips driver. There must be a wide  
variety of types internationally to compound the issue. In the UK we seem to  
have two types. The earlier Phillips British type which still appears in  
instrument screws and has a quite sharp pointed shallow angle tip. The current  
usage is with what is referred to as the "Posidriv" type which has an almost  
square end with a slight dome on the tip and has a much wider angle on the tip  
blades. Equivalent screws to this are used commonly on Japanese equipment  and 
are marked with a single dot on the screw head. Using one of the  earlier 
Phillips drivers on these screws is a recipe for disaster. With the  Stanley 
drivers we buy here, the Phillips has a red plastic handle and the  Posidriv has a 
blue one to easily identify the type.
 
The K2 case screws seem to fit my Phillips British type driver  better and 
even using a small Posidriv driver with a no.1  point would soon trash the heads 
due to the poor fit. May be different with  Phillips drivers available in 
other countries.
 
Bob, G3VVT