Re: [Amel Yacht Owners] Re: re caulking of stanchion base


James Alton
 

Mark,

   Thanks for your input.  I am really curious to know if you found any data confirming that the Phillips head can transfer more torque to the screw than a slotted head because I would really like to know!   I have generally had worse luck with removing old Phillips screws than slotted but that could be the tools and or technique.  If you have learned any tricks l would be interested to know. 
     Without a doubt the slotted head fastener can be the most difficult to deal with in regards to slippage since there is nothing there to keep the centering.  Also the slot width seems to vary and the available tools seldom fit properly which is critical as Bill K. also states to successfully avoid slippage when applying high torque.  Proper fit usually requires me to grind a fatter tool down.   Finally, the shape of the tool tip is very critical.  Many of the tips I buy are tapered which will cause the tool to cam out of the slot.  What you want is a tip that is actually slightly undercut in that the very end/ tip of the tool is slightly thicker than the part of the tool that would otherwise contact the top of the screw head.  You want to put the pressure on the very bottom of the screw slot, not the top or else the pressure tends to open the slot creating the dreaded Vee shape that wants to cam out.  The bottom edges of the tool should be sharp which seems to cause the tool to bite into the fastener eliminating slippage and allowing the maximum torque to be applied.   I also like to apply a very slight undercut to the bottom face of the tool tip which helps to insure that the tips of the tool are fully engaged.  If you follow all of these steps I think that you will find that the tip will lock into the screw slot quite well so long as the screw itself has the original square slot.  If the screw slot has become Veed in shape due to using an improper tip, corrosion or slippage, carefully reshaping the slot with a dremel, or a tiny sharp file can often restore the slot.  This ability to recover the slotted head shape and potentially the maximum torque for another try at removal is unique I believe to the slotted head as compared to the center drive type fasteners.    I have recut a lot of slotted screw heads and often cut the slot a bit deeper in the process.  

    In the Automotive world I believe that you have another factor that makes the slotted fastener difficult to deal with.  It seems that  corrosion of steel slotted fasteners tends to round off the sharp edges of the slot.  Add that to a bit of oil and they can be almost impossible to remove!

Best,

James Alton
SV Sueño
Maramu #220

On Aug 8, 2018, at 9:08 AM, mfmcgovern@... [amelyachtowners] <amelyachtowners@...> wrote:

I work in automotive and have dealt with my share of seized fasteners.  Which bolt head type is "best" is an age-old question and one that does not really seem to have a definitive, scientific answer.  Here's a pretty good run-down of most of the available options:  https://www.wiha.com/en/screw-head-types/


In reality, the four head types that you can find relatively easy in 316 Stainless Steel in the sizes we would use on an Amel are:

1. Slot Head 
2.  Phillips Head
3.  Socket Head/Allen Head (internal hex)
< div>4.  Hex Head (external hex)

In my experience, Slot Head is by far the worst choice in terms of both the amount of torque you can apply and in keeping the tool on the fastener head.  However, it is available in the most sizes/lengths and is usually the cheapest option.  

Phillips Head will let you apply the most torque to the screw head.  However, you have to be able to apply a good bit of axial force (pushing the screwdriver down into the screw head) in order to avoid the screwdriver slipping out.  

Socket Head/Allen Head/Hex Head is a good choice when you have limited access to the screw head and you can't apply a lot of axial force.  However, you cannot apply a lot of torque to the head before stripping it out.  Socket Head/Allen head are "prettier" and come in a flat head version which can sit flush in countersunk holes like the ones in the SM stanchion bases that we are talking about in this thread.

www.mcmaster.com and www.grainger.com are two good places to find 316 Stainless Steel fasteners in the USA.  


Mark McGovern
SM 440 Cara
Deale, MD USA


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