Re: [Amel Yacht Owners] Re: re caulking of stanchion base
Mark,toggle quoted messageShow quoted text
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!