Screwheads; was 5 floppy?.

[Chuck Guzis]

On 25 Nov 2008 at 18:45, David Griffith wrote:

> I don't follow on the automatic centering.  Yes, a slotted screwdriver can
> slide out, but torx or robertsons?

To engage a Torx or Robertson, the screwdriver bit must be fairly 
precisely positioned so it enters the head.  With a Phillips, one can 
still engage the head successfully even if one starts off-center due 
to the property that both the slot and bit are conical in profile--
the bit will naturally tend to slide to center in the slot.

The price you pay for this is that it's not easy to preload a driver 
with a screw without some sort of clip or magnet arrangement.  Torx 
and Robertson-headed screws can be preloaded onto the bit which is 
one of the reasons that manufacturers like them--which is also, why, 
I suppose that square-drive drywall screws have largely replaced 
phillips-head ones.

> That's why you're supposed to use a drill with a slipper clutch.

I did better than that--I used a special-purpose screwgun that 
releases as soon as the head is driven flush with the surface.  The 
problem is that stainless deck screwheads are rather soft.  Driving 
4" #12 screws into green Doug-fir joists requires a fair amount of 
torque, even if one predrlls the first inch or two of the hole.  
 
Cheers,
Chuck