Screw Drive Types

[Phillip Ford]

>I have a very hard time believing these statistics.  Are you sure you read
>them correctly?

I sent scans of the articles to be posted, so you can see for yourself 
later.  The testing was on pan head screws (such as you might see in a 
piano action) - not on heavy duty machine screws, so your mileage may 
vary.  Also, as I understand it, they used a uniform end load on each 
fastener and what determined max torque was drive failure, which I took to 
mean cam-out, but I suppose could mean rounding off the drive.  So cam-out
on an internal hex of the type used on ordinary pan head screws must not be that high
or the material strength is such that they round out.  They didn't specify what grade
fasteners they were using.

>   You can tighten a socket (Allen) head screw so tight you'll
>either break off the screw head or twist the wrench into a pretzle.

Interesting.  Just a couple of days ago I was tightening the allen head set 
screws which hold the needles on my super-duper Yamaha voicing tool and 
managed to round out one of the internal hex so that I can't get the screw 
out - long before I bent the wrench into a pretzel.  Perhaps this only 
applies on allen head screws large enough for holding bridges together or on
high strength socket head screws, like Unbrako or some such.

Phil Ford

>   Socket
>head and hex head capscrews are used almost exclusively in building machines
>where torque is critical.  Torx heads are occasionally seen, but only on
>critical items such as bearing lock collars...we usually just replace them
>with socket heads since many maintenance crews don't have Torx wrenches.
>
>Ordinary machine screws (like slotted or Phillips head) are generally used
>only for mass-produced items where speed of installation and cost preclude
>strength or torque.  A Phillips (cross-recess) screw head will cam out
>and/or strip long before you get any serious torque out of it.
>
>Don A. Gilmore
>Mechanical Engineer
>Kansas City
>----- Original Message -----
>From: "Phillip Ford" <fordpiano@earthlink.net>
>To: <pianotech@ptg.org>
>Sent: Friday, February 06, 2004 1:42 PM
>Subject: Screw Drive Types (was Re: Slotted Wood Screws)
>
>
> > In what way are they superior?  What's wrong with TORX?
> >
> > I have an article comparing torque that can be developed on fasteners with
> > various drive types using power drivers.  Interestingly, the Phillips is
> > about the same as the square drive.  The TORX can develop almost twice as
> > much as either one.  And the TORX PLUS slightly more.  (Also interesting
>to
> > me is that the internal hex drive develops less than half the torque of
> > the Phillips or square drives).
> >
> > I can post scans of the article if anyone is interested.
> >
> > Phil Ford