TESTIMONIAL
May
1,2004
Dear
Mr. Murtha:
I have tested the Presets that you sent me and find that they are
as good as you claimed they would be. I could detect no observable
tearing of the face paper on the sheetrock which, combined with the
backing paper provides most of the strength of the sheetrock. The
tearing which occasionally occurs when using screws is in my opinion,
one of the major causes of failure. Another factor to consider is
the increased shear area that derives from the diameter of the Preset
being larger than the diameter of the screw alone. Consider a ceiling
application: The sheetrock panel is supported by the holding capacity
of the screws, which is limited by the shear strength of the sheetrock.
The area in shear at each screw is the surface area of a cylinder
that would be extruded by whichever holding device is selected(screw,
nail, etc.). That area is described by the formula A= Dt where t represents
the thickness of the panel and D is the diameter of the extruded cylinder.
From this you can see that a device with a larger diameter provides
a larger area to resist shearing forces. Based upon the sizes of the
Presets and screws that you sent me, the 0.336" diameter Preset would
result in a shear area that is almost 7% larger than that which the
0.3215" diameter screw head would provide. I think that your idea
to modify a pneumatic nailer to utilize the Presets also merits serious
consideration. I examined one model of such a tool, and believe it
could be easily adapted. If so, installation of sheetrock using pneumatic
nailers could become the industry standard once the cost vs. benefit
is realized. The time to install a panel of sheetrock could be reduced
by a factor of about four by my estimate.
I
wish you luck with your endeavor.
Cordially,

Richard
C. Macy
Professor
Emeritus
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James
Murtha
67
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