Re: making the case for self-tapping screws

Dennis Storzek <destorzek@...>

--- In STMFC@..., Denny Anspach <danspach@...> wrote:

Truck makers make bushings peculiar to their truck bolsters?


Denny S. Anspach, MD

I fail to see why truck makers need to be responsible for other
manufacturers' poorly designed body bolsters. The de facto standard in
the hobby for the last forty years has been a clearance hole for a
1/8" dia. boss, so the truck doesn't pivot around the threads, and the
screw can be tightened solid without binding the truck. If it wasn't
for the fact that Kadee persists in adhering to the outdated and
obsolete NMRA standard, the available trucks would have matched this
standard 100%, at least before the recent wave of designed in China
stuff started diverging again.

There is no reason why resin kit makers can't mold the boss on their
parts; I was even able to have it included on white metal parts. The
fact that it might need to be removed to accommodate a few trucks is
no excuse; it's easier for the modeler to carve it off rather than
cobble it up from nothing.

That being said, If you buy Accurail trucks, you get the added value
of someone actually giving this some thought during the design
process. Accurail trucks come with the clearance hole for the 1/8"
boss, and so will fit most any other injection molded kit. The inside
diameter of the screw head recess is designed to be a decent running
fit on the ANSI standard dimensions for the pan head on a #2 screw;
either a wood screw, type AB thread cutting screw (sheet metal screw)
or machine screw. So, if you use pan head screws, the O.D. of the head
should give acceptable results, although the standard for pan heads
does provide wider tolerances that the molded bosses are usually held
to. You can even trim the bushing off the ubiquitous Kadee #5 box, and
you will find that the thickness of the Accurail truck bolster is such
that the Kadee bushing is the proper length.

Dennis Storzek
Accurail, Inc.

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