Wheels/gaps/turnouts


Mike Brock <brockm@...>
 

Jack Wyatt writes:

In the way I understand the NMRA HO track standards, the distance between
the wing rail and rail is 0.050 inches, so a 0.088 wheel will not drop
until
it gets to the gap in the frog.
Well, to be precise, the drop occurs when the wheel...let's say heading from
the frog towards the moving points...rolls along looking for something to
support it. Now, if you look at NMRA RP-13.7 Frog and Wing Rails, you'll
note that "35" is part of the the wing rail as measured from the theoretical
point of the frog back past the frog. This dimension is not very important
in our study...it just has to extend some distance behind the frog as shown
by "35". To be sure...and a little bit of history here...there is, IMO, an
important dimension missing, the distance from the theoretical point of the
frog...where "20" and "21" meet [ real RRs don't have this point as part of
the frog...realizing long ago that it wouldn't survive very long ] and the
point where the wing rail begins [ where it bends away from the closure
rails ]. I asked Brad Bradley [ by phone ]...neighbor and member of the
standards committee long ago...you'll see his name on many of the
standards...to put this dimension in the standards and all I heard was a
loud click as he hung up on me. Noooo problem, it's easy enough to figure
out...I think approximately 0.5" for a number 10...but it's really hard to
build an accurate turnout without knowing this dimension. Anyhow, the wheel
tread will find support from the wing rail long before it finds the closure
rail. The wider tread of the code 110 wheel.....080" compared to .063" of
the code 88...does have an effect IF the distance from the frog to the
position where the wing rail can be encountered by the code 110 wheel is
great enough to allow a code 88 built wheel to drop because it cannot reach
the wing rail before dropping. This distance is great enough on a number 10
and may be great enough on a number 8.

But a 0.110 wheel will drop at least 0.003",
or maybe more (minimum depth of flangeway is 0.028" - flange on 0.110
wheel
is 0.025"). The 0.088 inch wheel only drops 0.002" futher (0.023 flange
depth). I don't see what the big deal is about 0.002".
An interesting point. However, the code 110 wheel actually doesn't drop at
all. The reason is that the turnout frog/flange gap dimensions for track
standard S-3 matches the code 110 wheel. As I think I may have said, code 88
wheels made with the proper flange size won't drop either...if the track
frog/flange gap is built for it. But then, we have that screeching sound
from the code 110 wheels trying to get through.

Mike Brock

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