Re: How far do we go?


soolinehistory <destorzek@...>
 

--- In STMFC@..., Andy Carlson wrote:

Concerning the code 88/110 compatibility with switch work... This is where the sharp point of the frog makes a difference, as the tip of the point
extends out just a bit more than a blunt frog, enough to catch the semi-scale wheel tread.
You have discovered the main problem with commercial track... blunt frog points. The prototype specifies the point of the frog at 1/2" wide... that's .0055" in HO scale. Most commercial track is something more like .015" or .020". Surprisingly, the NMRA track standards have never put a limit on this dimension, which is a glaring omission.

I have been making some switches for several months using the Fast Tracks turnout assembly fixtures, and with careful construction, I don't even hear the metal wheels click upon passing through the frog. I can not see me ever using commercial switches in the future.

Jack Parker showed me many years ago that track work can be made to work flawlessly for both code 88 and code 110 wheel equipped equipment.
The limit for wheel width is that it has to be wider than 2X the flangeway plus the frog point. Since the minimum frog flangeway in NMRA S-3.2 is .036", 2(.036)+.006 =.078, leaving .010" for tolerance and gauge widening before the wheels drop, so it can indeed work, at least for locomotives with two axle trucks. The reason the NMRA is never going to adopt this as standard is it won't work for various combinations of long wheelbase locomotives, tight curves, and short turnouts that the hobby has come to expect as the norm. There is nothing wrong with building to standards "tighter" than the norm; you just have to realize what you can't expect to do.

If you do need additional gauge widening, you can always fill the frog flangeways to .025", and let the wheels be supported on the flange through the frog. The prototype doesn't do it this way (other than street railways) because the loads imposed tend to break chunks out of the flange, with potentially disastrous results. I've never seen a broken flange in HO scale :-)

I ponder the feasibility of having track work which performs flawlessly with a mix of code 88 and P:87 wheels? Fat wheels would need to be excluded.
This one isn't going to work. The P:87 wheel is .064 - .069 wide, and two times the min. flangeway is already .072. NWSL at one time sold HO scale Code 72 wheels (.072" wide) and this is likely the reason why, but they never got enough support to make them worthwhile. You can't fill the flangeways, either, because the P:87 wheel flanges are only .013" deep. The same reason the NMRA won't support filled flangeways in their standards; they exclude all the pre-RP-25 wheels with deeper flanges.

Dennis

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