Spot on Bill! You can't change one dimension and not take the others into consideration. If you simply mount a code 88 wheel using the current SHS (NASG/NMRA Standard) 0.800 back to back for a code 110 wheel, you will probably have a bad day. The wheel set will run a high risk of falling between the rails! The manufactured code 88 (or P64) wheel sets have a wider back to back, 0.824 in the standards. This insures the wheel set "gauge" will always be greater than the track gauge.
Also, my recollection is the standards (NMRA and NASG) use some engineering models to drive certain dimensions. One is that the flange way is half the wheel width. As your wheels get narrower, for the best operation the flange ways need to be narrowed up a bit too. For more empirical results, we have a couple of brass air slides on the DPV layout that have code 88 wheel sets with the 0.824 back to back. The DPV layout has some of the best trackwork I have ever seen - possibly because I had nothing to do with building it!! <G> Anyway, these cars still "bump" on turnout frogs. They generally do not derail and run fine for the most part, but they visibly bump on the turnouts... Finally, it is my understanding - confirmed earlier today - that PRS and SHS use the code 110 wheel set while AM was mainly code 125 to 130. Recently, AM has moved to the code 110 width. The standards actually list the wheel width as 0.108 minimum. An inexpensive caliper or micrometer should be part of any modeler's workbench, along with a hand full of NASG track and wheel gauge tools and coupler height gauging tools. Jim Kindraka Plymouth, WI --- In [email protected], "Bill Nielsen" <wrangler@...> wrote: > > The NASG/NMRA track & wheel dimensions were developed to work together as a > set for optimal operation. These dimensions also allowed for some tolerance > (usually only a few thousandths of an inch) to provide some room for > construction variations. The original wheel tread width dimension is a > critical one that allows the wheel to cross over the gaps at the frog without > dropping, and also will require that the track gauge be more accurate. > Theoretically, if your track and turnouts are made to current NASG standards, > optimal operation will be with the use of NASG wheel profiles, and operation > with code 88 wheels will be less reliable. In other words, for optimal > operation, if you change the wheel tread dimension, you should also change > some of the track/frog dimensions too. This also means that ALL of your > wheels need to have the same profile (locos included), whichever dimension > you decide upon. Trying to run both sized wheels on the same track means that > operation with one (or both) will be a compromise. The only commercial > turnouts I have seen (in S or HO scales) that are truly NASG/NMRA are those > built using Fast Tracks fixtures. > > Best of luck, > Bill > ------------------------------------ Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/S-Scale/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://groups.yahoo.com/group/S-Scale/join (Yahoo! ID required) <*> To change settings via email: [email protected] [email protected] <*> To unsubscribe from this group, send an email to: [email protected] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
