Fast Tracks

I am using a standard fixture for HO Scale Code 70 rail and I am finding that no matter what I do my Intermountain semi-scale wheels are droping into the gap between the frog point and frog. I have went so far as to fill down the base of the frog wings so that the point can be pushed closer but it still is not resolving the issue. Are the semi-scale wheelsets just not going to work with a standard fixture?

Thanks,
Gary Gealy
Daphne, AL

Gary,

The code 88 semi-scale wheels require a finer (smaller) flangeway to work 'correctly'. While a sharper point at the frog will assist and give more support - there will be a gap that is unsupported in all possible conditions. In many cases, the gap will allow supporting the wheel tread - but not all cases. The larger the turnout number and the longer the gap, the more the issue will certainly arise.

To have the code 88 wheel treads cross the gap and ride on the wing onto the closure rails requires that the flangeway at the frog be held to at least 0.042" maximum, and preferably to 0.040". The NMRA gauge has the flangeway nubs that are the exact width of 0.042" - which can be used to space the flangeway. Be certain that you check and set the guard rail with the NMRA gauge correctly to the track check gauge.

When building with the narrower flangeway, you have to file the rail base on the wing rail portion to get the wing rail to come closer and set the flangeway. You could also fill in the flangeway and frog throat with some bonding material or solder and then file it out such that the flanges will ride on the shelf and stop the wheel drop. Again, those flange nubs on the gauge are set to the exact correct height for fitting the filled in shelf. Don't use the NMRA gauge as a scraper to clear out the flangeway if you chose teh fill method - it's an instrument and subject to wear if used as a scraping tool, rendering it then unreliable for specification checking.

GOOD NEWS - frogs built to support the code 88 semi-scale wheels are still fully compatible with standard code 110 wheels (provided all the wheel sets - code 110 and code 88 - are properly set with the NMRA gauge).

-ed-

_________________
-ed mccamey-
COSLAR RR - http://www.coslar.us/
NMRA Standards and Conformance Department
PROTO & FINE Scale Coordinator
I estimate I have about 5 pounds of coupler springs somewhere in the vicinity of my workbench.

Hey Ed,

Does it matter that the fixtures are built to the mid-point of the NMRA track guage tolerance? If they were cut closer to the minimum allowable tolerance would you have better, smoother results with the the code 88 wheels?

Donnell

Donnell,

As you know, I recommend and prefer dead tight gauge for all guarded track work. It allows for better control of the properly gauged wheels and eases especially the track check gauge issues.

However, code 88 wheels are governed by the gap that is created at the frog flangeway. So long as the guard rail is set correctly for the track check gauge, the actual track gauge has only a modest impact when TOO wide (allowing the wing rail to serve as a conflict point when wheel set rides at the stock rail). With a dead tight track gauge, one can have perfectly symmetrical flangeways of 0.043" (on each side), leaving correct check gauge, and also providing a flangeway gap correctly safe for code 88 wheels. This also is conforming and compatible for the 'standard' code 110 wheels.

At issue is that there is far less allowances for construction variability and 'oops' mistakes (with BOTH track and wheel settings). One also has to have a rigious program of checking and correctly setting the wheel check gauge on all equipment. Even with a wider track gauge, setting the frog flangeway at the 0.043" and having the check gauge set correctly gives perfectly conforming and correct compatibility - but the the stock rail flangeway will be wider. So, no - the track gauge is not the controlling factor for code 88 wheels - it's simply the frog flangeway and of course having the correct track check gauge (which does not change when using the "semi-scale code 88 wheels).

By the way, the flange nubs on the top of the NMRA gauge are at 0.0425" width - so long as they just glide through the flangeway, you've constructed the 'optimum'.

-ed-

_________________
-ed mccamey-
COSLAR RR - http://www.coslar.us/
NMRA Standards and Conformance Department
PROTO & FINE Scale Coordinator
I estimate I have about 5 pounds of coupler springs somewhere in the vicinity of my workbench.