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RP-8 Three Point Track Gages

RP-8

The Three-Point Track Gage mentioned in STANDARD RP-2 is a convenient way of widening Track Gage in a curve without exceeding Gmax in STANDARD S-3. It is also useful as an assembly jig for the curved closure rail (see RP-12 series) when constructing a turnout.

There is enough clearance between minimum Track Gage (Gmin of S-3) and the non- STANDARD maximum "Wheel Gage" = 'Zmax' = Kmax + Tmax of S-4 and RP-25 to provide for 0 degree (tangent) to some degree of curvature, depending upon the length of the equipment Class (see S-8), without need for widening Track Gage. Curvatures in excess of this will require widening Track Gage up to, but not to exceed, the maximum (Gmax of STANDARD S-3).

The two end lugs of the Gage should be spaced apart by the Gage Length 'L' of Table 1, and should be positioned over the outer rail of the curve when using the Gage. The single lug on the opposite side should be located at the centerline as shown in Fig. 1.

The slots in each lug for the railhead should be spaced such that the inner face of each defines the Gage Line of the track at Gmin. For different width railheads, as with different weight Rail (RP-15.1), separate Gages may be made with suitable width slots. The two outer lugs should have slots accommodating both curved and tangent track. If slots are wider than the railhead, the rails should be biased to bear against the inner faces of all slots.

The Three-Point Track Gage presented herein provides for a gradually increasing Track Gage from Gmin at O degree (tangent) to the allowed Gmax at the maximum curvature shown for each Class of equipment in STANDARD S-8. A smooth transition in Track Gage from Gmin for tangent track to the widened Gage of curved track should be coordinated with the easement recommended in STANDARD S-8.

TABLE 1.
Scale S-8 Class Minimum Radius L Gage Length
O II 33" 2 23/32"
I 41 1/2" 3 1/16"
Ia 58" 3 5/8"
S II 25" 1 7/8"
I 31" 2 3/32"
Ia 43" 2 7/16"
HO II 18" 1 5/8"
I 23" 1 13/16"
Ia 32" 2 5/32"
N II 10" 1 1/32"
I 12 1/2" 1 5/32"
Ia 17" 1 11/32"

When the Three-Point Track Gage is used on wider radius than the minimum shown for its Class in S-8, Track Gage will not be widened to the maximum allowable. Since equipment of that Class does not require the full widening when running on wider radius curves, the characteristics of both the Three-Point Track Gage and the equipment are in harmony.

To be most effective, the three downward projecting lugs of the Gage should hold Track Gage close to Gmin for tangent track, while spacing between the outer lugs should be at Gage Length 'L' (Table 1) in order to produce dimension Gmax at the sharpest curvature for each Class in S-8. Gages shorter than this cannot produce the Gage widening allowed by STANDARDS.