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F Gauge Wheel & Track Standards

In the early 2000s the National Model Railroad Association (NMRA) Large Scale Standards committee worked up a series of Wheel and Track Standards in the interest of interchangeability and uniformity among both modelers and manufacturers. The Standards for 1:20.32, or F Scale, are known as the Proto20.3 Standards since they duplicate nearly exact American Association of Railroads (AAR) practice. F scale models are physically large enough that scale wheels, flanges and trackwork function reliably indoors and, to the best of our experience thus far, out-of-doors as well. The Standards below are also available in tabular form on the NMRA website:

The wheel tread design below is the property of Mr. Gary Watkins of Sierra Valley Enterprises and may only be used commercially with his permission.

F Gauge Track Standard


1:20.3 Dual Gauge Track: F & Fn3

G

Track Gauge1

Min

2.781

70.64mm

 

 

Max

2.842

72.19mm

C

Check Gauge

Min

2.679

68.05mm

 

 

Max

2.688

68.28mm

S

Span

Min

2.568

65.23mm

 

 

Max

2.596

65.94mm

F

Flangeway at Frog

Min

0.086

2.18mm

 

 

Max

0.092

2.34mm

F

Flangeway at Guard

Nom

0.102

2.59mm

H

Flangeway Depth

Min

0.062

1.57mm

P

Switch Point Spread

Max

2.547

64.69mm

 
Notes:

(1) Cumberland Model Engineering flex track is designed to split the difference between the NMRA minimum and maximum track gauge tolerances by arriving at 2.800" between the rails. On our dual gauge track, the third rail for Fn3 is designed to mate with Llagas Creek Fn3 track at about 1.793" between the rails.


Watkins Tread Profile Applied to CME Wheelsets

F Gauge Wheel Standard

K

Wheel Check Gauge

Min

2.654

67.41mm

 

 

Max

2.681

68.10mm

B

Back to Back

Min

2.597

65.96mm

 

 

Max

2.627

66.73mm

N

Wheel Width

Min

0.271

6.88mm

 

 

Max

0.282

7.16mm

T

Flange Width

Min

0.057

1.45mm

 

 

Max

0.067

1.70mm

D

Flange Depth

Min

0.050

1.27mm

 

 

Max

0.062

1.57mm

Journal Diameter  (outside bearing )

3/16

4.75mm

Axle Length (outside bearing, Type D)

4.183

106.25mm

Coupler Center Height (34 proto.)

1.698

43.13mm

Wheel Tread Profile

The Watkins tread profile has proven itself in both indoor & outdoor use, especially in Fn3. All Cumberland Model Engineering wheelsets and driver tyres are cut to this profile. Flange height, though greater than 1 scale inch, is just slightly over the condemning limits for prototype wheels. Please note: This wheel tread design is the property of my friend Gary Watkins of Sierra Valley Enterprises and may only be used commercially with his permission.

Last update: 20 August 2013

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