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It should be noted that NMRA RP 24.3, "Axles", specifies only the MAXIMUM length, which is 1.035". They also illustrate Type I axles, with the cone ends we commonly see, and Type II with square ends, which I vaguely remember on a Bachmann tender. (Off topic)
This document was last revised in 1982. It seems like a proposal to update it would be timely, and something between the two Accurail designs of 1.010" and 1.025” would be a good “preferred” value. Lifelike seems to be the dominant replacement wheel at 1.015”. Given Bowser’s use of the above maximum, and European use of 0.990”, those might be the minimum and maximum values. The revision ought to suggest a maximum value for the difference between the truck and the axle; clearly using 1.015” wheelsets in a Bowser truck doesn’t work very well. The minimum value is, of course, zero.
Has anyone measured Central Valley trucks to determine what wheel set would be a good replacement? The need to replacement of wheel sets on those is driven by wheel shape, not getting rid of plastic. I realize there were many different styles and the values may vary, and of course passenger and freight used different wheel sizes.
From: main@RealSTMFC.groups.io [mailto:main@RealSTMFC.groups.io] On Behalf Of Dennis Storzek
Sent: Tuesday, August 06, 2019 5:25 PM
Subject: Re: [RealSTMFC] Metal Wheels
On Tue, Aug 6, 2019 at 01:33 PM, Denny Anspach wrote:
Probably the most ubiquitous trucks used in the RPM freight car modeling community are the Accurail “Bettendorf". Their consistent and reliable maximum rollability/minimum end play axle length choices have varied slightly among molding numbers 1-4, the most common being 1.010”, with 1.025” occasionally. Their superb Andrews trucks benefit consistently with 1.025” axles.
I've been finding this whole discussion amusing. The move to shorter axle lengths isn't because of "CAD design" whatever that is, but simply the result of paying attention to the actual prototype dimensions. When Athearn tooled their plastic trucks decades ago, they adopted the 1.035" axle length because that was NMRA recommended practice, and the overall width of the truck came out to whatever it came out to. Red Caboose did something similar years later when they made a truck with the full profile of the journal boxes on the back of the sideframe... only problem was that forced the overall width of the truck to be overly wide, to the point that the journals stick out from under older prototype cars.
When I designed the Accurail truck mold, close to thirty years ago now, I tried to keep the overall width of the trucks to scale... and had all sorts of complaints that the common replacement wheels of the day wouldn't fit, so I jumped through some hoops to squeeze a few more thousandths of depth into the scale size journal boxes. Now I'm seeing a general trend toward an axle length that would have fit the original design well. I'm sure this is driven by the desire to make the trucks scale width, and that is good, but the width of the trucks is one of those things that NOBODY was thinking of in years past.