GP9 Frame Material: Aluminum vs Brass

Aluminum vs Brass, I have seen some debate over the years touting brass as a superior frame material, but I have to disagree!

My chosen material for machining GP9 frames is 6061-T6 Aluminum alloy and for good reason. Some argue that the brass frame being sold by others is a better solution because it adds additional weight, but that is a short-sighted argument. In reality, flat brass frames raise the profile of the locomotive, and to me, that negates any benefit of additional weight gain. 

Relief Pockets and Bolsters

Unlike the flat brass frame counterpart, the FineScale aluminum frame features machined relief pockets on the underside of the frame to facilitate proper placement of the bolster (truck mount). The placement of the bolsters is critical when assembling the frame.

The bolsters included with the original GP9 kit, seen in the image below, were designed to mount on the top side of the plastic frame. The relief pockets I have machined into the aluminum frame allow space for the locomotive trucks to rotate without rubbing the frame. As a result, the trucks sit lower on the frame and give the locomotive a more prototypical stance.

Red Caboose GP9 Aluminum Frame With Bolters Installed
GP9 Frame With Bolsters Installed

In addition to the relief pockets for the trucks, I have added relief pockets along the sides of the frame. These side frame reliefs let the frame tuck under the locomotive shell and create the side profile of the steel beam that can be seen in the section drawing of a prototype GP9 underframe.

If you need the extra weight, stick-on lead weight can be added to my frame in any configuration needed to fit the many types of DCC decoder installations, battery onboard installations, and sound installations.

Once you add in the absorbent cost of quality brass, along with the details listed above, I see a clear winner in the aluminum vs brass debate.

GP9 Cross Section

2 Responses

  1. The coupler height still comes out correct with this aluminum frame?

    Does it fit the Atlas O GP9? I always wanted a retrofit to get rid of the twin motors.

    I wish you would do the same thing for the P&D hobby F units!

    1. I have tried to get an F unit to measure but so far I have not been able to get my hands on one. Coupler height should be the same as the stock plastic frame and no one has ever mentioned there was any issue with that so you should be good to go. This frame fits the Red caboose GP9. I have never tested the Atlas shell onto a Red Caboose frame.

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