Modifications to Chassis to improve shell to chassis mounting
(and some minor cosmetic changes)
I have never been a fan for 'snap on' shells and much prefer a screw on fixture which firmly attaches the shell without placing it under any undue strain.
There is little room to provide for screwing the shell to the chassis unless it is combined with the attachment of the couplers and that is the way I have chosen to go. I decided to attach brass blocks to the underside of the shell which would provide (1) a platform at the right height for coupler mounting and (2) a firm base to screw into.
I found that the correct thickness of the block would be 4mm. I didn't have any, so I used 3.0 mm and shimmed it both sides with .5 mm styrene (that's the blue plastic in the photo to the right). The brass blocks were drilled and tapped 2.0 mm before being glued to the shell. The exact placement of the holes was determined by temporarily fitting the brass blocks to the shell with double sided adhesive tape and then offering the shell up to the chassis after first having drilled out the coupler mounting pads on the chassis with a 2.0mm bit and marking the placement of the holes on the blocks with an awl through the chassis holes.
There is one more modification to make.
The total space required between the coupler mounting pad on the chassis and the underside of the shell is 7.5 mm. That is made up of 4.0 mm for the brass block that will place the couplers at the right height and 3.5 mm for the thickness of the Kadee draft gear box. ( I used Kadee number 5 couplers in '30' series boxes). But the clearance between the top of the coupler pad cast on the chassis and the top of the chassis which fits to the underside of the shell is only 6.5 mm (approx). (I found the two ends were not quite consistent with about 0.25 mm difference). The 'sandwich' was all made to fit by thinning the cast on coupler pad by up to 1.0 mm so that the clearance was increased to 7.5 mm at each end. The photo to the right shows the coupler pad thinned on the TOP surface. It looks flimsy in the photo but is quite strong because it is thicker in the centre than it is at the edges which show in the photo.
So, how does it all go together?
The chassis is offered up to the inverted shell and the assembled couplers are slid in through their slots in the pilot beams. A 2.0 mm screw is inserted through the hole in the cast coupler pad, through the coupler and into the brass block on the shell and tightened to be a firm but not overly tight fit. Too much tightness will result in distortion of the coupler draft gear box and interfere with coupler centering.
Bits 'n' Bobs
A new (longer) fuel/water tank was fabricated from styrene sheet and fits over the whole area previously occupied by the original fuel tank and air tanks. Athearn Blomberg 'B' truck sideframes were fitted after adding brake air lines.
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