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Sunday, 3 November 2019

0 Gauge Class 33 Scratch Build - Part 5

The roof is made in five sections.The first photo is of No.1 end and shows the roof fan grill.

A couple of methods were tried to 3D print the grill. The problem is the ribs are very fine and to print this in situ requires supports to stop droop. The ribs were just too delicate and came away when the supports were removed.

Another consideration is that the grill centre sits proud of the roof and each rib is at a different angle to fit the roof curvature.

The solution was to print the grill as a separate flat component and to print a central column in situ with the roof. The grill was placed on top of the column and each rib gently bent to locate in a slot in the rim of the fan hole. The column was then cut away when the glue had set.

Second photo is of No. 2 end. The brown marks are sanded Wickes wood filler used to fill imperfections.

The printer threw a wobbly and failed to print the last few layers so, plastic padding had to be applied and sanded to complete the roof curvature.

The body and roof sections were sanded with coarse sandpaper to remove most of the layered plastic stratification. Then a coat of acrylic matte medium was applied and this sanded with fine emery paper to completely smooth the plastic.

Finally, details like door handles and ribbing were applied. This part is now ready for the paint shop.

What about the gap between roof ends?

The centre of the roof on the prototype is a removable fibre glass translucent panel finished in a beige colour that serves two purposes. First, to gain access to the top parts of the engine for service and second, to flood the engine room with natural light.

On the model it is the same except used to allow access to a control panel for lights, fan and sound. (no DCC here.)

The panel was printed in transparent plastic and then coloured with brown, fawn and black pastel scrapes; finishing with a coat of hairspray used as a fixative. Unfortunately, the diamond grid of inner plastic fill* has showed (I should have configured the print for solid infill). I have convinced myself it is fibre glass reinforcement.

* 3D printing thick sections normally results in the core being printed as a grid to save on plastic use.

The other part in the photo is one of two panels that fit to the sides of the roof. Not sure what it is, either coolant radiators or vents? What it does have is an array of vanes in each square covered with mesh.

This could be tricky to make. However, the first method I thought of worked first time. The core is one piece comprising square holes with printed in vanes (vanes just discernible in the photo). This is covered with mesh (described in Part 4). An overlaid frame is glued over the mesh. This frame was printed flat and then moulded to shape over a metal rod of required diameter under heat from a hairdryer to soften the plastic.

Interestingly, I can now feel the body & roof assembly has weight (100 gms) with more to come, which shuld help with track adhesion.

To Part 6.

To Part 1 of this series.

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