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Thursday 24 October 2019

0 Gauge Class 33 Scratch Build - Part 4

The raw body shell is in place, held to the chassis with one central nut and bolt. There is a lot of finishing and detail work to do, which will be done after the roof is permanently fitted (roof still in development).

I have four model magazines with Class 33 articles. On perusing these again after printing the body, I discovered in one article the comment that the cab sides taper towards the nose. I had not accounted for this. It is not on the plan drawing I am using and it is imperceptible in photographs of the prototype as it is only about a one degree angle. Fortunately, I made the body sides thick enough to form the taper by sanding it, which has thinned the sides by half at the nose. Like the prototype it is imperceptible on the model. Why bother doing it? That is a good question, I guess it would niggle me every time I looked at it if it was not present on such a large part of the model.

I have also been designing and printing some of the details to be added later. I am particularly pleased with the radiator grill and the roof fan turned out well to.

The fan will be driven directly from a small motor. Running off only 1.5V. It spins less vigorously than if a higher voltage was used, which the motor is capable of.

The wire safety mesh of the grill was cut from a nylon mesh bag used for small gifts like wedding favours. This one had a yellow tint. I turned it black by sponge dabbing black acrylic paint over both sides taking care not to block the holes with paint. The green bar across the middle will be over painted with a pale grey coach line after fitting to the body.

To Part 5.

To Part 1 of this series.

Tuesday 15 October 2019

0 Gauge Class 33 Scratch Build - Part 3

Bodywork Commences

Like any diesel locomotive the body is just a rectangular box - right? - wrong! There are complex curves and angles going on here that are a real challenge to model in 3D CAD.

The first decision was where to make the split line since the entire body length is too long to fit on my 3D printer bed. The best place is either side of the central door as the split lines mostly fall in the gap between the door and its frame. Thus, the body is in three parts with the roof being a separate entity also.

The three sides of the body shell shown in the photo is one piece printed from the base up (except for the curved base explained below)

The design must take into account printing limitations with respect to overhangs and bridges. For example, the ends of the body have overhangs that curve below the buffer beams. Clearly, they cannot be printed below the print bed. I could have configured 'infills' that fill the gap beneath the body sides and the overhanging end, these being cut away after printing but, the complex curve of the overhang and the curved bottom edge of the sides just compounds the problem. I chose to split the body again just above its base and print the base upside down. This printed part is seen on the right in the photo above.

Most of the apertures in the sides needed infills configured to support their top frames, otherwise they would droop.

I was unsure whether it would print satisfactorily at all.  Thankfully, it did. Sanding needs to be done to eradicate the stratification of the print layers and there is a lot of added detail yet to be designed, including the radiators that fit in the biggest apertures.

The roof has even more complex curves. It had to be designed along with the sides so that a convenient split line could be identified.

To Part 4.

To Part 1 of this series.

Friday 4 October 2019

0 Gauge Class 33 Scratch Build - Part 2

The chassis floor was made in two halves due to the limited size of my 3D printer bed. The halves were butt glued together and a strengthening bridge glued across the join, perhaps not long enough as there is minor bowing. When a body is fitted it should pull it straight into line.

The chassis design turned out to be just as complex as the bogies! Below the floor in the centre is an early period fuel tank and battery box. The battery box spans full width but in the prototype there are two separate boxes with some other mechanical gubbins in between that would not be seen on the model. There are other small fittings to the chassis sides faithfully reproduced from photographs but I don't have a clue what their function is!
The next photo shows the speedo cable. that connects between chassis and bogie axle box. The axle box speedo connector is removable so that bogie and chassis can be separated for maintenance purposes. The cable run is a little lower than it should be.

Note the green chassis side indicating the finished model will be a Class 33/0 in green livery.

I assumed the buffer beam was a simple rectangular block with buffers and coupling. On closer inspection it is far from it. The ends are angled and  there is a mass of fitted pipework and ports, about half of which are hidden by the buffers in the photo below.

I looked at the intricate screw link coupling and decided it would be too difficult to make (or was I getting bogged down with the model and wanted a quick way out). So, I purchased the Dapol Terrier spare (shown in the photo below). Unfortunately I misunderstood the suppliers product description thinking the 'set' on offer was a pair for each end of the loco. In fact the 'set' was one hook and one link array, except they failed to supply the hook! I needed a second 'set' but, this would become a very expensive solution for what are very small parts. I had a think about it, had a eureka moment and devised a simple, Dapol look alike, yet fiddly method of making a link array from wire. It was so successful I should have taken photos and write a tutorial. Maybe later.

Sprung buffers use an adaptation of the innovative Peco method, the method is shown in the photo below. The springy wire is cut from square section 4mm scale point roding steel wire that I had in stock The buffer shank is a nail with a plastic disk stuck on the head.
The question is, will it traverse a curve without impediment. I don't yet have track so I tested it satisfactorily on a Peco turnout paper template. If problems arise in practice I'll need to rework the chassis side fittings that hang down to increase bogie swivel.

To Part 3.

To Part 1 of this series.
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