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Designing a NMBS class 55 Diesel

Once you know the tricks then succesful 3D printing of a Nohab diesel seems fairly easy, thus this allows to tackle other diesels. The class 55 is a logical step, because it was developed from the Nohab design, sharing bogies and motorisation etc. but it has a different cab to ease construction. This allows to swap the locobody and use a Nohab model as base for a new loco not available on the market. This avoids the search for a fitting model or constructing an entirely new one from scratch.
Of course, when finished, having a class 55 drawing then it will only be small step to a shorter version in the form of the class 62 diesel, same cab but shorter body. But with only 4 axles this needs a search for feasible donors for use as base for motorisation.

Designing the cab

The followed process is identical to that for the Nohab and carriages, described on other pages. A 3D drawing designed for the printing process is made in C4D(V21) and exported as STL file. The printer produces the hard item. What remains after printing is detailing the item with paint and adding all the elements that cannot be printed or are better printed seperately, such as buffers.

class 55 design in genesis
Design of a class 55 in genesis.

class 55 design during detailing
Adding detail to basic design.

class 55 design in version 10 now completed with all basic elements
Screendump with all main elements, pending further detailing

class 55 design in version 14 with further details
Screendump, most of the larger details on upper works are now there, the fronts need further work witk skirts, sanding boxes, brake detail, steps and handgrips etc.

class 55 design in version 16 more or less complete
Screendump showing a more or less complete locobody, some simplified detail is added to the skirt as trial to save work in finishing the fronts.

I am certain that most of that detail like brake hoses etc. can be printed, but they will simply fail during handling the model on cleaning and painting, thus it is probably less work to add the free standing parts from metal wire. A trial worth an experiment will be to print the skirts complete with all brake hose detail etc. as a seperate unit and fit/glue this to the body after painting. This will save time, not only because fragile detail will then survive easier, but also because less height means less time needed for printing and can make these fragile details an easy to replace part that can be printed seperate. It will still allow use of metal wire for brake hoses etc. that didn't print well. But first I will test what the printer delivers, such as it is now, to find errors and forgotten items.

first print
First print with primer for visibility.

This is the first print and it comes out quite well, although some refinements on the nose are necessary, but with a bit of filling and sanding it can be used such as is. This problem is due to not having enough subdivisions in the front, which is generally an adaptable setting, and then cutting out the opening for the lamps, this leads to these triangular distortions. There is a bit of streaking on the sides but that can be easily filled and sanded here. The side front panel needs smoothing it with more divisions, but the top one is more complex. Alternative approaches are integrating the holes for the lamps into the spline before extruding it or partition this spline into 3 or 4 smaller sections or use an entirely different modelling method for this part, such as stepwise extruding along a path or built it up from straight splines and use a loft function.

first print repaired
Problem repaired with a bit of filling and sanding.

Here we see the same model, but after a bit of careful applying of filler and than sanded with a makeshift file of a strip of PS with a piece of #600 wet and dry paper stuck on with double sided tape, not more than about half an hour work. The Nohab besides it is one of the versions with the seperate printed roof, difficult to make this entirely invisible. This application took some days as drying times of filler and paint are currently very long due to low temperatures in the loft. The next step will be painting it yellow, like the Nohab in RAL 1021, as next step towards another trial in lining a diesel, this time I will try a blue version, thus one of the 7 loco's with an installation for electric heating for international traffic, period 4 from early seventies and later. In the mean time I acquired some rolls of Tamiya lining tape, maybe the advocated properties of this tape help to prevent underflow of paint, but I am a bit sceptical on this.

class 55 design in version 24

The above version has a new nose on basis of a loft function from splines. As experiment I added a set of numbers. I don't know the exact font, but this one looks quite reasonable thus suffices for an experiment. Also incorporated the changes made to the nose side of the 62 and fixed several errors which came to light such as the height of the port holes and repaired the lettering which showed inverted normals on the sides of the figures and thus didn't print correctly.

class 55 in green
green 5513 parading

Class 55 in green as 5513. Not yet entirely finished, but it has received its windows. The front ones needed a redo to arrive at a better fit.
This result shows that the Tamiya tape does make a difference. But it is a lot of work, you can easily spend over a full hour cutting and sticking tape to best effort, where the airbrushing itself takes only a few minutes. The yellow is painted over the green but to get good coverage it is necessary to first set up a layer of primer, I used Vallejo tan, and the yellow directly on top over that. No drying time in between apart from a quick blow with a hairdryer, remove the tape immediately after painting.
To do are couplings and buffers, yellow paint on the numbers and steel on the handrails and of course I now need to produce an etch for the ladders on its front. It nicely fits that MTX Nohab body with sound, but a new tank section for that still has to be drawn up. A new print for a blue/yellow 5531 is still in row in the paint shop.

class 55 testruns

2 photos of a test run on the Fremo meeting in Rheda with an international train on its hook

class 55 testruns

Spin-off: the class 62

The class 62 is a lighter four axled diesel sharing the cab design. Thus having the class 55 this one took only 3 hours for studying and implying the differences between the cabs. There are several small differences with respect to the frame at front and thus needing a modified lower cab edge, cab door etc. The roof vents also have a different size, but everything is editable.

class 62 design, short version of 55
Screendump of the class 62 derived from the 55

class 62 design, printed
The first print, the redesigned nose comes out well, but a layer of primer is necessary for a good observation of defects and errors. There is something amiss with the numbers, they don't come out well.

first layers of colour
Both first prints together. The blue needs another lining step, but it is considerably sharper than the Nohab attempt. The Tamiya tape does make a difference. First the paint needs to harden before the top line is attempted. Compared to photos there needs to be more blue on the nose, which means that those port holes on its side sit too low.

class 62 design, printed
The first print now painted and lined, slowly there is progress in lining. The yellow lines are painted on top of the green and have sufficient cover. This livery is the least amount of work, but making various strips of paper tape stitting all parallel is not easy at all. Thus taping is far more work than painting.

Now it is time for preparing the glazing and thinking about the motorisation for this one.

class 62: motorisation under development

drive design in 2d
Screendump of cross section bogie with 1:24 reduction

drive design in 3d
Screendump of 3D bogie

drive design in 3d
home produced parts on the desk, new wheels, spat with special M1.4 screw, wormwheel and gears, looks promising

bogie side
completed bogie

bottom view
bottom view with base plate fitted with 2 screws

to be continued...

copyright: Henk Oversloot
date: 6 Dec 2022
updated: 4 Feb 2024