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Fire Fly class - Part Five




Adding some details


After a rather intensive period of model building, I’ve slowed down a little, while other activities have called for my attention. The train of early Broad Gauge vehicles, including the Posting Carriage etc. still raise a smile as I pass by them on their shelf. They are, however, still waiting for their engine, so I need to press on with my ‘Fire Fly’ class model.



my three recent GWR Broad Gauge models


I always find that momentum is easily lost, once the main structures have been completed and several major design problems have been overcome. Nevertheless, there are still several tricky areas, such as the brackets that support the boiler, smokebox and firebox above the outside frames.  Some of these small parts need as much design effort, or more, as the larger items.


I decided to make a list of parts that I would construct as my next objective, to provide a focus for the next phase of this build.


For the body, my list includes:


  • support brackets for the boiler
  • chimney and safety valve cover
  • front buffer beam and buffers


For the chassis, there are the wheels and inside motion.


These items should create the overall appearance of the engine, leaving various small items, such as water feed pipes, handrails, and controls to be added.


In this post, I shall cover the ‘body’ items and leave the chassis for next time.


Support Brackets


When I started to think about the brackets, I was by no means sure that my 3D-printer would be able to create these rather delicate structures, which is what they become at 4mm scale.  I found a couple of drawings, shown below, that provided the details of these brackets.  I have used these as the basis of my designs.  The brackets at the smokebox and firebox sides are similar to one another but different from the central brackets that support the boiler.


Fire Fly Brackets – (left) Firebox and Smokebox, (right) Boiler support


I decided to start with the end brackets, as I felt these were potentially easier to create. I had already marked the positions on the sides of the smokebox and firebox, to provide reference points for attachment of these items.


I brought up a front view of my 3D model of the smokebox in ‘Fusion 360’ and drew the bracket lines and circles with reference to the main model. After drawing the cross section of the bracket, I used the ‘push/pull’ tool in ‘Fusion 360’ to create a solid object. My test print showed that they could be reproduced very effectively by my ‘Geeetech E180’ printer, despite their very small size, as shown in the following photos. Incidentally, the set of four brackets took only 5 minutes to print and they were ready for immediate use – no post-processing was required.



My 3D-printed Brackets as printed and then attached to the Smokebox


The design of the central boiler brackets presented another challenge in that, on the prototype, they provide direct support to the boiler itself and, therefore pass through the cladding. This can be seen in my photograph of the Fire Fly replica at Didcot, below:



Fire Fly replica


I decided not to attempt threading my model bracket through the cladding but to truncate the design at the outer surface, I did, however, decide to show the plate at the top of the main strut, as this is how it appears in my reference photo of ‘Argus’.


My 3D printed Boiler Bracket (attached to cladding)



Chimney and Safety Valve Cover


I 3D-printed both these items, using the methods I have described in previous posts:


  • For details of how I created the chimney see this post:
  • For details of how I used the ‘revolve’ tool for safety valve covers (and domes) see this post:


As I build more models, I find I can draw on previous designs to solve many problems and I frequently refer back to my earlier posts as aides memoires.


Front Buffer Beam


The font buffer beam is a simple rectangular bar from which I extruded two cylinders to represent the leather buffers of the period.


Assembly of my Fire-Fly class ‘body’


Adding these details to the main components of the body was straight-forward.  I used 'superglue' to attach the brackets into the prepared recesses on the sides of smokebox, boiler, and firebox. I had been concerned that the contact area might be too small for successful bonding but, in fact, after allowing time for the glue to polymerise, they proved to be very firmly attached indeed.  I provided the bases of the chimney and safety valve cover with spigots, which fitted into holes provided for them.


For attaching the buffer beam, I used my tried and tested method of running a low temperature (200°C) soldering iron tip along the inside joins, to weld the parts together.


The model shown below has a good solid 'feel', contributed by the brass tube that forms the boiler underneath the cladding.



my model of a Fire Fly class engine


Computer Visualisation


To help visualisation of the planned end result, I colourised the various parts I have made so far on the computer screen. Such views provide plenty of inspiration to keep me going :)


3D computer model of the Fire-Fly class body



Edited by MikeOxon
Restore images

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Recommended Comments

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Nice work Mike, the brackets certainly add character. Little projects like that can be as gratifying as the bigger ones, I find. The trick seems to be to take them seriously, as you have done.


BTW, I can't help thinking of canopy brackets now. A brunelian station with all the parts 3D printed... 

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You're getting some great quality out of your printer Mike - it looks fantastic.

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My thanks to all who commented - these are a great incentive to keep going!


5 hours ago, Mikkel said:

Nice work Mike, the brackets certainly add character. Little projects like that can be as gratifying as the bigger ones, I find. The trick seems to be to take them seriously, as you have done.


BTW, I can't help thinking of canopy brackets now. A brunelian station with all the parts 3D printed... 

These little projects can absorb more design effort than big ones, Mikkel.  The idea of canopy brackets is a very good thought.


4 hours ago, JCL said:

You're getting some great quality out of your printer Mike - it looks fantastic.

I have done a lot of tweaking to the print parameters in 'Cura' to improve the result.  The biggest improvement came when I changed the default line width from 0.4 mm to 0.3 mm.  I think this has caused successive passes of filament to fuse together better and so cause less 'banding'. 


The banding is still there, if you look closely , but barely visible at normal viewing distance, except on vary shallow curves.  When possible, I aim to choose an orientation of the model to minimise the effect.  My photos are all taken without any additional surface treatment after printing, except for removing any stray filament at edges.


While it cannot approach the surface finish of Stereolithography, I like the simplicity of the FDM process and find it adequate for my needs.

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I think you've done wonders. On the banding, it doesn't matter what consumer tech we use, it will be there. Even with the resin printers, there are lots of conversations about banding going on in the Mono X thread in the 3D printing area.


The 3' rule always applies :)

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Thank you Jason.  I enjoy experimenting and am often pleasantly surprised by the results.

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Thank you, Annie - you have seen your copy in NZ before mine's arrived here!.  I've even got around to painting my model although there are still pipes and handrails to add.



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My newsletter arrived as a digital copy via email Mike.  I think they must do that for us colonial types to save on postage.

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