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An Ugly Duckling – 4


MikeOxon

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Now, wake up at the back there, @Mikkel, this is a new post on this subject.

 

At the end of my previous post, I wrote “Next, I shall turn my attention to designing and constructing a suitable chassis.”, so that’s the subject for today.

 

Frames

 

The frames of these early engines were rather unusual in that they stopped short in front of the leading drivers. The front bogie was attached directly to the boiler in traction-engine style. The frames were also quite light, with sizeable cut-outs between the driving wheels.

 

Following my usual method, I imported a drawing of ‘Aurora’, originally shown in ‘The Locomotive Magazine’, 1896, into ‘Fusion 360’ as a ‘canvas’. I copied over the outlines of the frame, using the sketch mode, and then extruded the enclosed area to a depth of 1 mm, to form the frame. I used the ‘offset’ command to create a rim 0.5 mm in depth along the top edge of the splashers and then extruded this area a further 5 mm, to form the tops of the splashers. Similarly, I made an offset below the outer edge of the extruded splasher tops, to form the front valance.

 

 

Aurora_frame-Annot.jpg.a78b5b4f9cdf5f76384915046791d452.jpg

3D extrusion over imported drawing

 

Experience has shown me that my printer can cope with this amount of valance overhang, when printed with the design laid flat on its back on the printer-bed. There was no need to create a different frame for the opposite side of the engine, as all I had to do was apply the ‘mirror’ command before printing.

 

Alignment

 

The next step was to align the pair of frames at the correct separation and create components to represent the buffer beams and footplate. Rather than do this by measurement, I simply used the ‘move’ tool in ‘Fusion 360’ to align the frames with existing boiler and tank components. Once they were in correct alignment, I sketched rectangles to represent the front and back buffer beams and extruded these to create the appropriate ‘spacers’. At the back of the engine, I also extruded the upper part of the buffer beam forward, to represent the footplate for the crew and support for the firebox end of the boiler.

 

I find it useful to assemble the various parts in the computer, to check that everything aligns correctly, even though I print them individually. The following screen-shots shows how I designed these parts in ‘Fusion 360’:

 

 

632485951_AuroraFullAssyAnnot.jpg.f32aee2293778cd7871f912d00b94470.jpg

Additional spacers aligned with Frames

 

Bunker

 

Once I had set the correct separation of the frames, the next part to consider was that splendidly curvaceous bunker. I tackled this by first sketching the profile over the drawing that I’d imported into ‘Fusion 360’, as shown below:

 

 

2125024789_Aurorabunkersketch.jpg.ab95e458503a9e73b91eae1230afcf77.jpg

Extruded drawing of bunker side

 

I then created two duplicate sides and placed them into their correct positions on the 3D model shown above. I sketched a rectangular backplate and extruded this to form another body that I combined with the two sides. Finally, I used the fillet tool to provide the curved corners between the back and sides of the bunker, to create the overall design shown below:

 

 

648242648_AuroraBunkerannot.jpg.e9b3819fdfdf7e9c4a62a44c1ff5491b.jpg

Bunker created to fit onto the existing computer model

 

Boiler Fittings

 

Three fittings are needed on top of the engine: chimney, sand-box, and safety valve cover. In the past, I have made a bit of a meal of creating such items but it is, in fact, extremely simply to create circularly-symmetrical objects in ‘Fusion 360’

 

To take the sandbox as an example, the first step is to sketch the half-profile and then to use the ‘Revolve’ command in the ‘Create’ menu to create solid body.

 

 

678644613_RotateTool.jpg.6b77496f8540204d11729d2812897012.jpg

Using the Revolve tool in 'Fusion 360'

 

I used the same method to create the chimney and the safety-valve cover. I added these parts into their correct positions on the computer model, to complete the assembly, as shown below.

 

 

1187427703_AuroraBoilerfittings.jpg.1f0718c5013ccd870508d03e8efe218c.jpg

'Aurora' components assembled in 'Fusion 360'

 

Having checked that all the parts fit together, I simply transferred the various parts to the 'Cura' slicing software and printed the resulting files. Most parts only take a few minutes to print.

 

Bogie

 

One more component is needed to complete the main features of this engine and that is the front bogie.  In the prototype, the bogie pivots on a central ball-and-socket joint attached below the boiler. I feel that this arrangement would not provide sufficient side-swing for a model engine on practical track curvature, so I have decided to adopt the more usual swinging link method of attachment.

 

Lessons learned (so far)

 

I feel that I’ve learned a few more useful techniques with ‘Fusion 360’, such as the use of the ‘Revolve’ command.  I’ve also appreciated the various modes of the ‘Pattern on Path’ command.

 

Moving separate parts into the correct registration with one other, within my computer, has proved to be very useful for ensuring that everything will fit together when printed.

 

I am now much more aware of the limits set by the fused deposition method of printing. The extruded filament has finite diameter, which sets a limit to the details that can be printed.

1989186452_extrudedfilament.jpg.cfbb4c066c2a17faecab18c8acb68856.jpg

If too small, features are simply ignored by the ‘Cura’ software, so it is essential to check the appearance with the ‘Preview’ option before committing to print. Very tiny adjustments to the computer model can make significant differences to the final appearance.

 

The software can still tie me up in knots sometimes but I think I’m now better at getting out from them :)

 

Printing and Assembly

 

Now comes the easy bit, once the design has been completed. By printing parts separately, the print times can be very short. I made a list of the ‘Cura’ estimates for print times of the various components:

 

  • Tank 1h 2min
  • Firebox 39 min
  • Footplate & Buffer Beam 27 min
  • Smokebox 21 min
  • Frame (each) 19 min
  • Bunker 15 min
  • Chimney, Safety Valve, Sandbox (together) 14 min
  • Backplate 7 min
  • Front of Smokebox 6 min

 

It’s easy to refine the prints, in order to optimise detailing within the limitations of my printer, in view of these short times. Printing individual parts also minimises the need for support structures, by choosing the orientation of individual parts to eliminate these wherever possible.

 

Printing more at once can be appropriate, once the details are known to be correct, but small print-times encourage ‘trial and error’ improvements.

 

My current printed set of parts is shown below, after assembly of the individual components. A bogie frame appears in front of the engine itself.


1936198590_AuroraAssembled.jpg.4f83b796e4c40f4d032475f92f8a752e.jpg

‘Aurora’, assembled from 3D-printed components, including bogie frame

 

The way ahead for this model will now follow conventional lines, adding wire handrails, pipes, and similar details. I have not yet decided about wheels but may consider these in another post. My method for constructing 3D-printed wheels has already been covered in an earlier post.

 

I expect that here will now be a pause, while I continue through to the painting stage.

 

Mike

Edited by MikeOxon
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Now, wake up at the back there

 

I was about to say this reminds me of school, but in that case it's the best school ever :)

 

The bunker looks to be well captured. I wonder why it is was designed with that elegant slope in the first place. Why not just make a square? To make access to the footplate easier for the crew, I suppose. Or to save materials. But it does raise the question, how much did aesthetics mean inn loco design at this time.

 

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I expect that here will now be a pause, while I continue through to the painting stage.

 

Your regretful sigh is almost audible :lol:

 

Edited by Mikkel
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4 hours ago, Mikkel said:

 

I was about to say this reminds me of school, but in that case it's the best school ever :)

 

The bunker looks to be well captured. I wonder why it is was designed with that elegant slope in the first place. Why not just make a square? To make access to the footplate easier for the crew, I suppose. Or to save materials. But it does raise the question, how much did aesthetics mean inn loco design at this time.

 

 

Your regretful sigh is almost audible :lol:

 

Thank you for your comment.  I know my posts are somewhat didactic but if others find them of interest, I am pleased.  It's interesting for me to look back through these posts and follow my own learning curve!

 

The bunker shape is interesting, especially as the rest of the engine seems rather oddly proportioned.  Getting on and off the footplate must have been rather difficult, even with that curved side.  Steps are something else that I need to add.  I can see why the B&ER resorted to step ladders over the driving wheels.

 

Aesthetics certainly mattered to some people.  Brunel wrote to T.E.Harrison in 1838 "...Now your engine is capable of being very handsome, and it ought to be so" [Harrison was the designer of the engines 'Thunderer' and 'Hurricane']

 

You are correct that I do regret that what I find the exciting part of creating a new model is over.  Adding fittings etc. is a bit of a chore :)

 

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