I’ve had one or two messages from people who say they have enjoyed reading through my blogs. I should therefore sound a note of caution, especially in the field of 3D printing – my posts follow my own, often halting, progress along a learning curve and I still feel myself to be a long way from an end-point. I was looking back at some of my earlier designs and although they came out reasonably well in the end, my methods were something of a ‘dog’s breakfast’. I hope you won’t repeat too many of my mistakes!

 

What’s changed

 

I would not now start by importing drawings from a package such as Autosketch. I never did find out why some sketches could be modified in ‘Fusion 360’ whereas others apparently could not. As a result, some of my designs became a hotchpotch of amended bits of drawings, when the imported parts didn’t fit properly. That was especially true of my broad gauge cattle wagons, with their slatted windows, where the slats were created individually and are not very regular – I hadn’t discovered tools such as ‘pattern on path’ and tried to place all the items by hand. Also, I hadn’t understood the various options when moving bodies, such as ‘cut’, ‘join’, and ‘new body’.

 

If I want to derive a model from existing drawings or photographs, I now import these into Fusion 360 as a ‘canvas’ and use the drawing tools within this software to create the outlines to be extruded. If I have existing drawings, they may be usable directly but I know that several difficulties can arise, if any modifications are needed.

 

Extruding a 3D model from a ‘canvas’

 

Bodies and Components

 

My 3D printed cattle wagons represented my first step along the road of printing various parts of the model separately – the floor and ends were one ‘body’ and the sides were designed to be printed flat on the printer bed. I then ‘welded’ the parts together using a soldering iron set to 200°C. It actually worked quite well, although I made several basic mistakes, such as forgetting to allow for the thickness of the sides when I designed the roof, which ended up too narrow.

 

Nevertheless, I felt that printing a model as a series of component parts was a useful step forward and made it much easier to make modifications through trial and error, since individual print times were fairly short. Another step was forced upon me when 'Autodesk' decided to restrict personal (free) users to only ten active designs. Up until then, I had made each part as a separate ‘design’, which only came together after the parts had been printed.  Now, I started to included several different ‘bodies’ within the same overall design, which led me to the idea of assembling these parts within the 'Fusion 360' software, by using the move tools to bring them into their correct relative positions. This was very useful for checking that the parts actually fitted together as I intended, before committing anything to print.

 

I have, at last, discovered that I have not been using ‘Fusion 360’ in the way the designers intended!  Most 3D design software works on a ‘bottom up’ process, which is what I have been doing – designing individual ‘bits’ and then bringing them together as an array of separate ‘bodies’. ‘Fusion 360’ can work like this, as I have found, but the preferred method is to work ‘top down’, i.e. to think of the assembly as the ‘Design’ and then break it down into ‘Components’. It’s all explained succinctly on this webpage: https://productdesignonline.com/tips-and-tricks/understanding-bodies-and-components-fusion-360-rule-1/

 

In ‘Fusion 360’, a ‘component’ differs conceptually from a ‘body’, in that it has its own reference planes and design history. Also, a component can be copied between different designs and, if modifications are needed to a ‘component’, they will automatically carry through to all those designs making use of this components.

 

For example, one might make a Dean bogie as a ‘component’. It can then be used for various carriage ‘designs’. Components can be moved around as required in each individual design but still retain their individual ‘history’, which allows them to be modified if necessary. From now on, I shall consider how I can adopt this concept in practice.

 

Modifying my Cattle Wagon

 

Although I have identified several ways by which the overall design of my cattle wagon could be improved, I have not made any major changes. I have, however, imported the various section of the model, which were all in separate design files, into a single file, where they appear as ‘components’. I then ‘assembled’ the components within ‘Fusion 360’ so that I could inspect the 3D model as a whole. This process immediately identified the problem of the narrow roof, which I could correct by using the ‘move’ command on various individual ‘faces’.  Once assembled, the overall model within ‘Fusion 360’ looks as shown below:

 

Perspective-view of my 3D model of a Cattle Wagon.

 

Incidentally I also discovered that the ‘camera’ view can be set to be either ‘orthographic’, which is better when checking how parts fit together, or ‘perspective’, which is better for gaining an overall impression, as in the illustration above.

 

New Assembly Methods

 

Once I have printed the various components, I have used a combination of superglue and application of a soldering iron, to fuse the parts together. When I assembled my model Britzka , I mentioned the possibility of trying a 3D Pen as another tool for joining parts together.

 

I have now bought an ‘RP 900A’ 3Dpen, which is described in this ‘YouTube’ video: https://www.youtube.com/watch?v=WJzdReSxk7s

 

It appealed to me because of its slim design and metal casing. It also works with standard 1.75mm PLA filament, exactly the same as that used by my 3D printer. There are controls to start and stop the flow of filament and to vary both the speed of delivery and the temperature of the print head. There are two pre-set temperatures for PLA (190°C) or ABS (220°C) but each of these can also be varied in 1°C steps. The controls take a bit of getting used to, as each of the three buttons has several different actions, depending on the context. I was amazed by how much technology had been packed into such a slim body – for anyone interested, there is another ‘YouTube’ video showing the internal construction: https://www.youtube.com/embed/7A7ZkJNFZ8g

 

I had a short practice session to get the hang of the controls as shown below:

 

Free-hand Drawing with my 3D Pen

 

One of my thoughts had been to use the pen to make seam ‘welds’, as I have done previously with a soldering iron. In practice I found that, although this pen is slim, it is still much fatter than the shank of my soldering iron, which makes it more difficult to manoeuvre the pen tip into enclosed spaces. The heat shield also make it difficult to see exactly where the tip is placed.

 

Comparison between Soldering-iron tip and 3D Pen

 

I had intended to extrude a strand of filament to help complete the join but so far I have found it rather difficult to adjust the flow-rate to match this requirement. The extrusion nozzle is larger than on my 3D printer – 0.7mm vs. 0.4mm on my printer – so the extruded thread is relatively large. I tended to get unwanted blobs of filament as I tried to negotiate my way along the joint lines. Perhaps this will improve with practice but, for the moment, I find that a soldering iron with a fine tip does a better job.

 

An alternative method I tried was to make ‘spot welds’, with brief jabs of the 3D Pen tip. This may be useful in some situations and I shall experiment further.

 

Adding Details

 

On the other hand, I have found that the 3D pen is very good for adding linear details to a model. To test this possibility, I decided to add a rim around the inside of the cattle wagon roof, to provide location strips to fit inside the tops of the sides and ends. To do this, I marked the required locations for the strips on the flat underside of the roof and then laid a metal ruler along the marked line. I then laid a strip of filament along the line, using the ruler as a guide for the 3D pen. This method was successful in forming a ‘lip’ around the sides of the roof, as shown below.

 

Adding a lip around the inside edges of a wagon roof

 

After adding this alignment-aid, I fitted the new roof onto one of my existing cattle wagon bodies:

 

New Roof on my Cattle Wagon

 

The roof now fits neatly across the width of the wagon. The body of the wagon has been sprayed with red oxide primer, followed by a coat of GWR Brown acrylic paint. It can be seen that any residual surface texture from the FDM printing process has been completely masked by the paint. This was an early model and I realise that I had forgotten to emboss any planking into the end walls. This does, however, reveal the smooth finish provided by my printer.

 

I have found that careful adjustment of three parameters during printing is crucial in achieving a smooth surface finish.:  

 

1. Bed levelling is critical to ensure even adhesion to the (unheated) printer bed.  I now check it regularly before each print job.
2. When using 'Cura' slicing software, I set the line spacing to less than the print nozzle diameter.  In my case, I use 0.3mm spacing with a 0.4mm nozzle.
3. Temperature of the print head is important for a smooth finish.  The filament must remain 'fluid' long enough to fuse smoothly to the adjacent layer but not so much that the threads start to 'run'.  With the eSun filament that I'm using at present, I find that 202°C seems optimal.

 

Now I have to decide what I might build next, in order to make use of this new-found knowledge.

 

Mike