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Killian keane

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  1. 3D-printed Broad Gauge carriage
    3D-printed Broad Gauge carriage

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    I have already described my halting progress with 3D printing on my other Pre-Grouping blog, with the previous post having been made there on 3rd May.

     

    Since then, I decided to have a go at printing a Broad Gauge carriage of a type I have previously constructed using layered card sides, cut with my Silhouette Portrait machine.  This meant that I had already produced side elevation drawings of my chosen prototype in 4 mm scale.

     

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    Thus, my latest ‘build’ was mainly an exercise to see what I could do with my 3D printer, and to combine various aspects of the carriage body into a single operation.  As I thought about it, I realised that all the internal partitions could be included in the print and then I added seats as well.

     

    A feature of early broad gauge carriages was that 1st-class compartments were sometimes divided into two sections, on either side of the centre-line of the carriage.  This resulted in two separate 4-seat compartments on either side of the carriage, with a connecting door between them, to allow the passengers on one side to reach a platform on the opposite side.  I decided to incorporate this feature into my design.

     

    The following illustraion, although not a Broad Gauge compartment, shows several interesting details, such as the cords to hold top hats, mounted under the low ceiling.

     

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    As described in my earlier posts, I used Fusion 360 software to develop a 3D model of my chosen prototype on my computer.  My method was to extrude an open-top box from a profile of one end of the carriage, which included a ‘tumble home’ on each side and a curved top over which the roof could be mounted.

     

    The software allowed me to ‘paste’ a 2D drawing of the carriage side onto the computer model and I then used the ‘push-pull’ tool to inset the droplights and to open out the window openings.  I then drew the seat bases and partitions on the floor of the carriage and, again, used the ‘push-pull’ tool to raise these to the appropriate heights. 

     

    I still find that it needs a lot of trial and error to get all these details in their correct places and, when I make a mistake, I find it easier to delete and start again rather than attempting to correct my mistakes.  Perhaps, when I understand the software a little better, I shall find it easier to make such modifications.

     

    Once I had reached the point where it seemed worth trying to make a print, I used my Cura software to ‘slice’ the model into the format needed by my printer.  I could have used the Fusion software to do this but preferred Cura because I had already set this up with the characteristics of my Geeetech E180 printer.

     

    After slicing, the display on my Cura software indicated that it would take about 7 hours to print, which struck me as rather long but I didn’t investigate further.  In fact, it proved to be a fairly accurate estimate.

     

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    Once it started printing, I realised the first of my mistakes!  After a previous test, when the carriage sides had turned out too thin, I had set the ‘infill’ to 100% which meant that the seats I had provided in the compartments were printed as solid blocks, which was very time-consuming!  At least it meant that the finished body had a reasonable weight (c.40 g) and was very rigid.  In spite of my profligacy in the use of plastic filament, the cost of materials was still only about 60 p!

     

    My second mistake was that, somehow, I had made some of the transverse partitions much too thin, so that they came out rather skeletal in form.  This can easily be corrected by adding some small rectangles of plastic card, although it has defeated my object of an ‘all-in-one’ construction.

     

    Thirdly, I had made the moulding lines too shallow so that they hardly appear at all on the model.  I must practice making such features, to find suitable dimensions for them to appear in 4 mm scale.

     

    In addition, the fact that I have had several reliability problems in the past meant that I was reluctant to leave the printer unattended for too long at a stretch.  If I can gain more confidence, then it would be preferable to do the printing overnight.  The printing would also have been a lot quicker if I had not included the unnecessary solid infill.  If I had set up for a 25% infill, the Cura software estimated a time to completion of only 4 hours, for the same model.

     

    On the positive side, there is no limit to the thickness of the side panels of the carriage, so there is no need to build up a side from several laminations, as is the case when using the Silhouette cutter.  Also, in spite of my concern, the printing proceeded without a hitch.  After having had some of my early models detach themselves from the base during printing, I was pleased to find that this model was quite firmly attached to the blue masking tape that I had used.

     

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    In fact, for a model like this, which is mainly flat surfaces, it would almost certainly have been easier (and a lot quicker) to fabricate the carriage from Silhouette cut panels.  The trouble with my type of 3D printer is that the process takes such a long time that it becomes off-putting to make trial prints.  I had put off starting this model for some time for this very reason.

     

    I am expecting that the 3D printer will come into its own, when I make the chassis for this model.  I shall be able to use a suitable thickness of material, to make strong side frames, and will include spring and axle-box details as part of the process.

     

    That will be my next project ...

     


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