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3D-printed Broad Gauge carriage, Part III

MikeOxon

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After printing my 1854 Composite body and its chassis, described in my previous posts, I turned my attention to making the very similar 2nd class carriage, built to an 1857 design.  

 

Model conversion to 2nd class carriage

 

The prototype had the same overall dimensions as the Composite, so I decided to see if I could easily ‘convert’ my computer model into this different type.  In essence, all that needed to be changed were the window locations and the compartment partitions.

 

BG_2nd-0.jpg.68b390b497565e0ca2b380fc8fef8a1f.jpg
2nd class BG Carriage from 1857

 

To my relief (and some surprise), this proved remarkably easy to achieve, when using Fusion 360.  This software keeps a record of each stage in the development of a model, so I could go back into my design, to the point before I added windows and partitions to my original carriage body. From that point, I could bring up my 2D drawing of the 2nd class carriage side and ‘paste’ it onto the side of the 3D drawing. 

 

Next, I could simply use the ‘push-pull’ command to open up the window openings on both sides of the carriage.  I followed up by repeating the ‘push-pull’ operation on the window frames but only inset these by 0.5mm from the outer faces of each side of the carriage.  

 

To make the partitions, I drew rectangles on the carriage floor, spanning the interior of the carriage and of 1mm width.  I placed these rectangles at each partition location and then used the ‘push-pull’ tool to raise them to the height of the carriage sides.  A simple operation, as all the partitions can be selected and extruded as a group.

 

I saved the revised model and exported it as an STL file, for use by my 'Cura' slicer software to convert it into GCODE for my 3D printer.  The actual build process was then simply to copy the GCODE onto an SD card for the printer and press the ‘print’ button.

 

BG_2nd-1.jpg.2998393678d858df4a426954c2816e5a.jpg

BG 2nd class Carriage Model

 

Following my experience with the solid seats in my Composite carriage, which took a very long time to print, I reduced the ‘infill’ setting to 20%, which caused the 'Cura' software to build up the seats with an open grid structure, as shown below:

 

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Carriage Seats with 20% Infill

 

Printing problems

 

Fortunately, I stayed with the printer, to watch the operation, and soon noticed that the model was lifting from the printer bed at one end.  This was a surprise, after having completed several successful prints, when the adhesion to the bed was, if anything, too firm!  

 

I had, however, noticed that the first layer of the ‘Brim’ around my recent models seemed to print more firmly at one side than the other and had made some very small alterations to the bed-levelling screws, to see if that would even things up.  It seemed to have done so but, at the same time, my adjustment had decreased adhesion at the opposite side of the bed.  This brought home the lesson that bed-levelling is critical to obtaining uniform adhesion over the whole area of the model.  I suspect this factor is made more critical by the fact that my E180 printer uses an un-heated bed.

 

This problem led me to undertake a very careful re-adjustment of all the levelling screws.  The first stage is to select the centre adjustment, which is done electronically from the touch-panel.  The bed height can be moved in 0.05mm steps until the print head just ‘grabs’ a sheet of file paper, slid across the bed.  

 

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E180 Touch Screen Levelling Controls

 

After that, the print head is moved to the four corner locations, in turn, and the levelling screws adjusted until the sheet of paper is grabbed to the same extent as at the centre.  To do this accurately needs several iterations because, obviously, raising the bed at one side tends to tilt it, so affecting other points.  After a couple of ‘laps’ of all the screws, the paper ‘grab’ felt the same at every point, including the centre.

 

I was pleased to find that this cured the adhesion problem on subsequent prints.  I shall now make a point of checking the level adjustments before each print-job, since it may well vary when a new layer of masking tape is applied to the bed.  Another ‘lesson learned’.

 

Carriage Build

 

Since I noticed the lack of adhesion very early in the printing process, I used adhesive tape to hold down the loose end and continued printing.  I was surprised to observe that, although the first few layers had been skewed, the printer was able to recover and laid down even layers for the rest of the model.   This allowed me to check that all the ‘new’ features of this carriage printed successfully – the window apertures all opened-out correctly and the partitions were of adequate strength.  The floor of the model, however was distorted at the loose end.


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First (distorted) Print of 2nd class Carriage

 

I could still use this initial model, with some filler to close the gap between the carriage body and the chassis at one end.  The good thing, however, is that a re-print is very easy since, although it does take several hours to complete, the construction costs are extremely low and the ability to print, without tying up my computer, means that there is little penalty, in terms of taking up my time!

 

Completing my Mail Train

 

It is now over three years since I conceived the idea of modelling the train that was involved in the Bullo Pill accident of 1868.  The accident report contains a detailed description of the make-up of the Mail Train, so I could model each vehicle to re-create an authentic train of the period.  I described my original concept in a blog post from 2016 .

 

To re-cap, my Mail Train consists of the Waverley-class 4-4-0 locomotive ‘Rob Roy’ with three carriages and a luggage van at the rear.

 

  • My model of ‘Rob Roy’  is still not complete but, with the aid of my 3D printer, I am now able to make some of the necessary fittings, included the unusual inverted springs that link the leading wheels.  In fact, I have already printed a ‘fret’ of carriage springs for use under the Luggage Van at the rear of the train, as shown below.  
     
  • The first two carriages are the 2nd class carriage, described above, and the 1st/2nd Composite described in a previous post.  After printing these, I have sprayed both these bodies with red-oxide primer and have painted the chassis black.  
       
  • The third vehicle is a Mail Coach, which I built from a Broad Gauge Society (BGS) kit, as described in a series of earlier blog posts .
     
  • The Luggage Van is another BGS kit, this time with a laser-cut resin body, described in another earlier post.

 

 

BG_2nd-6.jpg.70926e188b8903b9dd7963599104d70f.jpg

Springs for Luggage Van

 

Although there is still a lot of work to do on all the individual models, I could not resist setting out the complete train, in its current state, on a shelf and photographing the result:  

 

BG_2nd-5.jpg.0cca06985e4cd4dcdb4dd41a0ff7d563.jpg

Model Mail Train (unfinished)

 

I do find that taking these photographs provides me with the inspiration to keep going and I feel that, with the aid of my 3D printer, I now have the means to complete outstanding tasks.  I shall next turn my attention back to ‘Rob Roy’.

 

Mike

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Mikkel

Posted (edited)

Quite an achievement, Mike. You have made something unique.

 

I suppose as blog readers we tend to focus on the individual post and project, and often forget or loose track of the overall/longer term aims of what a modeller is trying to do. For me that last picture brings together a lot of the experiments, challenges and successes that you have been posting about in recent times. Must be very satisfying.

 

Edited by Mikkel
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Thank you Mikkel.  I had laid out the train, in the configuration described in the Bullo Pill accident report, on a shelf in the living room. 

 

Later in the evening, I was sitting in a chair and I glanced up and saw it from the angle of the photo.  It somehow had a very 'real' look, as though the train was striding along an embankment, so I grabbed my camera and took that last shot in the post.

 

I use this Blog as a diary that produces a very useful overview to myself and I frequently refer back to earlier posts.  If others find it helpful and/or inspiring, that is a bonus for me. 

 

I do remember someone once commented that "blogs are the most boring part of this site".  I guess he preferred the 'banter' that goes with the forum threads but, for my purpose, that just gets in the way

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