3D-Printed Cattle Wagon - 3
Building the Chassis
This is an addendum to my previous post about building a Broad Gauge cattle wagon body. Although I built a chassis at that stage, I found the construction was too light and would not support wheel-sets adequately. I should have remembered that I had the same problem with the first design I did for a carriage chassis, so this post is an aide memoire to help me avoid the same mistakes again.
My chassis is basically a rectangle to fit under the body, with axle-boxes and springs added in the appropriate places. Building the rectangular plate in ‘Fusion 360’ is straightforward but adding the axle-box details proved more tricky.
My staring point was to make a 2D-drawing of one side of the chassis, showing the locations and sizes of the various components that make up the under-gear. For this, I used ‘Autosketch’ to produce the drawing shown below:
Next, I produced the base rectangular plate in ‘Fusion 360’. I started by drawing a rectangle 66mm x 34mm and extruded this, using the push-pull tool, to make a plate 3mm thick. I drew additional rectangles on the surface of the plate and recessed these by 2mm (push-pull again) to form a basic chassis with sole bars around the edges and some internal support at the centre.
Next, I imported the 'Autosketch' drawing (saved in DXF format) and extruded the various elements of the drawing to form the running-gear components along the side of the chassis. This was quite complex, since I first extruded inwards to make a firm attachment to the sole-bars and then outwards to form the outer faces of the axle-boxes and springs. These Steps are illustrated below:
Step 1: the 3D chassis; Step 2: adding the side drawing
Step 3: extruding over solebar; Step 4: extruding outside faces
Once I had completed the axle-boxes along one side, I realised that the various parts all appeared as separate ‘bodies’, so I used the ‘Combine’ command on the ‘Modify’ menu to make the whole assembly into a single ‘body’. This is important because only a single ‘body’ can be exported to ‘Cura’ for 3D printing.
The next stage proved tricky since I fell foul of one of Fusion 360’s quirks.
My aim was to split the chassis lengthwise and then make a mirror image of the side with the axle-boxes and use it to complete the opposite side. My first step was to create an offset plane along the mid-line of the chassis, using the 'offset plane' command in the ‘Construct’ menu. I could then use the ‘split body’ command in the ‘Modify’ menu to create two ‘bodies’, one for each side of the chassis. When I tried to delete the unwanted side, however, I received error messages :
If one is foolish enough to continue, then large parts of the model disappear! Clearly, this is not the right approach.
Eventually, I succeeded after several attempts, during which I learned to understand the difference between ‘Delete’ and ‘Remove’, when applied to ‘bodies’. Everything worked fine, providing I used ‘Remove’ from the drop-down menu that appears when right-clicking on the relevant ‘body’. Another step on the learning curve I have summarised the steps needed to complete the model in the following diagram:
In step 5, I set up an offset plane half-way across the chassis, then selected ‘split body’, to cut the chassis into two halves. In Step 6, I selected ‘Remove’ from the drop-down menu associated with this body.
In Step 7, I used the ‘Move/Copy’ command to copy, rotate and move a copy of the original body (complete with axle-boxes) to lie alongside the original. It is important to check the rather insignificant box near the bottom of the menu to ensure that the original is copied and not simply moved!
After aligning the two parts, I used the ‘Combine’ command to join all the parts into a single ‘body’, which, in Step 8, I could export to my 'Cura' 3-D printing software.
One additional action was to mark and extrude rectangles behind each axle-box, to allow the wheels to protrude through the chassis floor. After all this, I could send the model to my 3D-printer to produce a chassis for my planned fleet of 9’ 9” wheelbase cattle wagons. Phew!!!
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Learning curves are strange things. I now do with aplomb, things which seemed almost impossible a few months ago but I can still come to a grinding halt when faced with how to remove an unwanted body.
Similarly, the adhesion problems I had initially, when printing, seem to have disappeared. In fact, the adhesion has recently seemed too strong and I also noted that the filament was tending to form blobs at times. Reducing the print temperature from 200°C to 190°C appears to have solved both these difficulties.
My second print head has, however, just failed. Since this is a special clip-in component, no longer readily available in UK, this may bring my time with the Geeetech E180 to a sudden halt, as I now have only one spare remaining. They do not seem to last very long!
I can now show my first cattle wagon body standing on its wheels – Broad Gauge, of course 
Still a lot of work on fittings and painting.
Mike
EDIT: I made some minor adjustments to the 'push-pull' features on the axle-boxes / springs, which have made a significant improvement to their appearance - photos updated.
Edited by MikeOxon
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