By the end of the previous post, I had completed the chassis for my planned Luggage Box. I expected the Luggage Box itself to be a simple construction: two panelled ends, two sides, and a roof.
Following my now usual practice, I created each of these parts as a separate ‘body’ in ‘Fusion 360’, so that each could be laid flat on the printer bed and could be printed in a few minutes, to the required panel thickness. A wave of a 200° soldering iron to seal the joints and that would be that – Bob’s your Uncle, etc.
It didn’t turn out like that because one of those pesky Danes @Mikkel raised a challenge (I thought King Alfred had settled things with them a long time ago), so Wessex honour was at stake.
The challenge was to provide hinged sides, so that it could carry the wedding trousseau of the future mother of Amy and Blanche from Gloucester to North Leigh, for her marriage to Lord Wilcote.
I’ve never tried to build jointed parts with ‘Fusion 360’ and had little idea of how to begin but a cunning plan soon emerged. In fact, I started exactly as originally intended by drawing the ends, sides, and roof to the required dimensions. One thing I learned, when thinking about moving parts, was how different the necessary clearances look on a computer screen from when reduced down to a 4 mm scale model. What I thought were gaps large enough to drive the proverbial bus through, turned out to be impossibly tight in the actual model.
Once I had drawn the end profile of the roof and extruded the drawing to create a solid roof, I added more drawings, to form two cylinders running along each side of the roof, as shown below. I used exactly the same procedure to add tubes to the side doors:
After creating the cylinders, I used the ‘Hole’ tool in ‘Fusion 360’ to open them out into tubes, to take standard 2 mm diameter axles. In the case of the tubes along the roof, I drew two rectangles on the top of the roof and used the ‘Push-pull’ tool in ‘cut’ mode, to open apertures that would accommodate the hinge parts on the two side doors. Similarly, I limited the length of the tubes on the side doors to fit into the gaps that I had cut out from the roof.
My 3D-model showing hinged components.
The first attempt was far too tight and although the sides fitted in the closed positions, the axle pins would not thread though the relevant tubes. Rather than trying to calculate the clearances required, I took an empirical approach. I examined the first set of test prints and estimated the amount of extra clearance that was needed. I then returned to the design on the computer and used the ‘Move/Copy’ tools to re-shape the hinge components on the side panels. Amazingly, the 2nd test print fitted together quite well. I’m sure a little more fettling and adjustment would improve things further but, for the moment, I’m satisfied that the method works
Hinge mechanism as printed.
I covered the roof with a film of black self-adhesive vinyl. The roof is slightly curved, with a one-inch rise to the centre (in the prototype). My FDM (layered) printer showed obvious lines between the deposited layers, where it had tried to follow the curve. The vinyl hides these ‘steps’ and also masks the (small) gaps around the hinges
Components of Luggage Box
On the subject of roofs, I read an interesting snippet in D.K.Clark’s ‘Railway Machinery’, dated 1855, page 274: “The roof is covered with ox-hides stretched tightly over it, or stout canvass, well saturated with white lead; ox-hide is superior to canvass, when luggage is to be carried on the roof. The covering is turned over at the edges of the roofing and fastened under the cornice mouldings.” I have not read before of hides being used in this way.
I extended the side rails from those shown in my previous post, so that they could pass through slots in the end panels and stand slightly ‘proud’, as shown in the ‘Bourne’ lithographs. The whole model looks quite complex, when viewed on the computer screen but, by breaking it down into separate ‘bodies’, I created a collection of simple components that could be printed in just a few minutes each and modified independently, if adjustments were needed.
Once I had welded together the various components, my model looked like this:
Two views of my model, as printed and assembled
There’s a lot of ‘finishing’ to be done but I’m pleased to have the basis of an interesting model. I now need to move on to thinking about a complete train, perhaps with a ‘Fire-Fly’ class locomotive in charge.
The heading image to this post shows my models headed by one of the Gooch singles
Edited by MikeOxon