Multi-Scale 3D Printing (TT3 - 7mm)

[Marbelup]

As I bit of an experiment, I have recently tried designing a 3D-printed bogie hopper wagon with the intention of being able to print it in various scales from TT3 to S scale.  Virtually all of my 3D printed designs over the last 2 years have been in S scale, but this project started with an enquiry from a UK-based modeller interested in Australian narrow gauge (3' 6") in TT3n3.5 scale.  The prototype wagons were quite unusual for Australian narrow gauge as they were moved around the country and ended up operating in 4 different states/territories.  Because modellers of the different Australian narrow gauge railways work to a variety of scales, I envisaged the model could be of interest to modellers in TT3n3.5, HOn3, HOn3.5, OO and Sn3.5 scales.  Somewhat surprisingly, I have had enquiries about O scale versions as well, both 1:48 and 7 mm.

 

My approach was to initially design the model to suit the print specifications (wall thickness, etc. for i.Materialise Prime Gray) for TT3 scale, although I drew the 3D model in S scale (using Rhino).  For example, 0.5 mm minimum detail size in TT3 scale equated to 0.8 mm in S scale.  My plan was to simply scale up the TT3 model for both HO and OO scales.  For S scale, I drew different versions of some parts based on the actual 0.5 mm minimum detail size to make the small details look crisper at the larger scale. I also added some extra details such as bolt heads on the air cylinders which wouldn't have printed in the smaller scales.  Because the enquiries for O scale versions came along later, I simply scaled up the S scale model, although I did do another version of the main hopper body with reduced wall thickness to reduce the printing cost for the O scale models.

 

Another complication was catering for coupler and bogie mountings for each scale.  All the models are designed for Kadee knuckle couplers, but the mounting arrangements don't simply scale up with the model scale.  I ended up adding specific coupler mounting blocks for each scale and/or specific parts to be subtracted (e.g. where the top of the coupler box is higher then the bottom of the end sill) as well as parts to be subtracted to create holes for the mounting screws for both couplers and bogies.  

 

To further complicate the issue, the wagons were modified during their life for their different working roles, the major modifications being the covering of the angled ends with solid sheeting, and the addition of hungry boards to increase the cubic capacity for lower density loads.

 

All these "mix and match" parts are on different layers and sublayers, so it relatively easy to produce the final STL file for each scale and body style.  So far, I have had orders for 4 different body styles in TT3, HO, S and O scales.

 

The attached photo shows an unpainted O scale (1:48) body between painted examples in S and TT3 scale (with other S scale rolling stock in the background).  There are some more model photos and links to information on the prototype wagons on my blog at http://marbelupmodels.blogspot.com.au/2014/09/nh-enh-qa-ha-ahaf-hopper-wagons.html.