Back in February 2014 I showed you the drawings and designs for my N scale Union Pacific auxiliary excursion train water tenders. You can find the first post here.  These proved to be very popular and it soon became apparent that modelers in other scales would also like to have the 3D printed model.  In this post I will show you some of the things I have done to turn the N scale model into a HO model.

Below is a pair of the N Scale tenders, as currently run by UP with their heritage fleet.  Some of the details were omitted from the print due to them being simply too small to print and, as is often the case with N Scale, some details needed to be made larger than real life.  A good example of this are the steps at each end and the ladders.One of the most noticeable details missing from the print were the handrails running along the top.  Several customers have added their own, as shown below on Mark Peterson’s Tenders.

With the HO kit I wanted to add the missing details in and also improve the scale of the chunkier parts.  HO being at a scale of 1:87 is just about twice the size of N scale which is 1:160.  This means that everything will be, just about, twice the size and therefore the detail will be more defined. However this also introduces another issue.  Re-scaling an N scale model to HO will not simply make it twice the price.

The 3D printers charge by volume of material used or cubic capacity in cm³ to produce the print, plus a fixed charge per print.  So for example, if you had a 1 meter square cube (roughly 3 foot square) it would have a cubic capacity of 1m³ or 1,000,000cm³. If this was printed at 1:160 it would have a cubic capacity of 0.2439cm^3.  But if you printed the same cube at 1:87 it would have a cubic capacity of 1.5161cm³ which is significantly higher.

To overcome this there are a few things we can do.  The first thing is to look at the thickness of the parts as these are now all twice the thickness they need to be to print. The 3D printers specify the minimum wall thicknesses which they can print for all their materials.  My N scale water tenders were designed to print in Shapeways Frosted Ultra Detail (FUD) material which has a minimum unsupported wall thickness of 0.6mm.  Details such as the end steps and ladders will be reduced in thickness anyway to remove the chunky look I mentioned earlier, but the biggest difference is made in the large side panels and roof section.  By reducing these thicknesses it greatly reduces the cubic capacity of material in the model.  Below is a section though the N Scale water tender, you can see the thickness of the walls in light blue on the sides and top of the main shell.

After re scaling and adjusting the wall thickness for HO the section looks like this;

The second thing we can do is look at printing in other materials.  The FUD material is one of the more expensive plastic materials due to the high level of detail that is achievable.  Shapeways also offer a Frosted Detail (FD) material.  This is printed in the same way but the level of detail is slightly less.  FUD can print detail which is embossed or engraved in the parts as small as 0.1mm (0.0039″).  FD can print detail which is embossed or engraved in the parts as small as 0.2mm (0.0078″).  This difference doesn’t sound a lot but in N Scale it is equivalent to 27.2mm (1.07″) and therefore using it for N scale is not practical.

However as we will basically printing an N Scale model at twice the size, printing in the FD material would make sense as the difference in detail will not come into play.  The FD material is cheaper than the FUD which also brings the cost per cubic capacity down.

The third thing we can do is to look at parts of the model which don’t have any detail, such as the chassis, which are required structurally but not cosmetically.  These can be printed in very cheap materials such as Shapeways White Strong & Flexable (WS&F).  WS&F is almost two and half times cheaper than FUD and even though parts in WS&F need to be thicker than in FUD they are still significantly cheaper.

So for the HO Scale UP Water Tender the main body, ladders and trucks will be printed in FD and the chassis, truck bolster pins, tool boxes and flag plates will be printed in WS&F.  I have included the top handrails as part of the main body print.  The ladders are still separately applied details which makes painting easier as they are Harbour Mist gray and not Armor yellow.  Below is a rendering of how they will look.

The test print has been successfully printed by Shapeways and is due to be delivered to me this week. In a later post I will cover more in-depth details such as couplings and the wheel sets I have used for this model and how they fit, and I will also share with you how the test print came out.