One Model... Many Scales


Full article

Today we're showing you a very simple trick with 3D printing that enables you to print an object designed for one scale in another. This is very easy to do and is done without needing to change the 3D model. Essentially if your 3D model is designed well, then you can print the same file in multiple different scales by simply adjusting the scaling factor in the slicer.

So what is a slicer? This is software that takes the 3D model, the profile for your 3D printer and generates what is called g-code for your printer. To keep things simple, g-code is basically instructions for the 3D printer to print the object, think of it as telling the printer to go left, right and so on. The slicer is a powerful piece of software as it enables you to generate support structures, control printer temperatures, determine bed adhesion and an insane level of tweaks and customization for individual print projects. Technical advances in the slicer is what has driven FDM to a very viable modeling technology.

Identifying the Original Scale

The first step is to identify the scale being used in the 3D model you are trying to print. If you have downloaded a model from Trackside3D then those files are in OO scale, so OO is the source scale. If you have downloaded an STL from Thingiverse, then the designer will usually indicate if a model is N, HO, O or some other scale.

Calculating the Scaling Factor

Once you know the original scale and the target scale, you can calculate the scaling factor.

To calculate the scaling factor use:

Original Scale / New Scale = Scaling Factor

So for OO scale, the scale is 1:76.2, to convert this to HO Scale (1:87) you would do the following:

76.2 / 87 = 0.87586

So we round this up to 0.876, when the scaling factor is less than 1, then you are scaling the model down. If you have a scaling factor greater than 1, then you are scaling up.

To convert the Scaling Factor to a percentage, simply multiply it by 100.

So the final formula is:

( Original Scale / New Scale ) * 100 = Scaling Percentage

The Scaling Percentage is what you place into Cura with Uniform Scaling enabled.

So for our OO -> HO conversion, it is:

76.2 / 87 = 0.876 * 100 which yields 87.6%. So we drop 87.6 into Cura.

Scaling Cheat Sheet

The above cheat sheet shows the scaling conversion factors with the target scales on the left:

  • N (2mm - 1:152)
  • N (standard - 1:148)
  • HO (3.5mm - 1:87)
  • OO (4mm - 1:76.2)
  • O (USA - 1:48)
  • O (UK - 7mm - 1:43.5)

With the source scales along the top. Here are the conversion factors that we typically use for Trackside3D:

  • OO -> N (1:152) 50.13%
  • OO -> N (1:148) 51.49%
  • OO -> HO (1:87) 87.59%
  • OO -> O (1:48) 158.75%
  • OO -> O (1:43.5) 175.17%

Now you can watch it in action:

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