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This is the second entry in a series of posts discussing MakerBot & Miniatures.  Check out last week’s post!

My journey to 3D modeling started at a drafting board and most of my CAD work still ends up in two dimensions on a piece of paper as a plan, section or elevation.  As many of the things I model in CAD are much larger than a piece of paper, it is common practice to create full scale geometry in a CAD program, and then choose a scale in which to depict the project in a layout. When I sat down to design my first model for 3D printing, I wasn’t sure how to get started.  Should I continue to create in full scale, and then scale down when I wanted to make it with my MakerBot?  Or should I design directly in scale?  I currently use both methods in my work, and today I’ll talk through the pros and cons of each approach.

I already had a workflow to go from CAD to 2D, but how would 3D printing change that?

Approach 1: Work in Full Scale Now, Scale Down Later

How it Works

As you design your CAD model, draw every measurement in full scale, or 1:1.  A three foot cube will be 3’-0” x 3’-0” x 3’-0” in your drawing. When you are ready to print in 3D, import and scale within your slicing software.  Or, scale a second copy of your object before leaving your CAD program.  Use the process below to figure out what values to use.

Figure out the decimal value of your scale factor.  In this example we’ll use 1:18.

1/18 = .056

Scale your object by .056 to convert to 1:18 scale.
If necessary, scale your object by 25.4 to switch from inches to millimeters.
Your file is ready to go!  A three foot cube will be 51.2mm x 51.2mm x 51.2mm in 1:18 scale.

Note: As you design, remember the calculations we made last week to figure out the smallest features we can produce with a MakerBot in a given scale.  Keep these measurements in mind as you design, so you don’t design unprintable details in your model.

The Pros & Cons

The Pros: Designing in full scale is straightforward, as every measurement in your CAD drawing corresponds to the actual measurements of an object.  It’s easy to use your model in multiple ways, and shift between scales in your output.

The Cons: It’s difficult to harness the properties of your 3D printer on complicated details if you can’t subtly manipulate your CAD model.  It is also easy to create too much or unprintable detail when you are working in full scale.

When Does it Make Sense to Work in Full Scale?

1. Your CAD model will be reproduced in multiple scales
If you plan to represent your object in multiple scales and mediums, create your CAD model in full scale. Use your CAD model as you typically would in your design process for 3D renderings or printed elevations. Then, reduce your model before 3D printing to an appropriate scale.

2. Your process starts with 2D elevations
If you start by drawing 2D elevations or line work, and then move to 3D, draw your elevation in full scale. The elevation can be printed in 2D in whatever scale is necessary. Editing 2D line work is often simpler than editing 3D solids, so before you translate your design into 3D, scale your elevation, and switch to metric if necessary, so you can work directly in scale. You can make subtle changes to your model for better printing, to take advantage of thread widths and layer slicing heights as you extrude your shapes to 3D.

3. Your subject matter doesn’t have complex or small features
Massing style models, with few small details, will print well in many scales. Take advantage of the simplicity of modeling in 1:1, and scale your model afterward to make in 3D.

Approach 2: Work Directly in Scale

How it Works

To work directly in scale, you need to translate an object’s dimensions using the scale factor of your choice as you create your model.  If your measurements are in inches and feet, you also need to convert to the metric system. Use millimeters as your drawing units.  Layout important dimensions, such as overall size and important features, by referencing a conversion scale chart like the ones I have provided on Thingiverse, or use this equation:

(# inches) * (scale factor) * (metric conversion)  =  measurement, in scale & in mm

Let’s translate a 3’ measurement for a scale project using 1:18.
1:18 expressed in decimals is .056 and we will use a metric conversion factor of 25.4.

(36”) * (.056) * (25.4) = 51.2mm

Using this method, you would draw a 3 foot cube as 51.2mm x 51.2mm x 51.2mm in your CAD program.  Your geometry has already taken a scale factor and a metric conversion into account.  Continue to add more details to your project by consulting a conversion chart, or using the proportion of your model as a reference.

Note: Last week, reader Miles shared an excellent resource:  This awesome online calculator is suited for this exact purpose.  You can choose from a variety of scales, and convert easily from imperial to metric.

The Pros & Cons

The Pros: You can take best advantage of your 3D printer because you are designing directly in the units that your printer understands.  Design successful bridges, push the limits for fine details, and design to take advantage of slicing height.  It’s easier to keep the amount of detail in your model in check and save modelling time.  Easily iterate and manipulate your model without the need to return to a full scale drawing.

The Cons: Designing directly in scale requires an additional layer of translation.  It can be complicated to think in two measurement systems at once, especially if you are not comfortable working in the metric system.  Models designed directly in scale are of little use outside a 3D printed scale model – it is not easy to create a 2D elevation in a different scale, or incorporate the 3D CAD model in a rendering with objects of different scales.  Adjustments made for print-ability may have unintended consequences in other applications.

When Does it Make Sense to Work Directly in Scale?

1. Your CAD model will only be used for a scale model.
The advantages of working in full scale mostly apply to models that will be used in multiple ways, so work directly in scale if this does not apply to you.

2. Your CAD model has complex features including bridges, skinny towers, and small details.
Choose to work directly in scale so you have tighter control over complex details, and can iterate new designs quickly.

3. You plan to share source files with others, as part of a larger project.
Your final STL files will be in the right scale regardless of working method, but if you design directly in scale, so will your source files.  Make it easier for others to build off your work without the need to explain your scaling procedures.

Choose a Method

Balance your needs and abilities and choose the method that is right for you.  Feel free to approach different parts of your model is different ways; I certainly do.  When I started, I began with a method that was familiar.  My Queen Anne Chairs started as a full scale CAD model, but I was quickly frustrated.  I needed to carefully manipulate parts of the model to print successfully.  I found it difficult to go back and forth between a full size drawing in feet and inches, to a scale representation in the metric system, so I switched to a new working method.  Many of my scale furniture pieces are exclusively for scale model use; they will never be built in full scale.  When I create these designs, I keep a conversion chart handy and design directly in my model scale.

I still design in full scale.  The CAD work I do is often used in multiple ways.  I create 2D printed elevations that will serve as a plan for a fully built set, and I use the same CAD work to create details for my scale miniatures on my MakerBot.

Switch between working methods to suit your process, just makes sure to keep track of what scale and measurement system you are in.  It can quickly get complicated.  Next week, I’ll walk you through an example project.  I’ll also give some handy information about common sizes of furniture and architectural elements that can help as you begin to design a scale model.

Kacie Hultgren is a scenic designer in New York City using MakerBot 3D printers to explore her craft.  You can find her on Thingiverse under the handle PrettySmallThings.  Visit her online shop at www.prettysmallthings.com.