Approach 1: Work in Full Scale Now, Scale Down Later
How it WorksAs 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 & ConsThe 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 WorksTo 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) = 51.2mmUsing 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.