User responsibility

To produce a set of printed 2D construction drawings, certain preparation must be made; layouts arranged, sheets put in order, print jobs configured, etc. Similarly, to 3D print a model certain steps must be taken to ensure a successful outcome.

The first order of consideration is referred to in the industry as print tolerance. Tolerance, as it applies to 3D printing, is how small a detail can successfully be 3D printed and survive the process. Every 3D printer has a different tolerance, so there is no definitive rule for how small a detail can be on a 3D printed part. There are several factors in determining the appropriate adjustments to make to a model to get the tolerances right such as level of detail desired, scale of printed model, the model's native CAD format, and printing technology, to name a few. Almost always, smaller details on the digital model must be enlarged so that they can survive the 3D printing process and be visible at a physical model scale. See the section on tolerances to learn more.

Most 3D models are drawn realistically, where 1” in the model = 1” in the “real world.” These models must be scaled to fit into a 3D printer. When a model is scaled uniformly to a size that will fit into a 3D printer, everything becomes much smaller. The level of detail that 3D printers can produce is limited in size. It is safe to assume that anything smaller than .01” will not resolve well on most 3D printers. Therefore, certain details of a 3D model may be too small to be seen in the 3D printed version. Others will be too small to survive the printing process. These details must be adjusted or removed.

A window mullion, for instance, drawn at 1” thick, will be too small to be printed at a typical model scale such as 1” = 16'. The 1” mullion at 16th scale is roughly .005” thick; too small for the 3D printer. This mullion needs to be enlarged to 3”- 4” in the “real world” model in order to make it large enough at model scale to be visible in the 3D print.
A column supporting a deck, as another example, will need to be much larger than .01 to support itself and survive the 3D printing process. Freestanding objects like columns generally need to be in the .05” - .1” range to print successfully. A 16th scale model's .1” column is actually 20” thick in the “real world” scale 3D model.

Print tolerances for 3D printers vary between manufacturers and 3D printing technologies. It is important to find out what the tolerances are for the type of 3D printer you are planning to use in order to properly adjust the thicknesses of the 3D model. Use CADspan's 3D print thickness calculator to determine the proper amount to thicken a model for 3D printing.

Holes and Gaps
Once tolerances have been correctly accounted for, the model must be checked for openings. To 3D print a model, the input file must be one continuous, solid object, usually in the STL file format. The printer must be able to clearly distinguish between the inside and outside of the object it is printing. There cannot be holes or gaps in the model, because the 3D printer will not be able to tell what is inside the object and what is outside. This applies quite literally to a house - the exterior of the building must be sealed. There are tools that can help identify and close holes and gaps, like CADspan, but the majority of these areas should be found and closed within the original CAD model for best results. Window and door openings, wall/roof intersections, chimneys, and the bottom of buildings are a few common sources of holes and/or gaps in a model that cause problems when 3D printing. Always check these areas, and the rest of a model, before moving toward 3D printing a file.

The visualization style tool can help identify holes, gaps, and other problem areas in the model.

See this tutorial on the AEC 3DP community website for a step-by-step description of preparing a SketchUp model for 3D printing.

Next section: using the CADspan tools


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