OpenSCADCookbook

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Contents

Model Design for Re-Use

This chapter's purpose is designed to get you thinking in terms of model re-use.

Positive and Negative Space

Your code-fu may be strong, but even the simplest of models may be less than manifold. Here are some tricks to help force the issue.

Keep 'em Separated

  • Design your object body parts separate from your object holes

Add Glue Objects to Faces Intended to Bind

  • Design-in simple cube, cylinder and/or sphere geometry at the interface where two parallel object surfaces are intended to join. Helps accomodate floating point errors.

Extend Holes Beyond the Edge

  • Design-in extensions to the holes to fully cut thru the positive space boundary. Helps accomodate floating point errors.

Intersection Masks

Adding a Bevel to a Cylinder

  • Simple example to illustrate masking operations.

Creating Shells - 2D

  • Introduction to the concept for 2D outlines of areas. Creating the second, inner wall.

Creating Shells - 3D

  • Embrace and extend the 2D example.

Model Design for 3D Fabrication

Parametric Tolerances

  • Designing for interlock and separation.

Design Simple Unit Test Print Structures

  • Think up the simplest object you can print to measure the limits of your fabrication process.
  • Laser kerf versus thermal expansion.

Holes

  • 3D printed holes may shrink in diameter by up to the deposited material wall (path) thickness.
    • Is often compensated for in the slicing software and/or printer calibration. More of an issue with low-end printers or two-stage manufacturing processes like bronze-infused stainless steel.
    • Circular holes are only as precise as the line segments that define them.
    • See Polygonal hole test by nophead.
  • Laser cut holes grow in diameter by the laser beam's width.
    • Most laser cutters don't know anything about inner vs outer points of enclosed areas

Pegs

  • 3D printed peg-type structures may grow or shrink in diameter by the deposited material wall (path) thickness.
    • Is often compensated for in the slicing software and/or printer calibration. More of an issue with low-end printers or two-stage manufacturing processes like bronze-infused stainless steel.
    • Circular pegs are only as precise as the line segments that define them.

Just Say No to Bell Bottoms

  • Bottom layer edges sometimes flair out in 3D printed designs
    • Design in a bevel around the perimeter to compensate.
    • Is often compensated for in the slicing software and/or printer calibration. More of an issue with low-end FDM printers when printing without a raft or other sacrificial material.

Magnetic Perimeters

  • Close object surfaces tend to merge.
    • All 3D printers have design rules that specify how far apart distinct surfaces must be to remain distinct.
    • Applies to sharp inner angles and longer, narrow-diameter holes.

Orient for Your Strengths

  • Many 3D printing processes are strong in two of three dimensions. In fused deposition modeling (FDM) techniques like those used in MakerBot and RepRap printers, the Z-axis is weakest to shearing forces.
    • Design long, thin parts in the XY plane.
    • Consider orienting irregular shapes at a diagonal X-Z or Y-Z angle for compromise.

Over Hangover

Teardrop Tunnels

  • Design in 45-degree maximum overhangs in horizontal holes using tear-drop and truncated tear-drop shapes.

Polar Diamonds

  • Think polar coordinates to create diamond-shaped tunnels and channels at any elevation.
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