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.