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Tutorial Edge_Face_Sets

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Adrian Mariano edited this page May 13, 2026 · 1 revision

Edge Sets and Face Sets

Overview

When working with BOSL2 shapes like cuboid(), you often want to round or chamfer only specific edges, or apply masks to certain faces. BOSL2 provides a flexible system for selecting edges and faces using direction vectors and string constants.

This tutorial explains how to specify which edges and faces you want to operate on.

Faces

A face on a cube-like shape is identified by a single direction unit vector pointing toward that face. For convenience, all six faces of a cube have easy to remember names associated with them. The six faces and their vector names are:

Name Vector Description
LEFT [-1,0,0] Left face (-X)
RIGHT [1,0,0] Right face (+X)
FRONT / FWD [0,-1,0] Front face (-Y)
BACK [0,1,0] Back face (+Y)
BOTTOM / BOT / DOWN [0,0,-1] Bottom face (-Z)
TOP / UP [0,0,1] Top face (+Z)

Edges

A cube has 12 edges. BOSL2 identifies each edge by combining two face direction vectors. For example, the edge where the TOP and FRONT faces meet is TOP+FRONT.

The 12 edges of a cube, grouped by level are:

Top edges:

  • TOP+FRONT
  • TOP+BACK
  • TOP+LEFT
  • TOP+RIGHT

Bottom edges:

  • BOT+FRONT
  • BOT+BACK
  • BOT+LEFT
  • BOT+RIGHT

Vertical edges:

  • FRONT+LEFT
  • FRONT+RIGHT
  • BACK+LEFT
  • BACK+RIGHT

Individual Edge Selection

Some shapes in BOSL2 offer rounding or chamfering of their edges. In cuboid(), for example, you can add a rounding=10 argument, to cause the cuboid's edges to be rounded to 10 units radius. By default, all edges will be rounded, but you may only want to round one of the edges. Using the edges= argument, you can specify which edge by summing two adjacent face vectors:

include <BOSL2/std.scad>
cuboid([50,60,70], rounding=10, edges=TOP+FRONT);

Figure 1

If you want to specify more than one edge, you can make a list of edges:

include <BOSL2/std.scad>
cuboid([50,60,70], rounding=10, edges=[TOP+FRONT, RIGHT+FRONT]);

Figure 2

You can select as many edges as you want:

include <BOSL2/std.scad>
cuboid([50,60,70], rounding=10, edges=[TOP+FRONT, RIGHT+FRONT, BOTTOM+FRONT]);

Figure 3

Selecting All Edges Around a Face

A single face vector selects all four edges surrounding that face:

include <BOSL2/std.scad>
cuboid([50,60,70], rounding=10, edges=TOP);

Figure 4

This rounds all four edges around the top face. Similarly, edges=FRONT selects the four edges around the front face.

You can also specify multiple faces in a list, to select all edges around any of them:

include <BOSL2/std.scad>
cuboid([50,60,70], rounding=10, edges=[TOP,RIGHT]);

Figure 5

Selecting Edges Around a Corner

A corner vector (sum of three face vectors) selects the three edges meeting at that corner:

include <BOSL2/std.scad>
cuboid([50,60,70], rounding=10, edges=FRONT+RIGHT+TOP);

Figure 6

Again, you can make a list of corners to select all edges around any of the corners.

include <BOSL2/std.scad>
cuboid([50,60,70], rounding=10, edges=[FRONT+RIGHT+TOP, FRONT+LEFT+TOP]);

Figure 7

Axis-Aligned Edge Sets

You can use string shortcuts to select all edges aligned with a given axis:

String Selects
"X" All 4 edges parallel to the X axis
"Y" All 4 edges parallel to the Y axis
"Z" All 4 edges parallel to the Z axis (vertical)
"ALL" All 12 edges
"NONE" No edges 
include <BOSL2/std.scad>
cuboid([50,60,70], rounding=10, edges="Z");

Figure 8

This rounds only the four vertical edges.

Again, you can use a list to select multiple of these:

include <BOSL2/std.scad>
cuboid([50,60,70], rounding=10, edges=["Y","Z"]);

Figure 9

Combining Edge Selections

You can mix and match any or all of the above described edge descriptors in a list, and BOSL2 will combine them in a union:

include <BOSL2/std.scad>
cuboid([50,60,70], rounding=5, edges=[TOP, FRONT+RIGHT]);

Figure 10

This rounds all edges around the top face, plus the single vertical edge at the front-right.

This can even be done with the axis aligned edge descriptors:

include <BOSL2/std.scad>
cuboid([50,60,70], rounding=5, edges=[TOP, "Z"]);

Figure 11

This rounds all the edges around the top face, and all the vertical edges.

The except Parameter

Use except to remove specific edges from the selection. This is often simpler than listing every edge you want to keep:

include <BOSL2/std.scad>
cuboid([50,60,70], rounding=10, edges="ALL", except=[BOT, FRONT+LEFT]);

Figure 12

This rounds all edges except those around the bottom face and the front-left vertical edge.

The except parameter accepts the same descriptors as edges: individual edges, face vectors, corner vectors, and axis strings.

include <BOSL2/std.scad>
cuboid([50,60,70], rounding=10, edges=TOP, except=TOP+BACK);

Figure 13

This rounds the top face edges, except for the top-back edge.

Edge Sets with Chamfers

The same edge selection system works with the chamfer parameter on cuboid():

include <BOSL2/std.scad>
cuboid([50,60,70], chamfer=5, edges=[TOP+FRONT, TOP+RIGHT, FRONT+RIGHT]);

Figure 14

Edge Sets with Masking Modules

The edge_mask() and edge_profile() modules also use edge set descriptors to control which edges receive a mask.

edge_profile()

Extrudes a 2D profile along selected edges. Here, we're diffing the resulting extruded mask away:

include <BOSL2/std.scad>
diff()
cube([50,60,70], center=true)
    edge_profile([TOP, "Z"], except=[BACK, TOP+LEFT])
        mask2d_roundover(10);

Figure 15

edge_mask()

Positions a 3D mask shape along selected edges:

include <BOSL2/std.scad>
module round_edge(l, r) difference() {
    translate([-1,-1,-l/2])
        cube([r+1, r+1, l]);
    translate([r, r])
        cylinder(h=l+1, r=r, center=true, $fn=quantup(segs(r),4));
}
diff()
cube([50,60,70], center=true)
    edge_mask([TOP, "Z"], except=[BACK, TOP+LEFT])
        round_edge(l=71, r=10);

Figure 16

face_profile()

Face vectors can be used with modules like face_profile() to apply a 2D mask profile to all edges and corners of a given face:

include <BOSL2/std.scad>
diff()
cube([50,60,70], center=true)
    face_profile(TOP, r=10)
        mask2d_roundover(10);

Figure 17

Practical Examples

Rounded Top, Sharp Bottom

A common pattern for enclosures: round only the top edges.

include <BOSL2/std.scad>
cuboid([60,40,30], rounding=5, edges=TOP);

Figure 18

Chamfer Only Vertical Edges

Useful for grip surfaces or decorative columns:

include <BOSL2/std.scad>
cuboid([30,30,60], chamfer=3, edges="Z");

Figure 19

Round Everything Except Bottom

A box that sits flat on the build plate:

include <BOSL2/std.scad>
cuboid([50,40,25], rounding=4, edges="ALL", except=BOT);

Figure 20

Summary

Descriptor What it selects
TOP+FRONT A single edge
TOP All 4 edges around the top face
FRONT+LEFT+TOP All 3 edges at a corner
"X", "Y", "Z" All 4 edges along an axis
"ALL" All 12 edges
"NONE" No edges
except=BOT Remove bottom edges from selection

These selectors work consistently across cuboid(), edge_mask(), edge_profile(), corner_mask(), corner_profile(), and face_profile().

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Indices

Table of Contents
Function Index
Topics Index
Glossary
Cheat Sheet
Tutorials

List of Files:

Basic Modeling:

Advanced Modeling:

Math:

Data Management:

Threaded Parts:

Parts:

Footnotes:

STD = Included in std.scad

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