15 KiB
Rounding the Cube
One of the shape primitives you'll use most often in your OpenSCAD designs is the cube. Rounding the edges of cube-like objects impacts both the visual appeal and functional aspects of the final design. The BOSL2 library provides a variety of methods for rounding edges and corners.
There are four different 3d shape primitives that you can use to make cube-like objects:
-
cuboid() - Creates a cube with chamfering and roundovers.
-
cube() - An extended version of OpenSCAD's cube() with anchors for attaching children. (See the Attachments Tutorial).
-
prismoid() - Creates a rectangular prismoid shape with optional roundovers and chamfering.
-
rounded_prism() - Makes a rounded 3d object by connecting two polygons with the same vertex count. Rounded_prism supports continuous curvature rounding. (See Types of Roundovers).
BOSL2 provides two different methods for rounding the edges of the cube-like primitives above.
-
Built-in Rounding - Cuboid(), prismoid(), and rounded_prism() all have built-in arguments for rounding some or all of their edges.
-
Masking - BOSL2 includes a number of options for masking the edges and corners of objects. Masking can accomplish rounding tasks that are not possible with the built-in rounding arguments. For example with masking you can have a cube with a different rounding radius on the top edges than the rounding radius on the bottom edges.
Cuboid Rounding
You can round the edges of a cuboid() with the rounding argument by specifying the radius of curvature:
include <BOSL2/std.scad>
cuboid(100, rounding=20);
Cube-like objects have six named faces.
You can round just the edges on one of the faces. Here we're rounding only the top edges:
include <BOSL2/std.scad>
cuboid([100,80,60], rounding=20, edges = TOP);
...or just the bottom edges. Here we're using the teardrop parameter to limit the overhang angle to enable 3d printing on FDM printers without requiring supports:
include <BOSL2/std.scad>
cuboid([100,80,60], rounding=20, teardrop = 45, edges = BOTTOM);
We can round only the edges aligned with one of the axes, X, Y, or Z:
include <BOSL2/std.scad>
cuboid([100,80,60], rounding=20, edges = "Z");
If you want to round selected edges you can specify which edges using combinations of the named directions LEFT, RIGHT, TOP, BOT, FWD, BACK. See Specifying Edges for more details.
It is possible to round one or more of the edges while leaving others unrounded:
include <BOSL2/std.scad>
cuboid([100,80,60], rounding=20, edges = TOP+FRONT);
...or exclude the rounding of one or more edges while rounding all the others:
include <BOSL2/std.scad>
cuboid([100,80,60], rounding=20, except = TOP+FRONT);
You can fillet top or bottom edges by using negative rounding values. Note that you cannot use negative rounding values on Z-aligned (side) edges.
include <BOSL2/std.scad>
cuboid([100,80,60], rounding=-20, edges = BOTTOM);
If you do need to add a fillet on a Z-aligned edge, use fillet():
include <BOSL2/std.scad>
cuboid([100,80,60], rounding = -10, edges = BOT+FRONT)
position(FRONT+RIGHT)
fillet(l=60, r=10, spin=180);
Chamfering the edges of the cuboid() can be done in a manner similar to rounding:
include <BOSL2/std.scad>
cuboid([100,80,60], chamfer=20);
You can specify edges as with rounding:
include <BOSL2/std.scad>
cuboid([100,80,60], chamfer=20, edges = "Z", except = FWD+RIGHT);
##Prismoid Rounding
The prismoid() differs from the cuboid and cube in that you can only round or chamfer the vertical(ish) edges using the built-in parameters. For those edges, you can specify rounding and/or chamferring for top and bottom separately:
include <BOSL2/std.scad>
prismoid(size1=[35,50], size2=[20,30], h=20, rounding1 = 8, rounding2 = 1);
You can also specify rounding of the individual vertical(ish) edges on an edge by edge basis by listing the edges in counter-clockwise order starting with the BACK+RIGHT (X+Y+) edge:
include <BOSL2/std.scad>
prismoid(100, 80, rounding1=[0,50,0,50], rounding2=[40,0,40,0], h=50);
##Masking Edges of the Cuboid, Cube and Prismoid ###2D Edge Masking with edge_profile()
One limitation of using rounding arguments in cuboid() is that all the rounded edges must have the same rounding radius. Using masking we have the flexibility to apply different edge treatments to the same cube. Masking can also be used on the cube() and prismoid() shapes.
2D edge masks are attached to edges using edge_profile(). They have a default tag of "remove" to enable differencing them away from your cube using diff().
We can use a negative rounding value to fillet the bottom of a cuboid and edge_profile() to round the top. Here edge_profile() applies a 2d roundover mask to the top edges of the cuboid.
include <BOSL2/std.scad>
diff()
cuboid([50,60,70], rounding = -10, edges = BOT)
edge_profile(TOP)
mask2d_roundover(r=10);
See mask2d_roundover() for additional mask parameters. Here we use the inset parameter in mask2d_roundover:
include <BOSL2/std.scad>
diff()
cube([50,60,70],center=true)
edge_profile(TOP, except=[BACK,TOP+LEFT])
mask2d_roundover(h=12, inset=4);
In addition to the simple roundover mask, there are masks for cove, chamfer, rabbet, dovetail, teardrop and ogee edges.
The mask2d_ogee() only works on cube() and cuboid() shapes, or a prismoid() where size2 >= size1 in both the X and Y dimensions.
include <BOSL2/std.scad>
diff()
prismoid(size1 = [50,50],size2 = [80,80], rounding1 = 25, height = 80)
edge_profile(TOP)
mask2d_ogee([
"xstep",8, "ystep",5, // Starting shoulder.
"fillet",5, "round",5, // S-curve.
"ystep",3, "xstep",3 // Ending shoulder.
]);
You can use edge-profile() to round the top or bottom of a prismoid(). Because the side faces of a prismoid() are not strictly vertical, it's is necessary to increase the length of the masks using the excess parameter in edge_profile(), and to set the mask_angle to $edge_angle in mask2d_roundover().
include<BOSL2/std.scad>
diff()
prismoid(size1=[35,50], size2=[30,30], h=20, rounding1 = 8, rounding2 = 0)
edge_profile([TOP+LEFT, TOP+RIGHT], excess = 5)
mask2d_roundover(r = 15, mask_angle = $edge_angle);
###3D Edge and Corner Masking
BOSL2 contains a number of 3d edge and corner masks in addition to the 2d edge profiles shown above.
The 3d edge masks have the advantage of being able to vary the rounding radius along the edge. 3d edge masks, such as rounding_edge_mask(), can be attached using edge_mask(). The 3D edge masks have a default tag of "remove" to enable differencing them away from your cube using diff().
include <BOSL2/std.scad>
diff()
cuboid(80)
edge_mask(TOP+FWD)
rounding_edge_mask(r1 = 40, r2 = 0, l = 80);
While you can specify the length of the mask with the l or h argument, edge_mask() sets a special variable, $parent_size, to the size of the parent object. In the case where the parent is not a perfect cube, you need to mask each edge individually:
include <BOSL2/std.scad>
diff()
cuboid([60,80,40]) {
edge_mask(TOP+FWD)
rounding_edge_mask(r = 10, l = $parent_size.x + 0.1);
edge_mask(TOP+RIGHT)
rounding_edge_mask(r = 10, l = $parent_size.y + 0.1);
edge_mask(RIGHT+FWD)
rounding_edge_mask(r = 10, l = $parent_size.z + 0.1);
}
As you can see above, using only rounding_edge_mask() to round the top of the cube leaves the corners unrounded. Use corner_mask() and rounding_corner_mask() for a smoother corner.
include <BOSL2/std.scad>
diff()
cuboid([60,80,40]) {
edge_mask(TOP+FWD)
rounding_edge_mask(r = 10, l = $parent_size.x + 0.1);
edge_mask(TOP+RIGHT)
rounding_edge_mask(r = 10, l = $parent_size.y + 0.1);
edge_mask(RIGHT+FWD)
rounding_edge_mask(r = 10, l = $parent_size.z + 0.1);
corner_mask(TOP+RIGHT+FWD)
rounding_corner_mask(r = 10);
}
As with the built-in rounding arguments, you can use edge_mask() and corner_mask() to apply teardrop roundings using teardrop_edge_mask() and teardrop_corner_mask() to limit the overhang angle for better printing on FDM printers. Note that the vertical mask on the RIGHT_FWD edge is a rounding_edge_mask().
include <BOSL2/std.scad>
diff()
cuboid([60,80,40]) {
edge_mask(BOT+FWD)
teardrop_edge_mask(r = 10, l = $parent_size.x + 0.1, angle = 40);
edge_mask(BOT+RIGHT)
teardrop_edge_mask(r = 10, l = $parent_size.y + 0.1, angle = 40);
edge_mask(RIGHT+FWD)
rounding_edge_mask(r = 10, l = $parent_size.z + 0.1);
corner_mask(BOT+RIGHT+FWD)
teardrop_corner_mask(r = 10, angle = 40);
}
##Rounded Prism You can construct cube-like objects, as well as a variety of other prisms using rounded_prism(). The unique feature of rounded_prism() is the ability to use continuous curvature rounding. Rather than using constant radius arcs, continuous curvature rounding uses 4th-order Bezier curves. For complete details on how this works see Types of Roundovers.
Two parameters control the roundover k and joint. The joint parameter is specified separately for the top, bottom and side edges; joint_top, joint_bot, and joint_sides.
The k parameter ranges from 0 to 1 with a default of 0.5. Larger values give a more abrupt transition and smaller ones a more gradual transition. A k value of .93 approximates the circular roundover of other rounding methods.
If you want a very smooth roundover, set the joint parameter as large as possible and then adjust the k value down as low as gives a sufficiently large roundover.
include <BOSL2/std.scad>
include <BOSL2/rounding.scad>
rounded_prism(rect(20), height=20,
joint_top=10, joint_bot=10, joint_sides=9.99, k = 0.5);
A large joint value and a very small k value:
include <BOSL2/std.scad>
include <BOSL2/rounding.scad>
rounded_prism(rect(20), height=20,
joint_top=10, joint_bot=10, joint_sides=9.99, k = 0.01);
A k value of 0.3
include <BOSL2/std.scad>
include <BOSL2/rounding.scad>
rounded_prism(rect(20), height=20,
joint_top=10, joint_bot=10, joint_sides=9.99, k = 0.3);
A k value of 1:
include <BOSL2/std.scad>
include <BOSL2/rounding.scad>
rounded_prism(rect(20), height=20,
joint_top=10, joint_bot=10, joint_sides=9.99, k = 1);
A k value of 0.93 approximates the circular roundover of other rounding methods:
include <BOSL2/std.scad>
include <BOSL2/rounding.scad>
rounded_prism(rect(20), height=20,
joint_top=4, joint_bot=4, joint_sides=4, k = 0.93);
right(30)
cuboid(20, rounding = 4, $fn = 72);