Cut angular section (pie section) out of cylinder

Question

In general, I'm wondering how to cut a pie slice out of a cylinder. I have done an extensive search and I'm sure it's not that difficult, but I haven't managed to find anything I could apply (possibly because of my novice status in Blender.)

For the moment, my more immediate need is to cut out part of an octogonal prism. So, consider the octogon built with the following code:

import bpy
Create a 3D octogonal prism.
myRadius = 2.0
myDepth  = 1.0
bpy.ops.mesh.primitive_cylinder_add(
        vertices = 8, radius = myRadius, depth = myDepth,
        location = ( 0, 0, 0 ) ) # location could be other, using origin for simplicity here
bpy.context.object.name  = "myOctogon"

Ultimately, what I want is to end up with is 7/8 of the original prism rotated clockwise by pi/8 so that the gap faces "northeast".

UPDATE: I have discovered that I can do it as follows, though I don't know how to script it all:

import bpy
from math import pi
Create a 2D octogon.
myRadius = 2.0
myDepth  = 1.0
bpy.ops.mesh.primitive_circle_add(
    vertices = 8 , radius = myRadius,
    fill_type='TRIFAN', 
    location = ( 0, 0, 0 ),
    rotation = ( 0, 0, pi / 8 ) )
bpy.ops.object.editmode_toggle()
Select the 'northeast' edge.
bpy.ops.mesh.subdivide()
Select the new vertex, move it to ( 0, 0, 0 ).
Select the whole 'pac man' shape, extrude to desired height.
bpy.ops.mesh.extrude_region_move( ... ) # need to work out appropriate details

Related https://blender.stackexchange.com/questions/101446/cut-mesh-with-circle-pie-chart-like-mesh-for-animation https://blender.stackexchange.com/questions/34685/how-to-create-a-circle-pie-chart-with-separate-adjustable-variable-triangle-c https://blender.stackexchange.com/questions/84372/rotated-array-modifier-around-constant-origin To create as a mesh would use create a profile and spin, in this case seven eighths of 360 degrees. To animate look at creating the modifiers (potentially one all or any of spin /solidify array) with code. Answer below shows how to add solidify mod. — batFINGER, May 14 '21 at 07:38
eg spin a single x axis aligned edge around Z and solidify in Z makes a wedge, array makes copies._ — batFINGER, May 14 '21 at 07:45
Thanks, the first two of these I'd seen after posting, wasn't sure how to adapt them to my purpose but it was getting late. Will see what I can manage with it today. I don't want to animate, I'm building a deck ;) — K.G. Feuerherm, May 14 '21 at 14:58
@batFINGER I did it successfully by hand in Blender, so I know it works (my explanation may well be lacking). But no matter. Your solution works for me. — K.G. Feuerherm, May 14 '21 at 17:29

Ratt · Answer 1 · 2021-05-14T03:15:44.073

Below is a quick and dirty method using a circle and solidify modifier with operators.

import bpy
from math import pi
verts_total = 8
verts_fill = 7
my_radius = 1.0
my_location = (0.0, 0.0, 0.0)
my_rotation = (0.0, 0.0, 0.0)  # use radians
my_depth = 2.0
def make_pacman(verts_total, verts_fill, my_radius, my_location, my_rotation, my_depth):
    # create a circle mesh and create triangle fan fill
    bpy.ops.mesh.primitive_circle_add(
        vertices=verts_total,
        radius=my_radius,
        fill_type='TRIFAN',
        calc_uvs=True,
        location=my_location,
        rotation=my_rotation)
obj = bpy.context.object
# add solidify modifier to simulate cylinder
mod = obj.modifiers.new(&quot;SOLIDIFY&quot;, type='SOLIDIFY')
mod.thickness = my_depth 
mod.offset = 0
# if full cylinder then done
if verts_total == verts_fill:
    return
# select vertices to delete
bpy.ops.object.mode_set(mode='EDIT')
bpy.ops.mesh.select_all(action='DESELECT')
bpy.ops.object.mode_set(mode='OBJECT')
for i, vert in enumerate(obj.data.vertices):
    if i &lt;= verts_fill:
        continue
    vert.select = True
bpy.ops.object.mode_set(mode='EDIT')
bpy.ops.mesh.delete(type='VERT')
bpy.ops.object.mode_set(mode='OBJECT')


make_pacman(verts_total, verts_fill, my_radius, my_location, my_rotation, my_depth)

I tried this, but it ends up deleting 1/4 rather than 1/8; I had to run the code step-by-step and then try it manually to see why. Maybe if one moved the 'deleted' point to the centre? Otherwise, maybe I can delete 7/8 and use the remainder as a Boolean and do a difference? — K.G. Feuerherm, May 14 '21 at 15:35

batFINGER · Accepted Answer · 2021-05-14T16:43:54.720

Bmesh version.

Make a profile, basically this is just a plane. Have simply made this 1 x 1. Could replace with width and height in x and y respectively (or make a scale matrix)
Rotate it about z axis thru origin to some staring point. Rotated such that middle of gap is x = y
spin it in 7 eights of 360 degrees in 7 steps.

Test script:

import bpy
import bmesh
from math import pi
from mathutils import Matrix
context = bpy.context
profile.
coords = (
    (0, 0, 0),
    (1, 0, 0),
    (1, 0, 1),
    (0, 0, 1),
    )
bm = bmesh.new()
bm.faces.new(bm.verts.new(co) for co in coords)
bm.transform(Matrix.Rotation(3 * pi / 8, 4, 'Z'))
bmesh.ops.spin(
        bm,
        geom=bm.edges[:] + bm.faces[:],
        axis=(0, 0, 1),
        angle=2 * pi * 7 / 8,
        steps=7,
        )
me = bpy.data.meshes.new("Pie")
bm.to_mesh(me)
ob = bpy.data.objects.new("Pie", me)
context.collection.objects.link(ob)

One edge, with screw and solidify modifiers.

As commented, here is same result with one edge, screwed around then solidified.

import bpy
from mathutils import Matrix
from math import pi
context = bpy.context
verts = (
    (0, 0, 0),
    (1, 0, 0),
    )
edges = ((0, 1),)
me = bpy.data.meshes.new("Pie")
me.from_pydata(verts, edges, [])
me.transform(Matrix.Rotation(3 * pi / 8, 4, 'Z'))
ob = bpy.data.objects.new("Pie", me)
screw = ob.modifiers.new("Screw", type='SCREW')
screw.angle = 7 * 2 *  pi / 8
screw.steps = screw.render_steps = 7
screw.use_smooth_shade = False
solidify = ob.modifiers.new("Solidify", type='SOLIDIFY')
solidify.thickness = -1
context.collection.objects.link(ob)

Cut mesh with circle pie chart like mesh for animation

How to create a circle pie chart with separate (adjustable/variable) triangle "chunks"?

Rotated array modifier around constant origin?

This works. I ran across the concept 'bmesh' yesterday but have not been able to follow up on it yet; is there a downside to it not just being a 'mesh'? In the interim, I found a way to do it but haven't worked out how to script it all; will add update above. — K.G. Feuerherm, May 14 '21 at 16:23
It is simply used to create / edit a mesh. See the API docs. — batFINGER, May 14 '21 at 16:47
I don't understand the details of either solution at the mo but I can work on that! Appreciated. — K.G. Feuerherm, May 14 '21 at 17:20

Cut angular section (pie section) out of cylinder

Create a 3D octogonal prism.

Create a 2D octogon.

Select the 'northeast' edge.

Select the new vertex, move it to ( 0, 0, 0 ).

Select the whole 'pac man' shape, extrude to desired height.

2 Answers2

profile.