Overview

I have a piece of wood and want to add some cam operation on it, to create a small bowl. The problem is the non geometrical shape. We need the picture of the shape in Blender to create an object which can be milled later on.

This workflow shows, which steps are necessary

Prerequisite

units mm, top orthographic view, ("import image as plane" addon is no longer necessary. You can just use new Blender feature to import images)

prepare object

• draw a rectangle cross on the wood
• measure from the middle of the cross on both sides the same maximum distance (called now maxrad) and add markers
• draw a border line on the wood to have reference curve later on if you want
• make a picture of the wood from a fare distance to reduce paralax error. Zoom in to see the hole wood. You should be able to see the cross and the borders

prepare picture in Blender

• start blender, change to Eevee Renderer and switch to top view ( numpad 7 ) otherwise the image plane has wrong orientation
• switch "viewport shading" to material preview
• import picture as reference (A Image/Reference)
• put the picture in the back and make it only visible in Orthographic top view: (Object properties dialog)
  1. Depth Back. Now you can see the raster
  2. Show in: only check in Orthographic and Only Axis Aligned
• rotate the image plane around the z axis to align the cross on the wood with the raster in the top view (r z). Make the fine tuning with shift key to slow down your mouse movement
• move the image plane to the origin/cursor (g). Make the fine tuning with shift key to slow down your mouse movement
• add a circle with a radius maxrad
• move the circle on top of the image plane (g z 1)
• change the pivot center to 3D cursor (3D cursor should still be at origin)
• scale the image plane to make the marker fitting to the circle. Make the fine tuning with shift key to slow down your mouse movement

create geometry

define shape

• add a simple Mesh plane and go in edit mode ( A m p tab )
• deselect all ( Alt a )
• switch to vertex select mode
• delete two vertices and move the other two to the border of the wood where you want to start the bowl
• add the subdivision surface modifier with Levels Viewport = 4
• select one vertex and extract ( e ) a lot of times until the shape is drawn. The shape should be only a rough estimation of the border, because the subdivision modifier make a smooth curve. You can switch the visibility of the poly line on and off in the modifier
• make as less vertex/extrudes as possible. You can reduce also later some vertex by selecting and remove with dissolve vertices. Adjust the other vertices with selecting and moving ( g )

Alternative 1: 2.5D

we are more or less ready

• switch back to object mode and convert the mesh to a curve
• move down the mesh in z direction as depth you want to mill

Alternative 2: 3D

• now select all, extrude and scale down ( a e s )
• change to side view (numpad 1) and move the edge loop down (g z )
• extrude again and scale and move down nearly to the end depth of the bowl
• extrude again and scale and move down a little bit
• fill the middle ring (f) now we have a bowl

fine tune the geometry

• make the geometry more visible: change the material: create a new material, set Metallic to 1.000 and Roughness to 0.12
• make sure that the normals are correct: in edit mode Mesh Normals recalculate outside ( Alt n )
• move and smooth vertices
• got to object mode ( tab )

calculate the cam paths

• select and hide the picture ( h )
• change back the viewport shading to Solid
• change the Renderer to Cam

Alternative 1: 2.5D

• select the curve and make your pocket milling (first rough cut than fine cut)

Alternative 2: 3D

• select the surface and use parallel strategy