Hand machined mechanical pencils

Procedural texture in Rhino (02/12/13)

In the background of lots of our jewellery designs, I use either a linear or radial "clearout" toolpath. See, for example, this pendant:


The background shading in that design was done with lines 0.25mm apart using a 0.5mm ball-nose cutter. The linear shading pattern than results is very nice, but I realised that some pieces might benefit from a more random texture.

All our design work is done in Rhino. This comes with a very powerful scripting language called Rhinoscript, which is based on VBScript. I haven't used it much, but it can automate any of the tasks which are normally performed by the user. For example, I used it to do some basic animation.

I whipped up a little script to create a series of control point curves through sets of points which had a slight random variation added to them - this resulted in nice lines which were predominantly parallel and straight, but with slight random wiggles. Here's the code (you can download the script here):

' 20/11/13: for 0.5mm ballnose

Sub drawWavy()
  ' Definitions
  Dim arrPoints(50)
  ' Delete everything
  If IsArray(allobj) Then Rhino.deleteobjects allobj
  ' Draw lines
  For y=0 To 50
    ' Load point array with data
    For x=0 To 50
    ' Draw the control points
    Rhino.currentlayer("Layer 01")
    Rhino.addpoints arrpoints
    ' Draw control point curve
    Rhino.addcurve arrpoints
    ' Slow things down so user can see it drawing
    Rhino.sleep 100
End Sub

' Run the sub

For each Y position from 0 to 50, it creates an array of 50 points in the horizontal direction with random variations in both their X " Y coordinates and then draws a control point curve through them.

By simply varying how the program calculates the points, it's possible to create some interesting effects. For example, by using


instead, it will create a very effective wavy ripple pattern. Download wavy script here.

Here's a quick video showing the creation of the lines. I've added a small delay between each line so you can see the progression.

Lastly, here's some actual examples of the shading produced. The green stuff is modelling wax. I also tried one in acrylic, and then embossed some thin (0.1mm) copper foil in the hydraulic press - it worked pretty well.

"Straight" lines

Wavy lines

Straight lines in modelling wax

Wavy lines in modelling wax

Wavy lines in acrylic

Copper foil pressed into pattern

Reverse side

Here's a quick video overview of the different samples I tried: