Drawing and cutting a Triangle

Let’s say I have a cube 16x16x16 mm

In the middle of the top surface I wish to create an equilateral triangle 8x8x8 mm with its base parallel to the near edge. Then I want to extrude the triangular surface 2 mm down into the cube such that the finished article will be a cube with a triangle etched into its top surface.

This procedure must be one of the most common in Mechanical Design Modelling (with endless variations on the theme - boring holes, cutting keyways etc. etc. etc.) yet none of the video tutorials I have covers the subject and Mr Google is no help.

Would someone please either direct me to the appropriate video or step-by-step me through the process. To an absolute Rhino Newbie like me that would be one giant leap for mankind and much appreciated.


Hello - start Polygon, NumSides =3. The trick will be to set the radius correctly for a 8 mm side - you could work that out but I think the simplest is to make your triangle using the Edge option in polygon - place a point, anywhere in the CPlane, type in 8 and Enter and place the other end of that edge.
Move the polygon from its Center (Cen OSnap) to a Between snap on opposite corners of the top face of your box. ExtrudeCurve, BothSides > Solid=Yes. BooelanDifference the resulting prism from the box.


1 Like

Hmmm. :thinking:
I finally got that to work by drawing a diagonal line across the cube face, Moving the triangle to the MID Osnap on the line then deleting the line. Yay! :smiley: Progress! :star_struck: Now … if you don’t mind …

  1. Is there such a thing as a Construction Line in Rhino6?
  2. How would I incline the base of the triangle to an edge of the cube face?

Hello- use the Between Osnap for this. Use AddGuide to add ‘construction’ lines.
Please post your file for the alignment question.


You could also set the cplane to the top surface of your cube and draw the triangle directly on the top surface and then extrude and boolean.
cube.3dm (90.3 KB)

You could also set the cplane to the top surface of your cube

Thanks dmoyes I think I am getting the hang of how to do that but it took a few videos and a couple of hours to find out what you were saying. :slightly_frowning_face:

I appreciate that you took the time and trouble to reply, but please always remember that out-and-out Rhino6 newbies like myself know absolutely nothing. I did not know that I could set the cplane to another surface.

Thanks again Pascal but I do not seem to have a ’Between Osnap’

As far as I know I am using the latest version of Rhino6. Where is this Osnap hidden?

Here is my cube with the inset triangle. I will be interested to see how you realign the triangle.
Arrowed Cube.3dm (67.3 KB)

If you hold down the SHIFT key, then you’ll see the Between option.

// Rolf