Creating "Real" Drill holes for clean Step Export

Hi everyone,

we created a lot of Step File for Sheet metal production using Rhino Common.

Our general approach was:

  • extrude a Profile Curve as an Extrusion
  • change it to a Brep
  • select an Extrusion from the document
  • change it to a Brep too
  • cal the Boolean Difference from both.

If we export this File as a STEP file, the cut in drill holes are not “real” holes, but made out of two Half Circles (red an cyan)
The Edge curve is not a circle, nor an ARC

Other Software packages can’t detect these holes to be drills - which raises the question.

How can we create “REAL” Round Holes and “Revolved” Holes through Rhino Common

Not sure if this example is actually better - but the edge curves are ARCs here. This was created by the “_roundHole” command. Still the edges are split though.

This is an Example of a STEP File created by Inventor:

It’s one Surface and 3 Arc Edges (also not a circle)


@chuck, it this anything you know about?

I think STEP export splits closed surfaces because back in the day some
programs couldn’t handle them. I’ll see if it’s easy to change that.

There will be an option in v6 STEP export to split closed surfaces or not.

Hi Chuck,

What do you mean by “will be” - will be in the next WIP release or will be in the final V6?


Hi Martin,

I made the necessary changes to the low-level export code already. Someone else will be adding the option to the export dialog. Once that happens you will be able to change the behavior. I assume within the next week or two.

Great! Thank you!

  • Martin

Looks like it’s in this week’s build. Please try it out and let me know if it does what you expect.