The old DesignSpark Mechanical forum where I posted quiet a few "Tips and Tricks" has completely disappeared.
It seems that this company doesn't care of their customers and have no respect to the people that contributed there, which is a BIG SHAME !
Because of such an inacceptable attitude, I won't write anymore tutorials about DS Mechanical and invite you to use other softwares.
I will let you know which other alternatives you have.

In this little tutorial I'm gonna show you how to import a STEP file in DSMech for further modifications.

You will need to have the following apps installed :

And for the SketchUp part of that tut you will also need Jim Foltz's STL import/export plugin.

Let's start...

You have a STEP file that you would like to import in DSMech for further improvement or modifications.
DSMech can import STEP files but unfortunately the imported geometry is locked and can't be modified...
But DSMech can also import SketchUp files (.skp) and deals very well with them. They are seen as "solids" and can be modified with the DSMech's powerful tools.
So the idea is to make a SketchUp file out of your STEP file.

SU doesn't import STEP files but can import STL files with the help of a plugin.

For that tutorial I downloaded a STEP file from www.te.com and I choose this one.

Part 1 : making an STL out of your STEP (FreeCAD)

There's several apps that will eat a STEP and shit out an STL. One of them is FreeCAD.

1 - Open your STEP file in FreeCAD

2 - Convert your solid into a mesh

3 - Choose your tesselation settings

4 - Export as STL

Part 2 : making an SKP out of your STL (SketchUp)

5 - Import your STL in SU (you will need Jim Foltz's plugin)

6 - Select all (CTRL+A) and Make Group

7 - Check it's a solid and Smooth Edges

8 - Save as a SketchUp file (.skp)

Part 3 : modify your model (DSMech)

9 - Open the SKP file

It is now seen as a "solid" which means you can now modify the design...

10 - Bring your modifications to the design

Et voilà !

I hope you liked this tutorial...

Edited 29/04/2014

As mentioned by Didier in the comments, there's a much easier way !

  • import your step design in DSMech
  • create a new solid (a cylinder for ex.)
  • right-click on the top-most assembly name in the tree
  • unlock

You should now be able to modify your imported step geometry !

Thanks for this tip goes to Didier from Tours's Funlab (France).