Triangles? Draw the cross members instead.

Instead of looking at the part as a series of symmetrical, triangular holes; Look at it as a big, rectangular hole broken up with a series of parallel cross members (ribs).

Instead of drawing (and trimming) all the edges of all the triangles, just draw a single line for the center of a rib, and then use the CAD tools (such as mirror and pattern) to duplicate the ribs.

  1. Step 1:

    Here's the part:

    Do you see triangles?    Do you see cross-members?

  2. Step 2:

    Start with a sketch of the outside shape

    and make an Extruded Boss/Base

  3. Step 3:

    Cut out the big hole in the part.  Since this part has a member right down the middle, I sketched half the hole and mirrored the cut.

  4. Step 4:

    For the first cross member, just sketch a single line at the center of the member. Dimension the line to be 60° so it's symmetrical. The length of the line isn't important, as long as it extends beyond the part.

    Use the sketched line to make another Extruded Boss, using the Thin Feature option to define the width of this member.

    And mirror it for a second member:

  5. Step 5:

    And now we can pattern the two members across the remainder of the cutout holes using the pitch distance and number of members.  Don't worry if pattern goes too far.

  6. Step 6:

    The final step is to trim off the excess members. Just use Sketch1 for the profile of an Extruded Cut.