2V dome entrance design by DiscoDave

2V door front view 2V doorway right isometric
front view isometric view

The 2V dome's geometry allows the creation of a simple but strong entryway using only 4 struts:

Before After
small dome before
small doorway

The entry is made by removing the 5 short struts (black) in the interior of one of the dome's pentagons (framed by long struts in green).  Holes are drilled midway along the length of the two top struts of the now-open pentagon, allowing the installation of two new vertical elements for bracing top to bottom.  There is no crossbar at the top, there is not sufficient headroom to allow it.  I will be first to admit that this design is a compromise among simplicity, strength, and headroom; without a crossbar at the top, the strength is somewhat diminished, but there was no way to realistically include one while retaining headroom.

I could have gone with a triangular-shaped entrance for optimum strength and rigidity, but only at the expense of shoulder width.

why no triangular door?
The hypothetical triangular-shaped doorway (purple) may be stronger, but its 14" shoulder width is unacceptable.

This will require making two new struts, plus modifying or remaking two of the dome's long struts.  Compared to the 3V dome entryway project, this is a breeze!  Again, the best time to make these new struts is when you're making all of the struts for your dome.  As this design removes 5 short (black) struts and 2 long (green) ones, you may opt to make fewer of these struts (or keep them as spares.)


small labeled

(from above) name Quantity1 normalized hole-to-hole length2 bend angle for each tab3
1 short 2V strut (black) -5 0.8843
16
2 long 2V strut (green) -2 1.000 18
2* long 2V strut with hole  2 1.000 18
3 entrance side  2 1.2487 23
1As compared to the original, intact 2V dome.  A negative number (in red) means you remove those original struts (you can keep them as spares).  A positive number indicates how many of the new struts are needed to make the doorway.(back)
2As your dome's hole-to-hole dimensions may differ from mine, I am providing the spacings in relative terms, with the longest normal 2V dome's strut length defined as 1.0000.  Multiply your own dome's longest strut's hole-to-hole dimension by these factors to get the right sizes for your dome.(back)
3While not crucial, getting your bend angles correct, or close to correct, makes dome assembly much easier. (back)

The long strut with the hole

special green strut
The upper two vertices of the entrance are made by drilling a hole into two of the dome's long struts.  The hole's position is halfway along the length between the holes in the end tabs, and is oriented in the same direction.  As in the 3V case, drilling a hole in a strut will naturally weaken it around that spot (stresses are concentrated ~ 3X in the vicinity of the hole), so it's a good idea to remake these two struts out of larger diameter tubing.  In 2002 we used 1" EMT conduit to build the regular dome struts and 1" EMT for the drilled pieces (1" EMT is 2 times stiffer and twice as strong as 1".)  They have stood up to the abuse over the years exceptionally well.