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Manufacture of a cardboard dome of packaging


First of all get back boxes of packaging, dismantle them and put them flat.
Those that I used suit perfectly:
- Cardboard doubles layer 6,5 mm in thickness,
- For a dome of 65 cms of radius and 160 degrees of opening, are needed 8 parts of 91x49 cm.

It is an approximation of a sphere,
in the form of umbrella.
It consists of 8 slices
Every slice can be made with cardboard
or quite other flexible material.

The dome can be a complete hemisphere (opening 180 degrees)or not. Mine has a 160 degree opening (less cumbersome, but with a satisfactory immersion).

- Calculation of a slice
 It is necessary to realize at first a strong paper "pattern".
As the slice is symmetric, we fold the paper in two in the lenghtways.
We use the software compaCoupole ( see farther ) to obtain the dimensions of the slice.

Calculation of the pattern of a slice of dome:

  Number of slices :      8 
  radius of dome   :     70 cm
  opening of dome  :    160 degres
  length pattern   :     98 cm
  width  pattern   :     53 cm
  size      	   :    138 cm


  x=  0.00   d=  0.00  
  x=  9.77   d=  3.73  
  x= 19.55   d=  7.38  
  x= 29.32   d= 10.90  
  x= 39.10   d= 14.20  
  x= 48.87   d= 17.22  
  x= 58.64   d= 19.91  
  x= 68.42   d= 22.21  
  x= 78.19   d= 24.08  
  x= 87.96   d= 25.48  
  x= 97.74   d= 26.38

Example of output of the software compaCoupole
Put back the values of x and d on the pattern.

Cut the pattern, then, by means of this one, cut 8 slices from the cardboard.

- assembly
Build a temporary square frame of dimension equal to the size + twice the thickness of the cardboard.
Important trick : not to bend the flat broke cardboard, it leaves visible folds. But wet generously the external face with a toweling. After some minutes the cardboard takes friendly the adequate curvature.
Other important trick : keep cool !


 Collect 4 extremities and

fix them with an adhesive tape.


Make the middle of the slice coincide

with the environment of the frame.


Fix temporarily with an adhesive tape.
Remove a slice,

then stick edge to edge

slices one to one.


Stick with some wood glue (white)

or with some glue on the néoprène.


Maintain in place with an adhesive tape.

Once the glue dries, the square frame can be replaced by a frame with a U shape.

Then we paint the inside.
I used a white and mat painting for internal woodwork.
It would seem that a light gray gives a better impression of contrast.

- Improvement of the dome shape

The plan (above to the left) indicates us two things:
- The user faces the bottom of the dome. It is thus necessary to us to look particularly after this zone.
- In the low part, the projection arrives in a tangentielle way (while it is perpendicular on the high part). The defects of the screen will thus be amplified in the low zone.

We improve easily the sphericity of the dome by increasing the number of slices
- I added 4 slices of 1/16 ème, (blue on the plan)
- Then two slices of 1/32 ème (red on the plan)
These supplementary slices are calculated in the same way with the software compaCoupole.
They are realized with strong paper (drawing paper for example) capable of bearing} the glue and the painting without crinkling. We position them by hand and we draw their outline on the dome. We coat the edges of néoprène glue (the wood glue is too liquid), as well as the corresponding part of the dome. We let dry approximately 5 minutes before sticking.
Then we paint.

 - Small software of calculation compaCoupole
 Download the program compaCoupole for Windows.
Download the code source C++ . It is very simple.

 User manual:
question
answer
internal radius =
Type the radius of the "ideal" sphere in cm, then press Entry
degree of dome opening (160/180) =
180 for the complete hemisphere
Number of slices (8/16/32) =
8 for the basic dome, 16 and 32 for joins
Number of points has to calculate =
Approximately 20 (everything 5 cms)
create a file \\comPanrama\\coupole.txt ? (y/n) =
"n" output only on the screen
"y" create a printable file