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Tolerances for quality-control testing

Once your viewer prototype is die-cut, examine it to ensure it meets all specifications within allowed tolerances. Measure critical dimensions and tolerances, and inspect alignment of parts as well as the overall construction of the viewer.

The sections below explain the various specs and product tolerances for each part of the Cardboard viewer. For easier distribution within manufacturing teams, you may also find it useful to download the full Cardboard Manufacturers Kit of specifications and tolerances.

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Corrugate tooling

Verify the critical dimensions for the corrugate tooling (e.g. die-cuts) before proceeding to production.

Critical dimension tolerance

Parameters Value Unit Diagram detail
Distance between two fold lines defining the thickness of Cardboard chassis 40 (+/-0.5) mm A, C
Distance between the centers of lens holders (IPD) 64 (+/-0.5) mm B
 

From left to right. Critical “A” and “B” dimensions on the Cardboard “t-shirt” part. Critical “C” dimension on the Cardboard “chassis” part.

Lens verification

To ensure the best possible user experience, it is vital that established tolerances be respected for Google Cardboard lenses.

Lens measurement tolerance

Inspection item Tolerance Unit
Center thickness 8.794 +/- 0.1 mm
Lens diameter including tabs 40.0 +/- 0.1 mm
Lens diameter without tabs 34.0 +/- 0.1 mm
Lens tab thickness 1.65 +/- 0.1 mm
R1 surface form (figure error) < 10 µm
R2 surface form (figure error) < 10 µm
R1 surface roughness (angstroms RMS) < 0.05 µm
R2 surface roughness (angstroms RMS) < 0.05 µm
Surface decenter < 20 µm
Surface tilt < 20 arcmin
Surface quality (scratch/dig) 160 / 50  

Lens visual verification

After receiving the lens first articles and verifying that the tolerances from the table above are respected, you need to perform visual lens quality checks for any surface distortions, blurry areas, blemishes, etc. Common lens surface problems arising from manufacturing process issues like incorrect cooling/cycle times can be detected by “sliding” the lens over a high-contrast straight line and visually inspecting for any distortions.

The image on the left is a good lens, while the image on the right - bad lens (notice the wavy distortions of the straight line on the lens surface). Here’s another example:

When inspecting your lenses, yours should look like the image on the left, not the right.

Assembled first article

Inspect the first articles of the fully assembled viewers to ensure that these critical tolerances are respected.

Conductive strip specifications

Parameters Value Tolerance Unit Note
Distance from the back surface to the screen (see picture below) 37.3 +2/-0.5 mm D
Distance between the centers of lens holders 64 +/-0.5 mm B

 

Measure the distance between the back surface to the screen of the viewer.

Cardboard layer alignment

There are a number of criteria which should be met when reviewing your Cardboard layer alignment:

  1. All layers of cardboard lens cutouts should line up and the outlines should have <1 x E-flute thickness of misalignment. Lens tabs should not be visible.
  2. Button side flaps should have <0.5 x E-flute thickness misalignment, as it’s critical for the button travel distance. If the units are assembled manually, the button side flaps should be aligned first.
  3. The bottom seam of the cardboard (next to the rubber band) should not have a gap of more than 1 x E-flute thickness. Very importantly, that gap should be even across the seam and should not be tilted/wedged.
  4. Layers with phone-facing apertures should be securely glued together.
Button functionality

Buttons allow users to easily interact with Cardboard-enabled apps. In order to provide a great consumer experience, you need to ensure that your viewer button works properly.

  1. Various parts of the “hammer” should not come unglued. This can happen when the assembly stage takes too long and the glue dries up, or from not applying sufficient amounts of glue.
  2. The button should be easily pushed down. After releasing it should spring back.
  3. The conductive pillow should be centered within the phone-facing apertures, and the bottom edge of the conductive pillow should be lined up with the corresponding cardboard edge.
Velcro alignment

All 6 velcro pieces should be present and should be >95% aligned. Here is an example of velcro that does not meet alignment criteria:

 

Upon closing and re-opening the velcros, the PSA should not start peeling off from the cardboard.

Additional quality checks
  1. There should be no exposed glue or tape showing from the cardboard edges.
  2. The viewer should not have any false scores.
  3. The lenses should be free of contamination, such as glue, velcro loop/hook pieces, cardboard chips or other debris.
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