Shape Measurement Basics     Accurately Scan A Thin Object

Step 1 – Attach Spheres to Object

Use glue and pliers to attach BBs to part. Here are important notes regarding attaching spheres:

  • Ensure that the BBs are attached securely, so that they do not shift. Test by trying to wiggle each sphere after the glue is dried. If you detect movement, remove and start over on that BB.
  • Place the BBs on the edge of the object, so that they are clearly visible from both sides. Be careful that the BBs are located so they do not touch the table or fixture when you set the part down. If the BBs touch when you set the object down, they will move causing less than optimal results.


     

Important notes regarding sphere selection:

  • Spheres should be opaque. Avoid translucent spheres, such as ping-pong balls.
  • Spheres do not need to be precisely spherical for this method. We are using geometry based alignment in this example. Other processes may require a precision sphere.
  • Spheres should not be too heavy. If they are too heavy and not properly secured, they can shift when repositioning the object. Heavy balls can also cause flexible objects to change shape.
  • Spheres should be the appropriate size.
    • Tele Lens. Use balls that range in diameter from 0.13” [3.18 mm] to 0.25” [6.35 mm]
    • Wide Lens. Use balls that range in diameter from 0.25” [6.35 mm] to 0.63” [15.9 mm]

Suggested spheres:

  • BB gun BBs – 0.177” diameter (copper coated steel)
  • Airshot ’s – 6mm diameter (non-translucent, biodegradable model is best)
  • Wooden craft spheres – available in many diameters
  • Precision steel ball bearings – available in many diameters