Putting everything together

1.

The back shell of our yoyo in the two images above is a relatively simple part.  The distinguishing features are the text on the outside, and the bevel on the inner diameter.  This allows the holder part to be press fit into the back shell.  We didn’t encounter much difficulty with this part, as it is very thick and did not experience much shrinkage.

Front and back views of the holder part.  Each yoyo has a pair of these, one on each half.  The nut in the center holds the shaft that connects the two halves.  This part went through a number of design changes.  It has to be able to press fit into two different parts, the back and front pieces of the yoyo, and must be very precisely sized.  In our first iterations, the ring around the edge was too thin, and was unable to hold a tight press fit.

The front filler piece is the front part that attaches to the holder.  The inner cavity is very similar to the corresponding back shell, as it has to fit the same piece.  The front surface is patterned with Mike’s eye, horns, and teeth.  The horns and teeth poke out through holes in the front outer shell.  This part didn’t see a lot of re-designs, as long as we kept it consistent with the back piece.

The gap between Mike’s teeth.  This part press fits in between the two rows of teeth.  Despite its unusual geometry, this was one of the easiest parts to design – our first mold design worked perfectly, once we tweaked the cooling time to make it fit properly.

The front shell is Mike’s face.  You can see the holes for the mouth, eye, and horns.  The inner diameter is sized to press fit around the inner fill.  The most notable feature is visible in the second picture – the thermoformed eye fits in the center hole, where it is held snugly in place by the pressure of the press fit and the ring that surrounds it.

This bit of transparent thermoformed plastic is Mike’s eye.  It is sandwiched inside the front shell and front fill pieces, held in place by the pressure between them.

Here he is, all put together.  This isn’t quite the final version – it’s the wrong color, and our fully assembled Mike has a sticker inside his eye for the pupil and iris – but the dimensions and parts are all the same.

2.

General Parameters	Parameters of Interest	Specifications	Measurements
Length Dimensions	Diameter	2.3 in	2.289 in
	Width	1.26 in	1.266 in
	Gap Width	0.15 in	0.16 in
	Height of Oscillations	2.5 ft	2.5 ft
Mass Dimensions	Mass	0.12 lbs	0.12 lbs

Our specifications were generally on-target.  Due to material shrinkage, the diameter is slightly smaller than the one specified.

3.

We manufactured 112 holder parts during our production run, with an average diameter of 1.7187 inches. As shown in figures 1 and 2, the process was well within control limits, and displays no trends that indicate a problem with the process. With a standard deviation of 0.000369 inches and a tolerance of +/- 0.002 inches, the process capability is measured to be 1.807. This value is high enough to be satisfactory.

R-Bar control chart for the Holder part

X-Bar control chart for the Holder part