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                                                                                                                          Figure 1: First iteration ball holder                                   Figure 2: Soft Ball Cover

        One of the initial problems identified was how to constrain the ball while trying to remove flash.  The first iteration design intended to create a cup-like ball holder that had the pins that leave the flash on the golf ball to hold it in place.  This bottom piece would have a wide flange that would be able to be bolted down, as well as have spherical features that would allow a soft 3D printed cover to be stretched over to further hold the ball in place.

                                                                             Figure 3: Load Cell Ball Holder                         Figure 4: Load Cell Base                     Figure 5: Alignment Tool      Figure 6: Load Cell Ball Holder Assembly

        The load cell ball holder design was intended to help measure and take data that related pressure, RPM, and bit material to the quality of the flash removal.  However, this design did not work because the load cell was not precise enough and experienced errors in reading because it was operating at forces well below what it was rated for, therefore the data experienced a lot of error due to the instrument not operating in its "sweet spot".  The integration of the ball holder and the bottom load cell base also caused problems; the contact between the upper ball holder part and the load cell base resulted in instability and wobbling, which is unacceptable when dealing with such tight tolerances.

       Figure 12: Friction Drive System (Bottom View)                    Figure 13: Friction Drive System (Top View)

It was believed that in order to eliminate these issues, the 6 probe system design idea was eliminated while 3-axis rotating stage was included in the design in order to meet the requirement of being able to buff out all of the flash. In order to determine the amount that the stage must tilt, the angle between the center pentagon, flash-containing dimple and a hexagon, flash-containing dimple is determined below to be 18.8 degrees.

                                                                                                                       Figure 14: Side View of Golf Ball                                     Figure 15: Calculation Angle Between Center and Hexagon Flash

    However, since the stages that are able to tilt in 3-axis to this degree, freely rotate and tilt instead of having discrete positions, a device is required that would constrain the stage to the necessary positions. As a result of the project deadline quickly approaching, it proved to not be feasible to design and construct this constraining device with the desired tolerance in the necessary timeline.

The dimple location solution that was implemented into the final design solve the issues presented by the 6-probe system and the rotating stage. The locator functions by placing it into the slot that is on the side of the ball holder. The ball is then rotated in the holder until the pin at that is on the dimple locator is positioned in the flash containing dimple. The locator is then removed and the desired dimple for buffing is now perpendicular to the XY plane and facing in the positive Z direction. This positioning allows for the end bit to be lowered easily onto the dimple. This dimple locator was 3D printed using Vero Clear as the material and the Connex3 Object350 as the printer.

Determining Optimal Depth:

An imperative factor of the final design is determining how much to lower the end bit such that desired buffing would occur. The suggested method for identifying this depth would be to determine the ideal force that the bit must apply to dimple for this optimal buffing and then lowering the end but until the bit is exerting this force.

The initial proposed solution would ascertain the optimal applied force and maintain this force continuously throughout the buffing process through the use of a closed-loop system. In this system, a load cell would be placed under the golf ball, as shown in figures below,  and communicate to the CNC machine the force that the bit is applying to the dimple. Based off of the force reading, the CNC machine would then lower or raise the bit to ensure that the optimal force is being maintained.

     Figure 16: Ball holder with an integrated load          Figure 17: Ball holder with integrated load cell

                        cell in bottom piece                                                 with top and bottom pieces

This proposed solution failed for multiple reasons. The first reason is that the attempts to integrate the golf ball holder with the disk load cell such that the golf ball would only be in direct contain with the load cell and not have any friction, which would be caused by the golf ball holder being pushed down with the golf ball, impact the force measurements caused there to be a gap between the top and bottom piece, as shown in Figure B.3.2. The presence of this gap led to the top piece, which is solely balanced on the load cell, wobbling from side to side and preventing the ability to take an accurate measurement. Additionally, the tolerance of load cell that was bought may be too high to determine changes in force that would be associated with minuscule alterations in depth. Since the tolerance for the tube height, which is the height from the bottom of the dimple to the top of the tube, is 0.0003 inches, it is necessary that the load cell be able to detect these very small changes in force with a high level of accuracy and precision. It is unknown what tolerance is needed for the load cell for the correct depth to be determined from the force. Designing and performing a test to determine this information would be an arduous and time-consuming task that may show that the necessary tolerance is either not feasible to achieve with current load cells or is only feasible with load cells whose exceed the budget. As a consequence of these issues with integration and tolerance of the load cell, the proposed solution was replaced with a solution that was predicted to be more feasible.

This new solution involved determining the optimal force and depth through the use of a scale. A scale would be placed under the ball holder device. The end bit would then be lowered until the scale perceived a chosen force being applied onto the dimple by the bit. The buffing process would then be initiated at this height. This process would then be repeated until an acceptable sample size of 24 balls was obtained. The tube heights would then be measured using a 3D profilometer and an average tube height would be determined. The difference between the average tube height from the test and the acceptable tube height would be established, and from this difference, the depth that the bit would have to reach to eliminate this difference would be determined. The bit would then be lowered to this depth each time during the flash removal process, and this would ensure that the optimal force and depth that would ensure that the final tube height is within the tolerance would be used during the buffing process. However, a problem arose with this solution as well.

The solution involving the scale failed due to the fact that the dimples deform when force is applied to them. This failure is due to the fact that the buffing process will be implemented before the balls are hardened in the cross-linking process; consequently, the balls continuously deform under applied force and, as a result, do not allow for a consistent force reading to be taken on the scale at a certain end bit depth. Due to the reality that the force that the bit exerts on a dimple is not stable at a certain depth, it is not possible to infer how force between the bit and dimple varies with end bit depth. Therefore, it is not possible to ensure that buffing occurs at the chosen force during testing, and, as a consequence, the scale method is ineffective.

Figure 18: Ball Holder on Scale Risk Reduction

The current solution avoids using force to determine optimal depth by buffing each dimple at a chosen depth. During testing, the buffing process would be initiated at a chosen height instead of a chosen force for a sample size of 22 balls. The rest of the process for determining the optimal depth mirrors the scale process closely.  An average tube height of the buffed dimples is determined using a profilometer. The difference between the average tube height from the test and the acceptable tube height is then ascertained, and the depth that the bit would have to reach to eliminate this difference is determined. This determined depth is the optimal depth.

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