High Back Tab Manufacturing

The high back tab on the existing Mad Jack alpine model is the only component that Mad Jack Snowsports makes in house. Congruent with Mad Jack’s current production method, this component was manufactured by hand in the Mustang 60 Shop. The engineering drawing for the component is presented in Figure 51.

Figure 51. High back lock out tab engineering drawing.

This part was machined from Delrin bar stock supplied by Mad Jacks. Delrin is a highly machinable material, and therefore the team anticipated the machining process to be relatively smooth. Our goal was to make 12 total high back tabs – 5 for testing purposes, 4 for confirmation prototype assemblies, and 3 extras in the event of a mishap.

The first step was to cut the large pieces of Delrin stock to the approximate dimensions for the high back locking tabs. To accomplish this, the team used the vertical band saw and rail guide as seen in Figure 52. Because this was a rough cutting operation, we oversized the high back tab measurements by about 10 thou in all directions to allow for some flexibility.

1.50 .75 .32 .38 .20 .80 R.05 .22 .39 2x .13 .23 .48 .19 NOTE: KNOCK ALL EDGES 0.03 INCHES

NOTES MATERIAL DELRIN 500P NC010 COLOR BLACK TOLERANCES _{X.XX 0.03}X.X 0.3 P N: 1010 D : 4 30 19 C . B : D . B : A STIN GASBARRA D . : 5 T : LOCK O T TAB S : 2:1 MC P M S E S

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Figure 52. Bandsaw and rail guide used to rough cut Delrin stock.

In previous iterations of this process, we had tried to make the measurements on the block by hand and then hand-feed the stock through the vertical bandsaw. Not only was this process inefficient, but it often resulted in inconsistent and poor-quality pieces. Instead, by utilizing the scale of the rail guide and straight surface that it provided to guide our measurements and cuts, we were able to quickly and accurately cut all 12 pieces to size. The completed rough tabs are shown in Figure 53 and a close up is presented in Figure 54.

Figure 53. Complete rough cuts of the Delrin stock. Figure 54. Close up of a rough machined tab. The next step was detailed machining of the tab features. While the length and width of this sample were within the specified tolerance of the engineering drawing, the height of the sample was well outside of the indicated allowable tolerance. Furthermore, the tab still needed a step and the appropriate holes to be added for completeness. The team used the manual Bridgeport vertical mill to add these remaining features. Per the recommendation of a shop tech, a low spindle speed of 400 RPM was used due to the ease of machining Delrin. An image of the spindle speed indicator of the Bridgeport is presented in Figure 55.

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Figure 55. Bridgeport Manual Mill spindle speed indicator.

With the Bridgeport settings properly adjusted, a 7/16” end mill and appropriately sized collet was inserted into the Bridgeport spindle using the pneumatic actuator. Additionally, parallels were chosen such that the rough tab would stick out far enough above the jaws to prevent the machine from crashing during a cutting operation. The soft jaws were then brushed clean, and the rough tab clamped firmly in place. Finally, a soft tap from the mallet was used to ensure that the tab was resting properly on the parallels and projecting slightly out from the jaws. The setup is presented in Figure 56.

Figure 56. Milling set up for the high back tabs.

The zero was set for the coordinate system by touching off on the rough side of the tab cut, using

the smooth side of the tab stock as our datum surface against the opposing soft jaw. This allowed

for the increments on the hand cranks to be used to cut the appropriate indicated dimensions. Slop

in the hand crank was accounted for and mitigated throughout the process.

Since the tab length had already been verified to be within the indicated part tolerance, the team

moved straight to cutting the step out of the rough tab shape and repeated this process for all 12

tabs in the same orientation. Because this step was consistent among all tabs, it was easy to

streamline the milling process for this step feature. The feature was cut using a face milling

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process, adjusting the X and Y feeds of the mill such that material was taken off in 0.03-inch

increments until the desired dimensions were achieved. The cutting process and finished step

feature are presented in Figure 57 and Figure 58, respectively.

Figure 57. Step cutting process of the high back tab. Figure 58. Finished step on the high back tab. Once all the high back tab step features were completed, the dimensions were verified using a set of digital calipers. All 12 of the high back tabs were found to be within the tolerance specifications of the engineering drawing. The completed stepped high back tabs are presented in Figure 59. A similar verification method was used to validate all further part dimensions.

Figure 59. Completed step features on the high back tabs.

The high back tab thickness was the next feature to be milled. Using a machining process similar to that of the step feature, the team adjusted the knee of the mill to the proper Z-axis height and used a face milling process to take off the excess material in 0.05-inch increments for all 12 tabs. This cutting process is presented in Figure 60.

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Figure 60. Milling the high back tabs to the correct thickness.

Having completed the bulk dimensional machining of the tabs, all that remained was to drill the holes. To accomplish this, the tab step was clamped in the soft jaws and the mallet was used to ensure proper datum adherence against the parallels. Then, a #29 drill bit was used to drill the two small holes for the cables in the side of the tab. A picture of this process is shown in Figure 61.

Figure 61. Drilling operation on the high back tabs.

In order to drill these holes efficiently in all 12 of the tabs, the hand cranks were zeroed at the first hole position, the hole was drilled, the X-axis crank was adjusted to the appropriate dimension for the second hole, and the second hole was drilled. Upon completion of this drilling process, the cranks were reset to their original location and replaced the completely drilled tab with a new one. A similar process was used for the larger holes on the step of the tab using a #5 drill bit.

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