force can be produced using a second spring 150 having a spring constant of approximately 4 1 lbs in and which is slightly preloaded when the actuator 44 is raised the difference in spring constants also ensures that the retaining force produced by the first spring 146 is not significantly offset by the opposing force of the second spring 150 each of the springs 146 and 150 may be made from music wire suitable for providing the desired spring characteristics for example the first spring 146 may have a wire diameter of 0 125 inches an outer diameter of 0 97 inches and a free length of 1 75 inches the second spring 150 may have a wire diameter of 0 062 inches an outer diameter of 0 97 inches and a free length of 4 0 inches it should be appreciated that the particular spring constants and sizes are exemplary only and other materials sizes and spring characteristics may be used in accordance with the present invention a housing 160 is secured to each horizontal leg 110 and 112 of the front frame 38 adjacent the outer leg 36 to capture and retain the bumper biasing components as described above to the frame as shown in fig7 and 11 the outer edge of the bumper stem flange 152 engages the inner wall of the housing 160 and the flange 154 on the outer leg 36 of the frame engages the outer surface of the stem 148 to hold the stem in a horizontal position as it is retraced and extended similarly the translating link connector 144 includes a connector.