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| SOP's for the
NCMR Catapult |
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SOP's are Standard Operating Procedures. They should be
required reading for anyone conducting Six Sigma training. These
SOP's were gleaned from hundreds of courses taught by multiple
Master Six Sigma Black Belts and provided to you by NCMR Company
LLC for your use. These and other items are contained in our
publication available elsewhere in this site. We strive to
create a successful learning experience and this can only be
done with the proper knowledge and well designed equipment.
Shooting Techniques: Release motion - "As the arm
is released, the operator should take care not to jerk and
change the release point.
Shooting Techniques: Release technique - "The operator should use a smooth and consistent release technique. Don’t drag the fingers over the arm, or jerk as the arm is released. Some teams have added very elaborate mechanisms to aid the grip and release."
Shooting Techniques: Pull back angle measurement -
"The pull back angle is critical. A one-(1) degree shift in the pull back angle may change the shot distance one foot or more. Some teams have used spacers to ensure a consistent pull back angle. This is fine for that pull back setting, but if the angle changes, a new fixture is needed."
Shooting Techniques: The fear factor - "Often the techniques used by the operator change in subtle ways. Be sure the operator is comfortable with the sequence of activities and executes the shooting action in the same manner each time."
Shooting Techniques: Ball placement in cup - "Place the ball in the cup gently, without pressing. On some Catapults, the ball fits tightly in the cup creating a suction that may change the impact point by more than two feet."
Shooting Techniques: Grip - "The operator should carefully grip the cup in the same way each time. Various grip methods have been used such as holding the edge of the cup, holding the arm, holding the wing nut behind the cup, or having one finger over the arm just below the cup. The grip we have found to be best is holding the sides of the arm between the thumb and index finger."
Measurement Techniques: Distance - "The team should use a tape measure to estimate downrange distance."
Measurement Techniques: Ball impact location - "The ball impact location is very difficult to estimate. The team should use a mechanism that yields a positive indication of the impact location. Various methods have been used. Balls have been dipped in water, graphite and powder. Each of these would leave a mark on the floor. We prefer to use aluminum foil in the landing area. The ball makes a nice dent on impact. Each mark can be labeled for future reference."
Measurement Techniques: Ball impact elevation - "The Catapult can be shot from the floor, but we prefer to shoot from a tabletop. The ergonomics are better and it is easy to secure. The ball can be shot down range to another tabletop, or to the floor. We find it better to shoot from a table to a location on the floor. The impact is more vertical, and the impact point is easier to identify."
Alignment Techniques: Arm in slot - "After the Catapult has been used for a while, the space between the sides and the arm can grow. Shot variability increases as this spacing grows wider. Teams frequently place shims between the arm and the sides, or lubricate this area by using powder. The slot width can be adjusted by loosening the screws on the base. Place papers against each side of the arm and adjust slot width. Then remove the paper."
Maintenance Hints: Alignment Techniques: Rubber band nicks/cracks -
"The team should inspect the rubber band frequently. Small nicks and cracks do influence the shot distance. Crack propagation occurs quite rapidly. Before the rubber band breaks, though, changes occur in the shot distances. If the rubber band is changed, shot distances will change significantly. Exercise the new rubber band by extending it fully 50 or more times before conducting your experiment."
Maintenance Hints: Bumper pad - "When released, the arm impacts a rubber pad. This pad takes a lot of punishment. A groove forms. Cracks in the pad start in the back, and the shot distance will drift long before the cracks propagate to the front and become visible. The team should carefully monitor the state of the pad. If the pad is changed, the shot distances will change significantly. To seat the new pad correctly, you should impact it 50 or more times by pulling back and releasing the arm."
Stability: Mounting - "The Catapult should be attached firmly to the mounting surface. If the Catapult is placed on a table, use a c-clamp to hold if firmly against the table surface."
Stability: Table Creep - "Be sure the table doesn't creep forward or backward as shots are taken. Very small changes in table location can change the down range shot location by several inches."
Stability: Table Stability - "Be sure the table is reinforced and rigid in construction. Flexible tables that move during shooting can influence shot distance."
Rubber Bands: Stretching - "If the arm is held in
an extended or stretched position for a long period of time, the
tension in the rubber band will relax. If the pull back time is
increased from 5 seconds to 1 minute, the shot length may
decrease by one foot. The operator should hold the arm back for
a given period of time."
Rubber Bands: Heating - "The shot rate also affects shot distance. Heat is produced if you shoot several shots per minute for an extended period. If you then stop for a while, the next few shots may be longer than before by several inches. Establish a warm-up procedure before shots begin."
Rubber Bands: Linearity - "The rubber band is a non-linear elastomer. Tension does increase as pull back angles increase, but not in a completely linear manner."
Rubber Bands: Tower pin - "As the arm is pulled back, the pin in the tower will begin to turn, allowing the rubber band tension to change. The pin often turns for up to 5 seconds after the arm is pulled back. The operator should hold the arm back for a given amount of time. We prefer to use a hold back time of 3 seconds after reaching the final pull back angle."
Rubber Bands: Placement - "The rubber band should pass over the tower pin without binding. It should be aligned before each shot."
Rubber Bands: Centering - "The team should identify the center of the rubber band and place it carefully over the wooden peg at the front base of the tower."
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