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Quincunx Demonstrations

Quincunx Demonstrations

.: Quincunx Demonstrations :.

The uses of a Quincunx are only limited by the ingenuity of the instructor. Once you use a Quincunx and see how effective it is in communicating statistical concepts, you'll never teach without one. The following is a sample of the types of demonstrations that are possible:


Can statistics really predict an outcome based on a sample? Demonstrate this by running a sample of 35 beads, calculate the mean and standard deviation and predict the six standard deviation limits. Try taking bets with the trainees that the next 100 beads will fall between the six standard deviation limits calculated. Run the next hundred beads and collect your bets.


Draw specification limits on the face of the Quincunx at the 5th and 20th column. Set the funnel to the left or right and demonstrate how a certain percentage of the measurement will fall outside of the specification. Now center the funnel and repeat the experiment. Watch the light bulbs go on with your students as they begin to understand the concept of centering a process' and how it could apply to their own processes.


This demonstration is as effective with machine operators as it is useful in showing management how they are part of the problem. Point out current random sampling techniques that have been determined by your company. i.e. check every 20th piece, every half hour, twice per shift. etc. Set up the Quincunx as in the process centering demonstration and shift the funnel near the upper limit. Point out how many operators run to the side of the tolerance so they can reduce scrap (you can always rerun the part if it is oversize but it is scrap if its undersize). Drop 19 beads then drop the 20th bead representing the inspected part and note whether it falls inside or outside the specification. Repeat the process five or six times. Chances are every bead checked will be inside the specification with about 10% of all the other beads being outside the tolerance. If a bead does falls outside the tolerance during one of the checks remind the student that most operators would run a second piece before adjusting the process. This demonstration drives home the reason why operators who are instructed to use random sampling techniques have trouble maintaining tolerance specifications.


Close the top gate on the Quincunx and without moving the funnel run and plot samples of five beads on an average-range control chart. Calculate and plot the control limits on the chart just as if the quincunx were a machine. After creating the control chart move the funnel and plot another sample of five parts. Students will be amazed how quickly they can detect a shift in the funnel which is analogous to a change in the process. To carry the point a little farther tape a piece of paper over the funnel portion of the Quincunx and then randomly move the funnel to different directions and let the trainees guess whether the funnel has been moved or not based on their control chart plot. This technique is very helpful in building confidence in the value of control charting. Another point can be made by sliding the funnel completely to the right and allow the beads to drop directly onto the pins. Plot another sample of 5 beads and demonstrate how the range portion of the chart detects an out of control condition. This erratic behavior is analogous to machine conditions where bearings are worn, fixtures are loose, etc.


Run a sufficiently large sample to accurately calculate or predict the six standard deviation range. Mark the tolerance limits and pre-control lines on the face of the quincunx with the appropriate tape or transparency marker. Drop a series of beads with the funnel centered and demonstrate the decision rules of the pre-control plan. Move the funnel to the left or right and show how pre-control would re-center the process.


The WD-5, WD-6, and WD-7 models have a narrow distribution pin block for demonstrating the effect of process improvement. Since it has less variability, the control chart demonstration will have a smaller range and consequently tighter control limits.

QT-5 "The Quincunx and Statistical Training"

The above described demonstrations and more are all described on our QT-5 Audio CD. This CD, which lasts over an hour, is one of our customer's favorites. Trainers keep telling us that it is a real help in getting them to understand the power of the quincunx to illustrate the principles of variation and the need for quality improvement.



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