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.: Quincunx Demonstrations
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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.
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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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