A router is used to cut locating notches on a printed circuit board. The vibration level at the surface of the board as it is cut is considered to be a major source of dimensional variation in the notches. Two factors are thought to influence vibration:

bit size (A) and cutting speed (B). Two bit sizes ( 1 16 and 1 8 in.)

and two speeds (40 and 90 rpm) are selected, and four boards are cut at each set of conditions shown below. The response variable is vibration measured as the resultant vector of three accelerometers (x, y, and z) on each test circuit board.

Replicate A B Treatment Combination I II III IV

− − (1) 18.2 18.9 12.9 14.4

+ − a 27.2 24.0 22.4 22.5

− + b 15.9 14.5 15.1 14.2

+ + ab 41.0 43.9 36.3 39.9

(a) Analyze the data from this experiment.

(b) Construct a normal probability plot of the residuals, and plot the residuals versus the predicted vibration level.

Interpret these plots.

(c) Draw the AB interaction plot. Interpret this plot.

What levels of bit size and speed would you recommend for routine operation?