Segue CMR.

library(latticeExtra)

Parts$Sample <- factor(Parts$Sample,
                       levels = unique(sort(Parts$Sample)))
str(Parts)

nlev <- function(x) nlevels(droplevels(x))

resizePanels(
    bwplot(Diam ~ Sample | Machine,
           data = Parts,
           pch = "|",
           layout = c(NA, 1),
           scales = list(x = list(relation = "free")),
           par.settings = list(
               box.rectangle = list(col = 1, fill = c("gray70")),
               box.umbrella = list(col = 1, lty = 1))),
    w = with(Parts, tapply(Sample, Machine, nlev)))

À disposição.

Walmes.