Remove Plot Margins in ggplot2

I'm trying to produce a png chart using ggplot2 and ggsave (with Cairo) in R. I'm having an issue with customising the theme to remove margins. Currently I'm using: ``` ... + theme(plot.margin=unit(c(0,0,0,0),"mm")) ``` This seems to work for two out of four sides of my plot, it removes the top and right hand side margin completely, but there is still a fairly large margin on the left and bottom sides. Is there a way to completely remove these? Image below to illustrate the problem: If a reproducible example would be useful then let me know and I'll put one together. Edit: ``` library("ggplot2") library("scales") library("Cairo") library("grid") # Set chart values line.width = 0.45 axis.font.size = 2.9 # Generate some random data start.date <- as.Date("2011-07-01") x.month <-seq.Date(start.date, by = "month", length.out = 24) end.date <- max(x.month) period.a <- rnorm(12, mean=50, sd=2) period.b <- rnorm(12, mean=55, sd=2) x.value <- c(period.a,period.b) # Combine into dataframe x.data <- data.frame( "Month" = x.month, "Value" = x.value ) # Build chart p <- ggplot(data=x.data, aes(Month, Value)) + geom_line(size=line.width) p <- p + theme_bw() p <- p + scale_y_continuous() p <- p + scale_x_date(limits=c(start.date+20,end.date-20), breaks = "1 month",labels = date_format("%b-%y")) p <- p + theme(axis.text.x=element_text(angle=90, hjust=1, vjust=0.5, size=axis.font.size), axis.text.y=element_text(size=axis.font.size), axis.title.x=element_blank(), axis.title.y=element_blank(), plot.margin=unit(c(0,0,0,0),"mm"), plot.background = element_rect(fill = "grey"), panel.grid=element_blank(), panel.border=element_rect(size=line.width/2), axis.ticks=element_line(size=line.width/3), axis.ticks.length=unit(0.3, "mm"), axis.ticks.margin=unit(0.2, "mm")) ggsave(file="c:\\temp\\test.png", plot=p, width=40, height=15, units="mm", type ="cairo-png") ```