Plot frame border to start at zero?

Hello,

I am creating plots of hourly precipitation and accumulated precipitation
(on different axis, see attached image). I was wondering how can I have the
plot frame (black border) start at zero, it looks like it is plotted less
than zero?
The code I use to create the png files is below:

CairoPNG(PNG_file,width=1000, height=600, pointsize=14, bg="white")
? ? ? opar <- par(mai = c(.8, .8, 1, .8)) ? ?# Set margins
? ? ? plot(ppt,type="h",col="dark grey",ylim=c(0,max_ppt+1), lwd=6, xlab='',
ylab='', main=title, frame.plot=T, axes=F)
? ? ? axis(2, col="black", las=2)
? ? ? par(new=T) # R to overwrite the first plot
? ? ? plot(accum, type="l", col="blue", axes=F, ylab='', xlab='', lwd=2)
? ? ? axis(1, col="black", las=1)
? ? ? axis(4, pretty(c(0, max_accum) ), col="black", las=2)
? ? ? legend("topleft", legend=c('Incremental', 'Accumulated'), ?col=c("dark
grey", "blue"), lwd=c(6, 2.0))
? ? ? legend((length(n)-4),max_accum, legend=paste(round(max_accum,2)),
bty="n", cex=.90) ? ? ### max accum location
? ? ? mtext(paste("Lat:", .lat, "Lon:", .lon), cex=0.95)
? ? ? mtext("Index Hour", side=1, line=2)
? ? ? mtext("Incremental Precipitation (in)", side=2, line=2.5)
? ? ? mtext("Accumulated Precipitation (in)", side=4, line=2)
dev.off()


Thanks for all your help,
Doug

---------------------------------
Douglas M. Hultstrand, MS
Senior Hydrometeorologist
Metstat, Inc. Windsor, Colorado
voice: 970.686.1253
email: dmhultst at metstat.com
web: http://www.metstat.com
---------------------------------