[CentOS] tcl font size issue on centso 4.4 x86_64

I have a simply script that I cannot get a font size bigger than 40. 
Changing the font_size value to 80 does not make
the font any bigger just the background.

How do I get a bigger font than 40?

I run this script as "wish -f file.tcl"

What am I doing wrong to not get bigger fonts?

THanks,

Jerry
---------------------------------------------
set font_size 40
set show_window_title 0
set disable_window_decorations 1
set screen_width [winfo screenwidth . ]
set screen_height [winfo screenheight . ]
set window_x 0
set window_y 0
set my_message "This is my message..."

wm geometry . ${screen_width}x${font_size}+${window_x}+${window_y}
wm overrideredirect . $disable_window_decorations

font create ourFont -family helvetica -size $font_size
set c [canvas .c -height $font_size -width $screen_width -background 
black -highlightthickness 0 ]
pack $c
$c create text 10 4 -text $my_message -font ourFont -anchor nw -fill red
~
~