String concatenation problems

#! /bin/csh
set tt=12345_UMR_BH452_3_2.txt
set rr=`echo $tt | cut -d_  -f1`
set rr1=welcome
set ff=$rr $rr1
echo $ff

why $ff returned only 12345 and not 12345welcome? thanks

set ff="$rr $rr1"

try this

 
set ff=$rr$rr1