With the majority of power tools the difference in frequency would not present any problem as the motors on most tools are universal motors. Those types of motors will run off of 50Hz, 60Hz and even DC (although with DC many speed controls will not work, ON or OFF only) Large induction motors, as found on air compressors, may not like the frequency difference as much, but even in the case of induction motors, the lower voltage 110 vs. 120 will help offset the less than ideal reactance at 50Hz vs the 60 Hz they were designed for.
