spinning ignition key

Good day
I have a problem . When the ignition key is turned to start the car sometimes the switch doesnt seem to catch and the key can be rotated many times with no resistance . Then out of the blue it catches and i can start the car .
I can not work this out
????? Any ideas would be appreciated .
Thanks .....................Alan

I have a problem . When the ignition key is turned to start the car sometimes the switch doesnt seem to catch and the key can be rotated many times with no resistance . Then out of the blue it catches and i can start the car .
I can not work this out

Thanks .....................Alan