How far in?
Rookie question - how far into the collett does a router bit have to go?
I have done two workshop courses but Mark has swapped router bits - just been having a go with my router and realised that I can manage a deeper cut if I don't push the bit all (or nearly all) of the way into the collett - what is safe?
Sod it - make tea!
I always change the cutters here in the workshop on our courses - if a cutter comes loose then we know who to blame! I put them about half way in - but it does depend on the length of the shank.
I would suggest you need at least (12-13mm) 1/2" of shank in the chuck
use the spanner provided with your router - they are smaller than normal to prevent over-tightening
read the manual! You might find some info about this in the manual the comes with the router?
Measure twice, cut once...
Lots of cutters actually have a mark on the shank showing the recommended insertion depth. You may get away with 3mm or 4mm less but this will be putting excess strain on you cutter, your collet and potentially the routers bearings. If you are having to do this routinely then invest in a longer cutter.
Just as an aside to this, if you have never replaced your routers collets and collet nuts then you may be surprised at how much difference this can make to the quality of cut and the life of your cutters.