To be honest its a lot of work, ive done a few over the years and 1 late last autumn only because the tree/log was going on the fire if i did not remove them and it was a very big chunk. I would suggest cutting the log each side of the entrance until you exspose the top and bottom of combs/colony, this is a bit of guess work and will depend on width of cavity as to how long the combs are. I would take a say 1 metre each side of entrance. Sometimes top or bottom of log are soft in the interior so a little poking may give you a clue if you cut short. Once top or bottom are exsposed you can take a guess at average thickness of trunk and then cut 2 horizontal cuts into the cavity the lenth of trunk. The idea is to be able to access and remove combs down the lenth of cavity. Cut bigger than you think as curve of cavity ruduces as you get in...if you can move the log just cut in half LENTH WAYS. Your aiming to to send the point of chainsaw just far enough into cavity and not into combs, pretty impossible to get right but thats the idea. You will need club hammer/sledge and spitters or crowbar to remove the cut out.
Now at this point any bee worth their socks will be running in all directions so in an ideal world replace strip you have cut or cover with sheet and return next day if time/distance allow. This will allow the bees to return to the comb and more importantly the queen, i find a big issue with cut outs is queen will often disapear into some corner if theres been to much disturbance. Then its a case of cutting out the comb, dont bother trying to save honey and just concentrate on the brood comb with as little honey as poss it just complicates the whole process....Pm me your mobile number and i will send a pic/vid if i can dig it out
