Hi
@Desert Dweller -If the trees in question are Healthy a good time to chop would be early Spring as the new buds are swelling,
I guess if you get late frosts you may want to wait and consider mid-spring to early Summer.
I have never had an issue chopping a trunk on quercus suber, they always throw a great amount of new shoots.
Trunk size shouldn't matter so long as you can grow the cut out and heal it,not ruining the trunkline in the process.
I believe in some countries they use plastic bags over the tree after collecting or hard chopping to provide
much humidity,this helps promote backbudding.
this one below was chopped early summer from memory a few years back now,