Here's what I do, to keep from damaging the shaft.
Find the biggest field point you've got. Chuck it up in a bench vise with the field point paralell with the floor.
Twist the shaft and insert onto the field point JUST ENOUGH to securely engage the threads, not all the way down.
Apply heat using a propane torch to the tip of the field point (it's a lot easier if someone else holds the torch). Do NOT get the torch near the shaft.
Apply firm pressure to the shaft rearward, away from the point/vice. Keep steady, continuous pressure on the shaft while the heat is being applied. As soon as the insert has enough heat to break the glue bonds the shaft will pull off the insert.
The most important part is to NOT screw the shaft all the way onto the field point. If you try this with the field point all the way screwed on, the heat from the torch will pass right through the point and the insert into the shaft and damage it.
When you heat it with the shaft halfway screwed on, all the heat is directed into the center of the insert, not along its edges. This allows the insert to heat up but keep the shaft relatively cool.