I have a Bosch 1/2" battery drill. I removed the holding screw and placed a 3/8 allen wrench in the chuck as directed with the new chuck. I have struck it many times, soaked it with PB Blaster, even heated it some with a torch. All it does is spin. Is there some way to hold the shaft to remove it? The drill is worth saving.

If you are having trouble getting it off and you really want to save the drill, take the drill apart so you can put the shaft in a vise in order to keep it steady while you try to remove the old chuck.

Hi,
Just a question for thought; was the screw RH or LH thread? The chuck will be the opposite, just in case you did not know.
Peace and good luck,
Clarke

Try this How to Remove a Drill Chuck - YouTube