A couple observations.
First, have you gotten it OFF the mandrel??
If not, be careful how you hit it, the material is just as likely to come off the brass tube as the brass tube is to come off of the mandrel (DAMHIKT)
Second, a cool shop will not help glue set firmly. A couple trips around the mandrel, however, will add enough heat to really set that sucker!! Of course the closest thing to the heat (the mandrel) will be get the best adhesion.
Third: Trickling acetone down the mandrel, while holding it near vertically will help "unglue" a stuck mandrel
Hope these little tidbits help!