I recently purchased a hollow-handled "Tomahawk" brand survival knife, which has a handle tube with an inside diameter of about 7/8-inch and a tube length of about 3-1/2-inches.  In thinking about how I would make a really stout spear with this knife, it occurred to me that its tube diameter and length are quite small for the business end of a spear shaft.  Can anyone give me some tips on how to make (and reinforce) the knife end of a spear shaft so it won't break off as easily if it's bent?  Also, in case the knife end of the shaft were to break off under severe bending stress, how can I fasten the knife to the shaft so it won't come off the broken end of the shaft completely?  Thanks in advance for any tips you can give me.