It is tough to beat commercial "throwing knives" for spear tips. Remove wrapping from handle. Cut or split down the center of your shaft. Drill a cross hole. Insert point. Drive rivet or bolt. Wrap with wire, fish line or other cordage. Look for Sabre Tooth Tigers to ventilate.
|Avoid this style of blade for spear points. The backward pointing barbs can hang up on ribs and leave you vulnerable when the tiger's chums join the fray. The Romans had this figured out 2200 years ago.
They are also incredibly economical, often available for little more than one dollar a point.
What these "throwing knives" are not: They are not a viable defensive tool as throwing knives. For one thing they are much too light. For another, why would you give your opponent a weapon, i.e. throw your weapon to him?