A "caltrop" in ancient times was a four pronged device for stopping horses
And it makes a challenging project for wood turning
The "blank" is a pair of square section pieces, each 120mmx40mmx40mm
This diagram shows the four axes of turning to get the four spikes
The pine wedge is cut to 35 degrees. arcsin(1/sqrt(3)). Four tailstock holes are drilled to the centre
The 35 degree wedge holds the blank for the (shallow) headstock holes