This jig will be used to cut the radius on the base of each spike using a router table with a tall pattern bit installed.
I started with a plywood base with a center line drawn down the middle. At one end, I scribed a partial circle at the required radius, which will be cut out later. Two identical brackets with pivot pins hold the spike so that its base just clears the surface of the jig.
The brackets are positioned along the center line such that the base of the spike just protrudes slightly past the drawn radius line. The other bracket is moved up until it butts up to the narrow end.
A series of wedges matching the underside angle of the spike get glued to the base on alternating sides to form a cradle for the spike.
The final wedges will be glued later, after the curved end has been shaped. The bracket at the narrow end got screwed down to the base at this point.
I cut most of the waste at the band saw and then shaped the curve on the oscillating sander.
After shaping the curve, I glued on the remaining wedges, leaving them protruding slightly over the edge. They'll get trimmed off to match the radius on the router table. This will ensure that the end of the spike will be fully supported on the bottom to avoid tear-out when routing the curve.
A 'V' shaped caul surrounds the top of the diamond in a similar way.
Ready to shape.
I bought this bit on Amazon, but I wouldn't recommend it. It worked, but it did not leave a smooth finish. Fortunately, the slight scoring on the cut surface will never be seen once the spike is installed.
The jig worked very well.
Knocking out the remaining 11 spikes was completed in probably 10 minutes.
