One of the boats in the fleet needed to have a the rudder post flange to be replaced. As you can imagine you can't just run down to the old trusty Walmart and pick up a new one on a boat that is 40 years old and way out of production. So I sourced the material and routed one with some modifications.
The old flange was fastened with only 3 10-24 screws which I was not good as one of the bolts had broken and the other two allowed some serious play. I Programmed it to have 6 holes and a larger footprint to spread out the load on the fiberglass.
I used the CNC router to make the part. I first made 6 templates out of HDPE (High Density Polyethylene) with different size post holes (varying by .064) to get fitment as the old one had worn away some and was allowing some play in the rudder. The material is wickedly expensive. It is fiber reinforced Phenolic and cost $107 per square foot!!! Mistakes would be costly so I made one out of HDPE to test the height settings of the router first. In this picture you can see the original, fit test piece, the test run and the new one half way through the routing process.
The material is held down on the router with vacuum but since the piece was so small (4.25x4.5) I was concerned about it moving on the table and messing up the piece. For that reason I used a process called onion skinning. I leave a very thin skin on the bottom side of the part that keeps it attached to the rest of the material and with the added surface area it doesn't move.
You can see how thin the skin is as the light shows though it.
I then use a table mounted hand router with a round over bit to remove the skin. I put a piece of masking tape on the material so as not to scratch up the surface.
Final result looks pretty good. I am installing it tomorrow and will take some photos of it on the boat and post an update.