Casting a Catfish Fin Bone with Aluminum (Cast 131)

A catfish fin bone is scanned, 3d printed at 2x the original size and casted with aluminum alloy using ceramic shell casting. This is the pectoral fin bone (socket and spine) of a 20 lb flathead catfish that I caught.

To make the 3D model, I use a method called photogrammetry which uses pictures of the object taken from different angles to create a 3D model of the bone parts. After a few failed attempts, I added dots with marker to the bones to help the software (Zephyr 3DF) find the surface.

Once the model is made, pour funnels are added and in a program called Blender 3D. The bones are then printed at 2x their original size using a wax filament. The next step was to attach wax filament from the bone up to the top of the pour funnels to relieve any air pockets that might form when pouring the aluminum. I attempted this several times and added more air vents every time as it seemed to be the main reason the attempts were failing.

The wax prints are then coated with a ceramic shell (suspend-a-slurry), one thin layer at a time (13 total) and adding silica sand for strength and mass. The shells were then placed in a lab oven at 450 F to burnout the bulk of the wax. Then they went into the kiln and the temperature was ramped up slowly to 1700 degrees F over several hours. This hardens the ceramic shell and vaporizes the remaining wax. This method is called lost wax casting. The kiln temperature was then reduced to 1600 F and the shells were kept at that temperature for the pour.

The inspiration for this cast goes back to years ago when I made a cast of the inside of a black drum fish skull. Video here: https://www.youtube.com/watch?v=UmOMRoYe0Sc

I would keep larger fish (eating them also of course), and put them out to decay in the hopes of getting another large skull to cast. I noticed that these fin bones looked interesting so I decided to try to cast them. I had wanted to cast something with this method for a very long time.

The joint is very interesting, and it’s amazing how well it turned out. There’s a lot going on in the shape. For example the spine joint has a long flat part that slides into a curved channel on the main bone, allowing the fin to swivel back and forth. When it’s fully pushed into place as far as it will go (as though the fish is spreading its fin open), a bulb like structure on the spine joint enters a hole in the main bone, locking the it in place. If you’ve ever caught a catfish (or any other fish probably), you’ll be familiar with their ability to lock their fins open and it’s interesting to see that this is how they do it.

The final cast stats:
Anthill Art Cast # 131
Weight: 0.7 lb (0.32 kg)
Height: 8.5” (22 cm)
Length: 8” (20 cm)

0:00 Intro, Showing the Bone
0:23 Preparing to Scan
0:40 Taking Pictures
1:09 Making the Models
1:44 3D Printing
2:31 Finished Prints
3:31 Ceramic Shell
4:36 Wax Burnout
5:22 Pouring Aluminum
5:47 Breaking the Shells
6:23 Preparing/Mounting
7:03 Finished Cast

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