This is CNC cut art piece that was inspired by fossils I saw on a trip to the Jurassic coast in England, but taken in a more ancient-robotic-life-form direction. It takes power from a USB micro-b cable. There's lots of variations on this that could be fun: different shapes, more layers, making the LEDs controllable via a microcontroller hidden inside, different resin coloring effects, rusting the metal before the resin, 3D printing parts in the design, etc! This was for me a prototype of many of the methods involved, so I plan on making more and trying all of those things.
Step 1: You will need:
CNC plasma cutter
Hand plasma cutter
Angle grinder with metal grinding disk and flapwheel
Popsicle sticks for mixing resin
Disposable resin mixing cups
¼" plate steel, enough to cut 3 rectangles that are about 4" larger than your design in both directions
Thin gauge (14-22ga) stainless steel or copper, enough to cut your design 2 times
2 part casting resin
Powder pigments compatible with resin
Solderable magnet wire
SMD LEDs of your color choice
SMD USB micro plug
E6000 or similar
Hot glue and glue gun
Step 2: Creating your design
Create the design for your fossil. I used a Python program* that I created for making mathematically generated shapes, in addition to 3D modelling software. There are 2 parts for the design: The outline that will make the recess in the block of thick metal, and the design that will make the pieces of thin metal. You can also make several layers for the thin sheet and layer them to create a more interesting design!
Add a rectangle to the outline part of your design- make it about 1 ½" bigger than the design on the top and sides, and 1" on the bottom. Save this drawing for CNC cutting (I saved as a DXF). This will become the top of 3 pieces that you will cut out of the ¼" steel.
Now add a recess that connects to the design outline. This will house the resistors and wiring. Save this drawing, it will become the second of the 3 pieces of ¼" steel
Add a small rectangle, just big enough to fit the USB connector through, to the side of the pocket that is furthest from the design outline. Now delete the design outline and pocket, and save this drawing- it will become the third piece of ¼" steel.
*The program is at http://github.com/waywardengineer/shapeGen. It creates mathematically generated shapes and exports them to DXF. I haven't gotten to a point of making it easy to use for someone who didn't make it, but if you are a python programmer feel free to use it!
Step 3: CNC cut the pieces
Prepare the 3 drawings you just made for CNC cutting in your CAM software,
and cut them out of the ¼" steel.
Prepare the inner part of the design for CNC cutting. It will involve lots of small pieces that can get lost easily, so I cut it twice to account for lost pieces. CNC cut it out.
Grind any slag off of the CNC cut parts. For the small parts, it helps to clamp the drop containing the outline of the parts to the table, and set the small parts in their outlines. Be careful with the small pieces, they like to fly away!
Step 4: Create the rough edge around the outside (Optional)
Stack up the 3 pieces of ¼" steel, back to front
Make sure the pieces are lined up on the edges, and clamp them to the corner of a table suitable for hand plasma cutting. Clamp it in a way that leaves the top and side edges clear of the table. Use the hand plasma cutter around the top and sides to create a rough, "carved from stone" look.
After the pieces cool, separate them(this might take a bit of tapping).
Step 5: Start assembling and wiring
Use the E6000 to glue the back piece to the middle piece. You want a very thin layer of the glue all the way around- you want the recess to be watertight for the later step of pouring resin in, and you donít want any E6000 visible.
Solder 2 pieces of magnet wire onto the pins of the USB
socket that correspond to 1 and 5 in the diagram. Pin 1 will have 5V power from the USB cable, and pin 5 is ground. You will be able to plug your project into any USB port or charger to make it light up. If you decided to build in a microcontroller, you could also communicate to it over USB
Put the USB socket into itís opening in the back piece of ¼" steel, and plug a cable into it from the other side. Use hot glue to set the socket in place and seal off any holes in the back, being careful not to get excess into the plug area. The idea is to make things watertight so that you can pour resin into the recess later on, but not accidentally glue the cable in.
Magnet wire is wire that looks like bare metal, but actually has a thin layer of insulation on it. "Solderable" magnet wire has insulation that gets melted off at solder temperature and is made of good metal for soldering. Not all magnet wire is solderable- I had some from a Tesla coil project that would not stick to anything when I tried soldering it! Make sure to use lots of flux when soldering the magnet wire.
Solder 2 3-6" long magnet wires onto each of the surface mount LEDS. The wires will need to reach from where the LED is placed to the "pocket" where the resistors will be. I found it easiest to bend one wire in a "u" shape, put the base of the "u" about 1/4" past the LED and solder one side to each of the LED terminals. Once it was soldered, I trimmed off the base of the U, leaving 2 separate wires soldered on to the LED.
Determine which wire goes to the anode of the LED. You can do this by following the markings on the LED, or by just connecting it and seeing which way works(I found the latter to be easier).
Take the LEDs with the wires and place them one by one where you will want them to be in the design. Trim the wires so they are just long enough to connect in the pocket area. Use a dab of cyanoacrylate glue to hold each LED in place.
Solder the LED wires in the pocket- the anode(positive) wire from each goes to a resistor, and the other end of the resistor goes to pin 1 of the USB connector. The cathode(negative) wire from the LED goes straight to pin 5 of the USB connector. Cram everything into the pocket so nothing sticks above the surface of the metal, but be careful not to short anything out. This step was tricky for me- I would make the pocket bigger next time!
Step 6: Pour the resin
Mix up a batch of resin and add the pigment that you want for the top of the piece. I used a neat greenish/coppery pigment I found at a local art store. Pour a layer of this onto the top piece of steel(This should still be separate from the rest of the project) and set aside.
Make sure your wires and LEDs are where you want them to be. Mix up another batch of resin, this time coloring it with what you want for the back of the sculpture(I used iridescent blue). Pour a layer of it into the recess just deep enough to cover the wires.
Add resin until you are happy with the color of things and the diffusion of the LEDs. I ended up using one layer with deep blue pigmentation and a couple with less dense blue pigmentation. I also added some extra wires after the first layer, I wanted more "wiriness" in there.
When the resin on the top piece of steel has set and you are happy with the color, remove any stray resin from the back of it so it is clean and flat. Use E6000 to glue it onto the other half of the fossil, being careful to not get any stray E6000 anywhere visible. Make sure the top stays lined up as it sets, E6000 has a tendency to let things creep out of alignment if you're not careful.
Place the stainless steel pieces of the design in the recess. Fill the recess with clear resin, and overfill it a little so that you get one layer of resin over the whole top of the fossil. It may take a few coats to make the front flat.
Once everything is hardened, sand off any drops on the back of the fossil, and use a disc or belt sander to get the bottom smooth so that the fossil stands up. Plug in and enjoy!