Introduction: Organic Wood and Resin Object
The Idea behind this is to create an organic shape, place it inside a box, and make it able to be placed on at least 5 of the sides. I will be showing my workflow using Rhino modeling to create the shape, CNC Router to cut it out of a block of hard wood, and a mold to cast it into resin. The design is entirely open ended, and can be anything as long as it is possible to fabricate! And the process is loose too, as it could be created any number of ways. I will be running through the steps I took in rhino to create the object, and my trials and tribulations making use of these shapes after the CNC mill created them.
- Rhino modeling software
- Hardwood (I used mahogany)
- Clear casting resin
- Tubes of 100% Silicon
- Dish soap
- Formwork (I used foam core)
- Murphy's Oil Soap (for releasing from mold)
First, here are a couple tutorials that were essential for me in understanding how to fabricate
World Easiest Silicon Mold: https://www.instructables.com/id/Worlds-easiest-si...
Step 1: Rhino 1: Overall Lines
Since I was milling the final project on a 3-axis CNC router, I needed to make sure that the shape was able to be cut with one side being the flat base of the wood block. So I worked in plan, and began with the lines where I generally wanted my shape to follow. I made a circle at the end of each shape, and ARRAYCRV to make multiple copies along each curve, at a .5 in interval and free from rotation. This gave me a basis to start making my shapes.
Step 2: Rhino 2: Wireframe Shapes
Next, I started to scale the circles I had made to make some trumpet-like shapes. I kept the intersection area clear, as connecting these will be the last big part of the Rhino file. I just want to make sure that the center of the circles remains on the C Plane, as it will make cutting the entire object in half for the mill much easier. After I had made the rough outline, I used the LOFT command to make a surface out of each set of circles, with Normal selected in the loft dialog box, and 10 control points.
Step 3: Rhino 3: Center Linework
These next steps will basically make one side of the center, which we will mirror as the final step to create the solid in the middle. This is simply an easier way to make a curved solid from the existing surfaces.
To begin with the connection, we first need some geometry from the lofts. I use EXTRACTISOCRV, select one of the lofts, and pull both the two curves on the C Plane, as well as the ones directly above on each side.
Once all of the iso curves are there, we will start to create the outline. Use BLENDCRV and select two curves to connect. You can adjust the result, but the main goal here is to make it look "right", creating a natural looking curve.
IMPORTANT: the tight corners should not have a smaller radius than the bit size of the CNC router. I usually just make a circle the size of the bit and visually check it so it is not too drastically small.
Use the BLENDCRV command to create the outline on the C Plane, as well as to connect the iso curves that are above.
Step 4: Rhino 4: Surfacing Center
Now that we have two sets of lines, one on the C Plane and one above, we can start to make surfaces to join them.
First, we need to split the circular edges of the lofts that we made earlier using the SPLITEDGE command. Split them at each point where the blended lines intersect. This will give us the last edge we will need to make the surfaces.
Next, extrude the lines on the C Plane down. This will insure the surfaces on the sides will dive be steep on the sides, and will look cohesive when we flip them to create the bottom.
And finally, use the NETWORKSRF command to create surfaces from the C Plane to the Line above. You will have to select 4 curves, which will be two segments from the edge of the loft (which we split earlier this step for this reason), the blended curve above, and the edge of the surface we just extruded. Using the edge, and not just the curve that is on the C Plane, is vital. Make sure that Tangent is selected for each side of the network that it is available, which will be the three edges.
Step 5: Rhino 5: Patching the Top
Now that we have all the side surfaces, we just need to cap the top. We will use the PATCH command to do this, as it will make an undulating surface based on the edges we select. Again, it is vital to choose the surface edges around the top, not the curves that might still be there, as this will make it a smooth shape.
Step 6: Rhino 6: Mirror and Cap
Now that all the sides and top are complete, simply select them all, and JOIN them.
Next, MIRROR them over the C Plane to create the bottom portion of the center, and JOIN the top and bottom pieces.
Finally, JOIN the now complete center with the circular lofts, and CAP the resulting poly surface. This should create a closed polysurface, which means it is ready to be prepared for the CNC Mill!
Step 7: Rhino 7: Preparing for Mill
Now is when the process becomes more subjective, and it is up to you how you want to proceed. Ill show you what I did, but this is not the only way to create the finished product.
With the finished organic object, I created a box that was the size of the object, and started to move it around within it to create the shape I wanted. Note, I cut the flat sides on the CNC mill, which meant the plane I worked on was a direct diagonal. If you want to simply cut out the organic object and cut it to the box specifications later, skip this step.
I then formatted the object to the be cut in halves by using BOOLEANSPLIT to slice it along the C Plane. This made two distinct halves, which I then fit to my block of wood, and added tabs to connect the object to the border while the mill was cutting it.
Step 8: Physical 1: CNC Mill
Now is when we move into the physical world! Choose a hard wood to use on the CNC mill, as this will make the small elements of the shape stronger and less likely to break. Once it is out of the mill, glue the halves together and let dry before starting to sand it down.
Step 9: Physical 2: Mold That Didn't Work
The final product can go a number of different ways from here. I tried two different paths, one to slightly greater success. First, I tried making a silicon mold from the milled piece in order to cast resin in. I used a great Instructible for the mold recipe which can be found here: https://www.instructables.com/id/Worlds-easiest-si...
The problem I ran into was that it was difficult to remove the wood from the mold after it had set. And the mold was not held tight enough to keep it accurate. I would either need to use many more tubes of silicone in order to make it more rigid, or use a different kind of mold.
Step 10: Physical 3: First Mold That Worked
I also cast half of the wood piece in resin by making a simple box of foam core, with saran wrap on the interior to avoid leaks. I sprayed Murphy's oil soap on the interior to help aid removal from the plastic wrap. I also created a small heat box to keep the resin warmer as it cured during the night, because the temperature was well below the recommended curing temperature of the resin.
Step 11: Physical 4: Second Mold That Worked
I wanted the resin to be cast only in the center of the piece, so I made a mold out of foam core that would keep it at the angle I wanted. I then poured cast silicon into it to fill the space I did not want the resin to be, and let it set for about 6 hours. Next, without removing the piece from the mold, I poured the resin up to the level I wanted. After it set, I removed it from the mold and sanded it down on the edges, starting from 120 grit sandpaper, and moving up to 600, 1200, and 2000 to get it almost fully polished.
Step 12: Final Product
For my final, I did not have access to the CNC mill, so I created a contour model of the object using 123D Made, and then laser cut a sheet of chipboard. The resin seeped into the chip and created an interesting effect that was revealed through sanding. So again, this process is entirely open, and can be approached from many different angles!