As background, I built a CNC machine in 2008 and have gradually taught myself the ins and outs of using it over the past several years. I've gone from simple two-dimensional projects to bas relief to full 3D. It has a cuttable area of 36" x 24" x 5" and lands squarely in the camp of hobbyist CNC. Additionally, I am well-versed in a number of graphics and 3D modeling packages. To duplicate the results here, you'd need access to a similar CNC machine and be reasonably good with 3D software tools.
The subject of this instructable is actually the result of a modeling tutorial titled 3D Modeling in Silo: The Official Guide by Antony Ward, David Randall and Nevercenter. The chapters in that book take you through a character modeling exercise in which you create this figure using a program called Silo 3D. This is exactly what I did and the outcome is a compelling blond hovering in a rocket pack with a pistol in her left hand.
It was at the end of this book that I felt I wanted something more for my efforts. I figured that buildng her as a life-size sculpture would make a kick-ass exhibit and expand my abilities along the way.
Step 1: Assemble your tools
Silo 3D is the modeling software and, of course, the book I mentioned if you're looking to create the same exact character. Alternatively, you can use other programs such as Sculptris, 3D Studio Max, Modo, ZBrush, Blender, etc. There are a lot of choices out there along a whole range of price points. Silo is relatively inexpensive and it, along with the book, will cost under $200.00 total.
In addition to the modeling software, you'll need some software tools (generally known as CAM or Computer Aided Manufacturing) to prepare the model for machining. I own a program called Cut 3D made by Vectric Software and it is the application that allows me to position the pieces, set up the tool paths and create the G-Code that will ultimately drive the CNC mill. Again, there are other programs that let you do that, but I'll discuss the one that I use.
Next, you'll need something to make her out of. Since I was going to create a life-size piece, I wanted the material to be as light as possible. Inexpensive is nice too. I chose rigid foam insulation from a home improvement store. The product is Dow Foamular and it is a pink foam available (around me, anyway) in 4'x8' sheets up to 2" thick. The 2" pieces cost about $25 each and I think I went through about 6 pieces. I made some mistakes along the way, so it can probably be done with only 4 sheets.
I knew I would need something to tie her all together (a skeleton or armature) and for this I chose half-inch PVC plumbing pipe which is plentiful, inexpensive and easy to work with.
I'm sure some people are cringing at the thought of creating a sculpture out of foam. While it is light and inexpensive, the surface is not exactly smooth and it can be easily gouged with just a fingernail. This problem is solved by topcoating it with what essentially is a liquid plastic. A product called Styrospray 1000 from Industrial Polymers (http://www.industrialpolymers.com) is a two-part liquid plastic that can be brushed on as well as sprayed. It's about $120 for a 2-gallon kit and I probably used about a gallon on this project. Unless you have access to a supplied air respirator, I'd recommend brushing it versus spraying.
Other things you'll need are drywall repair compound (I used Spackle), epoxy modeling putty (Magic Sculpt), plywood for the stand and paint.
Step 2: Slice and dice
You can use the program you crafted the character in to accomplish this or any of a number of 3D "utilities." The goal is to isolate polygons from a particular region (say, the left hand) and save them off to a separate file. You'll need to reposition the orientation of this piece so that it imports correctly into the CAM software and scale it to the desired size. One program that can do this is open source and named MeshLab (http://meshlab.sourceforge.net/). You'll also want to select a file format that can be imported and exported between all the different software tools that you're using. I use the Wavefront OBJ format and have had good results with it.
One might think that since a CNC machine is used heavily in this project that you'll ultimately have precision parts that fit together exactly and result in a perfect assembly. This is far from the truth. While the CNC machine gets you the basic parts, there is a limit to what it can machine accurately when you are dealing with 3 dimensional objects. The router bit projects only downward from the gantry, so the highest fidelity is seen on a part that is perpendicular to that axis. As the part slopes away (say, the sole of the boot if you are machining the left and right halves of it), there is a rapid decrease in the detail that results.
With that limitation in mind, you often have to make choices about where to split an element in order to achieve the best look. With the boot as an example, I ended up machining the left and right halves and then separately just the bottom sole. I cut off and discarded the sole from the two boot halves since the detail was so poor in that area. I then replaced it with the sole that was machined separately. This approach was necessary in a number of places to produce detail that would otherwise have been lost.
Once completed, this phase of the project leaves you with a number of files respresenting the various body parts. In almost all cases, there will be a right and left (or upper and lower) half that will be brought into the CAM software for the creation of toolpaths.
Step 3: Toolpaths and foam preparation
I'm assuming that you're familiar with CNC concepts like feed rates, depth of cut and stepover values. In case someone reading this is not, I'll mention the following:
Feed rate is the speed that the router bit is actually traveling through the material. A common metric is inches per minute (IPM).
Depth of Cut is the depth the bit is cutting into the material on a particular pass. For example, if the material is 2" thick, you might use a 1/2" depth of cut (DOC) and make 4 vertical passes in order to completely cut through the material.
Stepover is the percentage of the bit diameter that the toolpath is moved to create the adjoining lateral pass (not to be confused with a vertical pass when discussing depth of cut). With a high stepover (like 40%), you easily see the ridges between each pass while with a low stepover (5% - 10%) they become much less visible. The tradeoff is that low stepover values can dramatically increase machining time since there are a far greater number of lateral passes. I've included a screen shot that illustrates the stepover concept
For the roughing pass, which is intended to remove the bulk of excess material around the part, I use a 1/2" endmill with a 40% stepover and a 1/2" depth of cut. For the finishing pass, I use a 1/4" ball nose bit with a 25% stepover (depth of cut is ignored on a finishing pass). In a harder material like wood, you would normally want a 7% - 10% stepover on the finishing pass, but in something soft like foam it's a waste of machining time. Since the foam sands so easily, you can erase the tooling marks with little effort.
I mentioned earlier that I used Dow Foamular rigid foam insulation as the primary material for this project. Even a 2" thick sheet was too thin for a life-size sculpture, so I would cut the sheets into sections (to fit on my CNC machine) and then glue two of them together to create a 4" thick billet. I used 3M Polystyrene Foam Insulation 78 spray adhesive and would weight the billets down with three 50 pound bags of water softener salt to ensure a good bond.
Step 4: Start machining
First comes the roughing pass and then a bit change and the finishing pass. Once the finishing pass is complete and you have the two halves of a particular part, you'll see what I mean when I say that there are limits to the CNC process. The parts will be close but due to the orientation of the part and other factors, they won't be perfect. Don't despair. This is where some 80 grit sandpaper, glue and spackle come into play. If the part is at the extremities (head, hands or feet) it's okay to glue them together and start sanding/Spackling. If the part it anywhere else (torso, legs, arms, rocket pack), you first need to create a channel between the halves for the PVC armature to reside.
It does take some planning on exactly how you intend to tie it all together because once glued, sanded and spackled, there's no going back. The 1/2" PVC used for the armature has an outside diameter of approximately an inch, so I created slightly oversized channels in all the limbs, torso and rocket pack for the PVC to reside. I then used expanding spray foam insulation such as "Great Stuff" to fix it in place.
Step 5: A hard outer shell
I found that each coat of Styrospray adds about 1/64" of thickness to the surface. It cures by absorbing moisture from the air, so I'd take the parts into a bathroom and run a hot shower for a few minutes in order to build a little humidity. An hour or two later, they would be dry.
The first coat would seal the foam but leave a number of coarse, grainy areas. I'd sand that down and apply a second coat to produce a hard, glossy finish. The material obscures a bit of surface detail, but likewise it hides small imperfections and tooling marks that weren't sanded off.
At the end, you have a nicely unified and durable body part that was formerly a bunch of construction foam, glue and spackle.
Step 6: Bring it all together
It gets pretty exciting as you see your collection of parts start to take form. The gaps can be filled and transitioned through the use of the 2-part epoxy putty. I used "Magic Sculpt" but there are a number of other choices available. It takes some effort to blend things properly. I had sizeable gaps where the arms join to the torso and where the lower half of her body joins to the upper half. Some time spent mixing putty and smoothing out the contours allowed me to eliminate the problem areas pretty easily.
Since my character is posed in such a way that she is not self-supporting, I had to engineer a stand that complimented her hovering pose. I designed a support using 1/2" baltic birch plywood that culminates in a threaded male PVC fitting at its top plate. I then embedded a matching threaded female PVC fitting in the area of her rocket pack. To attach her to the stand, you only need to hold her in position and thread the two fittings together.
Step 7: Special challenges
The gun in her hand was clearly something I'd need to create separately, but then there would be the problem of getting it into her posed hand once everything was painted. I really didn't want to break her fingers trying to slip the gun in there. After some thought, I realized that I could saw the pistol grip away from the body, embed magnets in each piece along the cut line, and then be able to get the gun into and out of her hand. This works very well and since the pistol grip is black, the cut line is practically invisible.
Tougher than the pistol was her helmet. I knew I couldn't create something that thin with compound curves on my CNC machine. I wanted to stay true to her foam/plastic medium and not cobble something together out of fabric. After struggling with this one for a while, I finally decided to use the CNC machine to create a wood "plug" that was the shape of the helmet. I then used styrene sheets in a vacuum form jig to forge a replica of that shape. I used the same technique with clear plastic for the lenses that fit in the helmet. The vane along the top is cut from flat styrene sheet. Altogether, I ended up with a helmet that fits her perfectly and is actually removable.
Step 8: Final details and photo gallery
She was quite an effort and makes a distinct impression when people see her. I hope you've enjoyed reading about my project and that some will be inspired to create their own superhero.
I've included a gallery of photos of the finished sculpture.