Building A Carbon Fiber Splitter For A Mitsubishi Evo

One of the benefits of being a university professor is that I get to be involved in interesting projects outside the classroom all the time (at least when my hectic work schedule will allow for it). Many of the projects I get to dabble in come about because of my connection with students from class. So when one of my past students, Josh McGuckin (of Camera Courage fame), told me that his friend needed some help with his race car, my interest was immediately piqued. I have a hard time saying "no" to car projects--for better or for worse. In this particular instance, Josh's friend, Dave Kern, needed a new splitter for the front of his highly modified Mitsubishi Evo that he would be racing up Pike's Peak during the summer. His old splitter had been damaged when he hadn't been able to adequately negotiate a high-speed turn during a race the previous year, and he wanted something a bit thinner, lighter, and stronger to replace his old, mangled part. After looking at the way the original one was built, I figured a rebuild of this part wouldn't be a hard task to pull off; the old splitter was basically constructed as a low-cost/low-performance composite sandwich construction with a single skin of carbon composite over either side of a plywood and a open-celled polypropylene core. It was plenty heavy and lacked the stiffness that is really necessary to make an effective aerodynamic control surface. I knew I could make a splitter with significantly more stiffness than the original part, and even include all of the custom features he needed for the shaping and performance of his particular car. So, I said yes to the design challenge...and this blog entry will give the quick-n-dirty low-down of how I made the part. (Readers will note that some of the build details have been left out of this "how-to". The reason for this is that I am held under certain contractual non-compete constraints because of the books I have written on composites; I simply can't duplicate/publish those things I've previously written about for my publisher. For more info on the details specifically related to techniques shown in this build, though, check out my book Composites Fabrication Handbook #2.)

I first started out with a cardboard mockup of the part. I cut and taped some corrugated cardboard to make a representative piece that fit under the actual car as closely as possible. It included references for all the body lines and connection points to the frame, as well as the shape of the ducts that would direct airflow around brakes (as shown below). This mockup process took about 3 hours, but this included consultation and drive time to the shop where the car was, so the build of the mockup itself was actually very quick:

After examining the existing part and the bottom of Dave's car, I could tell that the trickiest part of creating this splitter would be fabricating the ducts, since the rest of the part was completely flat on the bottom. Flat parts are simple to fabricate in composites because flat sheet metal or plastic can be used to make a mold for the part with relative ease. More complexly shaped parts usually require much more planning in the mold-making stage. One of the easiest ways to fabricate a section of the mold for something like these ducts is to cut out wood and then simply cover it in formed sheet metal. These pieces can then be attached to a sheet of acrylic plastic which acts as a base for the mold. (For this mold, I opted for 3/16" thick acrylic that would be fastened over plywood because it is already very smooth and easy to polish and wax...plus I figured it would be easier to shape into other future mold components after using it for this project. Acrylic is not recommended for molds where polyester or vinylester resins will be used...the styrene in these resins will actually attack the acrylic!) I stacked up some scrap pieces of plywood and MDF (making sure to get just enough height in the stack for the needed dimensions of the duct) and used wood glue to join them all together. Next, I cut the stacked wood pieces on a table saw in successive passes, raising the height of the saw blade with each cut as needed until I was able to complete the contour needed for the top of the duct. I followed this cutting step with some sanding using a large spindle sander to smooth out the rough steps in the surface of the wood piece. I then cut the sides of the duct with a bandsaw and sanded it to a smooth final shape. Here is a side view of one of the pieces...

...and here is the top view of the same piece (shown below). It wasn't pretty, but it worked like a charm!

To create a quick, non-porous, mold-ready surface, I cut some 24 gauge steel sheet with some shears (dressing out the edges with a file) and shaped it to fit over the wood piece:

I then covered the edges of the sheet metal and wood with the type of aluminum tape that is made for HVAC repairs (as shown below). This is a quick and effective way to get the edges completely sealed prior to molding over the form.

I should probably explain here that it was necessary to make a solid wood support under the sheet metal because the composite layup was to be vacuum-bagged over these mold components; even ambient air pressure would have crushed a hollow sheet metal construction like an empty pop can under a Mack truck, so support underneath this feature was critical. 

I used drywall screws to attach the acrylic sheet to a sheet of construction grade OSB (for added rigidity). When fastening acrylic to anything, always make sure to first create clearance-holes for the screws; acrylic cracks very easily under stress, so driving screws through an improperly sized hole in acrylic will quickly fracture it. I then adhered the duct forms to the acrylic base using double-sided mastic tape, and then sealed the edges of the forms to the base with modeling clay. Note that a couple areas of the modeling clay had been strategically removed at the edges of the duct forms to accommodate flat areas on the part where hardware would be used to mount the splitter to the car (as shown below). Fabrication of this mold for the splitter took only about 4 hours. 

After a nice, generous waxing (which took about 2 hours), I performed the layup: one ply of plain-weave 3K carbon fabric topped with a ply of +/- 45 stitched unidirectional (non-woven) cloth for enhanced torsional strength. These were both wetted out in succession using epoxy resin and a squeegee:

I added a layer of peel ply fabric and then applied a vacuum bag over the part and allowed the resin to fully cure (overnight):

After cure, I removed the bagging materials, inspected the part...

...and prepped the surface for the rest of the layup by carefully grinding down any resin wrinkles left on the surface of the part by the bagging materials:

Next, I used some craft paper to make patterns for the core materials that I planned to include in the second half of the layup. Since the part was symmetrical, I only needed to make half of the patterns and then double up on the cuts from the core material stock.

I marked and cut out the PVC foam core material based on the shapes of the patterns, paying close attention to  the placement of the patterns so I could use the core material as wisely as possible (because it ain't cheap):

I then "dry-fit" them over the lower half of the splitter that I'd previously formed. I beveled the outer edges of the core and scored the bottom side of the core pieces that would be placed over the curved faces of the ducts (since scoring the foam core helps it better conform to curved surfaces):

Next, I used epoxy filler to tack down and gap-fill the core to the bottom half of the splitter (as shown below). Baltic birch plywood worked well as an effective, lightweight compression resistant core in the areas where mounting hardware would be later used to bolt the splitter to the car:

I then laid up the second half of the composite sandwich (which was a reverse of the previous layup) and bagged the part like before (see the photo below). Layup of both sides of the part and prep of the PVC foam core took about 16 hours.

I then removed all the bagging materials from the part to reveal the nicely consolidated composite beneath:

Here is a view of the cured part, straight out of the vacuum bag:

I demolded the part to reveal its smooth, mold-facing bottom side...

...and then used a scraper to remove the modeling clay (as shown). A little naphtha and a rag cleans up any left over residue quite well. 

I then used the original cardboard pattern and an abrasive cut-off wheel on a rotary air tool to trim the edges of the part. (Note that the photo below shows the location of the mounting hardware, drawn onto the top of the part using a silver-ink Sharpie marker. These marks helped in aligning the part to the mounting locations on the frame.)

Here's a photo of the completely trimmed part, ready for final holes to be drilled for mounting to the car. Final demolding, part cleanup and trimming took about 4 hours.

The final part was significantly stiffer, thinner, and lighter than the original. After about 26 hours of work, the new splitter was ready for the race! Here's a little photo of the finished car peeling around the turns up Pike's Peak (notice the flames coming from the exhaust in the front!) with the new splitter mounted just below the front bumper:

With this little baby mounted to his car, Dave ended up getting second place in his class and fourth place overall. Not bad for any Pike's Peak racing machine! Maybe I can further help him get a first-place winning vehicle all dialed in for next year...if my day job doesn't kill me first.

As demonstrated here, high quality parts can still be fabricated in composites using relatively inexpensive mold materials and techniques. All that's needed is a little ingenuity and know-how (both of which come with practice). Now go build something for yourself!

My "Woobie"--The Comfort of a Sketchbook

Those of us who were raised in the 80's (or even those of you who otherwise experienced that wondrous decade after the fact) may remember the term "woobie", which (as far as I can tell) originated from the now-classic film "Mr. Mom". In the movie, Michael Keaton's young son has a very sentimental attachment to a blanket that he calls his "woobie". His son takes this blanket everywhere he goes and clings to it because of the emotional comfort it provides him. While I admittedly had a special teddy bear (home-made by my loving mommy) that had some similar woobie-like qualities for me as a shy little boy, I recently realized that I have a current, less obvious woobie that I frequently feel lost without: my sketchbook. It is something that I constantly have with me, constantly holding on to, and constantly using. Because of how much I’ve used my sketchbooks through the years, it gives me a certain degree of comfort having one close by. So, in today’s blog entry, I’ll try to explain my affinity to the sketchbook and how it may be of benefit to others to keep one as well. (Here's what my current sketchbook looks like...unassuming on the outside, but full of my "ponderous" sketches...)

I was exposed to the idea of recording my ideas at a very young age. My grandfather, who was a high school teacher, could tell that I was an inventive child, and he lovingly encouraged me to write my ideas down in a notebook. He taught me that it would be best for me to carry my notebook with me at all times so I could write down my inspirations as soon as they came. As a result of his encouragement, I recall making my own small notebook out of paper and staples, with a cardboard sleeve that would fit over it so that I could carry it in my pocket without worrying about bending up the pages. The notebook filled up very quickly because I ended up making a flip book animation with it called the "Omega Robots" in which two Transformer-like robots battled it out to an explosive end. It probably wasn't what my grandfather had in mind, but his encouragement to record my ideas planted a very important seed. I went through (and lost) many small notebooks when I was younger, but by the time I was in high school, I started keeping a full-size sketchbook and regularly sketching in earnest. As a freshman in high school, my art teacher (wisely) required us to routinely draw in our sketchbooks, regardless of the subject matter, to help us build our skills. If I could go back and talk to my gramps and that art teacher of mine, I'd thank them in the most grateful way possible, because the simple act of regularly drawing my ideas (rather than just writing them down) is what has helped form an important habit of design conceptualization and development that has turned my design skills into what they are today. From the standpoint of my professional work as a designer, my sketchbook "habit" has helped forge an important pattern of design documentation--something that has been especially important with projects requiring thorough documentation for competition, intellectual property, patent, and regulatory reasons. At latest count, I have over twenty five sketchbooks (that I can still find!) that document my thoughts and ideas sketched over a period of more than twenty years. Here’s what a small handful of those sketchbooks look like:

There are a variety of reasons why people keep a sketchbook. Some of these are discussed in a ThinkSketch by Paula Briggs of AccessArt--which is a nice little reference I found after I’d already written most of this blog. (Interestingly, much of this book's content aligned very well with my own reasoning for the usefulness of sketchbooks.) Similarly, I have a few personal and also pragmatic reasons for consistently keeping a sketchbook over the years. For one, sketching helps me work through my ideas--of which I probably have more than my share. Sketching (just like writing) is a sort of mental solidification process for ideas. It helps me take an amorphous thought from its original, ethereal state into something more gelled and tangible. With additional directed thought and sketch development, that simple idea will then solidify into a concrete, well thought out, concept ready for further physical testing and product development. It's as though sketching allows me to gather my bits of mental dust, use my pen to stick then together into a loose, muddy paste, and then carve them through more mental refinement into a well-defined conceptual sculpture that can then be fired in the kiln of physical modeling and testing. For example, here's a shot of a carbon fiber side mirror I created for a concept car that I'm working on, and the sketches from which that design was formed, designed, and fabricated:

I believe that sketching also helps me to communicate my ideas with others through visual means. Humans learn to speak by actually talking--by making mistakes, finding the proper pronunciation and grammatical structure in round after round of vocalized trial and error until effective communication is achieved. Likewise, a musical instrument is learned by practicing the proper muscle coordination and mental construction and deconstruction of notes, rhythm and harmony until real music is possible. These each take time and untold hours of practice. And sketching is no different.  Regardless of how many how-to books you read, how many sketchbooks you study, or how many video tutorials you view, it is still the act of practice that makes the sketches, and their ability to effectively communicate, better. (Here's a relatively recent sketch of some bike frames...with a little marker added for better readability...)

With sketching, I feel that I get to share my unseen thoughts with others in a way that helps me better connect my ideas with them through visual communication. Words can only express so much, and sketches are their own type of language. Sketches  requires some communicative refinement and style to avoid cognitive dissonance between the designer and viewer of the sketch. But pictures have their limitations, too...which is why I find that annotation is so important in design sketching. Art sketching tends to be very expressive and "free" in nature, leaving itself open to interpretation of the artist's intentions. Design sketching, on the other hand, requires a certain degree of responsibility to the needs of the viewer to correctly explain the intentions of the contents of the sketch. For example, here's a sketchbook entry I drew of a visitors' site in Japan during a work visit I made there several years ago...simply for artistic reasons:

By contrast, here's a sketchbook entry showing some of my design thinking on the form and ergonomics of a new digital SLR camera:

To a certain extent, the mental process of design problem solving is illuminated through the flow of ideas that are revealed through the sketchbook. I have to admit that this area, in particular, is of keen interest to me as a design instructor who is constantly called on to explain those mental processes to students. (Admittedly, it is probably this later focus of mine, and my natural tendency to try and explain complex processes, that has made my three books on composites so successful among composites enthusiasts.) Here's a view of some of the process thinking that is going into my current concept car project:

While my sketchbooks show my design focus, the iterative processes that I go through, and even my understanding of a given problem as my experience in that subject develops over time, they also provide an enlightening chronological record of my ideas as they develop and mature. This is especially evident through the level of quality and complexity that my sketches have shown over the years. Some interesting growth is apparent here between a sketch I did in high school in the late 80's ("Then..."), and one I did earlier this Spring of 2012 ("Now..."):

To a certain extent, my sketchbooks are even a self-affirmation outlet that helps me feel that my thoughts and skills are worthwhile and incrementally developing the more I sketch. They show a personal record of my thoughts--and the variety of thinking that goes on in my head. In one way, my sketchbooks were my private, low-tech blog-space before I ever decided to send out my written and photographic ideas through cyberspace in this public blog. They even help me express my (often suppressed) inner engineer...which is why I like exploded views so much:

Although I have become accustomed to certain sketchbook norms, such as drawing on white, smooth paper with ballpoint pen (because of its permanence and lineweight versatility), I am constantly on the lookout for another good sketchbook. I can't go into a bookstore without going to the journal section in search of an unruled sketchbook (since lines are too confining to my sketch processes) that could be my next design record keeper. I'm always looking for just the right paper (smooth and thick, yet flexible, bond feel best to me), with the right binding (something that allows the covers to lay flat or fold over is best), and even the right size (big enough to rest my big monkey hands on, but small enough for easy, unobtrusive transport). As you can see from this "wad" of sketchbooks in my office, I tend to prefer coil-bound sketchbooks (again, because they lay flat and the cover can be bent back during sketching...which tends to be more comfortable when sketching on your lap):

I am constantly looking for a better sketchbook outlet that will help me express my ideas even better...at least until technology makes it possible to perform direct mental downloads of my ideas (which would be sweeeeeet!). I've even looked for good digital sketchbooks over the years, and have tried several Wacom Cintiq, Intuos, and Inkling models, as well as spent considerable time sketching on apps using Apple's iPod and iPad and a variety of other touchscreen tablet interfaces. They all have some benefits in the range of image manipulation, color, and output formats that are available, but I always come back to paper. There are still some significant limitations in both the hardware interfaces and the software packages that help the designer draw, especially if you've got a significant number of "legacy" neural connections fused through several years of successful hand-sketching techniques on paper. Digital sketching interfaces are increasingly important in design, but pen and paper sketching still have their own substantial merits.

A few times now I've been asked by my students to make copies or to publish parts of my sketchbooks for them to have. At some future date, I may actually go through the hassle of publishing some of my sketched works and random designs...if it seems that would actually be worthwhile as a learning tool for others. But we'll see. Until then, I'll just keep sketchin'.

Composites Materials Fabrication Handbook #3--Another Shameless Plug

Still wondering how to build a good composite mold from an existing part, a clay model, or even a machined plug made from a 3D computer model? Maybe you want to make something without a mold at all using some off-the-shelf materials, but still want to give it the same strength as a typical composite part. Or, maybe still, you've got a hankerin' to understand how engineering analysis can be performed on a high performance part. Well, have I got a book for you! My latest book on composites, Composite Materials Fabrication Handbook #3, is now available for sale, and covers a wide variety of composite fabrication techniques that build on my previous two books. 

As with my previous books on composites, I've tried to incorporate answers to many of the questions that I frequently receive from students, readers, and composites enthusiasts. Each of these books has included progressively more complex projects, and this one fills in some of the gaps that existed in the prior two books. Here is a little "snippet" of some of this book's content:

• Analyzing an existing part for moldability
• Determining the most appropriate method to mold a part
• Simplifying existing parts for better molding in composites
• Adding positive and negative mold features based on an existing part
• Addressing geometric constraints on parts that need to be replicated in composites
• Preparing a part for replication using composite tooling
• Applying epoxy surface coats in a lamination
• Structural enhancements for effective, low-cost reinforcement of composite tooling
• Creating location fixtures for secondarily bonded components used with composite tooling
• How to begin using a chopper gun
• Spraying gel coat and tooling gel coat with a cup gun
• Proper use and care for cup guns
• Techniques for successful wet-out and consolidation of spray-up fiberglass parts
• Planning and developing plug structures
• Creating finished lip features in mating composite parts
• Developing flange forms for various types of plugs
• Designing composite tooling from a multi-piece plug
• Computer-based plug design techniques
• Plug finishing techniques
• Silicone compression molding techniques
• Fabricating clay models
• Developing composite tooling from clay models
• Employing epoxy molding compound as a bulking material in composite tooling
• Fabricating sheet metal and sheet plastic molds
• Laminating "moldless" composites using foamcore
• Using frameworks and draped fabric as a structure to form "moldless" composites
• Repairing scratches, dents, gouges, holes, and severe damage in composites
• Applying gel coat to repaired composite surfaces
• Technical terminology and design assumptions used in composite analysis
• Setting proper parameters, material designations, and load assignments for composite part analysis
• Interpreting Finite Element Analysis data derived from a virtual model of a composite part
• Simplified shop testing of composite parts

As you can see, there's a lot of meaty information in this book...which is part of the reason I haven't had a new blog post in quite a while. Books like this take a considerable amount time to develop. And in my case, it was done on top of having a full-time (50-plus hours a week) teaching job and raising a young family. My contract to write this book was only about six months long, but development of the book's content started several months prior to even signing the contract. With each of my books thus far, the actual contracted time for writing the book has been largely spent on typing, editing, and creating illustrations to explain the hands-on demonstrations shown in the photos (which were usually taken days, weeks, or months before). Looking back on the amount of work I put into this book, I'm amazed that my heart made it through. But I hope that this book will be helpful to all those composites experimenters and fabricators out there who want to build something that they may not have dreamed was possible before. All the best to ya'.