[Video] Large Scale Mold Making - Part I

About: Engineer making renewable energy products for African entrepreneurs.

This is another multi part series. This is a long project for the 2007 ASME Human Powered Vehicle team from the University of Central Florida. I will be breaking up major tasks into smaller instructables as the entire process is gargantuan.

Here's a Botched together video. The fast paced part is 1 hour of work ;)

Video - Mixing Polyester Resin
Video - Tool Making

Step 1: Background

We're making an HPV! That's human powered vehicle ;) We are required to have at least 1/3 of our frontal area covered by a fairing (a fairing is just an aerodynamic shell -- like your car's outer skin). We're going for a fully enclosed (aka "sealed") fairing.

To tackle this manufacturing problem, we will be making a "female" negative mold. Similar to how casts of fish are made. To make this mold, we first need to make a positive "male" plug.

This instructable is a guide! I'm not going to instruct you on how to make the shape - there's plenty of resources on that. Instead, I'm providing rough instructions on how to start this task.

Our mentor currently works for Lockheed Martin as a model maker. When it comes to composites, this man knows his stuff. This is my third year working on this type of project, and he has provided a wealth of information and advice. If you'll be tackling a similar scale project - find yourself someone that has the experience to guide you in the right direction.

Step 2: Foam and Cutting

We're using a high density insulation foam. If you have the option, get foam that is not scored - ours is scored, and it breaks somewhat easily along the scores.

This foam is some tough stuff. Our electric carving knife has some trouble cutting through - but a jigsaw does work ;) Our preferred method? A jet of 60,000psi water.

We had 37 sections (plus 4 additional sections to create NACA ducts) machine cut on a Waterjet. We used a company in Orlando called Crossroads Unlimited. In fact, we have used them for the past three years. They have a large Waterjet (72" x 144" cutting area) capable of doing abrasives. I highly recommend them if you're in the area.

Please keep in mind the cost scale. Each sheet costs $13. Luckily more than one section could fit on one sheet.

Step 3: Dry and Dry Fitment

Our sections were soaking wet. So, time to dry. We will be gluing them together, so we need a clean and dry surface.

Once dry, check your fit to make sure you've got everything in order. We labeled each section as it went into the machine.

When assembled, admire your work and do a little mock setup. We made that wood "bikamabob" a few months ago for kinematic analysis.

Step 4: Glue

Each section uses a 2X4" cutout for indexing and alignment. This ensures that the plug goes together straight and true (sometimes with a little adjustment).

Use a foam safe glue. Since last year, 3M changed the label on their "77" spray adhesive. The only change was the word "foam" -- after a test sample (comparing last year's can and this year's), we determined it to be safe in smaller dosages. 3M 90 will melt this foam on contact. As always, test first when working with your materials (especially new ones).

Our friend from Lockheed recommended 3M 74. Not available at the local hardware stores, but I'll remember that for next year and special order it.

Before spraying, wax your alignment "dowels." This will help the sections to slide down easily and prevent the glue from sticking together. Re-wax every few sections as necessary.

Spray an even fog over the edges of both faces to be mated and then spray a little bit in the center. It is key to get a good stick on the outside edge so that when it is sanded, you get a good gradient without separation. The key is (according to our composites master) to find the line between too little and enough. Remember that too much (of this glue formula) spells melted foam.

Once an even coat of adhesive is sprayed down, align your sections and stick down. We let the glue set for a few minutes with bricks on top to ensure a good bond.

When aligning, pick an edge to follow. In our case, we wanted the leading edge of the 2X4 to line up the whole way. So before sticking down, we lined up all three of our alignment 2X4's on their leading edges - then pressed down. Once we figured this out, we got perfect results.

Step 5: Weight

When done, add weight and allow to cure.

Alternatively, use shrink wrap. Just be careful that you're not warping your foam. A few layers should do it ;)

The idea works like a piece of string on your finger. One loop is fine, but each time you wrap around your finger the pressure goes up and up.

Next up... A whole lot of sanding. Unfortunately, I won't be there for it - so I won't have an awesome video for you. But hopefully the team is taking lots of stills ;)



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    43 Discussions


    1 year ago

    I realize this post has been inactive for several years, but...

    Can anyone PLEASE tell me where I can find either this blue (or pink) high-density foam, or Foamular for a relatively inexpensive price?? I've looked EVERYWHERE (in the Los Angeles area) and all home improvement stores stopped carrying it (they only have expanded polystyrene/"styrofoam" insulation boards), and whenever I do find it online it's in 2' x 2' hobby-style sections at around $47 per board (insane), and I need an amount equivalent for roughly 4ft long by 2ft wide by 30 inches tall (which equates to about 15 sheets of 7ft long, 1-inch thick sheets that will cost me around $400 in total, and that's craziness!).

    Thank you, and thanks for this post! It was immensely helpful in congealing the details of the process I'm going through for my project!!

    1 reply

    Reply 1 year ago

    That's odd. Look online for "high density polyurethane foam". If that's too expensive, look through "extruded styrofoam" for what might work for your project.


    10 years ago on Introduction

    hey, i'm hoping to do something similar to this for my senior design project at UCF in a couple years. I was just wondering where you get your materials(foam, fiberglass, etc.).

    1 reply

    Reply 10 years ago on Introduction

    hit me up on eMail --- same instructables username @ gmail.com

    I've got a digital copy of my logbook, contact information, vendors etc. etc. If you're serious about doing this, I get involved before it's your senior design project... The project is a lot of work (for the class, the competition and the actual project) ;)

    I'm going to be around next year - and I'm sure as hell going to be involved again (It's just so much fun) :D Check this:


    11 years ago on Step 5

    Too bad you weren't there to document the sanding/ post sanding procedure. After sanding, was the foam plug coated with some sort of body filler substance (like Bondo) to smooth out the surface? You may have mentioned this in a subsequent post, but I didn't catch it.

    1 reply

    Reply 11 years ago on Step 5

    Yes, I will make a post about that process... Not really any pictures (I might be able to dig up some), but I can give details. The plug is sanded to shape... Then coated with fiberglass and resin (no hardener). It's allowed to fully cure (a few days). Then, bondo filler -- sand - bondo - sand - repeat until you've got your shape....


    Reply 12 years ago

    My little avatar picture was made with a male mold and vacuum bagged to reduce weight :) It worked pretty well, except the vacuum kinda crushed the plug in the process :P


    12 years ago

    very cool...I use this blue foam to make models for metal castings...just out of curiosoty what are you using to make the negative? Of course I haven't seen your sanding process yet, but look into getting a sureform(or similar) wood rasp if you don't have one already. They work beautifully for rapid material removal in the early stages. I've also found that drywall screen gives an excellent final finish much faster than 400+grit sandpaper. WEAR A RESPIRATOR (not a dust mask)! Blueboard foam is extremely abrasive, like breathing in glass, and probably carcinogenic.


    12 years ago

    Just wondering, why copy Cheetah when the Varna has proven faster? Also I must say I really like the paint job on your Gold Rush clone.

    3 replies

    Reply 12 years ago

    Just wondering -- you haven't seen our frame design.... You've probably seen the three wheels - you could probably guess tadpole design from the foil shape. You don't know what steering method and mechanism we're using, you don't know how any of our parts are put together etc. etc. All you have to go on is a wood mock up that was used for rider kinematics and seat angle.

    1. WindCheetah uses a U-joint steering mechanism. We're not
    2. WindCheetah doesn't have an adjustable boom
    3. WindCheetah has a pretty cool off axis rear axle - we're doing more traditional chain stays
    4. The only company I've seen mass produce a 700c tadpole is Big Cat HPV
    5. WindCheetah is glued together
    6. We have never seen a cheetah in person (at least I have never) :P
    7. Hell, for a short while, there was a Kevlar drive belt in the boom (someone else did this, but there is a better way to do it :P)

    I don't know what you're referring to about the Gold Rush... We've never made a LWB :P Could you elaborate?

    Trikes have decades of experience and technology behind them. An engineer is obligated to learn from past experiences of others and him/herself and apply these lessons to his/her design. At no point during the design process did any team member take out any measuring equipment and place it near a manufactured design. This is why the general low riding 'bent tadpole shape is in fact general. This is why a SteinTrike looks like a Cheetah looks like a Catrike looks like Sun (well, maybe not a sun :P) looks sorta like a tripendo (minus the leaning :P).

    We sat down with successful vehicle designers and got lessons in vehicle dynamics, stability, angle tolerances, bump vs. brake vs. 0scrub, etc. Took in information about our rider sizes and built a vehicle around the riders. Applied all the "stuff" we've been learning as engineering students and out popped a design we couldn't manufacture. Add more research, some design tweaking and hey, the model actually works! and our shows won't hit the fairing!

    As for the fairing.... That starts off as a basic foil and then is fit to the vehicle ;) To be honest, I think it somewhat resembles a super high mileage car I saw awhile back (except we need peddle space) :P

    As for why tadpole? Well, lets just say some members had some rather nasty bruising because least year's SWB has twitchy steering and a steep learning curve (I finally figured out the problem -- the trail is terrible). So smack on a third wheel - stability problem solved (at leas that was the original thinking, they didn't know better at the time).

    What you must understand is.... If you can reliably put down power - you're now somewhat competitive - you've taken a huge step. I've been there with a terrible design put together in a quarter of the normal time it takes. I was there milling new parts on a hotel floor making "precision" holes with a power drill and then putting it together with JB weld and pipe clamps :P

    While speed is cool and all.... It won't win the whole competition ;) How many people do you know that are willing to commute to work every day in the Diablo II? I'd love it, but it's not practical.

    Lastly... Don't take any of this the wrong way ;) I'm not being nasty (but re-reading this, I can see how it could be taken the wrong way). Besides, if the senior design professors even thought we were copying someone else.... Heads, genitals and fingers would be rolling - and not on an HPV :P


    Reply 12 years ago

    Whoa. I didn't mean to seem critical. Just comparing the various fairing shapes.

    Your avatar looks a bit like a late model Gold Rush smoothed out into a plump Virtual Edge. And the blue plug looks a lot like Cheetah (not Windcheetah).

    As for advice or critique, there's none to give. Experience seems to be the only teacher in this game and mine does not really extend to streamlined machines, except for the one time I got a test ride in something called the Baby Varna.

    From your anecdotes, it's certain that the obstacles are common to HPV builders all over. For instance, I've had to pack sand into a joint repaired with epoxy to give it enought structure. My favourite quick set adhesive is a Vise Grip plier. And nothing speeds up your wheel-building skills more readily than a 2 hour deadline to finish a trio of 20-inch racing slicks.

    Good luck at the races. They're hard. And that's what makes them fun.


    Reply 12 years ago

    No worries :)

    As for the fairing in my avatar :P If I remember how it was done - it started (the model that is) as a foil and then bits were cut off and some bits were added on :)

    This year, my school is hosting the event. Se we got to pick the course :) It's going to have slower speeds, but the layout is more technical. We'll need an extra helping of straw bales :P


    12 years ago

    Ohhh... This is exciting. I'm writing an instructable on RTV rubber molds. Can't wait to see your technique.

    1 reply

    Reply 12 years ago

    What a great idea :) Sounds like a cheap source for small molds :P And it cures at room temp :P I've been away from this project (due to spring break and family), so I hope I don't miss all the fun parts :P And I hope my teammates are taking lots of pictures :P


    12 years ago

    Holy crap... 2200+ views today o.0