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Step 3: Method#2- lost foam molding

I used this method to create an air duct for the oil cooler on a friend's Porsche GT5R racecar. This is a very quick and easy way to mold a hollow component or a part that has severe undercuts that would not alllow it to be molded in a single piece female mold.

The first step is to cut a pattern from blue insulation foam and wrap it with clear packing tape.

Next, cover the taped pattern with a mold release wax.

Now cover the pattern with woven fiberglass cloth and wet out the resin. Make sure to leave a section uncovered- this is where the foam will be melted.

After the resin has cured, melt out the foam by pouring acetone on the uncovered section (note that in drawing #4 it says kerosene- this is incorrect). Make sure you have a decent sized tray or bucket under your part- this will get messy! As the foam melts you can reach into your hollow part and pull out the packing tape and you are left with a hollow molding.

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So I'm trying to make a mold of a laser rifle from fallout, how much would it cost to make? (Using method 3)
<p>The best way to do that is by making a matrix mold (sometimes called a mother mold.) This involves building up a layer of silicone on each half of the rifle and then this is supported by a fiberglass jacket. Molds of this type can cost hundreds of dollars (or more, depending on size.) You would have a really difficult time making a straight fiberglass mold for that. </p><p>Have a look at the Punished Props video of a matrix mold here- </p><p>https://www.youtube.com/watch?v=bjwvak9XjcU&amp;index=3&amp;list=PL6q0fd3ileWJxqvMYIkA8Yd1FoPPe897r </p>
Question about the wax release. Does it matter on the specific wax you use? I've heard different things.
I've only used specific mold release wax. I can't really say if any other type of wax will work.
Thanks for responding so quickly <br>Another question, could i substitute polyester resin for fiberglass resin?
<p>Absolutely- polyester resin is fiberglass resin. The other type of resin is epoxy resin. The difference is epoxy resin is tougher and it produces a nicer finished piece but it's a lot more expensive. </p>
Hi! So I am working on a 49 ford pickup and making a custom dashboard insert since the previous owner cut out a huge chuck behind the steering wheel. Since I have to do small cut out circles for the gauges do you think the taping will still work fine? Or do you have any tips on working on small areas? The whole gap is about 12&quot;x10&quot;. Also do you have to get your wax online? Or is that something a store would carry?
It's hard to say but you might be better off making the insert and then cutting out the holes for the gauges afterward. Some stores carry mold release wax, some don't -just depends on stores in your area. The local independent hardware store that I frequent carries fiberglass supplies and wax.
<p>Will this work to make a skid plate for a fuel tank for a 1979 F250? The old skid plate rusted out and it will cost hundreds of dollars to make something we don't even like. The old skid also held up the fuel tank and the fuel tank is the main not the reserve.</p>
Boy I don't know about that. For a skid plate I'd want something much tougher and more abrasion resistant. At a bare minimum you would probably want to use Kevlar material if you want to mold it.
<p>how do you trim those intserts</p>
Use something like a Dremel tool with a thin cutoff wheel.
<p>Awesome!!</p>
<p>thanks sir for being being generous in sharing your knowledge. such a big help to someone starting a project. THANKS again sir!</p>
I'm thinking about building an inner fairing for my Harley that will house a small stereo, amp and some speakers. Do you think that would be too much weight for either of these methods, or can you suggest another method that will work?
<p>There's absolutely no reason why it wouldn't work for that.</p>
Do you add the resin to over the fiber glass?
Yep- you brush it on using a stippling motion in order to make sure the resin has fully impregnated the fiberglass cloth.
<p>This has been quite helpful.</p><p>I recently bought an older 4x4 to play with and the wings are prone to rust. Although mine are in reasonable condition they could be better. I was thinking of using the existing wings to create a mold. then use the mold to make some rust free wings for myself and a few friends on the Nissan Terrano forums.</p>
This is really a good tutorial. I was unknown about all these facts. Thanks for sharing the info about <a href="http://cybglassfibre.co.uk/" rel="nofollow">fibreglass moulding</a>.
This is a great method. However, You're using a lot of fiberglass, about twice as much which I imagine could get pretty expensive quickly (resin).
I like this tutorial, but I have a few questions. Do the edges of the packing tape leave impressions in the fiberglass (like if they are overlapped)? And will the foam hold up to vacuum bagging?
The edges of the packing tape will leave an impression in the mold- any surface imperfection on your pattern will be reproduced in the mold. The foam I used will hold up to vacuum bagging.
Do you answer your private messages and not mind helping people who are just getting started with this?
I'm happy to help- just ask! :)
You gotta love an Instructable that even goes as far as the Author drawing Instructions, to make sure people understand it! <br>Nice! :D
Thanks!
:)
Since people keep asking me questions about carbon Fiber, on my Portuguese DIY Blog, I've made a Post, pointing to this Instructable: <br> <br>http://faz-voce-mesmo.blogspot.pt/2012/08/fibra-de-carbono-ate-fazem-um-boneco.html
Any instructable about how to make reversed identical body parts like fenders etc? <br> <br>That would help me immensely. i have half a car done, and need to replicate the work on the other side.
The best way to do that would be to design your body parts using a computer and then create templates to make your molds.
The parts are already made on one side. So my only option i guess would be building a home made 3D laser scanner, and then make a 3 axis CNC big enough to carve the parts in layered format. <br>Again, very expensive, and time consuming. i was hoping for a more ghetto, but works idea. <br> <br>Thanks
Honus - still checking in after all these years?<br><br>Re: lost foam method:<br><br>A year or so ago, I suspected this might be a great method to make an irregularly-shaped diesel tank to add to my truck's crowded underbed spaces, so I poked around on the web for info to confirm that the sludge/goo that would result from melting the styrofoam with acetone wouldn't be a problem (thinking it would stick to insides of tank, leave a residue, etc.) I didn't stumble across your instructable then - but a major web-retailer of resin/materials said it /would/ be a problem, and advised me not to do it. Your experience makes me think that might have been bad advice. <br><br>Would you say I should plan to do hand-cleaning of the interior surfaces after the initial melting - so I'd need to have good access to all interior spaces in the tank for this? If there's residue, does it seem like it's going to be forever sticky (and maybe get mixed into fuel or cause other problems), or is this a non-issue?<br><br>Also - you mentioned something about epoxy/CSM turning into a big mess? My occasional experience with almost nothing but epoxy resin in the last ten or so years is that there isn't really a problem wetting out CSM fibers, and I'd definitely prefer to work with CSM in a project like this tank, since it conforms better to irregular surfaces. Maybe this has changed since you wrote this a few years back - styrenes in polyester resin being recognized as rather nasty toxins, etc. and I hear all but replaced with epoxy in many industrial applications. I do recall how magically the fibers used to melt invisibly into the polyester resin when I used it before (doesn't do quite that with epoxy) but I've not observed any alarming lack of strength in my dabblings. Do you still avoid epoxy/CSM combination?
I wouldn't use a fiberglass container as a fuel tank. Any type of fuel will act as a solvent so that would be bad. Commercial composite fuel cells have an internal bladder.You would be better off creating a steel or aluminum tank. <br><br>I still avoid using epoxy with CSM since the CSM uses styrene as a binder and epoxy resin will not dissolve the binder. The only time I really use CSM these days is for making some molds using polyester resin, and even then not that often. I much prefer using epoxy resin.
I might not use epoxy for a more volatile fuel, but with diesel, I have no qualms. Also, I plan to slosh the finished tank with a sealer, so it's not a problem, really.<br><br>Anyway, repeating my question about the 'lost styrofoam' process: Would you say I should plan to do hand-cleaning of the interior surfaces after the initial melting - so I'd need to have good access to all interior spaces in the tank for this? If there's residue, does it seem like it's going to be forever sticky (and maybe get mixed into fuel or cause other problems), or is this a non-issue?
as someone who has melted styrofoam before as long as you melt and clear within the same day it won't be a problem. <br>day 1- slippery goo similar do a runny egg(pulverize styrofoam for best results) <br>day 2- still slippery has a bit more body <br>day 3- starting to harden but still shapeable <br>day 4- becomes even more hard but small holes are a problem <br>day 5- if you get rid of the smell of gas from styrofoam makes a interesting ball once formed
Boy, I don't know. A lot of it is going to depend on how well you tape the foam pattern. If you do a good job taping it and then waxing you shouldn't have much clean up. I'd say you would definitely want to have really good access to get rid of any residue.<br><br>Have you run a test do determine the impact resistance of the fiberglass tank relative to a steel or aluminum tank?
I imagine the final product has to resist compression/suction from air forces, and not vibrate/flap during a race. How many layers of CF did you use for the parts on this project to ensure strength?
It was so many years ago I honestly don't remember but it was several layers.
Nice info! Will need to try this!
ahahahah! brilliant!<br />
Woow! Nice idea, Boss... <br>I like the subwoofer idea! Will try to build one for my car too...
Honus you are a huge inspiration, I love those sketches, and thank you for your most helpful and detailed instructional. I am going to hook in and make my own panels for my circuit car. Cheers from Down Under.
Thanks! Make sure to post pics when you're done!
You mention using clear packing tape to seal. Is there a reason why you use clear over the brown packing tape?
I use clear because it's non absorbent. Brown packing tape would soak up resin and it's also not as flexible.

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Bio: I'm a former bicycle industry designer turned professional jeweler. I like working with my hands and am happiest when I'm in the shop ... More »
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