Making a fiberglass light pod

[Gabriel~]

I'm looking to start making/learning to make a rally light pod for my STI out of fiberglass rather than fork out 3-500 dollars for one, plus I enjoy spending time working on my car (who doesn't). I was wondering on what is the easiest way to make a mold for this? I'm planning on making one that sits on the hood, 4 lights across, 2 small on the outsides with 2 larger ones in the middle, similiar to the ones below. Obviously if I had a light pod in person it would be easy to copy but without having one what's a good way to start this?

http://www.piaa.co.uk/rally/images/Subaru_lights2.jpg

http://farm1.static.flickr.com/167/381012440_ce326f17ca_o.jpg

http://farm1.static.flickr.com/147/381012449_ff51637cc5_o.jpg

http://farm1.static.flickr.com/138/381012445_6776de16f2_o.jpg

[lorenkb]

*Still a work in progress...*

*Note: I've tried to be as descriptive as possible here, feel free to ask any and all questions so I can make this guide as useful as possible. This may very well end up as part of a DIY thread later on. Comments on re-organizing what I have written to make more sense are more than welcome as well!

If you are planning on making a mold for the part you should plan on shelling out more than 3-500 bucks to begin with. If you just want to make a one off piece you can do it very cheaply. The initial cash outlay for starting into composites without doing it half-assed is never cheap.

The basic steps up front are the same for either method. You will need to build a plug: a part that has the exact shape of the final product.

Building your plug

Laying a base

You can start out by laying up the base of your part on the hood. In order to do that you are going to have to mask off the area of the hood you are interested in copying. This can be done several ways, here are a couple of examples.

1) Use masking tape to completely tape off the portion of the hood you are interested in. Spread a layer of vaseline on top of the tape and you are ready to go. I'm not a fan of masking tape for this kind of thing; it's half assed and requires more finishing work in the end. Every ridge/overlap from the tape gets transfered to your part, and vaseline is a mess. It's a case of less work up front for more work later on, although in this particular case it would work just fine (you won't be worried about the marks left behind as this will be the backside of the piece)

2) Use wax and PVA. Getting used to spending the time waxing things is crucial in using molds for composites. A layer of wax gets rubbed on, you wait the recommended time before buffing, buff, and repeat half a dozen or more times. It's extremely boring and absolutely necessary. If you aren't amazed at how reflective the part you just waxed has become you aren't done waxing. PVA, polyvinyl alcohol, is a cool green liquid that gets brushed or sprayed on, and then dries to a thin solid film. It dries into something like a really thin plastic bag. PVA is damned nifty, you can peel it off and start over if you mess up, resin doesn't bond to it, and you can wash it off your finished part with water. After you have finished waxing, you apply a single layer of PVA and wait for it to dry (a matter of minutes).

So you have a masked off hood and need some fiberglass. Here's another portion that has a couple of options. You can use fiberglass mat or fiberglass cloth.

1) Chopped strand mat. This stuff is dirt cheap. It's basicly short strands of fiberglass randomly slapped together in all directions to create a sort of cloth, rated in weight per area (ie 3 oz per square ft of mat). Fiberglass mat can be difficult to work with in areas with sharp corners or large bends. I hate mat with a passion. It's an irrational hate that may or may not require counseling, but hate all the same, and I avoid that crap like the plague. Other people love the stuff.

2) Fiberglass cloth. Woven fiberglass that comes in a variety of weaves and weights. Lighter cloths will conform to all sorts of shapes and corners more readily than a heavy cloth. The really fine stuff, say 0.6 oz per sq. yard, is really really flexible. Cloths more towards the realm of 6 to 8 oz per sq yd are much better suited to a project like this. The weave of the cloth also determines how readily it will deal with corners. Plain weave is the stiffest, followed by various harness weaves, followed by twill weaves. Harness weaves are great for this kind of project as they are flexible enough and cheaper than twill weaves.

Right, so you have your masked off hood, you have your fiberglass, and you are ready to slap some resin in this bish! Oh yeah, resin...

There are lots and lots of various resins, and I'm not about to try to compare them all. The short of it is you don't need aerospace quality resin, but some two part 5 minute epoxy from the Home Depot isn't going to work either. Any laminating resin should do the trick, but there are a couple of things you need to care about in choosing a resin:

1) Curing time, AKA pot life. Each resin comes in two parts, the resin itself and the hardener. The resin doesn't cure until you mix the two together, and once you do mix them you have a certain amount of time to work with the resin before it starts to harden. Most resins come with a variety of hardener choices, from fast to extra slow, rated in pot life. Pot life is the time it takes for a small batch (say 100grams) of resin to start to cure if left in a small cup. Keep in mind that curing time is affected by how spread out the resin is. A cup filled with 100g resin will cure much faster than a 100g spread out in large tin pan, even though you have the same amount of resin either way. So even if you mix up a batch of resin with a 10 minute pot life, if you get all of your resing down quickly into the cloth it won't start to harden up for 60 minutes or so, giving you plenty of time to do other stuff like setting up your vacuum bag (more on this later)

2) Temperature. Yeah, that's right, I'm talking about the weather. Resins have a limited range of temps that they will work within. Too cold and they just won't cure. Too hot and they cure so fast you don't have any reasonable working time. Pay attention to what kind of temps you expect to see and order hardeners accordingly. Humidity also plays a role, but this is a problem most people don't have to worry about.

Now, before I talk about laying up the base itself, lets talk about strenght and stiffness. The more layers the stronger the part. To get stiffness, you want thickness. You can get this by using a lot of layers of glass, or by using a core material. Core materials can be many things, from foam to balsa to honeycomb. A good example would be CoreMat or AeroMat. These are both 2mm thick cotton like material. They are flexible, thick, and resin permeable. So, take for example two parts. One is 4 layers of fiberglass, and the other is a sandwhich of 2 layers of fiberglass, one layer of AeroMat, and then 2 more layers of fiberglass. These two parts will have essentially the same stength, but due to the added thickness of the AeroMat, the second part will be much stiffer. Note that parts with bends in them will be stiffer by nature than a flat part (like adding ridges in a flat steel plate to increase stiffness)

OK, so everything is in order. Mix up a small batch of resin (don't skimp on the mixing!) and spread a thin layer over your prepped surface. Disposable brushes are your friend. Start with small batches, and if you are worried about curing time transfer the mixed resin to a large baking tin or similar to spread it out and slow the curing process. You'll get the hang of mixing the right amount of resin soon enough. Once you have a thin film of resin over the masked out area drop an oversized layer of cloth on. It's a good idea to always have couple of inches of overhang on your part that won't get any resin applied to it. With a bit more resin wet out the cloth, making sure the cloth is conforming to your part as you go. You can tell when the cloth is wetted out by the cloth going transparent, and once this happens you don't have to lay on any more resin. Too little resin will give a splotchy appearance to the cloth... you'll know what I mean when you first do it. Lay on another layer of cloth followed by a bit more resin, and repeat as you see fit. For this particular project you are just after a base to build off of, so 3 or 4 layers at the most should do it. You really shouldn't have to use any core material either, but feel free to experiment with making two bases, with one having an "X" of core material sandwiched between a couple of layers of glass.

At this point you have the option of using another nifty bit of material called Peel Ply. Peel Ply is a chemically treated polyester that won't bond with resin. You can lay a piece of this over your entire wetted out part, and pat it down using a brush. The peel ply will soak up a bit of resin, and can me massaged into the part such that it becomes fully wetted out itself. Make sure the peel ply piece you use has a good amount of overhang past the wetted out portion of your piece, so that you have somethign to grab onto later when you try to peel it off. The whole point of this cloth is to give the topside of the piece a uniform surface that facilitates bonding later on. An uneven or glossy surface is not a good surface to bond things onto at a later time.

At this stage the wetted out cloth will be very easy to cut with the resin still uncured. You can do some preliminary trimming if you'd like, or wait for everything to cure. If you do any trimming pre-cure get a good pair of heavy duty scissors, and fill a glass with acetone/alcohol. When you are done trimming drop the scissors in the glass and clean them off. Post-cure, thin parts can still be trimmed with scissors, and thicker parts can be trimmed with the power tool of your choice (dremel with cutoff wheel, die grinders, etc.)

Let the part fully cure, and I mean fully. Laminating resins take a long time to fully cure, as in don't touch that thing for a full day. If you are operating on the lower limit of the resin's temperature range expect it to take even longer.

Once the part is cured, begin by peeling of the peel ply. This is best done before removing the part from the hood if at all possible. The peel ply will be hard to remove, but it will come off. Pop the part off the hood and do any final trimming and cleaning as required. You now have a base to build on.

Building on your base

Now that you have your base, you can start shaping the rest of your part. I really like working with a combination of 1/8" sheet balsawood and blue insulation foam. Both are easily sandable and relatively cheap. Bond the balsa with thin CA (superglue), and use oderless CA (AKA foam safe CA) when working with the foam. Regular CA will eat through the foam. This combination of materials is great for rapidly building up large shapes with minumum downtime.

Both balsa and CA can be had at hobby shops, and you can pick up large sheets of the foam from Lowes or Home Depot. I like the blue foam; it has a smooth beadless texture when sanded and isn't flimsy. Pink foam works just as well. Stay away from the white foam that have visable beads. If you need to create structural bulkheads or want a surface to act as a guide while sanding use plywood (the balsa and foam sand much easier than the plywood, so the plywood acts as a stop-guide while sanding).

If you are just making a one off piece, here is where you have to start thinking of the strenght of the part. You need a good internal framework of plywood to act as the structural core of your part. If you are making a plug to pull a mold from the internal structure is much less critical.

Start with referencing your critical areas. In this case these would be where you want your lights. Lay the piece back on teh hood to make sure it stays in the right shape, and then jig up a front plate that matches the profile of where you want your lights, and bond it in place. How you get it in place doesn't matter, random bits of balsa and foam, whatever, just make sure you have that front plate exactly where you want it. Plywood rings for the lights to mount to would be a good idea to include as part of the front plate.

If you are going with the one off piece, start tying your front plate into the base structurally. Plywood rings to mount the lights too, connected to a framework of plywood across the entire base.

From here, you get to shape the light pod to the desired shape. A framework of balsa/plywood with foam filling in the gaps to form a solid surface. Sand to shape.

to be continued...

[MrToad]

www.westsystem.com/ss/assets/Uploads/03-Lostfoam.pdf (http://www.westsystem.com/ss/assets/Uploads/03-Lostfoam.pdf)
This is a pretty simple technique. I recommend the WEST System epoxy resins highly. Source materials through boat building suppliers. Have fun and wear a mask when you're shaping the foam.
JT
PS, you'll need to copy and paste the full link to get it to work.

[socalximpreza]

http://board.tercelonline.com/viewthread.php?tid=20489

http://www.sl-i.net/FORUM/viewtopic.php?f=39&t=20161

[YOGI]

What process should you use if there isn't a pod made for your car get one close modify it and start reproducing them or just make one from scratch