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An exploration in body fab/mod - race tail section

zeefrenchspy

zeefrenchspy

New member
Joined
Sep 21, 2006
Location
Palo Alto and SF
Moto(s)
race NC35, 620 Multistrada
First of all, this isn't a "How-to", as I'm figuring out things as I go. Second of all, as Chris (tygaboy) has mentioned many times in his CF threads, if you just want the part, go buy it. Sharkskinz sells the end product for 200 for the tail and 60 for the undertail. It'll probably have a better finish and it'll be on your bike sooner. linky items 4104 and 4106

Working with composites (fiberglass, CF) is often the result of one of two things, you either want something custom made (i.e. no one sells the exact shape you want), or you enjoy creating things on your own, even if it's replicating existing products out there.

For me, this tail section work is also a great opportunity for me to practice using molds to build parts, as well as get back into the swing of composite making so that if/when I move on to CF, I won't be making many mistakes :blush

All the mods are being done to my '01 R6, for reference. So anyways, the idea was that I had 2 tail sections on my hand, and I decided that I would make one into a solo tail (with integrated cowl) for increased bling-age at the track :twofinger Then I realized that if I wanted to truly maximize the bling factor, I would also have to make an undertail with no holes for the lights :teeth

For the tail piece, the plann is to graft on a fiberglass cowl to the existing plastic part, making it a frankenstein of body work :green but since it'll be painted over no one will ever know!

These beginning pics are from Chris's seminar weekend where the initial shaping occured. Here is the donor part, with a piece of cardboard blocking the passenger seat hole, so that we can use that as a base to start building up the foam:

2951201-images00001.jpg
 
Here Chris is done mixing up the 2-part foam and has poured it onto the supporting cardboard. The foam wieghs nothing, so it's not really pushing down on the cardboard, and it will stick to the plastic on contact, so it will become self-supporting (i.e. the cardboard is only necessary for the initial step)

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Let the first layer of foam expand a bit, look at how it's shaping out and how it will effect the second pour:

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Next up, trim down the foam from the first pour so that the foam from the second pour will fill up all the gaps and you're not left with too many holes in the foam shape. As you can see, this is very general shaping.

2951226-images00011.jpg
 
Pour a second batch of expanding foam on top, and let it fully rise. The tail piece is truly starting to look like a frankenstein :green

(note: by this point, some people were starting to doubt the idea of what I was doing. no offense, it is a littel crazy :p )

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Now that you have all the foam that you could need to create your shape, whip out the cheese-grater thingy and shape that foam into what you want your final cowl to look like. In retrospect, you would probably want to shave it down an even 1/4" all over so that once you layer it with fiberglass, you're left with the shape you want, and minimal bondoing of the body is necessary. Of course I didn't do that and now I'm filling in tons of gaps and making the transitions smooth all over the place :cry

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Now that you have a solid support for the shape you want, you're ready to lay on the fiberglass. Note for the shaping, it helps if the light and the angle at which you look at your part is very small, so that bumps and divots in the foam create shadows. This way you will get an smoother result.

Layed on a total of 3 layers of glass (I think) here, so I might want to come back later and add a layer or 2 from the inside to make the cowl stronger. You never know when you're going to have to give some hottie a ride in the pits so it's gotta support minimal weight :teeth

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The next step for the tail piece, is lots of sanding to trim off the excess and non-cured glass. Then bondo over the bumps and divots, as well as all the edges of the glass so that you can sand it back down smooth. Sand off the excess and repeat until I'm satisfied. I'm not there yet, so I'll post up a pic of what it looks like when I'm done with the process.


In the meantime, let's start on the undertail. The stock one has holes in it to support the fender/plate bracket, as well as holes for the taillights, both of which are un-necessary at the track. Since I need a completely new part (and only have one undertail), I need to create a mold for this one and make a part out of the mold. Because I'm not making of copy of the stock undertail, but instead modifying it, I'm simply going to modify the mold so that it will produce the piece that I want.

Here is the original part, taped up and preped for the glass:

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Note that in the previous pic the excess tape doesn't matter, as I'm making the mold. So any protuberances on the part will result in depressions in the mold, which will be filled in prior to making the final piece.

Unfortunately I didn't have much fiberglass on hand, and was only able to lay down 2 layers over the entire piece, probably not ideal. :teeth

This isn't the cleanest mold, but it's an undertail, so who cares! Until I crash or someone sticks their nose up under my subframe, no one is ever going to see it, so having the edges perfectly draped is not much of a conern.

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Let it sit overnight and pop the piece out in the morning. As expected, it's a little flimsy and will need to be reinforced tonight. Also one thing I though of later on that might help, is making your mold out of many smaller pieces. Having one big piece of cloth makes for a stronger part, using less epoxy, but it doesn't provide the overlap and torsion resitance that you would want in the mold. So plan on big pieces of fabric for the final part, but smaller ones for the molds.

It's also very transparent :cool

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As I used tape to plug up the tail-light holes, it caused some irregularities in the fabric and allowed some air bubbles to sneak in. This would be bad if you were making a copy of the part, but since I'm planning on filling in the cavity left by the light housings, it doesn't matter in my case.

Admire my shody mold full of air bubbles (only in the tail light part, the rest is smooth :cool )

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That's it for now. When I finish touching up the mold and doing the bodywork on the tail piece I'll post up with an update :thumbup
 
I am planning to do the same thing.. with my cracked cowl.. where do you get he foam from.. and what do you use to cut and shape it???

lastly, how come I never get invited to these modding meet?


sweet...:cool
 
The foam was 2-part foam that Chris had on hand. I believe it's this stuff: linky. Not cheap :shocker , but Chris had it on hand :teeth If you don't need that much, some expando foam from Home Depot probably works as well, as long as it doesn't react with the plastic and isn't toxic when you sand it down.

To shape it I used a generic planer/cheese grater looking thingy. Can't find a link/pic off hand, but a basic scraping tool.

It's a lot fun, do it!

Edit: You have to move quick to make it to the modding seminar, as they fill up fast. I think this one was full in under 24 hrs!:wow
 
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zeefrenchspy said:
You never know when you're going to have to give some hottie a ride in the pits so it's gotta support minimal weight :teeth
Click to expand...

so much for that idea.. the foam cost half the price of a new solo cowl.

and FYI hotties are always at minimal weight..;)
 
what do you use so that the new fiberglass mold will not stick to the stock undertail. when cured?
 
You prep the part (in this case the undertail, when I go to make the undertail, you prep the mold) with PART-ALL so that it doesn't stick. You also put some PVA on the part so taht the part/mold that you are making gets a nice glossy shine to it.

It's this stuff:
PART-ALL
and
PVA

more moderately priced and you use it for pretty much every mold part that you make, so it goes a long way :)
 
Nice work! :applause
And you can always put that mold back on the part and add more 'glass and other reinforcements.
Looking forward to seeing the finished product.
 
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