Making a basic fibreglass panel

[agnoraan]

Here's a simple way to make one off panels like hood scoops, power bulges, spoilers etc


When I owned my Camaro I had intended to run a cross ram intake with twin Holley carbs as per the '69 Trans Am racing Camaros. The standard bonnet was built to take a single 4 barrel carb, so I decided to make an airbox on the underside of the hood from fibreglass to replicate the original steel Trans Am series racing ones. The airbox was designed to enclose the carbs to stop under bonnet hot air affecting the carbs performance, whilst allowing cool air from the high pressure area at the base of the windscreen to enter into the carbs, thereby giving it a ram air effect. My hood was an original cowl induction hood, but the underside would have fouled the new airfilter arrangement for the crossram.

I first started by placing the airfilter base to the underside of my hood to see where I needed to trim steel to make it all fit once completed. The tape marks show where the factory airbox runs under the hoods inner skin.






I drew a line around the filter base to see where things were. The two circles drawn on the hood shows where my carbs will fit.







A friend of mine in the USA sent me some dimensions from his friends crossram hood, plus I'd scaled it all up from photos to make sure it was correct in shape & size, to replicate the factory item. I then used some expanded foam and cut out the desired outline for the new airbox. This was then profiled and sanded down to replicate the original GM airbox shape and size.

[agnoraan]

Normally if I were to make a few of these then I'd make a mould to produce them, but because this was only going to be a one off I chose to make it direct from fibreglass instead. This is a similar process as to how Ed Roth the customiser in the USA built things from 'glass. Instead of making a mould he'd use plaster to get the shape of what he wanted to make & then 'glass over it, removing the plaster once it had cured leaving the desired fibreglass panel. Rather than use plaster for the "buck", I thought it better to use expanded foam as it was only a small panel and the foam is very easy to shape and work with. I put masking tape over the foam airbox & the surrounding parts of the hood, this would stop the fibreglass from sticking to the expanded foam & hood once it's pulled off from the "buck". Fibreglass doesn't stick to masking tape particularly well, so it forms a good, non stick barrier between the fibreglass and the item to be moulded.

[agnoraan]

The fibreglass resin & matt were then applied. I used two layers of 450 gramme matt, with the resin being rollered between coats to remove any air pockets or bubbles. Always be aware that too much catalyst will cause the resin to over heat, with the possibility of it catching fire. Many a laminating shop has burnt down due to this always mix the resin and catalyst in the correct proportions as per the manufacturers recommendations






Once fully cured I was able to trim out the centre to the desired shape to fit the airfilter. Next up is to grind down the new panel & give it a light skim of filler to finish it off. The panel was then removed from the hood, which enabled me to remove all of the expanded foam from inside & trim the surrounding edges to the desired shape. I could then cut away the surplus metal from the inner hood skin & repair that to make it look as if it rolled out of the factory that way.







After grinding the 'glass to shape & a light skim of filler here & there it was then ready to pull off from the bonnet & give it a final trim, I could then remove the foam from the inside. It's not nescessary to leave the new panel on the hood to repair it, but I found it easier than having it free at that point.

[agnoraan]

Here's the airbox having removed all of the foam from inside. I gave it a light coat of primer & trimmed the "opening" to the desired shape. I Just needed to prep the hood then prior to fitting the airbox.

[agnoraan]

Next up is cutting/shaping the underside of the hood to clear the carbs. As you can see from this pic the inner hood skin gets in the way quite a bit.





The bonnet was cut accordingly and re shaped with new metal as per the original Trans Am hoods. After the bonnet was modified to fit the shape of the new airbox, the filter and airbox were trial fitted for size. Once happy with the fit, the whole lot was sanded down and painted satin black.





This is a quick and simple way to make one off smallish panels such as spoilers etc, without the need to have to produce a mould to make it

cheers...Nige

[Paul Blore]

You're up early Nige.

Pace yourself, don't throw everything you've got at the forum in one go.

Paul

Just realised the forum clock is an hour out. Obviously still on GMT.

[agnoraan]

You're up early Nige.

Pace yourself, don't throw everything you've got at the forum in one go.

Paul

Just earliest the forum clock is an hour out. Obviously still on GMT.

Hi Paul, good morning to you . Yeah, I've just got in from a night shift, so it's now time for bed, I'm just winding down posting this up. I posted quite a bit of stuff up yesterday to give the new sections a bit of a kickstart, but will, as you say, pace myself from now on in as I don't want to give the forum content overload .

cheers..Nige zzzzzzzzz

[Roger King]

Good stuff, Nige - but (sorry) I'd do it a different way. I'd make a mould from the plug, out of fibreglass, then use a decent separating medium and line the mould with gelcoat resin, followed by one layer of surface mat. Then build up with CSM (chopped strand mat), I tend to use 3 layers of 600g. Doing it that way avoids the use of filler and keeps the whole thing 'glass and easier to work.
Gelcoat resin can be applied to the surface to finish, like filler, but it is air-inhibited so the very surface won't set. As long as you can overbuild, you can sand back easily enough but it's better to lay the gelcoat first against the mould for a mirror-finish. You can, however, get gelcoat to go off on the surface by covering with a piece of polyester release film and taping it down.

I can't emphasise enough the importance of using decent materials to get a great result. Avoid the motor factor's (or Halfords) 'Isopon kit in a box' sort of thing. I use these guys, great service and all the bits you'll ever need for fibreglassing:

http://www.ecfibreglasssupplies.co.uk

and they have copies of this, which is a brilliant book for beginners:

http://www.ecfibreglasssupplies.co.uk/p ... ckens.aspx

Just had to do major surgery on my footwell boxes (it'll appear eventually in the mag) so it's all pretty fresh in the mind!

Roger

[agnoraan]

Hi Roger, the way you describe is the "correct" way to make a fibreglass panel from scratch if you were looking to make more than one panel, or if you wanted a panel that was pure fibreglass. This is how all fibreglas panels are manufactured in volume, thanks for adding that, as it gives another insight into the world of fibreglass use. Do you have any photos etc that you could also put on here?

However, for a one off small item, making a mould can be a bit time consuming, plus you're doubling up on the materials to make it. Whereas the airbox buck was shaped from foam, to use the method of making a mould to produce a panel, you would have to make and shape the buck for the airbox from a different material, as foam and filler don't always work too well together. This again would be time consuming and more difficult to achieve the correct shapes required. For a one off item, foam is so easy to work with to make complex shapes

In most cases, filler would no doubt have to be used with either method to get the shape correct, I used it to finish the form of the item, and the "correct" method would use it at the beginning whilst making the buck if the shaping required it. The method I chose ie grinding down the surface of the fibreglass panel to form the shape, only required a light skim of filler to make it 100% correct.. Sanding down gelcoat is a right pain in the butt, as it's so hard compared to a filler, but as you say is perfect for the surface of a panel if used in a mould. I probably had about two hours worth of time in making that, so it was a quick, cheap, simple way to produce a panel


I used to own a fibreglass laminating shop that ran alongside my auto restoration business, so I'll take a look through my files and photos and see if I have any showing how to make moulds and panels from those moulds. If I have I'll post them up on here at some point.


cheers...NIge

[Roger King]

Yep, agree with all that - but I find gelcoat pretty easy to sand - I start with sandpaper, then go down a couple of stages of wet and dry and finish with Farecla. Gives a great shine and sands pretty quickly with a block.