Tips/suggestions on how to mold a fiberglass part?

[jnshk]

I'm working on version 3 of my gauges configuration, and this time I'd like it to look a little cleaner. This is what I've got so far:

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I've decided that it might be beneficial to make a mold and produce my own fiberglass part rather than trying to one-off this from multiple DIY components (because if I screw it up I don't want to have to start from scratch again). Also, if it's successful and there is interest, I might be able to make it available to others at some point.

The plan is just to make an overlay that sits on top of the cluster hood, not to make a complete replacement gauge hood. I've started masking the gauge cluster hood, and have almost got it ready. Obviously the masking tape will create a mold that will need some detail finishing and smoothing, but the overall structure should be what I want.

EDIT: I've just realized that I will have to do this as two halves, or else I probably won't be able to lift the fiberglass away from the hood as the angle of each pod would "lock" the fiberglass around it. So that's at least one complication I will have to deal with.

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The problem is, I've only got minor experience working with fiberglass, and none of that involved making a mold of any kind. Can anyone give me some tips, suggestions, etc., before I dive in head first?

[jnshk]

Well, I've been doing some research via Google and found that there are a LOT of different approaches to this that I could take. So far there's one that really appeals to me though because it would allow me to make a single mold and also require less finish work on the final pieces. Unfortunately, it will require that I do more finish work on the prototype and will probably be more expensive on materials up front (though perhaps not too terribly bad). I found this write-up [External Link] on using a silicone molding compound, and it should allow me to make a one-piece "glove mold" which I could reinforce with a 2-piece backing layer.

I'm still open to tips/suggestions/hints if you've got them though.

[HELLIONMX5]

wow man, this was my next project :/ well, great minds think alike. I just finished up my custom gauge plate. still going to work on it though. hopefully Thursday or Friday. I too am not good with fbrgls.

[— Malibu Q —]

Don't bother with the silicone mould.
The resultant fibreglass or carbon part will almost certainly be warped.

If you take a mould of the top of the hood and remake it it will not fit over the hood.
It will be too small.
To start, cover the hood top with release agent and a couple of layers of fibreglass cloth.
When it's dry sand skim with filler and smooth.
Fill the gauge holes in the accessory pods with fibreglass and filler.
Install the pods onto the hood cover.
Personally, i would make them sit as low as possible without the gauges cutting into the original hood.
Get creative with filler moulding them in.
Complete the perfect prototype by finishing to a high standard with automotive finishes.
The mould for your design will have be two piece with a split down the middle.
Apply release agent between two strong pieces of wood sheet or similar and bolt them together.
Carve an edge of the wood to match the join in your mould.
Cover the prototype with release agent.
Paint with gel coat then apply say five layers of chopped mat.
Moulds need to be strong to avoid warpage.
Glass in the wood to form the mould seam taking care to make it look straight.
When it is all dry destroy the prototype to remove it from the mould.
Use a 1mm cutting blade on a grinder to cut through the bolts on the mould join.
Using the 1mm blade again cut gently at the mould join through the gelcoat and fibreglass until the mould separates.
Use filler to finesse the mould join.
You are ready to make your custom carbon hood covers.
Good luck.

edit: Lots of work here. I'd jut bolt on the accessory pods to my original hood and leave the fibreglass itch behind.

[jnshk]

Thanks for the suggestions/guidance! I think you're right that I will definitely have to produce a "perfect prototype" as the first step. The more I reflect on this project the more I find minor complications.

I'm not yet ready to give up on the RTV mold option yet, but I may have to give in and do it old-school like you suggest. I've been practicing on the smaller and less complex scale by molding/casting my passenger air-bag cover. So far, the indications are that the mold is very effective, but my skill/technique at working fiberglass still needs some practice. I've been using a slow-cure marine-grade epoxy resin which exhibits minimal shrinkage and excellent flexibility, but the problem I seem to be having is how to get all of the air bubbles out effectively. When I mix the resin and hardener, I get lots of tiny air bubbles suspended in the mixture which I've been having difficulty in eliminating before/while applying the fiberglass to the mold. Any tips on how to deal with air bubbles in the resin-mix?

I've attached a couple pics of the first two practice pieces that I've made. I'm reasonably pleased considering I've basically got no clue what the hell I'm doing here, heh. Fitment is pretty much spot-on, but it's obvious that I need to improve my methods of laying the fiberglass to remove trapped air bubbles and get more "even" distribution of material.

Test #1
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Test #2
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You may not be able to tell from the photos, but the texture reproduction of the original is excellent (except where I failed to adequately remove air bubbles).

[—RuckkehrMiata—]

I have actually thought of buying some basic kit and foam etc and just molding random things to learn.
It sounds like an amazing skill to add to a tool belt.

What would people even recommend for beginner supplies for playing around / learning how to do fiberglass? I have read a bit about it, but I never know what might be missing as a useful or necessary tool to learn.

[— Malibu Q —]

Jnshk,
Well done with the air bag cover.
That's a neat thing to make from glass.
There may be a market for a airbag replacement glovebox door.
You could hold it down with Velcro to make a secret hidey hole.
Try using flat black gel coat on those covers.
Gel coat is your resin mixed with pigment and filler and will give a nicer finish
Paint it on and leave it until it sets off but is not cured before glassing over.
Those pieces will pop out finished.

RuckkehrMiata
Making from foam is great fun. You can build anything you can imagine. Cut with hand wood saw, glue bits together with clear wood glue (slow drying ) shape with #40, glass.

Beginners kit:
Release agent (many types available)
1 litre polyester resin
Hardener
Graduated syringe for hardener.
Glass cloth or mat. Mat is coarser and cheaper
Mixing cups
Stirring sticks
Disposable brushes, I like 2"
Plastic applicator cards for body filler
Acetone for clean up
Box of disposable gloves
Paper towels for clean up
Plastic drop sheet, I use auto mask film which comes on a roll
Freezer paper
Scissors

Cut cloth layers slightly larger than part
Position on glossy side of freezer paper
Mix resin and hardener
Paint some resin into the mold
Pour onto cloth and spread carefully with applicator card without damaging the cloth until the cloth becomes clear. Try not to have too much resin on the cloth in the finish as it adds weight and is more crack prone
Upend it into the mold, remove paper, pat down with resin brush. Second coat if required.
Cover with plastic sheet and press the glass into mold with the applicator card and your fingers. If the plastic is sticky (it probably will be) lay another sheet of plastic over the first. You're trying to remove air bubbles and any excess resin
Pull off the plastic after the resin has hardened. Full cure at room temp is a couple of days.