Working with Fibreglass. Making a Hatch

[jimmy19650]

Last time I tried to post a how to on fibreglassing it got deleted. So here goes again.

I have been making a fibreglass hatch for an AE86 to fit existing fittings and glass. The molds I will be using were made about 5 years ago and have been used a few times.

I wont cover the layup of the bits yet, as I dont have any pics, but will do a complete how to on the next project.

This post will cover the joining of the 2 halves, and fitting of all the mounting points.

The hatch is made in 2 halves, the inner and outer. Firstly the molds are waxed, and in this case, I sprayed several coats of PVA release agent to ensure a good release.

Next I apply a layer of white gelcoat, either by spraying or brushing, to a minimum thickness of 0.5mm. This thickness is very important, as is the consistency. Too thick-heavy and brittle, not too much of a problem. Uneven-will result in uneven shrinkage and distortion. Too thin-often results in tripe, which is the wrinkle like finish often found in cheap products. There are many other problems, but these are the most common.

Once the gelcoat has tacked off, 1 layer of split strand matt is applied to support the gelcoat. It is important that this layer be allowed to cure, and any air bubbles are removed or repaired. Once air bubbles and defects are repaired the structural layers are applied to the required thickness, and carefully rolled to remove air. In the case of the hatch, the joining areas are made slightly thinner so when the halves are joined, the thickness is not excessive for the window rubbers etc.



This pic shows the outer skin layed up in the mold. You can see the excess material which will be cut later. In the outer skin, I used only 2 thin layers of woven cloth preceeded by 1 layer of split strand matt to support the gelcoat. I used Unwaxed polyester resin, with no more than 2% catalyst. Regardless of what people say, the catalyst ratio is critical to prevent shrinkage and distortion.



A close up of the finished outer skin in the mold showing the woven cloth. Woven cloth is a lot more expensive than chopped strand matt, however, it results in a much stronger component.




Here is a pic of the hatch inner laid up in the mold. Here I have used 3 layers of chopped strand, about 2.5 times thicker than the outer skin. I used the chopped strand glass here because it is easier to mold to the complex shape. Holes will be cut out later.



A close up of the chopped strand glass on the inner skin




The outer skin popped from the mold. I use wooden or plastic wedges to remove items from mold so the product or mold isnt damaged. the outer skin is actually quite flimsy at this stage. But this is necessary so allow joining to be successful.




Lowering the outer skin onto the inner skin, which is still in the mold, to check for fit.


The outer skin lining up perfectly with the inner skin. I keep the inner skin in the mold to ensure dimensional stabilty while joining. Once I am certain everything lines up, I will trim excess.





Here are some Trueno light bezels I started preparing for molding. I blocked off screw holes with plasticine, then applied 5 layers of mold release wax. I then sprayed 2 layers of PVA release agent, just to make sure. Next step will be the gelcoat.

[Sam-Q]

very awesome, how on earth did you make the woven matt suit that shape?

I am guessing your not interested in making a few of these?

[jimmy19650]

Sam, last time I mentioned making some, or the word sell, the post got removed. And that post had some great info in it. As for the woven cloth, it is only 190 gram cloth, so it fits very easily on the outer skin. I only used 2 layers of woven with a third through the centre away fron the joins. If I was going to make more of these, I would vaccum bag these with a 3-5mm foam core, making them super light and stiff. On the subject of woven cloths, different weaves drape more easily than others. A plain weave, like the one used, drapes reasonably well. Twill weaves, which are used more frequently with carban or kevlar, drape even better. However, these weaves are also more expensive. Woven glass can be up to 3 times the cost of chopped strand or split strand cloth. Carbon is about 6-7 the price of glass, and kevlar is probably 7-8 times the cost of glass. Depends greatly on manufacturers and suppliers.

By using the thin flexable outer skin, the woven glass actually makes it quite strong still, I can flex it around the thicker inner skin which is almost 3 times as thick, and join more accurately. The inner skin gives it the rigidity, and it is on the inner skin where the metal inserts are fitted. Once joined, the whole unit is quite stiff.

I have made a few of these in the past with no problems. The biggest bonus is that they CANT RUST.

[Sam-Q]

I went to the liberty of looking in the trash can of the forums and saw your previous post. It was comercial in nature and hence without being a sponsor you where breaking the rules. So keep this thread without any mention of selling these and instead just about showcasing what can be done with some very good skills. If you want anything recovered out of that old post let me know and I can do it, perks of being the tech admin and all

- Now there is some talk about not being able to use gas struts because they put too much stress on the frame, any opinions on this?

- hows the weight of your prototype?

[haveaparty]

How did u make the moulds for them. I've always wanted to do this sort of thing but not 100 % on how to. I know how to fiberglass just not sure how to make the moulds.

[jimmy19650]

I will do a complete 'how to' make molds with the Trueno light bezels which I have showed the 2 first steps within the post already.I probably need to add the wax to use is a silicon free mold release wax. The bezels are obviously different in size, but identical in process. Making molds is a very precise process as the quality of the molds determines the quality of the finished product. Also materials in molds are slightly different to the materials that are used in products. As a general rule, a mold needs to be at least 3-4 times the thickness of the final item to maintain dimensional accuracy. A good mold will result in hundreds of items with minimal maintenance.

[haveaparty]

Yeah cool. I've got the idea of how it works just don't know wat to make the mould out of. Or if u need to make some sort of jig up aswell. I havnt got the room to practice now but I was gunna get an old bonnet and just practice on the until I work it out for my self. But couple how to make moulds would be awesome.

[jimmy19650]

Mold is made form exactly the same materials as the products, except we use a slightly different gelcoat, and the mold is thicker. You are correct about bracing, some bigger molds need a metal or timber sketeton to keep then dimensionally stable. A bonnet would definitely need bracing, as would the hatch mold.

[haveaparty]

Yeah I know that te moulds are just thick version of the product ur trying to make but didn't know how to go about making a mould.

Well wat I was thinking to do with the outta of the bonnet is get a big board of mdf or wat ever wood. Put the bonnet on it with the inner facing down. Get 4 other pieces of wood to make 4 walls, like fence pickets or wat ever, nail them on. Then pretty much fill it up with glass and resin, putting all the correct release agents down first of coarse and once its done crack it off. Then in theory u should have a nice strong mould of the outer of the bonnet. That's wat I was thinking with that cause they are relatively flat with out many curves or lines in them. Think I might just get all the materials I need then trial and error lol. Can't be that hard to work out my own technique.

[jimmy19650]

Sam-Q, weight is a bit lighter than standard, but not much. I would gues by feel 1 to 1.5 kg. The reason for this is that fibreglass does not posses the same stiffness as steel in similar sections, so I need to make the fibreglass section considerably thicker to compensate. Ideally, you would make what we call a sandwich laminate and use 3-5mm foam sandwiched between thinner layers of glass to add stiffness and reduce weight considerably. To do this, you really need to vacuum bag the item, (put laminate in a huge vacuum while resin is curing). This obviously adds cost and complexity. With the hatches I make, I generally make the outer skin light and flexable so I can glue it properly to he inner skin. All the strength and stiffness is in the inner skin, and it is here that the hinges, struts and locks attach, with the aid of aluminium inserts into the laminate. So to answer your question, yes the hatch will operate normally using all the standard mounts, hinges, latches etc. Many of the light weight hatches available use a thin layup on both halves, which then makes the struts and locks inoperative. Realistically, I think people need to understand that the steel hatch is actually quite light, it is the glass that adds the weight. The fibreglass hatch may shed under 2kg, but the glass panel is still the same. The real weight saving is by using poly carbonate or acrylic in place of glass. The major benifit of a fibreglass hatch is the fact it is RUST FREE.