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Q: creating a mould to fibreglass of an existing part


sky1911
04-30-2013, 06:03 PM
Hi guys,

I have a question that has been tormenting me for a while now. The issue at hand is that I want to recreate the body of a car (1/12 Tamiya 312T kit) using fibreglass, much like the real car. I have the kit mentioned above, so essentially I could just use the original kit parts as templates - after slight preparation (sanding, etc to remove imperfections, sinkholes and what have you and possibly to improve the fit of the parts if necessary). So I would need to create a mould of the original parts. This should be easy enough for simple parts like the sideskirts of a Formula 1 car. However what about the airbox? I am thinking this might be a two-part production, again like the kit part. First moulding one half, then the other and later joining the parts and maybe adding another layer or two of fibreglass to the mix.
As for building moulds of more complicated shapes like that of a 60's or 70's sportscar (think Lola T70) I intend to go about it much in the same way this guy (http://www.gt40s.com/forum/lola-t70-lounge/19604-canamsa-sa-stratch-build-12.html) did it for the build of his own Lola T70 clone - see around page 17 for details on creating the mould for the nose section of the car.

So after this long winded introduction, the question is what kind of wax & tooling gel would you recommend for using in this 1/12 application. Possibly not the same you would use on a 1/1 car, but something maybe a tad finer. But this is just a guess. Also what type (brand) of resin should be used to lay up the fibreglass, both for the mould and later for the actual part?
Fibreglass cloth is on its way to me. Various weights of 25gr, 48gr, 80gr and possibly 110gr for the backside of the mould to give it some strenght, maybe reinforced by some foam ribs where the T70 guy used wood.

I know ScratchBuilt did some fibreglassing in 1/8 scale and I have the weights and dimensions he gave during the 908/3 build and used them as reference. However, it seems ScratchBuilt didn't create a negative mould but rather built up the fibreglass on top of his foam base using vaseline as release agent. That technique won't work for me as it will screw up the size and fit of the parts. They would have the original size enlarged by the thickness of the fibreglass layered on top of it.
Dan of 1/8 GT40 fame created a negative mould and also shared his layup, which is what I intend to do / use. So I have a rough ballpark figure for the cloth / layer / strength I need. Sadly I'm missing the brand names - do I use automotive products or rather specialist modelling stuff (probably a sight more expensive). Any help regarding those brands is appreciated.

Also has anyone ever done this (I would think yes). And for the "why would you want to do that crowd": I want to learn and master (yea, right) a new technique. And in case my "experiment" fails horribly, I can still go back and just build the kits using the original Tamiya parts. That aside I'm also working on recreating the chassis parts in metal for both kits...

JeremyJon
04-30-2013, 06:28 PM
depending on the shape of the part you want to make, then probably just make an inverted RTV mold, cast the mold in a strong case (like a small box or plastic bin) so you can pull the mold out to de-mold, yet put back in for structure
with the mold cured, then spray with mold release, and lay up the fiberglass in the RTV mold, just like they do with boats in this same fashion
also you could then lay in a first coat of gel coat!

good luck!

sky1911
05-02-2013, 12:39 PM
Thanks for the reply! Well the shape will be different from car to car, of course, and of the models I have at this time (Lola T70 MK3 and Ferrari 312T) the Ferrari will be the test mule. For one its shapes are considerably less demanding to cast or lay up and two it was always considered to be my test bed for trying out new techniques. I want to try casting metal at some point as well.
The Lola has one of those instantly loveable shapes the GT cars of that period have - think 330 P4, GT40 MK4, Chaparral 2D, ...

Anyway, I have ordered the first few square meters of fibreglass cloth so I will have to move forward. I don't think I'm going down the RTV mould route with this - at least not on the first try. Much rather I'll be coating the body parts with some wax and will then start laying up fibreglass layer after layer to create a negative mould - maybe break them up into parts as indicated in the links I've posted. Then i will join those individual moulds and will cover them in wax again and will try to layup the actual body (copy) using a few thin layers of cloths.

Still need pointers on the wax or possible other release agents, resin.

jano11
05-02-2013, 01:43 PM
You will need a mold of some kind of the exterior of the body shell that you want to replicate. Then you can lay fiberglass cloth and epoxy layers inside it. Using vacuum bags during curing of the epoxy will help with the quality of the parts.

sky1911
05-02-2013, 02:48 PM
Hi Jano,

I want to create the mould of the body by treating the original body with a wax compound (serving as a sealant and release agent) and then laying a number of layers of fibreglass on it. Then, once that is dried and hardened, I will remove it from the body and thus have the negative mould. Then I will clean it and treat it with the same wax compound and start laying up fibreglass on that negative mould to get the actual body. Very much the same way the guy in my links did with a 1:1 car.
Only that for certain parts (say nose part of the Lola) I will have to break the shape down into a number of individual moulds (maybe upper half, lower half - maybe more) that will later be joined (cleaned and the gaps removed) to make one complete mould for the entire nose section.
If I were to create the mould for that piece in one step, there is no way I could remove the mould without destroying the original part - which is not an option. Hm, maybe RTV could work here :dunno:. I'm just not sure how well RTV would handle when you try to lay up fibreglass on it - it being flexible and all. hm

cinqster
05-02-2013, 06:57 PM
Just had a quick skim through your questions and I have a few suggestions as I plan to do a similar project in the not too distant future.

I've not done exactly what you are asking about, but I have done lots of small polyurethane resin castings and fibreglassed many 1:1 parts.

Firstly, I would suggest using a gelcoat on surface of the mould and the copied part. This hides any 'witnessing' of the cloth, or matt material through the surface. Gelcoat dries by lack of oxygen which is caused by the overlaying of the cloth, matt etc. The lay up resin is different and air dries OK.

On the mould use a bees wax parting agent, this needs to be applied and polished 6 times and is a very tedious job, then finish with blue PVA agent on top. This is normally painted on and I've had problems with it leaving brush marks on the mould surface, sponging is better. I considered airbrushing it on, but from what I remember it's nasty stuff so be very careful if you do that and use safety gear.

I also would be tempted to use grp tissue instead of cloth. It will take to compound curves far better and is suited to the body shapes you've mentioned. It also doesn't need stippling so vigorously to wet it out which may be an issue if using RTV moulds. Never tried it, but I imagine brush stippling cloth on rubber moulds may leave pressure marks on the copied surface?

I have poured polyester into RTV moulds for solid castings and the biggest issue for me it that the pieces always have a sticky surface, which never fully dries. Not sure if epoxy resin would behave the same way. I have been told it's a reaction to the RTV and that there are more compatible polyester resins, but not found them yet!

For something like the T70 nose section, I'd be looking at a 4 part solid mould if not using RTV. I would go for the centre top area with a join along the top of the wings to side sections and another part for the front lower valance. Watch out for details like air scoops and holes that may have too much return.

Hope this is of some help and let us know how you get on!:)

Meant to add, for epoxies, lightweight cloth, tissue etc. have a look at suppliers for RC model aircraft.

jano11
05-03-2013, 11:58 AM
Hi Jano,

I want to create the mould of the body by treating the original body with a wax compound (serving as a sealant and release agent) and then laying a number of layers of fibreglass on it. Then, once that is dried and hardened, I will remove it from the body and thus have the negative mould. Then I will clean it and treat it with the same wax compound and start laying up fibreglass on that negative mould to get the actual body. Very much the same way the guy in my links did with a 1:1 car.
Only that for certain parts (say nose part of the Lola) I will have to break the shape down into a number of individual moulds (maybe upper half, lower half - maybe more) that will later be joined (cleaned and the gaps removed) to make one complete mould for the entire nose section.
If I were to create the mould for that piece in one step, there is no way I could remove the mould without destroying the original part - which is not an option. Hm, maybe RTV could work here :dunno:. I'm just not sure how well RTV would handle when you try to lay up fibreglass on it - it being flexible and all. hm

You have to make sure that your negative mold made of fibreglass is sturdy enough not to deform during the curing of the epoxy resin, quite some heat is produced while the resin cures.

As for the RTV silicon mold, it depends on the type that you use. Some are more elastic and some are very little elastic, the thickness of the mold also plays a big role.

sky1911
05-06-2013, 02:21 PM
Cinqster,
using a gel coat seems like the way to go. The one thing I'm not so sure about is that the coat seems to be fairly thick - see 8 links below for a video tutorial on how to create a fibreglass mould of a plug and later to use that mould to lay up your fibreglass copy. It looks thick, but might not be as thick. I just wonder how much it actually adds to the mould in the sense of are the finished parts noticeably smaller than they should? I mean this is scale stuff, not 1:1 where half a mm may not be much of an issue.
A waxing compound (brazilian - j/k) is also on the shopping list, as is some resin and a PVA.

Regarding the PVA watching the videos below I thought that a brush might not be the smartest choice - for one occasionally a hair lets go and then your surface is buggered already, plus the brushmarks. So sponging, as you suggest, seems the best option since I don't have an airbrush anyway.
As for Cloth vs. GRP. Hm, I've thought about it. What I was told is that GRP is, as you say, probably easier to shape, whereas cloth should be somewhat stronger. So I've selected a few very light, medium and heavy cloths. We'll see. If all else fails, I will just have to get GRP. As for stippling - that could indeed be a problem. My first idea is to try and brush it on with little to no pressure, not actual stippling. We'll have to see how that turns out.

RTV is - for now - out, but might be used at a later stage for other applications.

The way you described the mould-setup for the nose is exactly how I intend to go about and is also very much like what the 1:1 guy did in the link in my first post (barely visible, the underlined text there).

Oh btw, I loved the buildup for your Porsche, until it stopped.... :(


Jano,
I hope to get a good copy of the shape first, then maybe add a few layers of heavy cloth on the outside, maybe at some light previously cut in shape foam to it to give it some extra strenght. As said, RTV is out for now.


Anyway here are the links to the videos ('93). The technique looks pretty solid to me - with the exception of the paste they create to strengthen some parts. It is clearly visible in the finished part, which i would like to not be the case. I might just try and create an unpainted body - much like scratchbuilt's 908/3 was for the most part. I just love that raw look.

part 1 (http://www.youtube.com/watch?feature=player_embedded&v=FCivvXA2FVU), part 2 (http://www.youtube.com/watch?feature=player_embedded&v=ARch2opQsbc), part 3 (http://www.youtube.com/watch?feature=player_embedded&v=Lse3JcphLNw), part 4 (http://www.youtube.com/watch?feature=player_embedded&v=K7khndQKS-c), part 5 (http://www.youtube.com/watch?feature=player_embedded&v=nrMr1-lzZRs), part 6 (http://www.youtube.com/watch?feature=player_embedded&v=0pVCR1Q2POo), part 7 (http://www.youtube.com/watch?feature=player_embedded&v=sbb7me-a5kA), part 8 (http://www.youtube.com/watch?feature=player_embedded&v=pzzFZPLndJE)
-- In case the links are removed again or not showing up, just go to youtube and search for "fibreglast" (=user) - you'll find them there in their list of videos (78 in total).

Other than that the process looks fairly straight forward. I was surprised to see they lay up 10 or so layers within 20 minutes. I was under the impression that you would do a layer or two, then have it rest a day and have a go at the next few layers - of course depending on how many layers you want to add and what thickness you are aiming for.
That aside my fibreglass cloth has shipped today, so I better get the other parts. The cloth was, per chance, bought via an Ebay RC-Model shop. They didn't offer any of the other ingredients though. But I'll be on the lookout.

Thanks for the pointers so far, much appreciated!

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