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I am wanting to start making some molds of my audi rs4 rear doors to eventually make in carbon. The drivers door is in perfect shape, but the pass. door has a very shallow indent from a door ding or the like. I am not afraid or new to doing body work as thats what I use to do for a living. My question is this. Is it better to do the body work ahead of time and get it all smooth or can I make the mold and then sand the raised area of the mold that is the reverse of the dent. I think it would be easier to block it down than to fill it up on the actual door. The dent is like 1 inch by .25 inch by .125 deep Also, I have read a lot about mold making and most posts I read about what weight glass to use is in metric measurements. What type of glass and how many layers should I use for making these molds, if I plan on making more than one copy out of them? I was thinking this Tooling gel coat Epoxy resin (tearing some strands of fg out and laying those down in the one 90 degree edge where the front door overlaps) 1.5 oz chopped mat for the first 2 layers 4 layers of 4 oz woven or 2 layers 4 oz followed by 2 of 6 oz Adding some sort of reinforcement of wood or something I have made molds of smaller one time use parts before so Im not entirely new to the process, but this will be my first larger reusable mold so to speak. Does this sound right, overkill, or not enough?
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To answer your first question, I definitely recommend getting your original door perfect before you make the mould. For one, tooling gelcoat is very abrasion resistant and very difficult to flat down. You can get away with minor imperfections, but a 1" dent is going to take you a very long time to sand. Secondly, 0.125" is ~3mm. Not only is that a lot of gelcoat to try and remove, but you run the risk of rubbing through the gelcoat if you don't apply it thick enough, and 3mm is quite thick for a flat surface, I think you will struggle if it is your first time mould making. So, you know how to fill the dent and get it flat, that is your best option. Second question; you say you are using epoxy resin yes? I'm going to assume you meant epoxy based tooling gelcoat then too (be sure of that). You mention using CSM, but regular chopped mat is not compatible with epoxy resin. You can use powder bound chopped mat, but why anyone would do that to themselves is beyond me, absolutely awful stuff to work with. You can either switch to using a polyester or vinyl ester based tooling system, such as EC's Unimould system, and use regular emulsion bound chop; OR you can use your epoxy tooling system and stick to woven cloths. To be honest, even if you switch to a polyester based tooling system I would recommend using woven cloths. Reason being, not only are woven cloths easier to work with but they use their own weight in resin, so if you've got 200g (6oz or whatever that is in ounces) then you will need 200g of resin to wet it out. CSM uses 2.5x their own weight in resin, so if you've got 200g of CSM then you need 500g of resin to wet it out. That difference for me generally makes CSM more expensive to use than woven, despite the lower purchase price. As for the weights of the cloths, if you stick to your epoxy tooling system and use woven, then you can use heavier cloths straight off the bat as the gelcoat won't shrink too much and develop print through. So I normally do 2-3 layers of 6oz plain weave glass, then 2-4 layers of of stuff called woven rovings, which is a 650gsm (22oz) plain weave cloth. Very heavy, very good for building thickness. You can also pull individual rovings quite easily and use them to build up your corners before laying your cloth down. Using 2 layers of the woven rovings will give you a thickness of around 4mm, which is good for possibly 10 or so pulls, potentially more if you treat it nicely. 4 layers of the woven rovings will give you around 7mm thickness, which will give you probably well over 50 pulls, and essentially last a life time if you are using a high slip chemical release agent that makes demoulding less stressful. Depends on heat cycles etc. as well, but really if you make it well there is no reason that a mould like that can't last a lifetime. And finally, adding wood to the reinforcement is good for getting the mould to sit flat while you are laying up, just be aware of print through to the mould surface. Apply your reinforcement layers first and let them cure fully, THEN add your wood. If you switch to a polyester based tooling system, be aware that even if you do it like that you may still get print through to the surface.
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Thanks for the advice Hanaldo. Its great advice and really cleared some things up for me and I will be changing up a few ways that I do the process. I agree and think that it is best to do the body work first and get the door smoothed out. Seeing your work and the doors you have made, I would be an idiot not to listen to what you have to say.
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Hanaldo, My supplier can get me 18oz roving or I can get 20oz woven. Would I be better getting the plain woven as it weighs more, or should I stick with the roving and use possibly another layer since its not the 22oz you explained about?
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Either or mate, the aim is to build up thickness. I've even used coremat before, but to be honest I won't do it again. Uses a heap of resin and isn't very cheap in the first place. You could try both and see which one you prefer working with.
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I was thinking es218 for a good tooling coat. Does this seem right?
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I'm sure they will be fine. How many are you planning to make?
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im hoping about 5 for starters, but im talking with a few others who may be interested. If youd recommend something else id be glad to hear it. I havent worked with epoxy tooling before.
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It's hard to recommend anything, as availability is always going to vary from place to place. Personally I don't actually have any off-the-shelf epoxy tooling systems available to me here in Aus, not in useable quantities anyway. So when I need an epoxy tooling gel, I blend my own using laminating resin and a variety of additives and pigments. Works very well. Not as nice to work with as the Airtech stuff I've got here, but still good. And doesn't cost the Earth. Point being, if it's an epoxy tooling gelcoat, it's likely going to be decent. If you're using a semi-perm release agent as well, then I'm sure you'll get an easy 5 pulls from the tool. Build the reinforcement to be about 7mm thick, the thing will last virtually a lifetime if you treat it nice.
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