Imperfect mould surface.

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Imperfect mould surface.

Author	Message
Tollaus	Tollaus posted 13 Years Ago HOT Topic Details
Group: Forum Members Posts: 10, Visits: 21	Hi guys! I've made the mould for my second piece of the project and its surface came out with a lot of imperfections. I have sanded it but I took off some black gel coat in some parts, so now the polyester resin from the mould is showing up in some spots and the surface isn't decently even yet. I knew the plug wasn't perfect but the mould came out worse than expected. Here are my questions: 1) can I continue to sand until I get a decently even surface, even though the yellow resin is visible? 2) do I need to re apply the gel coat and then sand it again? 3) I need to to even out the surface with bodywork filler and then apply the gel coat again? I do not want to make the mould again, so which is the best way to do it in your opinion? Many many thanks in advance!
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wozza	wozza posted 13 Years Ago HOT Post Details
Group: Forum Members Posts: 688, Visits: 5.4K	I have found myself in similar situations in the past, so this how I would deal with the problem for what its worth and the questions you need to ask yourself. 1- Is it a large/high value (in materials terms) part and can you afford to risk producing a sub-standard part. 2- Is the mould going to be used for a "one off" or multiple runs. 3- How bad are the defects in the mould. 4- Is the part for decorative or functional use. Once you have answered those questions its easier to decide how to proceed. If its a "one off" then your time may be better spent correcting the part rather than the mould. If its for multiple runs then spend the time getting the mould right. It is very satisfying releasing a part from a mould that only requires a trim and a quick polish. If it is a functional part as long as the imperfections don't affect the structural properties then does the surface finish really matter? I have repaired/altered moulds by reapplying gel coat many times with varying degrees of success. If the imperfections are small, pin holes etc be sure to make sure that you remove all traces of sanding dust grease etc otherwise the gel coat may not bond properly to the previous coat and you will be left with bits of gel coat stuck to the surface of the part. Resulting in more time wasted finishing the part.(I have learnt the hard way) I have even made the imperfection bigger with a stanley knife to increase the surface area to achieve a reliable repair. If the imperfections are relatively minor then gel coat and sand back. If another layer of gel coat is not sufficient then I would be looking at reworking the plug and a fresh mould. Sorry if this sounds like a long answer to a simple question and good luck Carbon Copies Ltd
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Tollaus	Tollaus posted 13 Years Ago HOT Post Details
Group: Forum Members Posts: 10, Visits: 21	Hi Wozza, Thank you very much for your answer. The mould is used to produce several prototypes, so at this point the finish is not "that" important, but I would still like to get e decent piece without having to make the mould again. I knew the plug wasn't perfect but for some reason the imperfections came out much worse than how they appeared on the plug and the mould is now full of humps and bumps which I would like to even up a bit. In case one gel coat layer is not enough to smooth it out, is the use of a bodywork filler plus another gel coat layer a good move in your opinion? Thanks in advance.
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Warren	Warren posted 13 Years Ago HOT Post Details
Group: Administrators Posts: 214, Visits: 782	The standard usage of unimould or most tooling gelcoats normally leads to a thickness of about 1mm. You ideally need your plug to be finished with that level of tolerance. You can cheat and do a second coat of tooling gelcoat if you are worried. To fix what youve done, you need to fill in with gelcoat again to seal the surface. Ideally sand down 1mm deeper than you need the surface, lay in a good thick coat of tooling gelcoat then let it fully cure. Remember to properly key the surface to ensure a good bond. Then you need to sand it smooth again. Just be careful not to break through the gel around the edges of your repair!!! As its a prototype it doesnt matter too much, however when making the plug for the finished item, get the tolerance as close as possible to save this issue occuring again. I really wouldnt go playing with bodyfiller. Not sure how stable it is under vacuum pressure. You could redo the entire surface with new gelcoat and as it begins to thicken when curing, level it out with a flat edge, but only do this if your part has the tolerance to accept the impact on the mould an extra thick layer of gel would have.
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Tollaus	Tollaus posted 13 Years Ago HOT Post Details
Group: Forum Members Posts: 10, Visits: 21	Thank You very much to you both for your suggestions! I'll let you know about the result. Cheers.
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wozza	wozza posted 13 Years Ago HOT Post Details
Group: Forum Members Posts: 688, Visits: 5.4K	Hi Tollaus, These types of problems can be very frustrating and I know how tempting it can be to cut corners especially at the mould stage just so you can get on with the actual part. However time spent now getting the mould right will result in a much better end product. It is all part of the learning experience and will help you in the long term to better judge what you can and cannot get away with. Good luck and be sure to let us know how you get on. Carbon Copies Ltd
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Matt (Staff)	Matt (Staff) posted 13 Years Ago HOT Post Details
Group: Forum Members Posts: 680, Visits: 1.9K	Is it OK to bump this over to general composites as I don't think it relates directly to any of our products at this stage? Matt Statham Easy Composites / Carbon Mods - Technical Sales
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