jetpack

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Hello I was wondering the best approach on duplicating large vaccum formed parts using the original as the master to lay up fiberglass copies.

I am sure there are threads on this but dont know what to search.

What I am thinking of duplicating are boat cowlings, some like the one pictured plus others.

Would taping it flat down on smooth surface, building a box around it and pour plaster over it to make the female for laying up the fiberglass in?

aussiesteve

Yes - that will work. As long as you only want to make one or two articles from the mold.

Make sure you put some form of release agent on the part before you pour the plaster (such as wax or silicone oil).
Here's another tip for you - To make the plaster mould work well for you, put a layer of "Shellac" (French polish varnish made from beetle wings and Methylated Spirits) on the plaster - it has excellent sealing qualities and will make the fibreglass part easier to release from the plaster.

If you wish to make multiple parts - just lay up fibreglass over the vacuum formed part to make the mold.

jetpack

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Thank you, Steve. Would laying up some fiberglass first and then pouring plaster over that work or how it is done to make a durable mold without twists or such?

Thanks for the Shellac tip, I'm sure I have seen cans of it at the hardware.

tail strike

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http://www.rcuniverse.com/forum/fb.asp?m=7076924
Check out this link it may have what you want.

Ed Smith

Funny you should ask that question. I popped a number of parts from the molds this morning. They are the plastic parts for a TF P40. I hate plastic parts, I usually make glass replacements. I finish the plastic part as if I was about to use it. I then apply many coats of mold release wax and one coat of PVA. I then make molds by laying cloth on the original. This is not a commercial enterprise so I do not make the molds to last forever, Just sturdy enough for the few times I will use them. From those molds I make my parts.

The picture shows some of the original plastic red and white , the molds and the parts yet to be trimmed. The plastic cowl was damaged removing it from the mold.

Ed S

Cub_Boy

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OK folks... time to bust this myth... shellac is NOT made from beetle wings... here is the real deal!

Shellac is a brittle or flaky secretion of the lac insect Kerria lacca, found in the forests of Assam and Thailand. Freed from wood it is called "seedlac".

Once it was commonly believed that shellac was a resin obtained from the wings of an insect (order Hemiptera) found in India. In actuality, shellac is obtained from the secretion of the female insect, harvested from the bark of the trees where she deposits it to provide a sticky hold on the trunk. There is a risk that the harvesting process can scoop the insect up along with the secretion, leading to its death. The natural coloration of lac residue is greatly influenced by the sap consumed by the lac insect and the season of the harvest. Generally in the trade of seedlac there are two distinct colors: the orange Bysacki and the blonde Kushmi.

When purified, the chemical takes the form of golden yellow/ golden brown flakes, this possibly providing the basis for the "Wing Source Story." Shellac is a natural polymer and is chemically similar to synthetic polymers, thus it is considered a natural plastic. It can be turned into a moulding compound when mixed with woodflour and moulded under heat and pressure methods, so it is classified as thermoplastic. But old mouldings tend to become thermoset, that is, they suffer chemical reactions over time and are no longer fusible.

aussiesteve

Cool - thanks for the info Cub Boy.
See what a great learning resource this is. I'd never really bothered researching the true source of shellac.

I think that the kids would still think that the wing source theory is a lot more cool sounding though

whatwheel

Hi Ed, I cannot find any info. on making a fiberglass cowl , I have a goldberg bucker jugmann bought used It has a good light weight plastic cowl with cheeks to use as a pattern. So far I am thinking about filling old cowl with some kind of plaster then split then the cowl to remove it from the plaster , then glass the male mold . That is my first thought?

I have no idea about materials to be used.


Thanks for any help, Glenn.

Ed Smith

Go here.

http://www.cstsales.com


Scroll down to the bottom. Select "Tutorials" then select "Making A fibreglass mold"

Ed S