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Rob de Bie

How to make a copy of a vacform model?

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A modeling friend asked me whether I knew a way to copy an old & rare vacform model. I know that's quite dodgy from a copyright perspective, but on a technical level I found it an interesting question. If possible I would like to limit the discussion to the latter. I came up with two basic options:

1. Cast or laminate a new vacform mold over the sheet. It involves mold release, laminating glass fiber or casting a layer of solid resin, and drilling numerous small-diameter holes. Plus you need to find a vacforming machine. The chances of the original surviving are small I think. Despite the mold release, the mold will stick, and the fragile polystyrene sheet will rip / break easily.

2. Cast a layer of silicone rubber over the sheet. You can then do 'slush casting' in the silicone mold to make thin-walled parts, or maybe make solid castings. The originals will not be damaged in any way, since the silicone rubber will not adhere.

Both options are laborious and fairly costly, so finding another copy of the vacform kit is always the cheapest solution.

But I must say I'm intrigued by the second technique, that basically converts a vacform model into a resin model. I'm now even tempted to try that on one of my (very few) vacforms, because I think it will be easier to build that way. Is there anyone who tried this route?

Rob

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Number 2 is the only way to capture the detail, since number 1 certainly won't, and will almost 100% guaranteed damage the original.

With number 2, depending on the size, fibreglass may even be an option. But as you say, it's going to get expensive quickly, and if you can find the original, it's probably a much more cost effective idea.

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I think in nowadays it is easy to copy whatever you want as long as you have the CAD files for the specific item. And a 3D-printer of course!!!

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2. Cast a layer of silicone rubber over the sheet. You can then do 'slush casting' in the silicone mold to make thin-walled parts, or maybe make solid castings. The originals will not be damaged in any way, since the silicone rubber will not adhere.

What is slush casting? And don't you have to use mold release on the original before pouring the silicone?

How about another technique?

1. Stuff inside of vacuform fuselage with modeling clay. Lay it facing down on a flat surface ( ie fuselage half where it's supposed to mate with the other half is flat down on a surface)

2. Spray mold release on the fuselage.

3. Pour non-heating resin over fuselage (like the stuff some women use for making jewellery).

4. After resin dries, pry open original from resin.

5. You now have a female mold made of resin.

6. Spray inside of resin mold with mold release.

7. Pour more resin.

8. Pry out copy.

Actually it's very similar to your technique no.2 but instead of silicone, you use resin ( 'cos it's cheaper than silicone, IIRC).

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I would go with option 2, maybe stiffening the silicon mold with an outer layer from planster of paris.

Cheers

Thorsten

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Thank you all for the comments and ideas!

With 'slush casting' I meant using a thick resin (most casting resins are thin), filling the open mold only partly, and tilt the mold in all directions while the resin solidifies. The result should be a resin 'shell' casting. I never tried that myself so far, but I'm pretty sure I'll try it soon.

You don't have to use mold release on the original vacform before pouring the silicone. I never ever used mold release in making dozens and dozens of silicone rubber molds.

Making a plaster mold could work too. Maybe I will give it a try, since I never tried plaster for modeling purposes.

I will report back after some experiments. But don't hold your breath, it could take some time.

Rob

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Keep in mind that plaster generates heat as it cures. Might be enough to damage the vacuform. I'd pack the inside of the vac with clay too.

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