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I'm starting a couple of vacuforms - Proteus C-131 and Welsh Models Gulfstream IV, both in 1/72nd...

Something I've always wondered - I'm used to marking around the pieces, cutting them out and sanding down the edges to the marked lines.

However, surely this narrows the fuselages by the width of the plastic?

Does this make sense, or and I misunderstanding how the masters are cast?

Thanks, and a Happy Christmas to all!


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I've always wondered that myself. The how-tos always talk about making sure that you sand away all the plastic to the marked line, but you'd figure the master encompasses the thickness of the plastic, and if you sand it away, you're part is now too small by that amount. I suspect the answer comes down to male vs female moulds, but I'd love to hear from someone in the know.


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The guys who make the masters take the thickness of the plastic into consideration.

The molds used are female molds, the plastic is sucked down into a cavity shaped like the part.

The centerline of the fuselage (for example) is flush with the surface of the mold, so, when you sand away the stock, you're left with a part that is complete to the centerline.

For male molds (which don't give you much fine surface detail) the cut line for the part is usually a bit above the surface of the mold, the master is raised a little over the substrate. Otherwise, the molding process won't capture the lower edge very well. Think vac-formed canopies, they're usually male molds.

Edited by Grey Ghost 531
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Here is what i do when i do a 32nd vac.U'er ok on the cutting of the parts and popping them off the carrier sheet and sanding them down.One would think the the thickness will cqause problems when gluing the parts together.But i use thin balsawood strips to the inside edges of the fuselage halves,then sand then even and flat to the edge.That way it will give strength annd will make it easier to glue the halves together.Larry

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