Mold Lines

[RyanGiorgio]

Quick question: What are mold lines? What do they look like?

[MikeDeuce]

They occur during the molding process when multiple pieces of a mold are put together and the plastic/resin/etc is injected into it. Mold lines will appear where the pieces of a mold come together, as some of the material will creep out into those areas.

They look like little lines of material where the surface should be smooth. Usually they're thinner than a length of thread. I've noticed Tamiya's tend to be barely noticable whereas other manufacturers incorporate a bit more slop.

If you've ever had to sand an odd thin line off a smooth round body part, that's a mold line.

[Veyron]

If you take a new model body out of the box and look at it, usually on all four corners you will see a raised, very thin line or a slightly uneven surface. The lines will be vertical and often go along where the fender and hood meet, then up the A post, across the roof, down the C post, along where the trunk and rear fenders meet, then down the rear bumper. These lines can vary depending on the model and how the mold was engineered. The molds they use to make the model are normally a three piece mold, and where these three pieces fit together, imperfectly, there will be a slight offset. Rub your fingers across the line and you will feel the change in surface.