jratuszn

After all the great threads on this forum, I've decided to take the plunge and am in the early stages of building a plug for a 82" -5N Corsair. Thinking down the road, I have heard some mention of putting details like panel lines and rivets right into the plug. How well do these transfer to the final part? My concer would be that between waking the mold, then the coat of PVA, then waxking the mold, and another coat of PVA, the detail I had worked so hard to put into the plug would be all but gone. My other concern would be that having all the ridges from these details would be like a million tiny undercuts, and make it impossible to pull my mold from the plug / part from the mold. Has anyone done this successfully, and could you give some tips on the best way to accomplish it?

Thanks

-Jeff

Mike Emilio

First off, you don't need duplicate coats of the PVA.
I use about maybe 3-4 coats of sprayed on wax (buff between coats), then the final spray coat of PVA. Don't touch the PVA, it's extremely thin! Imparative that the PVA is absolutely dry before you start any lay-up work.

There are two types of PVA:
- the cheep one that is very watery, you might need a second coat, and
- a more expensive high solid one that has a higher viscosity.

Mike Emilio

In regards to ridges.

Your right about that. Any significant ridge or undercut will LOCK the part into the mold.

When you make the female cast off the plug, you have to plan very carefully not to have any undercuts.
1 or 2 degree negative draft angle anywhere is enough to LOCK the part in!

Generally, such things as rivets etc, would be of a rounded top surface and relatively low in height, hence they will release providing the molds are sufficiently prepped.

jratuszn

Thanks Mike-

I just want to make sure I understand what you mean about the PVA - I wasn't planning on a "double coat", but one coat on the plug before laying up the mold, then after the mold is complete, one coat on the mold before laying up the final part. My concern was with the progressive degradation of the panel line detail with these sequential steps.

With regard to undercuts - I've been very careful in the design of the plug to avoid these. I was just wondering if the panel lines - only the depth of 1/64" chartpak tape - would pose problems when trying to pull the mold off of the plug.

BTW - what sort of spray on wax do you use?

Thanks again,

-J

LN-JET

If you look at the [link]http://www.su27.de/index.htm[/link] site, which I consider nearly a composite bible, you will see that you can have very much detail without creating any release difficulties. But for a first project you might consider placing only the most pronounced lines on the plug, so that you have some horisontal and vertical reference lines when finishing the model afterwards. Especially on a jet model, molded surface detail often looks exaggerated.


Regards

Lars