General Fiberglass ?

[Auburntsts]

I just got through reading the lastest issue of the EAA Experimentor and there's an article about creating wheel pants. The technique was to build a plug (male mold) which was then used to create a female mold, which inturn was used to create the finished parts. That got me to thinking if there were rules of thumb as when to use male vs. female molds to create non-mass produced finished parts. For the fiberglass gurus out there, any thoughts?

[cropdusterengineer]

The finished side (ie, the outside of wheel pants) is generally the side you want against a mold, because that will be the side with the smoothest surface finish. Especially for production parts.

For a one-off part, I think the most common technique is to use a "plug" or male mold........but you'll end up doing a considerable amount of finish work to get it paint-ready.

CDE

[Ramendala]

If you only use the plug your part will be somewhat dimensionally larger than you wanted and due to the finish work as described above (and in the article) you end up with a heavier part.

Making the female mold is the way to go for 1 or 100 parts in a case like pants or cowlings. It also makes it easier to vac bag IMHO.

Ryan

[cropdusterengineer]

Originally Posted by Ramendala

If you only use the plug your part will be somewhat dimensionally larger than you wanted and due to the finish work as described above (and in the article) you end up with a heavier part.

Making the female mold is the way to go for 1 or 100 parts in a case like pants or cowlings. It also makes it easier to vac bag IMHO.

Ryan

Wouldn't you just make the plug that much smaller, so the final dimension was what you wanted?

The "heavier" argument, I can agree with, except that in most cases don't you usually remove the plug after the layup dries?

To me, making a plug, a female mold, then a part for a one-off part would be overkill. For 2 or more parts (like wheel pants that need to be identical) then I can see it.

CDE

[Ramendala]

For the Cozy, we build parts such as the NACA fresh air vents out of carved left over foam covered in packaging tape followed by some glass. Once cured the part pops off the tape and it get's glassed into the plane. In these one-off cases there is certainly no reason to make a mold, but these parts are usually not seen so there is no filling/sanding requirement.

The weight penalty for things like pants and cowls comes from filling and sanding the surface that will be seen. This is similar to the article the way he fills the plug. Not much weight added but easily avoided and MUCH less finish work before paint.

What do you plan to make?

Ryan