(once again) plug question
 

hi to all,

i`m new in molding business. My first attempt is the cowl for my graupner extra 300s. I made a plug from blue foam. I didn`t cover it with glass just put couple of coats of car filler and wet sanded with 800 sandpaper. But still i`m not complitely satisfied with the result. And now the question: can i use some high closs car paint as the final coat? If yes, do i have to sand first layer and add another?

Maybe i got it all wrong from the beginning, and have to put some glass on?''


best regards
crow

RE: (once again) plug question
 

How many cowls do you plan on making? If it's one forget about making a plug, then a mold, then a part, go right to making the part. If the plug is almost done to make a mold, just use it as a lost foam mold. Lay glass and epoxy up on the plug you have, two light layers, 2oz/yd., I think that's about 50gsm, should do it. Let it cure, then pour gasoline or acetone on the foam to dissolve the foam, and you have a cowl. If you cover the plug with thin plastic shipping tape the foam will come out without leaving any mess.

RE: (once again) plug question
 

thanks for quick reply,

this came to my mind, but i`m still planning to make a mold for later use. Don`t know yet if i gonna use it for more than just one cowl but have spent too many hours on that plug that i don`t have a heart to break it.

so the previuos question stays.

crow

RE: (once again) plug question
 

soarrich, my brain is not clicking right now. will you expand on your method you were explaining.

Explain: "just use it as a lost foam mold"

I think what your saying is use it as a "Male" mold, instead of using it as a plug. am i right? if so, would it be a lot harder to get a good finish if the "good side" is on the outide of the plug. Im new to all this, but i wanna give it a whirl. Thanks for the help.

RE: (once again) plug question
 

yes he ment to use the plug as the male mold. And yes, the outside of detail will come rough and needs a lot of sanding.

crow

RE: (once again) plug question
 

Yes, but you can do it without as much sanding as crow thinks.

First you make the the male mold out of foam making it as smooth as you can using 100 grit sandpaper. After you have your shape cover it with packing tape, the thinner the better, keep wrinkles out by using lots of smaller pieces rather that just a few large pieces. I find it easiest now to lightly spray the form with 3M 77 spray glue now then lay on the fiberglass working out most wrinkles. Mist on a little more 3M 77 and then put another layer of glass. Now brush on epoxy, I use WEST 105/205, work it through the glass, when the epoxy is worked in the glass will be clear, any white spots aren't wetted out enough. Now use a roll of tissue paper and try to blot off the epoxy. The easiest way to do this is to roll the roll of paper over the epoxy in the direction that doesn't let the paper unwind, taking care to not lift the glass/epoxy mix. Once you have it so that it's wet but no drips, and in most places you see the weave of the cloth leave it to cure. After the cure, with 200 paper sand it for no more than one minute, you just want to get any little piece of glass that are standing up off. Now using the same 105/205 epoxy brush on a flow coat, you are just painting it on to fill the weave, let that cure. Now if you take a single edge razor blade and draw it backwards over the cowl you will quickly remove any excess resin. You should now have a cowl that after a few minutes of sanding with 200 grit paper can be primed, sanded, and painted.

I used to make whole sailplane fuses,(Weston Magics) this way. I did a cowl using this method, but over a balsa cowl that I had made, I'll see if I can find my pictures of it. It's covered with aluminum duct tape which have a few wrinkles in the tape not the glass.

RE: (once again) plug question
 

Hi guys, Ihave a good plastic cowl from a kit that is no longer made, have no fiberglass experance, can I fill this cowl being carefull not to bend it with plaster of paris ? cut off old cowl and fiberglass the plaster plug then remove the plaster? just a thought.

Thanks ,Glenn.

RE: (once again) plug question
 

Yes that will work. After you have the male mold, wax it, and layup onto the plaster.

RE: (once again) plug question
 

Of course you can, but if you already have the cowl, then this is a perfect plug for a female mold. It is making the plug that is the time consuming task, not making the mold from the plug.
Support it somehow, apply release agent (several coats) and lay up the mold.

Regards,
Magne

RE: (once again) plug question
 

Thanks magne, sounds good to me.

Glenn.

RE: (once again) plug question
 

Hey, I''m new in molding too. I''ve just made a new nose to an F3A airplane making it from foam and then laying over the fiberglass. Too much sanding after that but a nice new nose.

RE: (once again) plug question
 

I have a related question,I am going to make a cowl with some details that would prevent it from being slipped out of the mold is there a"best"or better way to make a split mold so I can open it up to reveal the finished product,I am trying to make a FW 190A8 cowl and would like to make a couple so I would like the mold to be reusable.
also I will be making a gun hood but this will only require a lay in mold,I do know how to use epoxy resin as well as polyester this is my first molding process.