Hi all,
first of, if my questions have already been answered on another thread (yes I did try the search  ) please be patient and re-direct me!

Okay, I am about to carve a nose cowling for my new stunt ship and want to use the wooden cowling as a mold to make a carbon veil cowling. I have not done this before but I am aware of the basic theory, I will state my assumption and then ask a few questions. I will be making a male and female molds so that I can sandwich the carbon and laminating resin in between them under pressure. I am intending to use Deluxe Materials Eze Kote as a laminating resin.

Assumption: I assume the male part of the mold will need to smaller than the female part to allow room for both the carbon and the resin.

Questions:
1) Is my assumption correct?
2) What can I use to cover the male mold while I make the female mold out of plaster of Paris so that the female mold is slightly larger (i want to end up with a 1mm or 1/16th gap between the two parts).
3) What would make a good release agent?
4) Is my plan okay or am I heading down a dead end and a world of pain and frustration?

Jonathan Chivers

Alan is right about the CF veil requiring many layers to build up to the required thickness.  As he said, a foam form covered with glass cloth is a much easier.  I make most of my hatches for my electrics that way.  After the resin is cured and the glass sanded and primed, I just dig out the foam with a large tweezers rather than using solvent.  I generally use Z-Poxy for the resin and 2 layers of 3 oz cloth and 1 layer of 1.25 oz cloth for my hatches.  I also build a 1/32 inch ply perimeter frame around the foam to help stiffen the assembly.  The frame remains after the foam is removed.  Another thing to consider is that the Eze-Cote is water based and probably will take forever to cure if sandwiched between a female and male mold where the air can't get to it.

I've molded cowls for all my stunters and some others.  I carve the plugs from balsa and finish them with something other than dope: dope sticks to Frekote 700, the release agent I use.  Then I build up a base for the cowl out of modeling clay (plasticine) on a board covered with MonoKote.  I give the cowl plug and board a toot or two of mold release.  I then put a wood frame around the plug, holding it to the base with clamps.   I pour casting epoxy over the plug to form the mold.  It is rigid when it hardens, so you can get the plug out only if it has some draft.  If not, use two-part silicone resin.   Now I remove the plug and toot Frekote 700 mold release on the mold.  You can also use PVA as mold release.  The finish isn't as nice, but it works, and you aren't going to make a lot of parts, so you can afford to sand them.  You can use nonwoven carbon (mat, veil, tissue) on the cowl surface to avoid the bumps you get with cloth.  Use .5 oz. or 1 oz./ square yard stuff, though, not the really light material that's fashionable for doping on stunt planes.  You'd sand right through the light stuff.  You'll have to cut darts in the nonwoven stuff to get it to lie down in the mold.  The guys above are correct about using woven cloth: the nonwoven stuff has no strength.  I make the body of the cowl out of a couple layers of 2-oz. (or so) carbon cloth.  I use runny epoxy, usually Epon 815 with DTA hardener.  There are a couple of ways of getting the right fiber/resin ratio.  The easy way is to cram the carbon in the mold, put on extra resin, then put in a layer of Teflon with little holes in it for the excess resin to escape through, then a layer of polyester batting or paper towel to sop up the excess epoxy, then the vacuum bag.  The best bag material is Stretchlon.  CSTSales.com can fix you up with the stuff to do vacuum bagging if you don't have it.  If you made your mold from silicone, the pressure will press the cloth weave into the silicone, making the cowls difficult to finish, as the people who finished the B-17 cowls I made can attest.  If you want to make an axisymmetric cowl like that, I can tell you a much better way to do it, based on painful experience. 

I left out details and pictures because nobody will read this anyhow.  I'll put in some effort if somebody's interested.

Hello everyone,
thank you for your replies and explaining why i was heading down a path of pain and frustration! Boy am I glad I asked.

On the up side, when I was talking to the local model shop about buying epoxy/glass as outlined above, the shop said they could do can vacuum molded plastic cowling for me (which is what they use on their planes), so I will try this first at is looks to be the simplest way out of this.

Jonathan

Try the condom method. I saw it in a model book......(and its fun asking the pretty young thing where the extra large unlubricated condoms are)  

Make your mold and stretch a condom over it. Add cloth and stretch another condom over the entire thing and wait for it to cure. Voila! A cowl.

Looks simple although I haven't tried it.  

Good luck, Jerry

Howard; I would've thought you would've picked up on this one.

Hi Tim,
start turning green about now please! Not only does Avicraft do laser cutting and vacuum molding, the shop is in the same place as it was when I started going there as a teenager in the 70's, but the same people that used to work there as a Saturday job, now own and run the place.

Bad news is, you need to move to Kent or south east London!

Jonathan Chivers