One Piece Moulds

[BruceWilkerson]

Hello guys,
Have a question regarding one piece molds. I have a mold that has had 30 or so sets of cowlings pulled from it already. I aquired it in a sale and my glass lay up experence is very limited.
Can anyone who has worked with these types offer a newbe any advise I was told to wax it real good then PVA and lay on a coat of resin then the glass then more resin.
You may notice the bottom has a small hole so I can use a blast of air the remove the part after it has cured. I really just looking for any advise as I do not want to mess the mould up. I'm debating on doing a 2 part mould from a good cowling I have just in case it turns out bad.
And another question can I use an epoxy layup vs Poly resin that it has been in the past? will be using West Systems

thx for any help BW

[davidfee]

You should have no trouble pulling epoxy/glass parts out of that mold. Sure, a 2-piece mold would be easier, but then you have to deal with the seam. Even if you lay the part up with both mold halves bolted together, you'll still have the join line to sand (or just live with it).

You should not have any problems using epoxy in a mold previously used for polyester. Basically, you'll want to apply several coats (5-6 would be good) of your mold release wax. Then use PVA also (at least for the first few parts). Apply one or two coats of wax before making each new part.

The glass may need to be cut into pieces due to the curves involved. Test this out with dry fabric and then, if you plan to make several cowls, make some templates when you're happy with the patterns.

Your cowls will likely need more than one layer of glass, so I'd brush in a coat of epoxy, lay in the first layer of glass, brush in more epoxy and then apply the second glass layer. As you are pushing and stippling the glass into place, you'll notice that you probably have way too much epoxy in certain areas. This can be blotted up with paper towels or even toilet paper. If an area is too dry, just add more epoxy. When you're done, the surface should look almost dry. If the weave is filled and the surface is glossy, your part will be unnecessarily heavy. You want just enough epoxy to wet out the fibers and no more. (This WILL take practice)

Let the part cure for 24 hours if it's at room temperature. If it's above 80F, you can probably demold it after an overnight cure.

Have fun,
-David

[BruceWilkerson]

Hi David,
Thx for the reply! Since I do want to get into other ideas < wingtips & a tail cone > I see CST Sales offers a complete moulding kit including Safelease product. Can I use that in place of the PVA or am I off base all together on the difference between them?
I need to place an order anyway with them but wanted to ask on the PVA vs Safelease stuff. I am sure you know what they offer in a kit but just in case: https://www.cstsales.com/Epoxy_&_Molding/molding-kits.htm
1 more question I normally use the 105 and 209 extra slow hardner as I like glassing my wings with the slower cure but would it be more benifical to use a standard cure hardner or stay with the 209 slow?

Thx again for the help...now off to read all these great threads on mould making! BW

[davidfee]

I think the safelease is a relatively normal release wax, capable of being used at elevated temperatures. I see no reason you couldn't also use PVA. PVA is like extra insurance really, and isn't absolutely needed if you have a good base of wax on the mold. It's also expensive to ship because it's considered a hazardous material.

PVA is a thin (usually green) liquid which is brushed or sprayed over the waxed mold. It dries and polymerizes to a thin plastic film. The film is water-soluble, so you can wash it off the molds and parts with warm soapy water.

The slower hardener should be fine, so long as you don't mind waiting for the part to harden. I've never used WEST myself, so I can't offer specific help form personal experience.

-David

[BruceWilkerson]

Hi David,
Thx again. Yes the PVA carries a 25 buck haz mat fee so I'll have to see what is avail locally.
I'll get one of their moulding kits on order and I'll let you know how it turns out.
Thx again BW

[hayman]

Try Hair Spray as a substitute for PVA.

Bill

[BruceWilkerson]

Hi Guys
what would be the best weigh cloth for these cowls? I have 100 sq yars of the .75 cloth and now have quite abit of 6oz my guess would be somewhere in the middle between around 3 oz but wanted to ask the experts :)
Thx, BW

[davidfee]

How big is the cowl? The 6oz is probably fine, depending on the size. It will help to use a layer of the 0.75oz glass as a surface layer to help bridge the weave pattern a bit to reduce pinholes and surface printing.

-David

[BruceWilkerson]

Hi Dave
Not that large of one looks like fairly light weight cloth was used on one that i have 4'' tall 2 1/2'' in width at the base. not sure if i could get away with 3 or 4 layers of .75 or not.

thx. BW

[davidfee]

That "looks like" (I could be wrong) 4oz glass. 3 or 4 layers of 0.75oz glass would be very fragile. You may break it just getting it out of the mold. I am, unfortunately, speaking from experience. ;)

There's really only one way to find out though... you just need to try it. It will cost you almost nothing.

Good luck,
-David

[BruceWilkerson]

Hi Guys
well here it is the one on the left is a newly pulled cowl vs the origanal one on the right. Still need to get the excess resin out of the nose end while doing layup but at least it came out all intact :D
Using a uv resin that has a amber color to it and the only stuff I had that was regular cure time vs long time cure with some work it could be improved upon but i'm happy with the results for the first one.
Thx for all the advise and help....btw no PVA just the coverall film CST sold in their kit. BW

[davidfee]

Looks like you're off to a very good start! :)

-David