flybyjohn

My Feedback: (2)

I was just using some really old z-poxy finishing resin that I had left over from an old wing tube I made along time ago. Might be 4+ years old. The hardener has gotten really brown as you can see by the extremely yellow cowl. I need to purchase some more resin however with most having a shelf life of 1 year, even ordering a pint I would probably not get through it for 8 years. I have loads of regular 6 min, 15 min., 30 minute and some System Three T88 but I know those are not recommended for fiberglass layup.

I do need to learn how to use the mud as the mud I used just pushed around and created more problems then it was worth. Maybe need to let it set up a little longer before placing the first layer of cloth. I was able to push the cloth tight to the mold in the areas the mud pushed out of and those spots turned out good but in the areas the mud remained it left air bubbles.

GREG DOE

John, It's all right to use the term "gel coat" for what you are doing, but generally in the industry "gel coat" refers to polyester work, and "surface coat" to epoxy work. Some people use the term "skim coat" in epoxy layup too. When I did fuselages in polyester I liked using gel coat, because it cures in the absence of air. The neat thing is that the side facing out stays tacky, so when you put the cloth on the mold it sticks down. As you noted, one of the biggest issues is with air bubbles on the part surface. Gel coat, or surface coat helps eliminate them, but the trade off is the extra weight?. Now if you have a gel coat spray gun, you can get amazing results, and I've done fuselages that did not require any primer, except on the seams, but it's an extra step, and requires several hours of cure time. I've never heard of spraying surface coat, but the alternative is to spray primer, or color in the mold. These are all part of the reasons that epoxy has pretty much taken over in model fabrication. Z-Poxy is a good product, but if you ever use something like West Systems you will like it. I have an assortment of epoxy, but probably do 90% of my building, and laminating with either 5 minute, or West Epoxy. T-88 is a good structural epoxy, but I just did some major repairs on my Mini Max ultralight with West Epoxy, and a friend who is a "go to" on home built, and ultralights said West was just as good as T-88. The last tip for the day is that epoxy doesn't like a wax surface, and tries to "bead up", just like water on a waxed car. This might be why you are having trouble with your mud. If you have PVA in your mold the mud will smooth out a lot easier. We all struggle with the air bubble in our parts, but with practice you will get better. There is a product called Static Conditioner, Violet sells it as Pin Hole Filler, which helps a lot when preparing parts for painting. Good luck again, Greg

Avaiojet

Nice work!

flybyjohn

My Feedback: (2)

Thanks Avaiojet.

I ordered some epoxy this morning to try and make the cowl a little better. I debated between getting an off brand economy epoxy and a known brand expensive epoxy. I opted for the economy, which I hope I don't regret. But at $36.00 for a half gallon, vs over 70.00 shipped for a quart of west systems or about $58.00 shipped for half gal. of US Composites 635 thin resin, I had to take the shortcut. I called the company to talk about the product and left a message, 30 minutes later I received a return call and asked him about the product. There were two viscosities I could have ordered. One was 600 cps and the other was 800 cps. Now West System 105 with 206 hardener is 725 cps and US Composites thin 635 epoxy resin is 600 cps. I am not sure what the z poxy resin viscosity was but it was just a little too thick to spread without thinning slightly. I didn't want to thin the resin I ordered so I went with the 600 cps viscosity. The pot life is 45 minutes and set time 6 hours, cure in 24 hours. The shore hardness is D-85 which is just about what the west Systems 105 with 206 hardener is (D-83), so it should sand just fine.

Scorpion Racing

The US 635 with the Medium Hardener is a very good product for the money. I have used it for some Q500 molds as well as parts, without an issue. The only thing I will caution you about is that if you plan to paint your mold and then lay up the part (so it comes out painted from the mold) do some testing with the paint & resin first. I ruined a set of molds when I didn't test compatibility prior to the lay up. For unpainted parts, no problems!

Scott Smith

GREG DOE

John, The US Composites 635 sounds good. I could have mentioned in a previous post that West 105, and 206 is what I use, and if I had to guess I've probably gone through 30 gallons. After trying an assortment of other brands, I found the West to be very consistent, from gallon to gallon, over 20 years of doing layups. I "choke" at the price too! It ain't cheap, and sometimes I use polyester, which is around $60.00 a gallon now. I'm looking forward to your continuing progress, and success. Greg

flybyjohn

My Feedback: (2)

Sorry for the confusion but the epoxy I purchased was some off of ebay and wasn't either of the two I described above, however the characteristics are the closer to the US Composites brand stuff. The stuff I got was called ClearCast 7000 and was 36.00 shipped for 1/2 gallon. If you are not satisfied with it you can return it for a refund. The epoxy had a long pot life and set up hard in about 18 hours. It gets tackfree but soft and flexible at about 12 hours and I almost thought I made a mistake in buying it but at about 18 hours it hardened right up and sands great. Instead of getting the epoxy pumps that pump one oz per pump, I bought some shampoo pumps from the beauty shop that pump a bit less per pump so when I only need a little, I can just pump a little accurately.

Well on with the second attempt at a cowl. I made this one out of one layer of 4 oz and one layer of 6 oz. on the sides, top and bottom and in the nose area I used 2 layers of .75oz, 2 layers of 1.5oz, one layer of 4 oz and one layer of 6 oz. With the thinner layers of cloth in the nose area, I was able to fill in all the bumps and humps without any mud. The nose came out really stiff and is super strong. The sides are quite flexible but when it is pushed on the fuse, they stiffen up well. I keep telling myself that this is just to direct air over the fuse and is not a structural part so I don't need the structural strength I keep wanting to build in to it. I used a different wax this time and on side of the mold popped right off but the other side got stuck down in the far corner of the mold. I tried air and sticks to the point where I was worried of cracking the cowl. I finally decided that this was a good enough cowl and cut the mold off the cowl. The cowl turned out nice with very few pinholes to fill. It will work well for my purposes.

Now that I have plenty of epoxy, I want to make some cowls for my hanger 9 corsair, an rc nobler, a great planes mustang kit and some cowls and nose for a scratch built twin. I am going to try to cast the molds out of homemade Ultra Cal 30. I might try to make a fiberglass mold but the ultra cal 30 looks super easy, (mix poor and let set). And the material is super cheap. The homemade stuff is supposedly 90 - 95% Plaster of Paris and 5 - 10% Portland cement. These are all for just one cowl so no need for a permanent mold. I don't have a picture of the second cowl yet but will try and get one on tonight.

Thank you everyone that commented with your helpful tips and techniques.

flybyjohn

My Feedback: (2)

I am sorry for the lack of the final picture, but RCUniverse is giving me fits with keeping me logged on. When I got ready to put on the picture, it would not keep me logged in. It looks like it is working today so I will try a picture tonight. Thanks again.