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Building a cowling plug

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Old 01-11-2013, 08:36 PM
  #1
Leroy Gardner
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Default Building a cowling plug

I started with a 1 gal. oil container and have cut it up to start the plug build from, problem is getting glue (CA) to stick to it. I washed it down good with laquer thinner but a test of two pieces did not stick. do you know what these jugs are made of and could there be a release agent on them that needs to be sanded off.

I think I remember reading some of you have done this starting with a jug or plastic bottle to make a cowling from, I welcome your help and thanks, Leroy
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Old 01-12-2013, 07:05 AM
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Default RE: Building a cowling plug

They are made from high density polyethylene and utilizing HDPE as a room temp mold surface works very good if you can layup on an existing thermally formed shape, however it is so slick that not much will stick to it, so utilizing it to create a master model/plug can be very difficult because it is next to impossible to add clean design features to HDPE without thermally forming it over a master model in the first place, nothing really sticks well enough to it to make a really clean master. I know that is probably not what you wanted to hear but it might save you time and aggravation in the long run to just build a little master from just about any other material other than HDPE.

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Old 01-12-2013, 11:24 AM
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Default RE: Building a cowling plug

Thanks Bob, yep, not what i wanted to here and it has a nice cowl shape to start with. Would styrene work to get started off the body, need something thin that resin won't melt after all the balsa is added and shaped. I want the engine in there to build to also. If I can get the right product to start with I can build out the rest to the point where I can fill it with spray foam to finish it.

Don't know if I'm on the right track here, I'm open for ideas and I know some of you know alot more than I do when it comes to this. thanks for your input.
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Old 01-12-2013, 01:32 PM
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Default RE: Building a cowling plug

For a one off cowl the easiest way to go is to make the plug out of blue or pink 1" insulation foam. Once you get the sape you want you simply cover the plug with low temp iron on covering or even mylar packing tape. Once covered you would wax with a good carnuba wax and then apply 3 layers of 3 to 4 oz cloth and epoxy resin over the structure. When cured you can sand the exterior smooth and pop free from the plug depending on the shape you may need to seperate into 2 halfs and then re-join. Whole process can be done in a weekend.
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Old 01-12-2013, 05:00 PM
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Default RE: Building a cowling plug

I agree with Speed, you will be done in no time.

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Old 01-12-2013, 10:49 PM
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Quote:
ORIGINAL: speedracerntrixie

For a one off cowl the easiest way to go is to make the plug out of blue or pink 1'' insulation foam. Once you get the sape you want you simply cover the plug with low temp iron on covering or even mylar packing tape. Once covered you would wax with a good carnuba wax and then apply 3 layers of 3 to 4 oz cloth and epoxy resin over the structure. When cured you can sand the exterior smooth and pop free from the plug depending on the shape you may need to seperate into 2 halfs and then re-join. Whole process can be done in a weekend.
Thank you this sounds like the way to go and I have the foam board in 1" and 2". Can that be covered with standard boat type resin or will the heat attack it, ? I even have the wax and the cowl shape will be such that a plug will not hang up if it comes lose, then I could dig it out if it hangs up. Whats this stuff some pour on the foam that desolves it ?

I'm really getting an education just building a cowl, the mould making aspects of it are way over my head so thats out. I simply don't know the first thing about any of this compatability with the stuff used to do this. I can build a very nice plane thow.

Thank you for your help, Leroy



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Old 01-13-2013, 08:40 AM
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Default RE: Building a cowling plug

As long as the foam is covered real good with the tape and sealed, everything will be fine. Polyester resin will melt styrofoam in a NYS so just make sure it is protected.

Bob
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Old 01-15-2013, 08:48 PM
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Default RE: Building a cowling plug


Quote:
ORIGINAL: sensei

As long as the foam is covered real good with the tape and sealed, everything will be fine. Polyester resin will melt styrofoam in a NYS so just make sure it is protected.

Bob
Bob I'm puting about 3 coats of epoxy on the cowl plug prior to polishing it , do you think that will do the job of protecting it. Plug to date can be seen at the build site.

Really glad to have your help Bob, thanks, Leroy

www.rcuniverse.com/forum/m_11326847/tm.htm
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Old 01-16-2013, 03:43 AM
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Default RE: Building a cowling plug

Quote:
ORIGINAL: Leroy Gardner


Quote:
ORIGINAL: sensei

As long as the foam is covered real good with the tape and sealed, everything will be fine. Polyester resin will melt styrofoam in a NYS so just make sure it is protected.

Bob
Bob I'm puting about 3 coats of epoxy on the cowl plug prior to polishing it , do you think that will do the job of protecting it. Plug to date can be seen at the build site.

Really glad to have your help Bob, thanks, Leroy

www.rcuniverse.com/forum/m_11326847/tm.htm
Hello Leroy,

I am assuming you are laying up part and not a tool. If you are going to layup your cowling with epoxy resin and cloth I would tell you to wax, and PVA the surface of your plug, then go ahead and lay up your cowling because I know that will work out for you. If you are planning to use polyester I would still carefully cover the entire plug with mylar tape because the polyester resin and vapor is very strong and if you have the slightest thin spot or undetected porosity on the surface of your plug, it very well could start melting and cave in before it cures. I would still use the wax and PVA prior to layup. I just don't want you to go through that potential aggravation.

I also at times create a plug and layup a part right on top of it. I do always use epoxy resin when I lay up parts and I generally lay 2 plies of cloth and epoxy resin on my plugs, after cure, this allows me to perform and bondo and primer work prior to waxing, applying PVA and laying up my part, but again what you have is fine as long as you protect your plug. Here is a couple of pictures of a cowling a made on top of a plug a few years ago. I hope this information helps you.

Bob
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Old 01-18-2013, 08:02 PM
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Default RE: Building a cowling plug

Bob there surely is no fault in your method and I will use it on mine. Looks like you used styro foam white, that can't be can it, ? At any rate mine is blue and if I can get nearly as nice a job as your's I'll be happy and you will get the credit because you provided the bulk of how to do.

Thanks alot and I mean alot, you will see the results shortly and I will be happy it's done. Leroy
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Old 01-18-2013, 09:01 PM
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Default RE: Building a cowling plug


Quote:
ORIGINAL: Leroy Gardner

Bob there surely is no fault in your method and I will use it on mine. Looks like you used styro foam white, that can't be can it, ? At any rate mine is blue and if I can get nearly as nice a job as your's I'll be happy and you will get the credit because you provided the bulk of how to do.

Thanks alot and I mean alot, you will see the results shortly and I will be happy it's done. Leroy
Yes it is just white styrofoam and there is no credit to me, your a craftsmen, I can see it all over your build.

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Old 01-19-2013, 09:48 AM
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Default RE: Building a cowling plug

Something to consider. There are many different methods to arrive at the finished part. However there is one constant. The finish on the plug has to be superior to the required finish on the final part.

The finish on the plug determines the finish in the mold, which in turn determines the finish on the final part to some extent. The surface finish will not improve through each stage of the process. There will be some detoriation from start to finish.

There is little point in making the plug, the mold and the final part if the surface of the final part has to be reworked to achieve the desired finish.

Ed S
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Old 01-23-2013, 03:01 PM
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Default RE: Building a cowling plug

I got the plug built and ready to do the fiberglass layup to build the cowl and it wasn't without some issues and alot of time. Shaping the plug out of blue foam was not the best choice, white would have been better but I'm in a learning mode. Problems started when I painted it with epoxy and the whole thing was a mass of air pocket bubbles, the plug was ok but now I have to sand it all down which is a job in it"s self and do it again. I mixed 30 min. epoxy and thinned with denatured alcohol so it would smooth out better and it did except on the top which was the last section applied and the bubbles showed up again. When I went to dip the brush again I found the cup of epoxy had foamed up and was getting hotter by the minute. I thought it was going to burst into flames, it didn't and I got it off the table to be safe. I have no idea what caused that, I never seen it before. Anyway this morning I sanded it down again polished and waxed it 3 times with carnauba wax and I hope thats enough to prevent sticking to the plug. Will find out tomorrow when I glass it. I don't expect to save the plug getting the cowl off.

Anyone know what was going on with the epoxy, I'd like to know.

Will post the out come of it all when I get it done, Leroy

Pict's. later as internet can't upload now.
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Old 01-24-2013, 02:33 PM
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Default RE: Building a cowling plug


Quote:
ORIGINAL: Leroy Gardner

I got the plug built and ready to do the fiberglass layup to build the cowl and it wasn't without some issues and alot of time. Shaping the plug out of blue foam was not the best choice, white would have been better but I'm in a learning mode. Problems started when I painted it with epoxy and the whole thing was a mass of air pocket bubbles, the plug was ok but now I have to sand it all down which is a job in it''s self and do it again. I mixed 30 min. epoxy and thinned with denatured alcohol so it would smooth out better and it did except on the top which was the last section applied and the bubbles showed up again. When I went to dip the brush again I found the cup of epoxy had foamed up and was getting hotter by the minute. I thought it was going to burst into flames, it didn't and I got it off the table to be safe. I have no idea what caused that, I never seen it before. Anyway this morning I sanded it down again polished and waxed it 3 times with carnauba wax and I hope thats enough to prevent sticking to the plug. Will find out tomorrow when I glass it. I don't expect to save the plug getting the cowl off.

Anyone know what was going on with the epoxy, I'd like to know.

Will post the out come of it all when I get it done, Leroy

Pict's. later as internet can't upload now.
What you experienced is a very common occurrence in epoxy volume mixtures of as low as a 300 gram mass, it is an exothermic reaction of the mixed resin and the hardener. In short you had what is commonly referred to as a case of thermal runaway, in mass it continues to generate heat until it exhaust the energy caused by the mixed chemicals, during this process it could and in most cases reach several hundred degrees before it cools back to ambient.

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Old 01-25-2013, 05:52 AM
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Default RE: Building a cowling plug

The most probable cause was incorrect ratio of hardener to resin, too much hardener. I have never mixed 300g of resin. I have frequently mixed as small as 7g of resin for very small jobs without heating issues. However the correct ratio of hardener to resin I do maintain no matter how small or large the mix.

I use the small amounts for say joining wheel pant halves. Next size up for laying up fuselage halves. The real big amounts for the thicker mold walls.

Ed S
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Old 01-25-2013, 08:10 AM
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Default RE: Building a cowling plug

When mixing larger masses of resin it's best to use a true laminating resin rather than a thinned out bonding resin.  Bonding resins are designed to be mixed in smaller quantities.
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Old 01-25-2013, 12:26 PM
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Default RE: Building a cowling plug

Hi guys, the product was epoxy not resin and I did use equal parts, not sure what part the alcohol played. Anyway I got it done and the fiberglass has been applied to the plug, just waiting for it to cure and there is still more work to do before I try and remove it (cowling) from the plug. It has been a learning experience to say the least. I don't expect to save the plug thow.
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Old 01-25-2013, 12:30 PM
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Default RE: Building a cowling plug

I agree with wyowindworks. I always use laminating resin. I do not use the cheaper resins available in hobby stores. It is an unfortunate fact of life. Always use quality epoxy resin do not even think of polyester.

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Old 01-25-2013, 12:35 PM
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Quote:
Hi guys, the product was epoxy not resin and I did use equal parts,
This could have caused the heating problem. I have never used an epoxy where the hardener to resin was equal. The epoxy I have used for many years is 10 parts epoxy to 4 parts hardener.

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Old 01-25-2013, 02:58 PM
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Default RE: Building a cowling plug

We use the West System epoxy and the pumps with the cans. That way it is always a proper mix.. no thinning needed.
With all that work you did, I would have went a few more steps and made a 2 piece plug and then had a 2 piece mold to make more cowls later.. But thats what we do...

good luck , hope it releases for you.

Scott
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Old 01-25-2013, 05:26 PM
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Default RE: Building a cowling plug


Quote:
ORIGINAL: Ed Smith

The most probable cause was incorrect ratio of hardener to resin, too much hardener. I have never mixed 300g of resin. I have frequently mixed as small as 7g of resin for very small jobs without heating issues. However the correct ratio of hardener to resin I do maintain no matter how small or large the mix.

I use the small amounts for say joining wheel pant halves. Next size up for laying up fuselage halves. The real big amounts for the thicker mold walls.

Ed S
This is such a misinformed statement, properly mixed ratios of epoxy gluing or laminating resins in a mass of approx. 300 grams or more will go into thermal runaway if not used very quickly, there are exception to this like the use of something like Shell 9000 series epoxy resins that can be mixed and set for literally days until placed in temperatures exceeding 350F. but that is another subject.

Just because someone adds to much hardener to the epoxy base does not necessarily mean that it will heat up and go into runaway, it could very well not cure at all, hardener's are generally oxidizers and require proper mix ratios in order to achieve maximum matrix performance. Now the over use of a catalyst mixture to polyester resin ratio will generally accelerate the cure cycle, however too much MEKP can cause a non curing condition as well.


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Old 01-25-2013, 07:14 PM
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Default RE: Building a cowling plug

Ed the epoxy I buy with the hardner comes in equal size bottles and the mix ratio is 1 to 1, I have been useing it for years with no problem. Like most things they all are not created equal, simply read the instructions that come with any product, works for me. Same thing applies to resins but the hardners can be cut 25% to slow down reaction some and reduced temps also. Most of these products activation and cure times are based on 72 degrees as are urethane paints.

Many of you have experience building plugs, moulds and casting parts, I don't but soon will. This has turned into quiet the project as it does for the first timers, truth is, it's not as easy as it looks.
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Old 01-25-2013, 07:58 PM
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Default RE: Building a cowling plug

Bob, I agree. I'm sure that you have heard just as many different horror stories about composite work as I have. Truth is I have found that the shortest pot life is when I have the mix ratio spot on. Of course as we know but I think it is useful information the ambient temp will affect the pot life and adding fillers auch a Micro Ballons or Cabosil will reduce pot life as well. leroy did nothing wrong except mix up too much product. Mixing and then pouring into a shallow container will slow it down a bit too. I am fortunate enough to work in a composites shop that has to set experation dates one year from date of delivery. This means I get to take lots of stuff home. I have one resin system that I can choose 3 different hardeners depending on the task. One mix is especially helpful when doing repairs, wet out to sandable is one hour at 70 degrees. The same resin can be mixed with a different hardener and used for sheeting wings. Plenty of time to get skins on and in the bag.

Leroy, mixing resin introduces air into the mix. There are two ways of dealing with this. First and least econmical would be to degass the resin. This means putting the mixed resin into a vacuum pot and pulling vacuum. Problem is you need to pull around 27 inches of vacuum. Not for the average guy. The next is to flow out the resin on the part and go over it carefully with a heat gun. The heat will work most of the air out but you have to use a fairly slow curing resin system.
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Old 01-26-2013, 04:02 AM
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Default RE: Building a cowling plug

Very nice thread! Even though I don't build plugs or cowls, this is very informative. [8D]
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Old 01-26-2013, 06:08 AM
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Quote:
This is such a misinformed statement
,

Realy?

I offer my replies based on my own experience after thirty years of making parts at the hobby level, not in an industrial environment. All I will say is follow my advice to the letter, use the material I use, do as I do and it will work. It always does for me.

Pictures show Prop mold and fuselage mold. One each of many.
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