A5fly

I'm interested in what others do for construction of plugs, to see if there is a better way of doing it.

To make a fuse or wing plug "quickly", I use a CNC foam cutter on extruded polystyrene (blue foam). I then seal the foam with a coat of latex paint to reduce some of the bubbles that I see when applying epoxy directly to the foam. After the paint is dry, I then mix talc with laminating epoxy resin and coat the foam plug. This gives me a good primer-type finish for coarse sanding. The final step is to apply a layer (or a few) of epoxy gel coat, which is then sanded and polished.

Doing the plugs this way saves the time of not having to laminate the plug with fiberglass (and sand and primer and sand, and sand...), but I still get a tough durable finish for the female mold making.

Anyone see any flaws in this, or suggestions for a better process for plug construction using foam?

Ron S

My Feedback: (2)

I'm curious if you've tried your method yet. I might be making some composite wings soon, and need to make the wing plugs. I'm not sure if removing the glass is going to give you a workable surface for plug surface finishing...

I was planning on building a normal wing set with the typical foam/balsa sheeting, then glass. Instead of using the typical 3/4 oz cloth, I'd probably use a couple of layers of 2 oz, to get the surface harder...

A5fly

I do use this method to make plugs and it seems to work well without adding the fiberglass. The layers of thickened epoxy and epoxy gel coat create a hard shell and smooth surface. I never liked the idea of putting fiberglass on the plug, because it requires not only more work to layer the glass, but it requires more sanding as well. Although it is not absolutely necessary, I have bagged the female against the plug before as well and the plug did not crack or deform. I guess that makes sense because the plug will only see compresion, which is what foam and epoxy are good at carrying.

I was just interested in sharing what I did, and hearing what methods others might use which might be even better or faster.

Atlanta 60

My Feedback: (18)

A5fly...if it works for you...your plug (master model) concept is great...the important thing is the process you choose works for your application...Ron I would not argue with your plan either...I think if I were building a wing tool I would use your concept for the master...if I were doing a fuselage (compound contours) I would lean towards A5fly's concept...the deal is...your master needs to be dimensionally stable...how you get there is sorta up to the individual...plaster, wood, foam and all sorts of other stuff are used in the composite tooling industry...when I was a tool builder we would basically look at the task at hand and go from there...now with Hi temp tools there are a few more factors involved...but room cure stuff it was basically whatever works...good luck and have fun!!!


P.S. It's kinda neat...see I thought I was the only person in the world doing this stuff in my basement...it's kewl to see all you guys doing it too...lol....now I can tell my neighbors that I am not all that crazy....actually...they think it's pretty kewl...all my neat tools and such...ya gotta admit...when one of your neighbors walks in and you got something in a vacuum bag with the pump goin' and the all gages and stuff...it's pretty impressive...they think they have walked into one of Lockheed's factories or something...lol...and they think I am sooooo smart...well maybe I won't tell them after all...lol

Jimbonk

A5fly, you might want to try this idea. Using some thin ( like .005-.007 ) thick mylar as carryers bag a layer of glass cloth onto the wings. You will still have to deal with the LE's but the rest of the wing will have a glass smooth finish on it in one step.

Jim B

What I am talking about here is a slight variation of the method used to produce glass/cf over foam composite wings. You cut the Mylar the exact shape of the wing getting as close to the LE as you can. Where the mylar will still follow the curve of the LE. ( this also applies to the wing tips ) Then you cut the Glass Cloth the exact shape of the Mylars. This is fussy work , getting the mylars cut exactly right , but it will save you a lot of hours of sanding.
Normally you would wax and paint the Mylars with your choice of color prior to applying the epoxy to the glass cloth, and this might be a good idea here as would give you color to look at when looking for flaws.
As far as doing both sides of the wing plug at the same time, I would suggest that you do this. Having the Mylars taped together at the TE makes getting them in the proper position easy.
It's hard to introduce a warp or a twist in already built wing with the standard Bagging method.

A5fly

Jim,

That sounds like a good idea for wings where the curvature is not compound. I guess the leading edges will still need sanding work as you say. Did you mean to say .005-.007 thick glass or Mylar? Would you bag the wing plug in an envelope bag, or bag it to a tooling board? I worry about twist with the envelope bag.

boater

My Feedback: (2)

A5Fly-- Did you find talc and epoxy easy to sand?? I tried it once and thought it was a little hard. Have you tried microballons-- very easy to sand.


One comment---- I have a friend who uses mylar on the outside surface, but instead of vacuum bagging he just squee-gee's out the resin underneath for a smooth surface. Anyone else do something similar? Good for when you can't bag it or when bagging it would be a hassle. Might be an added trick for when weight is not an issue, like in a plug.

Mike James

I've got mixed feelings about this, based on my experiences with certain projects...

The best, hardest, most stable male plug I ever made was the worst one to sand. I used what used to be called "Akemi", a VERY hard tooling resin. At the time, I hated sanding it, and thought it was overkill.

So, on future projects, I went back to a few layers of glass, (for stability) followed by a resin surface and/or epoxy primer.

The trouble with the nice sandable surfaces is just the obvious one... They're more fragile. Also, be careful what your ultimate use is for a plug. I recently had an experience where I created a "perfectly good" canopy plug, with a glossy, PPG paint surface, and made some female molds from it, for a standard glass layup and/or vacuum bagging. No problem. But...

I assumed that this plug would be good for vacuum-forming a clear part, but nooooooo... It turns out that both the epoxy (West Systems) and the PPG paint outgas due to the heat, and the plug for vacuum-forming had to be redone. Doh! (Acrylic lacquer primer was recommended by this very talented guy who does the vacuum-forming.)

Much as I hate to say it, (and I mean, I REALLY hate sanding tooling resin!) I think the harder surface coats are better and more versatile.

Atlanta 60

My Feedback: (18)

I agree with Mr James...that is one thing that crossed my mind when I read the first post...was the "material compatibility"...I am not a chemist so everything is trial and error..lol..when I find a process I like I stick with it... I use tooling surface coat...it works for me...everytime...yes it is tough to sand...80 grit sand paper is my friend...lol...then I will typically work to 240 grit finish...faster or easier is nice...but not if your doing it twice...lol...

A5fly

I appreciate the feedback, and all your comments above are helpful. I guess I should have listed the actual resins that I use so we have a basis for comparison. Here is a list of the major components:

Plug material: Blue or Pink extruded foam

Plug seal (to prevent outgassing from the foam through the epoxy which causes bubbles which are no fun to sand): White latex acrylic enamel spray paint

Intermediate surface layers: Decomp DLR-3400 laminating resin mixed with talc although I like boater's suggestion for micro-ballons if they are not too expensive)

Outer layer: Decomp DSC-1301 surface coat (lt. blue).

The intermediate layers I sand progressively from about 60 or 80 grit to 250. After the outer surface coat is applied and cured, I sand progressively from 250 grit to 1500 wet. I then polish with a polishing compound.

In past projects, I have bagged the fiberglass to the plug to make the mold, although after reading others methods, it looks like this may be overkill? I am going to try and lay-up right on the plug and parting board with the glass next time. It should save on bagging material costs and hassle.

boater

My Feedback: (2)

When you get to the mold making part, I recommend a couple of coats of tooling epoxy resin first (maybe thicken alittle with viscofil). Let the first one harden, then put on a second, etc. The resin won't have any pin holes or bubbles, which I tend to get when I apply glass cloth. Even if you get some bubbles from the cloth, they will be far enough away from the surface to not cause problems. Also you'll tend to build-up on the inside corners, which is good, its hard to get the glass to go there anyway. It'll tend to give you a more defect free mold.

A5fly

Thanks boater,

In that step when you are putting on the tooling coat, I assume you are putting it on over the PVA? Do you ever have problems with the PVA peeling off from brushing on the toolcoat, especially after it is thickened?

boater

My Feedback: (2)

Yes you are right I use PVA first. I don't thicken it enough to be a putty, I thicken it enough so it will not slide off the vertical surfaces, thin enough to let the bubbles out and still be fairly easy to brush. You can peel the PVA if you're too rough, but it's not much of a concern.