polystyrene and epoxy

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dnl2

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I had planned on making a boat tail out of a PML nosecone. I thought that if I roughed up the inside real good, the centering rings could be installed with epoxy. A friend told me from his experience it won't hold. Has anyone had any issues with this or tried this? The NC is 4" and I planned on flying H,I, and J motors. Thanks for any help.
 
I have done half a dozen boattails with various size nosecones. I rough them up like crazy (I like using a wood rasp), then use good long cure epoxy with milled and chopped fiberglass, then I foam around the fin can MMT section inside the boattail. With that combo I have never had a problem.
 
Sure you can make it hold with epoxy.The thing is ,if it was polystyrene it would be easier ,but those cones are a type of polypropylene a much different animal.

First thing is clean,clean and clean.Before you do ANY cutting or sanding of the part,take it to the sink and wash it with dish soap and hot water ,rinse and dry and wash again.The NC will have traces of release agent on it ,so if you sand before you wash ,you scrub it into the plastic and there it stays ,making proper glue adhesion impossible.

After it`s dry ,take yourself some isopropyl alcohol and wash the part down again and then wipe dry with paper towel.

Since the epoxy will not be absorbed into the plastic ,your epoxy joint will be solely mechanical (although it will bond to and into the wood CRs)so you want the roughest surface you can get or even better angled cuts.

Take you some 60 -80 grit sandpaper and give the areas to be bonded a good scrub ,but alternate the direction....criss cross pattern.

Now grab an Xacto knife or similar utensil and cut/score deep gouges into the plastic ,again in the area of bonding....use a cross hatch pattern and keep the cuts about an 1/8" or less apart.All these deep cuts will allow the epoxy to "KEY" into plastic and form your bond.

After you are done with the sanding and cutting ,wash the area again with alcohol.Alcohol is great as it dries/evaporates quickly ,cuts oil & grease and leaves no residue behind.

Now you are ready to apply your epoxy (15 minute may be a good start....30 may be too thin and not build up enough)

Apply it thickly and use plenty on both sides of the CRs ,to lock them in on both sides.

I`ve done this many times and it works quite well ,but it`s all in the preperation.





Ahhhh geeze.....I`m too slow.....I`m always last !




Paul T
 
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I never did buy that V2 kit. But if it were me, I think I'd use JB Weld. That stuff is amazingly strong. I'm assuming your motor mount will be going through the boattail. Will the motor tube extend up into the body tube? If so, I'd put at least one of the centering rings on it so it gets epoxied into the body tube.
 
Will there be fins passing through the boat tail? If not, I'd put two centering rings up into the main air frame to ensure strength in the bottom end. This is assuming your motor tube is long enough. Whatcha buildin'?
 
chadrog asked, Will there be fins passing through the boat tail? If not, I'd put two centering rings up into the main air frame to ensure strength in the bottom end. This is assuming your motor tube is long enough. Whatcha buildin'?


V2, streched a little bit as so I can put a payload bay in it. Yes the fins will be epoxied to the motor mount tube. I talked to the ex Pres, and he told me to use two CR's in the boat tail with surround tub caulk instead of epoxy. Then add one CR up on top of the boat tail inside the body tube. I just wanted to hear what others had to say.
 
Tub caulk?:eyepop:

What he said :confused:

Maybe the rubbery caulking will act like a shock absorber ?

I don`t know about that one......:2:


Also, since the fins are passing through and onto the MMT ,plenty of lateral/shear strength will be added right there.



Paul T
 
Tub surround caulk is a great bonding adhesive for polystyrene, plastic and fiberglass. Read the label on a tube of liquid nails. Will it work with the heat from the motors? I don't know, but this info came from a guy who has been lv 3 for years and who is very knowledgeable with this hobby. And thinking that epoxy won't bond real well with plastics I was given an alternative.
 
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Well if you go that route ,you can get high temp. silicone caulk (firestopping) that will take the heat ,we use it in my industry.What ever you do ,don`t get any on the surfaces you want to paint (silicone infection they call it) paint hates silicone.

But I do agree ,silicone is a great adhesive(good lubricant too), pretty much what it`s used for ,stopping leaks was the bonus in it`s use.

At any rate ,surface prep is paramount.

Good luck with your project !


Paul T
 
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