Fin Vacuum Bagging Process by rharshberger

watheyak

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I have used 3M77 spray adhesive as well as Fiber-Tac, which is supposed to be formulated to not interfere. In the past I've had great results but a recent delamination has made me nervous.

IMG-1478.JPG

There was a lot going on that could have caused this. Mach 2.7 with Aeropoxy and unprotected leading edges to name a few. But This was all stuck down with the Fiber-Tac beforehand. I can basically peel the rest of that off by hand. I don't think I got very good adhesion.
 

rharshberger

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I have used 3M77 spray adhesive as well as Fiber-Tac, which is supposed to be formulated to not interfere. In the past I've had great results but a recent delamination has made me nervous.

View attachment 423552

There was a lot going on that could have caused this. Mach 2.7 with Aeropoxy and unprotected leading edges to name a few. But This was all stuck down with the Fiber-Tac beforehand. I can basically peel the rest of that off by hand. I don't think I got very good adhesion.
I think you about covered it, I dont know what to say.
 

Greg Furtman

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I have used 3M77 spray adhesive as well as Fiber-Tac, which is supposed to be formulated to not interfere. In the past I've had great results but a recent delamination has made me nervous.

View attachment 423552

There was a lot going on that could have caused this. Mach 2.7 with Aeropoxy and unprotected leading edges to name a few. But This was all stuck down with the Fiber-Tac beforehand. I can basically peel the rest of that off by hand. I don't think I got very good adhesion.
The link I posted for 3M 71 does say it specifically made to work for composite work.
 

VFA-22-Bonefish

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First let me say thank you for producing such an informative, and exciting, post! I really got a lot out of this and cannot wait to experiment myself with the information you were so kind to share. One question though, is there a vacuum/food saver device that you can recommend that’s large enough for laminating large high power fins, even if it requires that I do one fin at a time?

thanks again!
 

rharshberger

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First let me say thank you for producing such an informative, and exciting, post! I really got a lot out of this and cannot wait to experiment myself with the information you were so kind to share. One question though, is there a vacuum/food saver device that you can recommend that’s large enough for laminating large high power fins, even if it requires that I do one fin at a time?

thanks again!
You can use the canister attachment on a Foodsaver, its the hose woth a barb on it, all thats needed is a port on the bag, a short section of hose and a valve in the hose. Plug the canister adapter into the hose an vacuum, once under vacuum close the valve and monitor the bag to see when re-vacuuming is needed. If the food saver going to be a permanent addition to the rocket construction equipment, then I would remove the end of the canister attachment and permanently plumb it for vac bagging.
 

jddj

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With (FoodSaver) vacuum bagging (a la John Coker), I only saw a roughly 4g increase on some BT-80-sized Patriot fins. Starting weights were 3.1g (1/8" balsa) and 9.1g (1/8" baltic birch ply). So, at least with vacuum bagging, I didn't see a dramatic weight gain for a huge gain in strength.
I've been using John Coker's FoodSaver method for a few years on little and medium-big rockets. Works great, adds little weight. 3/4 oz (or 1/2 oz if you can find it) fiberglass adds tremendous strength but little weight for small rocket fins. You do have to consider that you're stiffening fins, and that transfers what would've been absorbed flex to the root attachment: fins are less likely to break, and more likely to detach at the root from regular handling and dumb-ass rocketeer mistakes. Consider modifying your construction to TTW with this technique.

If the mentioned products work for you, that's awesome. My bagging materials (teflon release fabric, polyester breather) come from Aircraft Spruce, and I typically use West Systems epoxy (though I've heard good things about US Composites epoxy as well).

I've tried bagging tubes, and carbon sock on a mandrel (closet rod is just about BT-55) and had limited luck with those. I keep hearing good things about mylar-wrap surfacing, and will try sometime...

Thanks John for getting me started, and rharshberger for the write up and detailed info!
 

G_T

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I apologize I haven't read the first collection of posts in this thread, only the last few.

3M77, if sprayed on like a coating - like you want it to act as glue - is a very effective epoxy barrier. If you want to use 3M77 to temporarily locate fabric in preparation for wetout, then use a mist coating. And sorry, the fabric WILL tend to come loose. If it doesn't, then you used too much and the result is much less of an epoxy bond.

In any event, inclusion of 3M77 will result in a weaker layup. The more used, the weaker the layup gets. There are times though where this is not of primary concern.

Gerald

PS - To apply a mist coating, lay fabric out on bench. Stand back a couple feet. Spray a quick pass aiming over top the fabric, NOT AT IT. Let the mist settle on the fabric. That's it. Now the fabric will have some tack ability.
 
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