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Help with first fiberglass layup

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boatgeek

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I'm embarking on a project for my first fiberglass tube layup. I have reasonable fiberglassing skills, so I'm not too concerned about techniques. Where I'm not sure is on number of layers of glass and weights.

The project is an approximately 4" square rocket with a 54mm motor mount. I have a piece of 4x4 steel square tube with ~1/2" corner radius that I will use as a mandrel. I've laid up a test section and it worked fairly well, so I think I'm on the right road.

4" circular tubing is about 0.1" wall thickness for the thin wall filament wound stuff, so I think I want to go to about 1/8" thick. Based on the test section, that should be nice and sturdy. Online calculators put that at about 10 layers of 7.5 oz cloth, and a couple fewer layers of 10 oz. Does that seem like a reasonable number of layers to those of you who have laid up tubes before? Does that answer change if I twist a co-workers arm and get him to help me vacuum bag it? Finally, do you have any idea whether 7.5 or 10 oz glass cloth will still conform well to a 1/2" corner radius? In theory, it should be pretty similar to a fin fillet radius of the same size.

Many thanks! Build thread to come once I get some tube laid up.
 

cavecentral

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Most of my tubes are thinner / much lighter. 4 wraps of 9oz on 3.5", 4.5" and 6" diameter rockets. They weren't planned for Mach or anything, but still flew well to 5-6K feet are were light weight compared to the FWFG tubes on the market.

1/8" seems pretty thick IMO. Go with what works for you in terms of how heavy / sturdy you want to make it. Some things are built for a purpose - other personal preference.
 

REK

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I really dont see why go so thick, but thats your choice. Also why vacuum bag? Just use peel ply, no need to kill yourself (money wise as well) on such a simple layup.

As for your question about conforming to corners, it really depends on the weave style. If its plain weave it wont be as bad on a 4" square tube. Satins are the best for tight corners, but in your case it doesnt matter I would think.


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markkoelsch

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You are making a square odd rocket. You have your mandrel- make sure it is smooth as it not burrs as that would be bad trying to get the laminate off. Next, I would put a release agent on the mandrel, and then a layer of Mylar. Do the layup- if this it to be the entire airframe 5 or so continuous layers. Glass can work, and a half inch radius is not too bad.
 
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dford

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1/2" corner radius? Dude, you could lay up dang near any cloth weight in that. I've layed carbon into half a "pill shaped" tool with no wrinkles. That is to say the lay up was alternating 90 degree weave then 45 degree weave. Of course the 45 was easier and de bulking was required every other ply but you'd be amazed at what you can do.

Especially if you lay your FG at a 45, it will lay in there easily. Yesterday I did a contact lay up in 1/4" fillets at a 90. No problem

If I were you, at the very least, I'd peel ply the areas where you are going to bond anything on to make your life easier later.

I'd do three layers 6oz under vacuum just to get excess resin out and keep weight down. Alternate the weave. Pleat the fillets and layup edges.
 
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boatgeek

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I was debating whether to say this in my original post, but 1/8" seemed thick to me. It's nice to have confirmation of that. My test piece was about 0.8mm in the corners where the laminate was the best, and it's a little more flexible than I'd like. It was 3 layers of a tape that I had lying around, need to sort out exactly what weight that was, probably tonight. I was thinking vacuum bagging to cut down on bubbles in the laminate and get a more consistent product. I'd only do that if I can borrow the equipment--I'm not going to buy for this project. I'll have to check on pricing for satin weave for FG. I know I can get plain weave easily. Unless that's also available in bias cloth on a roll, I'm not going to alternate weaves, just roll from the bought roll to the mandrel. I'll do one more test piece before I do the final version.

Surface prep on the mandrel will be tonight if I can get the time. The test piece was 2" long, laid up on wax paper taped to the mandrel, then waxed with paste wax. That released from the layup just fine, but the single piece of tape holding the wax paper to the mandrel was a PITA to remove. Lesson learned!
 

dford

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Just curious, why would you not alternate the weave?
 

boatgeek

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I wouldn't alternate the weave on the body tube because I'm planning on basically rolling up the fiberglass on to my mandrel. It'll come off of the roll I buy it on and on to the mandrel in one layup. If I could get a roll with the weave at 45, then I'd seriously consider alternating. I'm not yet sure if I'll do tip to tip. If I do, I would alternate the weave on that.
 

cavecentral

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I do the same. Cut a piece from the roll for 4 wraps, and do them all at once.
 

cavecentral

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Releasing it and getting it to slide off the mandrel might be the tough part.

I use spray release on Mylar, then slide the Mylar off the mandrel while still green. Remove the mylar (5 mil thick) and slide it back on the mandrel to keep the shape.

Wait too long and some minor imperfection may lock it onto the mandrel and need cut off (wasted).
 

REK

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Use parchment paper for easy slip off. The parchment paper does not stick to the epoxy. I've used it on this 3" carbon tube and it slips off with ease.



Spiral wrap the parchment paper for easy prep. NOTE: not many tapes stick to it so you will have a hard time keeping it in place.




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