Carbon fiber layup questions from a newbie

I am attempting my first CF layup / vacuum bag this evening. Of course the piece is likely one of the most complex pieces and layups to attempt even for an experienced person, let alone a rookie...see below. This will have two layers wrapped around the outside with two layers from the bottom up the flat side and piece laid on the bottom with one final layer wrapped inside. The piece is made from a Madcow 4" x 8" coupler, cut down to 5" in length with 6 layers of the paper removed leaving the thickness at about .035". The plywood is 1/4" on the back and bottom and the bottom piece is internal to the half tube vs the tube sitting on top of it, this provided me the largest adhesion area to epoxying it together. The piece was made two weeks ago and is well cured and the tube was left rough both inside and out to help promote the epoxy to both saturate and adhere to the paper.

The CF is 3K 2x2 Twill, I have my vacuum bag prepped, my patterns made, peel-ply and breather cut, and I will be using Aeropoxy PR2032 resin with PH3665 hardener, which has a two hour pot life.

My questions are the following:

- considering the pieces are not flat or round where I can leave excess to be trimmed out later, what is the best way to cut this? I was thinking to cut the pattern large with masking tape on the edges, wet out then place on the piece and cut the tape off still wet. This of course will make a mess of my nice new and insanely expensive CF scissors, but I can't see another way. Tips appreciated. Keep in mind I want to lay this up in one go so it cures as a single piece.
- how do I measure out the epoxy so I have enough for the layup, taking into consideration some saturation.
- how do I cut and lay down the 2 layers so I can gain some strength, looks are not a concern.

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Well no answers and I had to get it done this evening.

So I wasted about 2/3rds of the epoxy I mixed but I now at least have an idea of how much to use next time. Also I am sure when I unwrap this it's going to be ugly as it was very difficult for me, based on my technique with zero experience. Besides the amount of epoxy to mix I also learned to be more generous with the peel-ply and that cutting CF cloth after it's been wet out is difficult at best to keep from the edges from pulling, so again I learned to be a it more generous with the CF cloth and deal with the excess overlap after, especially when it comes to corners.

Another 12 hours to go under vacuum. It's like Christmas I have no idea how this is going to look when I open it up, but it seems to of retained it's shape, mind you I am not sure of accurately. Regardless of how bad it does I will post pics for your viewing pleasure.

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Here are some pics and notes of my first CF inside and out lay-up/vac-bag.

First off the peel-ply and breather was very difficult to remove as the breather was saturated with epoxy including to the vacuum bag attachment piece which took a bit of effort to release. I believe this was due to several factors, too much epoxy, not using the optional perforated release film, and poor application of the CF to the piece. When I was able to free the piece there were several wrinkles as well as areas, mainly on the bottom, where the CF simply slipped off the piece instead of wrapping around. I was expecting this because I was struggling with keeping the CF wrapped on the edges and the layers were sliding over one another while I was wrapping it up. In an attempt to fix this I used my belt sander to clean it up, and in doing so sanded the CF completely off the piece in several places. Internally the piece didn't come out as bad as I thought, but as you can clearly see there are some dry spots as well as the corners where the CF simply did not tuck into.

What did I learn:
- how to estimate the amount of epoxy to use
- I will use the "optional" perforated release film in between my peel-ply and breather
- CF sands with a lot less effort than I thought so I will use my palm sander with 150 and adjust as required up or down

All in all it was a success as the failures lead to a lot of growth working with these composites and the piece worked like a charm on rocket during it's first flight @ URRF. I was surprised with all of the short-comings, of how strong it ended up being as well as how thin the 2 layers ended up being. I will re-make this piece, because it needs to be larger, with 3 layers wrapped on the outside and one from the bottom up the flat back. I will do this in 2 layups, first the bottom up the flat back, then remove from the vacuum, cleanup and wrap with one continuous wrap 3 times then vacuum again. I will not wrap the inside as it's just note required.

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With non-flat surfaces, it's a lot easier to do one layer at a time. (If you apply the subsequent layers before full cure, you can still get a chemical bond.)

And as you learned, you want to get as much epoxy out as you can by hand and get the fabric tight.

Hi John,

I value your feedback; especially when coming from someone such as yourself with a depth of experience and incredibly high standards that is tough to match.