rharshberger
Well-Known Member
This is the process I use to vacuum bag my MPR and HPR fins. The fins used here are for a SBR/Fusion Rockets 4" Thor and have a layer of 7oz fiberglass (RAKA Inc iirc), and a layer of 3K 5.8oz Carbon Twill from Soller Composites, since this rocket will not be a high performance rocket the twill fabrics were used without orienting the weaves to increase rigidity.
My foundation is a piece of 1/2" particle board covered with Dura-Lar (Dur-Lar?) drafting film from Hobby Lobby secured around the edges by blue painters tape. The particle board was chosen for two reasons, its easy to machine and its rigid but porous so it acts as a breather for the bagging process as well a the breather cloth does. The board was given a 1/8" radius on ALL edges to prevent puncturing the bag as much as possible. Another reason for the board is its easier to assemble the laminate on top then slide the whole unit into the bag.
The fins had already had one side done so I covered the reverse side with green painters tape then packing tape around the edges, excess was cut off flush with the edge. A loop of green painters tape is stuck to the back of each fin to hold it to the board during the wetting out process.
Fins laid out on board prior to wetting out, its important to make sure everything fits and is aligned the way you want before mixing epoxy.
The start of my mise en place, all of my materials are pre-cut and ready to go before I start I will reverse the order they are currently shown in the picture. Breather (white fabric) which is 1/4" thick cotton quilt batting from JoAnns Fabrics, the Blue fabric is nylon peel ply from ACP Composites, black cloth is the Soller 5.8oz Carbon Twill, and the barely visible stuff under the carbon is the 7oz fiberglass from Raka Inc. One trick to cutting Carbon Fiber I have found and seen has been to lay out the fabric and get the weave the way I want it (as straight as possible), I then use 1/4" masking tape to tape the outer edge of the area I plan to use, then I cut along the center of the tape with a rolling fabric cutter (Olfa and Fiskars are two common brands). The rolling cutter works well on Carbon and Fiberglass but sucks on aramids like kevlar and nomex. Make sure all the layers are larger than the area you need to cover as its easier to remove excess than to try and wiggle the layers around to cover missed spots.
I use Harbor Freight chip brushes for applying the epoxy, the bristles are normally pretty scraggly so I cut them off to about 1" long or so to even them up, it also seems to help stop the brush from shedding bristles as bad. The brush will still shed a few bristles usually during the first layer application so they are easy to spot and pick out.
Epoxy measured and ready to go (this was actually the second batch and is about half the size of the first batch I made. Epoxy is US Composites 635 Laminating Epoxy 3:1 ratio, I love the stuff, its easy to get good results with and its pretty forgiving.
Layer of fiberglass applied and then checked for proper wet out, properly wetted out FG cloth is usually clear (you can see the wood grain in this case through it), using extra epoxy at this stage is okay, its better to have excess than not enough as the next layer will pick up most of the extra.
Layer of carbon fiber applied, notice that the upper left corner section is still dry, its harder to tell when carbon is adequately wetted out unless you see excess standing on the surface, I use a tap tap motion with the brush bristle tips or a patting motion with the flat of the brush to work the excess epoxy from below up through the layer. I have found its easier for me to work epoxy from below than it is to get epoxy to pentrate the layers from above.
Carbon Fully wetted out and excess epoxy standing on surface.
Peel ply layer applied, at this point I actually had to make a bit more epoxy as I find the excess lubricates the peel ply and makes it easier to work around. All the large air bubbles are removed at this point leaving some really tiny ones. I like to see the peel ply fully wetted out with NO dry spots.
My foundation is a piece of 1/2" particle board covered with Dura-Lar (Dur-Lar?) drafting film from Hobby Lobby secured around the edges by blue painters tape. The particle board was chosen for two reasons, its easy to machine and its rigid but porous so it acts as a breather for the bagging process as well a the breather cloth does. The board was given a 1/8" radius on ALL edges to prevent puncturing the bag as much as possible. Another reason for the board is its easier to assemble the laminate on top then slide the whole unit into the bag.
The fins had already had one side done so I covered the reverse side with green painters tape then packing tape around the edges, excess was cut off flush with the edge. A loop of green painters tape is stuck to the back of each fin to hold it to the board during the wetting out process.
Fins laid out on board prior to wetting out, its important to make sure everything fits and is aligned the way you want before mixing epoxy.
The start of my mise en place, all of my materials are pre-cut and ready to go before I start I will reverse the order they are currently shown in the picture. Breather (white fabric) which is 1/4" thick cotton quilt batting from JoAnns Fabrics, the Blue fabric is nylon peel ply from ACP Composites, black cloth is the Soller 5.8oz Carbon Twill, and the barely visible stuff under the carbon is the 7oz fiberglass from Raka Inc. One trick to cutting Carbon Fiber I have found and seen has been to lay out the fabric and get the weave the way I want it (as straight as possible), I then use 1/4" masking tape to tape the outer edge of the area I plan to use, then I cut along the center of the tape with a rolling fabric cutter (Olfa and Fiskars are two common brands). The rolling cutter works well on Carbon and Fiberglass but sucks on aramids like kevlar and nomex. Make sure all the layers are larger than the area you need to cover as its easier to remove excess than to try and wiggle the layers around to cover missed spots.
I use Harbor Freight chip brushes for applying the epoxy, the bristles are normally pretty scraggly so I cut them off to about 1" long or so to even them up, it also seems to help stop the brush from shedding bristles as bad. The brush will still shed a few bristles usually during the first layer application so they are easy to spot and pick out.
Epoxy measured and ready to go (this was actually the second batch and is about half the size of the first batch I made. Epoxy is US Composites 635 Laminating Epoxy 3:1 ratio, I love the stuff, its easy to get good results with and its pretty forgiving.
Layer of fiberglass applied and then checked for proper wet out, properly wetted out FG cloth is usually clear (you can see the wood grain in this case through it), using extra epoxy at this stage is okay, its better to have excess than not enough as the next layer will pick up most of the extra.
Layer of carbon fiber applied, notice that the upper left corner section is still dry, its harder to tell when carbon is adequately wetted out unless you see excess standing on the surface, I use a tap tap motion with the brush bristle tips or a patting motion with the flat of the brush to work the excess epoxy from below up through the layer. I have found its easier for me to work epoxy from below than it is to get epoxy to pentrate the layers from above.
Carbon Fully wetted out and excess epoxy standing on surface.
Peel ply layer applied, at this point I actually had to make a bit more epoxy as I find the excess lubricates the peel ply and makes it easier to work around. All the large air bubbles are removed at this point leaving some really tiny ones. I like to see the peel ply fully wetted out with NO dry spots.
![20200430_132846[1].jpg](https://cdn.imagearchive.com/rocketryforum/data/attachments/331/331415-4e1f0c3624c26010a489e4b31ad10e0e.jpg "20200430_132846[1].jpg")
