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• CF overwrapped tube
• Systems 3000 epoxy (resin and hardener)
• Acrylic fillet radius tool 
• Gloves
• Respirator
• Cabosil
• Popsicle sticks
• Epoxy boats or paper cup (for mixing epoxy)
• Painters tape
• Ruler
• Acetone and shop towels (to clean up epoxy on acrylic tools)
• Vacuum 
• Root bond jig
• Sandpaper (220 grit)

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1. Add in cabosil in small amounts and mix until a peanut butter consistency is achieved.
   1. We used 9% cabosil for Crusty (i.e. if you have 100g systems 3000 resin and18g hardener, then it's 9g cabosil)
   2. When working with cabosil, A RESPIRATOR IS REQUIRED. You can take it off once all the cabosil is mixed in. 
2. Place the epoxy cup in the vacuum chamber, and wait 2 minutes. The epoxy should rise and then fall after the air bubbles have been pulled out. 
   1. 2 minutes was not enough. The fillets in Crusty were still very bubbly. See the Dusty procedure to figure out how to remove bubbles. 
3. Mark the radius of the fillet on the fin and on the fin collar with a sharpie, and then cover in tape. In this case, Crusty had a 0.75" fillet, but I'm reusing the Rusty pictures. 
   
4. Apply the epoxy in the fillet area, being careful not to go outside the tape. 
   
5. Use the acrylic fillet radius tool to remove excess epoxy. Be sure to swipe perpendicular to the root to ensure that the same amount of epoxy is being removed each time. 
   
6. Let it cure at room temperature for 24-36 hours. 
7. Place in the oven in the vertical position to oven cure for 12 hours. 
8. Sand the fillets .
   to remove high spots and roughen up any smooth areas. 

Tip to Tip Cut-Outs

The carbon fiber cutouts are the pieces of carbon fiber used in the tip-to-tip layup, which consists of laying plies from the tip of one fin, over the tube in between them, over the tip of the next fin (and repeat for the other three sides). The preparation for the tip-to-tip layup involves cutting out squares of carbon fiber and attaching them to wax/parchment paper using spray glue. The purpose of the paper is to prevent the carbon fiber from warping when it is being handled. Then, the actual shapes are cut out using a laser cutter. In general, fiberglass can not be cut on a laser cutter, but carbon fiber can, as long as the fiber is dry (i.e., not "pre-preg", referring to sheets of fiber that have already been impregnated with epoxy). Make sure that whichever laser cutter you use can fit the largest cutouts (the CSAIL laser cutter has a width of 18", too small for the final layer of the tip-to-tip cutouts, but the one in MakerWorks and N51 is big enough.) 

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The t2t layup refers to the process of applying epoxy onto the dry CF cutout plies, laying them on the fin can, trimming the wet plies, and then bagging. The prep takes about 2-3 hours with sanding and cleaning. The actual layup itself should be 2 hours (epoxy pot life) but it usually takes us 4 hours from first pot to full vacuum. The more prep you can do before you mix the first epoxy batch, the better. 10 minutes of prep can save you like 2 hours of layup time. If Drela taught us one thing, it was to be extremely prepared. 

Preparation

Layup:

Required Materials:

• Systems 3000 High Temp Epoxy Resin + Hardener
• Squeegees
• Popsicle Sticks
• Epoxy boats or paper cups 
• Acetone
• Shop Towels
• Microfiber Towels 
• IPA 
• Scale 
• Gloves
• Wax paper/Mylar 
• CF cutouts on wax paper
• Painters tape
• 3-4 tables in Gelb lab
• Layup jig (different from root bond jig and fillet jig)
• Music
• Vacuum tape
• Flash tape

Preparation Procedure (in Gelb): 

1. Grab two tables in Gelb and push them together. Grab two other nearby tables and clear them off. Replace the table paper, and mark everything with RT Composites and an email. 
2. The two tables that are pushed together: 
   1. cover them in wax paper or Mylar. This will be the layup table. Tape everything down with painters tape. 
   2. Take out 4 squeegees and place them on this table. 
   3. Put the fin can on the layup jig and place both near the side of the table. Put weights down on the sides of the jig to prevent any sliding. 
   4. Set out 3 of the #1 plies on the opposite side of the tables. Keep their wax paper on. 
   5. Grab a few empty cups and label them Spit Cup all over the cup. This will be for some excess epoxy during the layup. Place them on the layup table. 
3. The other two tables:
   1. Use one as an epoxy mixing station. Grab the nasty scale from the DBF area and plug it in near the work station. 
      1. This table should have: epoxy cups, popsicle sticks, shop towels, IPA/Acetone, gloves, Systems 3000 resin + hardener, scale
   2. The other should have supplies: extra epoxy, microfiber cloths, scissors, rubber spatula, GLOVES, extra squeegees, the rest of the CF plies, vacuum tape, the bagging materials kitted, flash tape
4. Make sure the fins are completely sanded and cleaned. 
5. Make sure the fillets are sanded (to remove high spots). 
6. DO NOT SAND THE CARBON FIBER. 
7. Clean everything on the fin can AGAIN with IPA. 
8. Make sure you have a full kit (CF plies ready, bagging materials fully kitted, enough epoxy, etc.) 
9. Table set up looks like this when laying up (during prep you won't have the yellow and green boxes, and you shouldn't have anything poured yet)
10. Image Added

Layup Procedure: 

*Once the first pot is mixed, you are on the clock. The pot life of the epoxy is approximately two hours, so the faster you can finish the actual wet part of the layup, the better. We want to vacuum as soon as possible to remove as much epoxy from the part as we can. 

Helpful tasks to assign: 

• 1 person at the epoxy station keeping track of the amount of epoxy mixed, regularly mixing more, and keeping track of the amount in the spit cut at the end. 
• 2-3 people pulling epoxy at the layup station
  • Always make sure there's a ply ready to go. Consider assigning someone just at the ready station.
• 1-2 people laying plies on the fin can
• 1-2 people prepping vacuum bag materials 

1. After ensuring the fin can is cleaned, use a piece of paper, a ruler, and a sharpie to mark the centerlines on the fin can. Draw the line along the entire fin can to ensure visibility. 
2. While the lines are being drawn, mix the first batch of epoxy. Start with 100g of resin and 18g of hardener, and then pour as necessary for the rest of the layup. Use a popsicle stick, and label the cup with its weight.
3. Using the popsicle stick used for mixing, drizzle the epoxy from the cup onto the dry plies. Use enough epoxy that you can spread it around with your squeegee, and pass the epoxy to the next person to do the same. 
4. As you initially spread the epoxy, the ply might move around on its wax paper. Slowly spread until enough of the ply is wet that it stops moving. Make sure all the corners and edges are covered.
   1. Pro tip: lift the wax paper up and check the underside to identify light areas you may have missed
5. Once you're sure you've covered the ply, start to pull epoxy out. There's a lot of nuance to this. Basically, press down with your squeegee and follow the direction of the ply until you near the edge. Then lighten up on the pressure and pull off the ply. 
   1. You should have a line of epoxy on your squeegee. Run your squeegee along the side of a spit cut to remove it. 
   2. Lightening up the pressure near the edges helps prevent warping. 
6. Once you can no longer see any large shiny pools on your ply, move it up to the next section of the table (yellow as shown in the table diagram above), and grab another dry ply. Repeat steps 3-6. 
7. Once a ply in the yellow section has sat for a few minutes, use a squeegee to continue pulling epoxy out and dumping it into a spit cup. Letting it sit allows excess to pool. 
8. Once a ply has been pulled enough, move it to the ready station. It's important to always have a ply ready to ensure that the assembly line process is moving as fast as possible so that we can quickly get to the bagging phase. 
   1. At the ready section, use a sharpie to mark the centerlines onto the plies wax paper. This helps the person laying up the plies with proper placement. 
9. Take the ply from the ready station, and line it up on the fin can using the wax paper. The trailing edges may not always line up because the plies are tapered. The two things to check:
   1. Are the leading edges lined up
   2. Are the center lines lined up
10. Slowly press the wet ply onto the fin can, starting from the middle of the wax paper and moving outwards. The ply should reach the tip chord of the fin if they're sized properly. 
11. Once firmly attached, pull the wax paper off. Then rotate the fin can and lay down the next ply. Repeat steps 9-11. 
    1. Trim the edges as needed. The carbon fiber shouldn't go over the leading edges. 
    2. If there's excess on the trailing edge, leave it. This is helpful for post-processing. 
12. Once you reach ply 6, have someone switch off of pulling epoxy and start prepping the vacuum bags. 
    1. For a room temperature cure, use the green stretchy one. 
    2. With one sheet of the pre-cut bagging material, lay down the vacuum tape as shown in the second square. You're basically trying to go ~1/3 of the way along the length on the top and bottom, and along the entire length on one of the sides. 
       1. Slowly apply the tape to the bag, ensuring that there are no wrinkles under the tape. Wrinkle = air path = leak
    3. Take the next piece of bagging material (the lighter green) and lay it on top of the previous sheet. Again, slowly seal the sheet to the tape to prevent leaks. 
    4. Fold the new sheet over, and repeat the step b-d. 
    5. Stop once you've sealed off three corners. It should kind of look like the diamond thing on the right of the diagram. The corners are for the fins. The last corner that hasn't been taped yet will be used to dress the fin can and slide the vacuum connector in. Leave the bag off to the side until all the plies are placed. 
    6. Image Added
    7. Cut some extra pieces of tape off to the side for the last corner and for the phenolic tube. 
       
       

Vacuum Bagging Procedure: 

*be conservative with flash tape because the epoxy can't travel through it, so if you have a ton of it on the peel ply and the release film, you're blocking it from reaching the breather. be strategic about placement

1. You better have everything kitted at this point.
2. Clean off the edges of the fin can (the exposed 1" of phenolic) with acetone and shop towels. 
   1. The vacuum tape does not like epoxy, so be sure to clean it off well. 
   2. If you have leftover vacuum tape from the overwrap cure, it might be easier to take a razor and scrape off the tape than to clean it. 
3. Lay down the peel ply (nylon, blue). Make sure to leave the 1 inch on the side for vacuum tape. 
   1. Cut off excess
   2. Make sure every part of the carbon fiber is covered in peel ply 
   3. Tape the layers of peel ply to each other with flash tape 
4. Lay down the release film (red, perforated). Make sure to leave the 1 inch on the side for vacuum tape. 
   1. Cut off excess
   2. Make sure every part of the carbon fiber is covered in the release film 
   3. Tape the layers of release film to each other with flash tape 
5. Lay down 2 layers of breather per side. Make sure to leave the 1 inch on the side for vacuum tape. 
   1. Cut off excess
   2. More breather is better than less. 
6. Lay down one ring of vacuum tape on either end of the phenolic tube. Press down really head to ensure that it sticks to the tube. Keep the white paper on until you're ready for the bag to attach.
7. Put the bag on over the fins. 
   1. Slowly remove the white backing of the vacuum tape on the ends of the tube, and slowly attach the bagging material to it. Have extra piece of vacuum tape handy to fill in gaps. 
8. Slide the vacuum connector in. 
   1. Put it on a bed of extra breather cloth to prevent wrinkles, and try to sick it towards the bottom of the fin can. 
9. Seal the bag with vacuum tape.
10. Find the connector, cut an X through the bag into the hole, and attach the vacuum hose to it.
11. Pull vacuum. Check for leaks. Your goal is -26 mm Hg. 
12. Leave the vacuum pump on for 24 hours at least. 
    
    

Oven Cure

After the initial room temperature cure for 24-36 hours, there is an oven cure. Systems 3000 epoxy achieves maximum thermal performance after a 12-hour oven cure. A vacuum is not necessary for the oven cure, but it won't hurt if you want to do it. We have a nice high-temp green hose for it. If you vacuum for the oven cure, make sure to use all high-temperature materials (The green vacuum bag will have to be replaced with the light pink, less stretchy one). 

Make sure to have people sign up for oven shifts and report oven temperatures on the hour. 

Oven Set Up Procedure:

1. Seeing as the cure cycle for System 3000 epoxy is around 12 hours, got people to sign up for shifts (this requires planning in advance!)
2. Positioned fin can vertically as shown. Positioning the fin can vertically is important so the fins don't splay and become misaligned. 
   1. If using vacuum: router the vacuum tube through a porthole on the right side of the oven. 
3. Followed the cure cycle for System 3000 High Temp epoxy. Note that the epoxy changes from clear to amber-colored after the cure is completed.
4. Once the cure cycle is complete and the fin can has cooled to room temperature, put on gloves. Then,
   1. If using vacuum: Turn off the vacuum pump and detach the vacuum fixture from the vacuum tube
   2. Remove the fin can from the oven
   3. If using vacuum: Carefully remove the high temp bagging materials and discard

Cure Cycle for System 3000 epoxy

• Increase from room temperature to 150F at a rate of no more than 2-5F per minute
• Hold at 150F for 3 hours
• Increase to 250F (no more than 2-5F per minute)
• Hold at 250F for 3 hours
• Increase to 300F (no more than 2-5 per minute)
• Hold at 300F for 3 hours
• Ramp down to 100F (no more than 2-5F per minute) --> decreasing temp takes a lot longer than increasing and lower temps are harder to control
  • Use the vents located on the left hand side under the shelf and the upper right hand side. They look like slabs with a knob. 
• Do not shut down the oven and leave it to cool down. Note that this takes longer than you think it will (as long as 1-2 hours)
  • At a certain point, it'll stop cooling down. Turn the oven off and open the door a little bit. Find the sweet spot that allows you to cool down at the desired 2-5F per minute. 

 Epoxy: 1312.9 grams