Purpose
The purpose of this procedure is to provide a step-by-step guide for members to construct a fin can, which consists of a phenolic tube with four fins attached, covered in either fiberglass (for a test fin can) or carbon fiber (for a flight fin can). Below is a list of risks, required materials, and a step-by-step procedure including the expected length of time that each step should take.
Prerequisites
All participants in the layup must have general lab safety training, and must have completed a respiratory medical evaluation at MIT Medical, and a respirator fit check in EHS. All participants should be wearing respirators and gloves when working with epoxy and colloidal silica, and safety glasses and dust masks when sanding. Participants should be under the supervision of at least one member who has performed a similar fin can layup previously.
Risks and Risk Corrections
Though this procedure is relatively safe and straightforward, there are a few chemicals that present risks, which can be mitigated through proper use of Personal Protective Equipment (PPE):
Epoxy
Risk: Inhaling epoxy fumes can cause respiratory problems, and skin contact with epoxy causes sensitization.
Risk Correction: Wear a respirator when working with epoxy, ensuring a positive/negative pressure test passes. Wear gloves when working with epoxy, and wash hands with cold, abrasive soap afterwards.
Colloidal Silica
Risk: Inhaling ultra-fine colloidal silica particles can cause respiratory toxicity and an increased risk for pulmonary diseases.
Risk Correction: Wear a respirator when working with colloidal silica, enduring a positive/negative pressure test passes. Wear gloves when working with colloidal silica.
Required Materials for Test Fin Can and Flight Fin Can
*Most of the materials used to make the test fin can and the flight fin can are identical, and cases where materials are only used for one or the other have been outlined in the materials list below.
Raw Materials
- Fiberglass (test) or Carbon Fiber (flight)
- Fin preforms (plywood for test, G10 + phenolic for flight)
- Phenolic tube
Layup tools
- West Systems epoxy (6 or 24-hour)
- 5-minute epoxy
- Colloidal silica
- Popsicle sticks
- Boats
- Fillet tool
- Squeegees
- Rollers
- Fin can jig
- Stabilizing feature
- Level
- Nuts
- Flight only:
- Aluminum mandrel
- Layup jig
- Proline
- Laminating epoxy
- Mylar
Bagging Materials
- Release film
- Bleeder fabric
- Vacuum bag
- Vacuum tape
- Peel ply
Miscellaneous
- Spray glue
- Scissors
- Painter's tape
- Shop towels
- Sandpaper (60, 120, 220 grit)
- Wax paper
- Sharpie
- Ruler
- Test Fin Can only: Dremel (with sanding bit)
- Flight only: 15 degree angled end mill
Personal Protection Equipment
- Gloves
- Dust masks
- Safety glasses
- Respirators
TEST FIN CAN PROCEDURE
Cut and Sand Fins (2 hours)
1) Cut plywood fins to shape on the laser cutter
2) Put on safety glasses and a dust mask
3) Sand the face of each fin using 120 grit sandpaper
4) Bevel edges of fins using a Dremel and sanding bit
Cut and Sand Tube (1 hour)
5) Wearing safety glasses, cut phenolic tube to size on a bandsaw
6) Put on safety glasses and a dust mask
7) Sand tube until it fits over the motor case (start with 60 grit, work up to 220)
8) Score the tube (using 60-180 grit sandpaper)
Prepare Tip-to-Tip Cutouts (4 hours)
9) Prepare paper cutouts for tip-to-tip layup
10) Stick wax to fiberglass using spray glue
11) Cut fiberglass shapes with scissors
12) Record mass of fiberglass (will use later to calculate wetness ratio)
13) Mark centerline of each piece with sharpie
Attach Fins to Tube (Root Bond) (1 day)
14) Score fins
15) Put tube in fin can jig
16) Put on gloves
17) Mix epoxy
18) Put 5-minute on root chord of each fin
19) Slide fins into slots in the jig
20) Finish assembling jig by putting the top layer of the jig on and securing the nuts
21) Attach stabilizing feature
22) Let cure
Root Fillet (1 day)
23) Remove the fin can from the jig
24) Put on gloves and respirator, ensuring the respirator fits well with a positive/negative pressure test
25) Mix laminating epoxy with colloidal silica
26) Use fillet tool to add fillets
27) Let cure (24 hours)
28) Sand the root fillets
29) Mark centerlines on the tube
Tip-to-tip Layup (1 day)
30) Put on your respirator and gloves
31) Mix epoxy
32) Record mass of epoxy used
33) Wet the glass sheets with laminating epoxy using squeegees
34) Remove the sheets from the wax paper and apply to the tube (layup)
35) Implement "Vacuum Procedure"
Post-processing (3 hours)
36) Sand fin can
FLIGHT FIN CAN PROCEDURE
Cut and Sand Fins (1 day)
1) Cut fins out of 1/8” G10 sheet on the waterjet
2) Cut phenolic leading edge on waterjet
3) Use a mill to cut slot into the phenolic
4) Use a mill to cut tabs in the G10
5) Attach the phenolic leading edge to the G10 fin core with epoxy and let cure
6) Score the fins
Cut and Sand Tube (3 hours)
7) Cut phenolic tube to length
8) Make sure it fits over motor case
9) If not, sand using 60 grit sandpaper, working up to 220 grit
10) Score the tube
11) Check to see that the tube fits in the fin can jig
Tube Layup Preparation (2 hours)
12) Prepare paper cutouts for carbon fiber tube layup
13) Spray the wax paper with spray glue
14) Apply the carbon fiber
15) Cut the carbon fiber/wax paper on the laser cutter (this is safe because the carbon fiber has not been wetted yet)
16) Record mass of each piece (to calculate wetness ratio later)
Tube Layup (1 day)
17) Put on respirator and gloves
18) Wet the carbon fiber pieces with epoxy
19) Record mass to use for wetness ratio calculation
20) Carefully separate the carbon fiber from the wax paper and apply it to the tube (layup), using more epoxy when necessary
21) Let cure for 24 hours
Root Bond (1 day)
22) Put tube in fin can jig
23) Put on gloves
24) Mix epoxy
25) Put 5-minute on root chord of each fin
26) Slide fins into slots in the jig
27) Finish assembling jig (put top layer on, push gently until the slots contact the leading edge, tighten the nuts)
28) Attach stabilizing feature
29) Let cure
Tip-to-Tip Preparation (4 hours)
30) Make paper cutouts for tip-to-tip layup
31) Spray wax paper with spray glue
32) Stick CF to wax paper
33) Use paper cutout to cut shapes
34) Record mass of shapes (for wetness ratio)
Root Fillet (2 days)
35) Put on respirator and gloves
36) Mix colloidal silica and epoxy
37) Apply inner fillets
38) Let cure for 24 hours
39) Sand inner fillets
40) Wearing gloves, apply outer fillets (Proline)
41) Let cure for 24 hours
42) Sand outer fillets
43) Mark centerlines
Tip-to-Tip Layup (1 day)
44) Mix epoxy
45) Wet the carbon fiber pieces
46) Record mass (for wetness ratio)
47) Separate the carbon fiber from the wax paper and apply to tube (layup)
48) Follow “Vacuum Bagging” procedure
Post-Processing
49) Follow “Oven Cure” procedure to cure fin can in Autoclave
50) Wearing a dust mask and respirator, sand the fin can