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Below is a picture of the fins used for the test fin can layup. These dimensions were obtained from our OpenRocket sim, but were not the updated shape of the fins. This was acceptable for the test fin can layup, but for the flight candidate layup the shape was different.

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Flight Candidate Fin Design Process

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• 1/8" (0.125 in) sheet of G10 (INSERT LINK)
• 1/4" (0.250 in) sheet of phenolic (https://www.nationwideplastics.net/phenolic-sheet/)
• 15 degree end mill (https://www.mscdirect.com/product/details/04153326)
• 1/16" cutting bit (for mill)
• End mill (0.3125") for cutting G10 tab
• End mill for cutting off excess phenolic
• West Systems epoxy (CHECK)
• Machine tape 
• Machine oil
• File
• Calipers

Part One: Waterjet G10 Fin Core (~2 hours)

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1. Clamp your phenolic piece horizontally (the 1/16" cutting bit will come in horizontally) on either side of the phenolic. It does not matter which side you select for the slot, as when you flip over the piece, it is symmetrical. 
2. Zero the cutting piece at the center of the phenolic. 
3. Before turning the mill on, have some machine oil ready, and set the mill to low speed because the phenolic heats up while it's being cut.
4. When you turn the mill on, make sure it's set to "Forward" and cutting in a clockwise direction (to the right). Cut out the 1/16" slot.
5. After cutting, use the air hose to remove the phenolic dust and use ethanol* to remove the machine oil. 

*After some brief research, we found that machine oil and ethanol doesn't have an adverse effect on phenolic. However, this could be incorrect, so more research should be done to determine whether a better procedure for cutting the slot exists, and whether either of these materials decreases the strength of the phenolic somehow.  

Part Five: Cut Phenolic Taper

1. Since the phenolic piece is long (11.66"), you'll need to use two clamps to clamp it vertically.
2. Zero the end mill at the middle of the part. 
3. Use a 15 degree end mill to cut a taper on either side.

Part Six: Mill Down Phenolic

Use machining tape to stick phenolic down, edge at edge of clamp thing

Take off 0.020" inch, adjust mill when you turn it over to take off additional 0.020"

Part Seven: Assemble Fins

This step was required because since the phenolic is twice as thick as the G10, some material had to be taken off each side so that it better matched up with the G10. You  may wonder why we didn't simply start out with 1/8" thick phenolic: this is because the phenolic has to be slightly thicker than the G10 so that when the carbon fiber plies are added during the fin can layup, the carbon fiber is flush with the phenolic on either side. Therefore, we took 0.020" in off either side to account for the thickness of two plies of carbon fiber. Ideally, the sides would be milled down before we cut the taper, but this worked out fine. 

1. Set up a 90-degree angle block on the mill and, after wiping down the top surface, apply machine tape and attach the phenolic such that the non-tapered edge lines up with the edge of the angle block. 
2. Select an end mill that has a diameter that is larger than the flat section of the phenolic (the part that you want to take off). 
3. Touch down on the surface and zero the mill. 
4. Move the mill off the part (to the left) and set it to Z = -0.020". Slide one of the G10 fins into the slot and hold it so that when you mill down the excess phenolic, the slot is supported and the ends don't break off. If you don't hold the G10 fin as you're cutting the part, the weight of the fin will cause the phenolic to pull up the tape and ruin your cut. 
5. Set the mill to "Forward" and cut such that the end mill moves to the right.
   
6. Vacuum the phenolic dust, then carefully remove the phenolic piece from the tape.
7. Lay down a new piece of tape and flip the phenolic piece over and attach it to the tape. 
8. Repeat step 4 except this time, to account for the 0.020" that you just took off and the extra 0.020" that you want to take off from the other side, set Z = -0.040". 
9. Repeat step 5-6, then repeat the whole process for the rest of the phenolic pieces. Make extras in case something goes wrong now or later. 

Part Seven: Assemble Fins

1. Make sure that each G10 fin core fits into the phenolic slots. 
2. Use West Systems epoxy (do NOT use 5-minute epoxy) to attach the phenolic leading edge to the G10. In reality, this step was done after we bonded the fins to the fin collar because the phenolic leading edge did not fit into our fin can jig, but this step could also be done before the fins are attached to the fin collar. 

Lessons Learned:

• When waterjetting 1/8" G10, delamination is a concern because G10 is a composite (made of several layers of fiberglass) and 1/8" is pretty thin. Make sure to use the "Low Pressure" and "Brittle Material" settings on the OMAX waterjet. 
• Make extra fins and phenolic leading edges. That way, if anything goes wrong, you won't have to go back and make them all over again. 
• When making the tab on the G10, don't mill everything in one go- use several passes on the mill so that you take off a little bit of material each time. This way, the tab will be more uniform/even. 
• When cutting the phenolic slot, use oil because the phenolic will heat up from the cutting piece.

Software

• I used Solidworks to model the fins that were used on Hermes. Solidworks will also be used to design the phenolic - G10 interface and assemblies.

• Are there any limitations of this software? Make suggestions for how you could design the part better if we had a different program/more time

Hardware/Manufacturing

• Once you know the requirements of the part, list the materials you need to build it

• Make a rough draft of the steps required to build the part

Laser Cutting the Part:

• Create a DXF file of the part

• Using illustrator, place the drawing on to an artboard the size of the wood

• Adjust the settings on the laser cutter to appropriate settings for material

• Cut!

Water Jet:

• Transfer DXF file onto USB stick and onto waterjet computer

• Place the material on the waterjet, set the origin, and make sure the drawing is within the limits of your material and the jet.

• Cut each fin, making sure to stop in between and remove finished fins

Delamination can be avoided by:

• Using the “Low Pressure” and “Brittle Material” setting on the waterjet

• Lead into the bottom corner of the trailing edge instead of the top corner of the leading edge

• Lead in before cutting (the waterjet turns on as it’s coming in to cut instead of starting right on the part)