What I wish to create

I’ve started creating some external fillets on my test fin using West Systems Epoxy. I wanted to make 1cm fillets on both sides. So 2 * 20 = 40cm of fillets in total.

The radius of curvature is 1cm.  With some simple calculations I determined that I needed about 17cm^3 of material. I decided to make a lot more, so that I didn’t run out.

Materials

So I used:-

• 25ml  of 105 Resin
• 5ml of 206 Hardener
• Approx 4 grams of 403 – to get it to peanut butter consistency, where it would not drip. This is a bit of a visual ‘job’, don’t try to measure it accurately as the scales aren’t accurate enough.

I put this mixture into a plastic bag and cut a small hole in the bag and then used this like an icing bag to squirt the epoxy material into the fillet.

The area to fillet had already been sanded with Grit-80 and cleaned. I used some clothe to ensure no dust/crud there.

After applying the epoxy material I used my new tool a 2cm side 10cm long stick with a 2cm diameter semi-circle at one end, to form the fillet profile I wished. I then used the other end to scrape off any material left over.

Here are some pictures taken during the job.

 

I did not use the whisk in the first batch, which in turn was on BOTH sides of the fin. The second batch was done with the whisk and was used to fillet up two pieces of wood. The consistency of the epoxy was significantly greater, though still not perfect.

 

Results after curing (before sanding)

I forgot to lay down tape 1cm from fin/wood interface. I will do this next time to ensure fillets are uniform along the length.

I tried using methylated spirits on my finger to smooth the paste, but this failed.

I will use a sieve next time to introduce the 403 into the epoxy mix, as I believe I’ve introduced air that is causing some issues with the quality of the fillet.

Sanding

I’ve started sanding with flexible sanding pads. I can bend them back on themselves to produce a pretty good sanding block with a semi-circle end. I have used coarse, then medium and finally the fine version. I used some water as well to get a finer finish.

 

I’ve purchased some real G10 material to practice on. What I wanted to practice was:-

1. Learning how to cut it well (even though this isn’t required for this build)
2. How to sand the Leading and Trailing edges to the profiles I’ve decided.
3. Sand the root and tang to Grit 80. Also sand other edges lightly with Grit 80 to remove any burs. (But I don’t want to change the shape)
4. Sanding back with Grit 240 to give it a good finish for painting. I sand it ALL over, except on the tang, and the root where it is glued on the motor mount
5.  Score the root of the fin (yes, on the thin edge) using a punch and a bit of elbow grease. Did this every cm, in both directions at 45 degrees
6. Score Tang of Fin that is going to be below the air-frame. I did this every 2cm at 45 degrees in both directions
7. Cleaning the surfaces thoroughly with Methylated Spirits
8. Inspect the fins to make sure there is no other dust, grime or dirt.
9. Perform the following preparation steps
10. Attaching to “motor-mount”
11. Test paints – to see how finish is.

 

Preparations Steps

Before I can begin attaching fin, I need to prepare my work area. The “main” steps are:-

• Clean desk
• Get Methylated Spirits
• Get Paper towel
• Get a clean wood board for mixing Glue and mixing stick
• Get my Timer
• Wood blocks
• Get G-Clamps.

Steps to attach the Fin

We can’t do these steps until the fins are prepared!

1. Then I mix up equal amounts of J-B Weld black and white on a clean surface for mixing.
2. I start time for 20 minutes. This tells me how long I have to go.
3. I apply this to the root of the fin as evenly as possible, and try and avoid it going over the side
4. Clean off excess J-B Weld off sides very carefully using Methylated Spirits and paper towel.
5. Carefully lower the Fin into the slot, make sure that the J-B Weld doesn’t get on to the “Air-Frame”
6. Apply a bit of a wriggling action to get the glue to fill gapes
7. Make sure the Fin is 90 degrees and use clamps and wood blocks to ensure that the fin cannot move
8. Leave it for 15 hrs minimum!

Here are some pictures:-

 

 

 

I need to create internal fillets against the fins between the motor Mount and the Air-frame. The gap is very small – ~12 mm. So I’ve purchased some 5 mm diameter tubing with some 50 mm syringes to get the glue down there. I have used some thin doweling with masking tape to help direct the end of the tube to where the glue needs to go. Below are a few pictures:-

 

The process will be:-

1. Suck up 25 cubic cm of Araldite into the gun
2. Clean end
3. Insert gun up to the ‘zero’ mark
4. Push 1 cubic cm of araldite in
5. Withdraw 1 notch

Repeat step  4,5 will tall the way out

I’ve finally purchased glues for the rocket.

I have West Systems 105, 206 and 403 filler for the external fillets.

I have J-B Weld Epoxy for the root fillets.

For the internal fillets, I’ll probably be using West Systems 105/205 (no filler). What I will need to get the epoxy up the rocket into the area of interest is a tube/syringe.

 

Yet to purchase the pipe.

I’ve discovered that the fins are not exactly (or even close) to 120 degrees apart. The distance between two sets of fins is the same, while the other Fin/fin distance is greater than the other two by 5mm. Not terribly good. What this means is that the Jig that I made to hold the Fins in place ONLY has perfect alignment in ONE position. i.e. I cannot rotate the rocket and have the fins line up in the slots of the wood.

This has meant that I need to change my fin install procedure, by allowing me to rotate the WHOLE Jig into position, so that each fin that is being glued is vertical. I’ve done it as follows

 

 

 

We can take the wood stand off and attach it to the Jig, pointing out the other side. This allows us to install the other fin pointing down to the wooden base.