Insanity Plea: A sub minimum diameter M2245 project.

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I pulled the last fin off the mill today. I had a few issues and scrapped a couple but in the end they came out great.

I added a picture to post #5: Fins machined
 
The set of four fins weighs about 400 grams. I expect to use about 5 grams of epoxy on each fin. That's approximately 14.8 ounces. The fins and fillets on my Blackhawk75 project weighed about 11 ounces.

This aluminum set is much stronger and stiffer and has a much larger glue surface than the G10 set did. I think they'll hold up well to the M3.5 flight.
 
I machined the prototype fin today. I had a few minor problems but overall it came out pretty well. I've cleaned up the problems with the CAM files so the production fins should come out cleaner.

I added pictures to post #4: Machining the prototype fin.
What rationale for the elliptical fillet tail as opposed to something pointy similar to the fillet nose?

Not a lot of people doing work in this area, so I'm curious about your thought process.
 
Mainly surface area for the fin to body tube bond. The fin doesn't have much area at the leading edge but there is a lot of area near the trailing edge.

What rationale for the elliptical fillet tail as opposed to something pointy similar to the fillet nose?

Not a lot of people doing work in this area, so I'm curious about your thought process.
 
Rocket Porn: I can't define it, but I know it when I see it. The pic of those fins is definitely rocket porn.
 
There have been some major in the APE workshop over the last couple weeks. I was going to have a friend turn some parts for this project but it just felt wrong. I had a lathe a few years ago and sold it before I got back into rocketry. Ever since I got back in I've been kicking myself for selling it. So, instead of paying someone else to turn some parts I decided to buy another lathe. I had to move and redesign the enclosure for my CNC mill. I was able to open up a 7' length of the garage wall. I've been keeping my eyes open on Craigslist and on Saturday this lathe came up. It's a 13" x 40" gear head lathe. Besides the chinese branding it's identical to one that Birmingham sells now. It was pretty dirty but underneath the dirt was the original cosmoline grease. The seller bought it on a whim, didn't really use it much and really didn't know anything about it. I've spent about 6 hours cleaning it up and it's almost ready to move into position.

Stay tuned. I'll be back to making flying things soon.

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Nice Chris - I kick myself too!


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Looks like a sweet lathe for the garage! Great size for sport rocketry. This Rocket looks like its going to Rip and those fins like great. Any idea what your going to use to bond the fins and when you might fly this?
 
That is a really smart idea you have for the nosecone. I've been putting some ideas and designs together to try and make an very similar sub minimum diameter 54mm rocket and have been dreading the idea of making my own mandrel to wrap a nosecone, but what your doing makes way more sense. if it ends up working out I may have to steal your idea
 
Speaking of nosecones, I finally received the nosecone and CF coupler I ordered from Wildman yesterday. I think they are finally caught up from BS.

I haven't worked on this rocket much in the last couple months, but I should be able to get back to it soon. I've been doing projects to pay off the lathe and tooling I bought.
 
Tonight I turned the thrust ring off the stock rear closure and installed the tail cone that James Marino turned for me. The cone was heated to 350F in the oven while the closure was cooled to -5F in the freezer. Then the cone was dropped onto the closure and they were pressed together in my vise. Once it cooled off I polished it on the lathe.

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Have you simulated your fin profile at tip thickness in FinSim for Mach 3.5 and at altitude it occurs?
 
I cut the shoulder off the nose cone this morning so that it will match the OD of the coupler.

I started with a piece of 3" body tubing that was perfectly square on one end. I cut a centering ring that matched the ID of the tube and had a 1" hole in the middle. I slid the nose cone into the coupler tip first so that the centering ring kept the tip centered.

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I used my band saw to cut the shoulder off the cone close to the point where the NC met the body tube. I used my belt sander to sand the cone until it perfectly matched the end of the body tube.

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I think it's good enough for government work.

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Next up is the NC to coupler adapter. It will be turned and milled from aluminum.
 
Thanks guys. I appreciate the complements.

I turned and then CNC machined the adapter to join the nose cone and coupler. It also serves as the mounting point for the electronics bay.

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I pulled the last fin off the mill today. I had a few issues and scrapped a couple but in the end they came out great.

I added a picture to post #5: Fins machined

I actually have a question about this. How do you hold the material still while its in the CNC mill? I mostly am worried about vibration near the end of the fin, not moving out of position really. Clamping it to a fixture block makes sense for one side but then when you flip it it isn't flat anymore. I'm working on some fins that have a similar layout but are considerably smaller. If you are wondering I'm also doing it because I enjoy the metalworking part.
 
Go back and look at post #2. I have pictures of the fixture I use. On the first side I only cut down to the center of the fin PLUS about .020". Then I machine the back side down to the same centerline PLUS .020" leaving a .040" tab all the way around. Then I cut around the profile leaving 2 short tabs on the leading and trailing edges that have to be cut off and sanded down. Then I hand file the edges to a ~.010" edge.

You really need think about vibration when you're building up your CAM files. Leave support until you absolutely need to remove it. On the back side you can add clay or putty to fill in the void and help minimize vibration too.

Contact me via PM if you need more help.


I actually have a question about this. How do you hold the material still while its in the CNC mill? I mostly am worried about vibration near the end of the fin, not moving out of position really. Clamping it to a fixture block makes sense for one side but then when you flip it it isn't flat anymore. I'm working on some fins that have a similar layout but are considerably smaller. If you are wondering I'm also doing it because I enjoy the metalworking part.
 
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