The fins came out straight, as far as I can tell, but I discovered that my nosecone was crooked. When I put the motor in and rolled it on the countertop, the nosecone tip wobbled about 1/4".
The main problem that caused the misalignment was that I put the CF tube section in too far when I was re-molding the nosecone, and it pushed up onto a wrinkle that was sticking into the nosecone, jacking it sideways. It's a little subtle, but you can see the wrinkle in the fiberglass section at the bottom in this photo and where that pushed the aft CF section out of round:
I checked and confirmed that the location of that wrinkle corresponded to the direction that the nosecone was crooked.
I decided to take fairly drastic action and cut off the cylindrical section at the bottom. First I made an alignment tool by cutting out two wooden centering rings that could work with the hollow steel rod that fits over the harness attachment hardware near the tip of the cone. Those were press-fit into the carbon fiber airframe section that I would glue in so that in theory, the straightness of the rod would ensure that with one end of the rod centered in the tip, then the airframe section at the other end would be aligned.
After I dremmeled out the old overlapped section of CF tubing and sanded down the front, I got a nice 1/2" of tapered overlap. I did a test fit and chucked the hollow rod into my drill to make sure it looked like it would be correctly aligned.
Meanwhile, I had some fillets to apply. Mixing up 15 grams of my Cotronics 4461 used up an alarming fraction of my remaining resin. Yesterday I ordered more but it takes them a while for Cotronics to ship. So I decided to go with small fillets. I may make them larger later.
Here is the rocket body and fins after prep for the fillets:
I oven-cured the nosecone joint and the fillets, and when they came out, the nosecone straightness was much improved, basically at the limits of what I can evaluate and the looseness of the nosecone over the motor.
The main problem that caused the misalignment was that I put the CF tube section in too far when I was re-molding the nosecone, and it pushed up onto a wrinkle that was sticking into the nosecone, jacking it sideways. It's a little subtle, but you can see the wrinkle in the fiberglass section at the bottom in this photo and where that pushed the aft CF section out of round:
I checked and confirmed that the location of that wrinkle corresponded to the direction that the nosecone was crooked.
I decided to take fairly drastic action and cut off the cylindrical section at the bottom. First I made an alignment tool by cutting out two wooden centering rings that could work with the hollow steel rod that fits over the harness attachment hardware near the tip of the cone. Those were press-fit into the carbon fiber airframe section that I would glue in so that in theory, the straightness of the rod would ensure that with one end of the rod centered in the tip, then the airframe section at the other end would be aligned.
After I dremmeled out the old overlapped section of CF tubing and sanded down the front, I got a nice 1/2" of tapered overlap. I did a test fit and chucked the hollow rod into my drill to make sure it looked like it would be correctly aligned.
Meanwhile, I had some fillets to apply. Mixing up 15 grams of my Cotronics 4461 used up an alarming fraction of my remaining resin. Yesterday I ordered more but it takes them a while for Cotronics to ship. So I decided to go with small fillets. I may make them larger later.
Here is the rocket body and fins after prep for the fillets:
I oven-cured the nosecone joint and the fillets, and when they came out, the nosecone straightness was much improved, basically at the limits of what I can evaluate and the looseness of the nosecone over the motor.