In this article, I will show a technique to get perfect looking nozzles, and I will also show a way to detail it with the cooling tubes used on most rocket nozzles.
The presented method might sound elaborate but once you have done it once or twice, it is really quite fast. As the picture shows the results speak for themselves.
First follow the instruction and assemble the nozzle the way the design requires.
The image shows the dowels I use. Any size will do depending on the size of the rocket nozzle. First sand down the hard edge on the end of the dowel so it has a very rounded end. Finish with some really fine sand paper 600-1200 grit. The proper dowel size should go into the cone about 1/3 to 1/2 the way in.
Now take a finished cone. Make sure, that the glue has completely dried. Insert it over the dowel as shown.
Start to roll the dowel around the inside of the cone. Do it gently, you do not want to dent the cone.
Make a small disc out of card stock. It should fit 1/3 - 1/2 way in. you can figure the right size by using a circle template available at any office supply store.
Then coat the inside of the cone with solvent based glue (water based will warp the cone).
Now it gets a little tricky. Use the dowel you made to insert the disc in to the cone. This way it will sit in the nozzle fairly straight. The disc should stop in the cone somewhere before the dowel hits the sides of the inside of the cone. Do not put too much pressure on the insert while doing this, as the glue tends to act like a lubricant and shove the disk too far into the cone causing an outside dent.
Now on this picture you will see a small disk that I have inserted about 2/3 the way into the cone.
You then paint the inside with a matt black paint to finish. The results are that no one will even notice the reinforced disk inside the cone and you now have a very circular cone to show off.
This is a new way I've found to put real detail on the exhaust nozzles, note that I have used .5 mm elastic thread with Mylar spun to give the appearance of the cooing tubes used in most rocket nozzles.
I finish the cone by painting it black on the outside and "dry brush" the accents back so the coolant tubes show.