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Sunday, January 11, 2015

L3 rocket update

I managed to get some work done on my L3 rocket today.

The centering rings' ODs were about 1/32" too large. I used a dremel and a sanding block to sand them down. I also drilled and mounted the U-bolts in the forward centering ring.

Marked the hole locations first. The X markings are to remind me to not line up the
U-bolts with fins because the front fin tabs will butt up against the back of this ring.

CA used on all nuts for anti-vibration.

I completed most of the nosecone modifications today. As mentioned in the last post, the goal is to be able to adjust the mass in the nosecone easily. I cut the bottom off of the nose cone and sanded it. I'll be using a ~5" diameter, 1/8" thick plywood bulkhead to brace the 1/4-20 threaded rod that will be glued into the tip. I drilled a 1/4" hole in it for the threaded rod and sanded a chamfer in the outer edge so that it would sit in the cone better. The threaded rod was cut to length so that an inch or so would stick above the bulkhead for attaching an eye nut for shock cord attachment. I also drilled some small holes in the bulkhead and superglued in some thread so that I could pull it out. This bulkhead will not be glued in place; instead, it will be held in place using nuts and washers. This allows me to add and subtract mass (in the form of 1.25lb lifting weights) from the nose tip be sliding weights on or off the threaded rod. The weights will be held in place using large washers and more nuts.

I then marked and drilled holes for 3/16" wood dowels to go through the nose tip. These will help hold the threaded rod and the epoxy plug in the nose.

I had to dremel these because I didn't get them straight the first time.
Markings for the second set of holes. I realized the lower
(original) markings were too close to the other holes.
Both sets of holes drilled. I also sanded the inside of the nose
 tip to help with epoxy bonding.
Supergluing washers to nuts. Probably should of bought flange nuts.
After many test fits, the final locations for the nuts were set with CA.
5 minute epoxy + silica was used to glue the dowels in.
These will be cut and sanded flush later.
Inside view before potting with epoxy
Washers help hold the threaded rod in.
Camera didn't resolve threads for some reason.
For potting the nose tip, I used 3x pumps of West Systems 105 resin and 206 (slow) hardener mixed with about a tablespoon of colloidal silica. I carefully poured it all into the tip, avoiding the threaded rod. I then shook/tap/hit the nose to get the epoxy into all of the crevices. After that, I poured a few ounces of steel BBs into the tip and repeated the settling exercises. After that, I put the bulkhead in and placed the nosecone upside down in a piece of body tube. It takes a few hours to cure, so I'll check it tomorrow. After this, I need to cut the dowels, sand and fill the tip, prime, and paint it with high temperature BBQ paint.

Left to do:
  • Finish nose cone
  • Purchase a bunch of stuff
  • Make motor mount
  • Install fins
  • Filleting 
  • Build altimeter bay
  • Minor stuff
  • Final primer coat, sanding, then painting
  • L3 paperwork

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