NEEDLE HUB – SYRINGE TIP / BARREL TOP
With all of the varying tube and centering rings sizes, I decided to cut the parts for the needle hub and the syringe tip and barrel top at the same time. The centering rings were cut with drill press mounted hole cutter, one for inside diameters and one for outside diameters, both with cobalt steel cutting tips (razor sharp).
This is an example of one of the rings:
After the tubes and rings were cut to size, when dry fitting the parts, I realized that the syringe tip and barrel top would need to be constructed first so that the needle hub tubes would be properly aligned (straight instead of potentially crooked).
The centering ring for the syringe barrel top was drilled for 1/4" - 20 T-nuts, and the T-nuts were glued in place with JB Weld. The end of the syringe tip tube (long coupler tube) was then glued inside that centering ring, and the syringe tip spacer (body tube) was glued to the bottom of that, abutting the centering ring, all with epoxy. That is the first of three parts of the syringe tip and barrel top.
Because I wasn’t thinking about doing a build thread when I began, I don’t have pictures of each step, but I think I have enough to follow this part. To begin the syringe barrel construction, T-nuts (with JB Weld) were pressed into a centering ring identical to the one above. And, the centering ring was then epoxied into a short 4" body tube, and the coupler tube was epoxied into the other end. After that, a body tube spacer was epoxied to the top of the ring using the syringe tip as a guide (the syringe tip is NOT glued to the syringe barrel, it is removable).
Next, the needle retention bulkhead was constructed with a 4" bulkhead and smaller centering ring. (See, the .ork file for dimensions) As can be seen, the 1/4" - 20 eyebolt passes through the bulkhead and screws into the end of the carbon fiber needle. The three bolts that bass through the bulkhead screw into the centering ring T-nuts shown above, locking the syringe tip in place. This function will be described in more detail later.
With the syringe tip nearly complete, the needle hub is next. This subsection is composed of three different sizes of body tube, with inner and outer centering rings.
The, the three pieces were nested inside each other, bottom to top, bottom to top. This is where the three subsections had to be assembled for gluing so that the pieces of the needle hub would be properly aligned.
At this point, you can see that the transitions are square edged. All of the nosecone transitions are made from
30 minute epoxy and micro balloons mixed to the consistency of thick toothpaste, so that there was no slump when pulled up in the mixing cup. Blades were made from basswood of different slopes to draw the mixture around the tubes. This was repeated no less than three times for each transition, until there were no visible defects.
The three subsections were disassembled and the tube spirals filled using
Elmer’s All-Purpose Repair System (a two-part epoxy putty). After that, the Blue Tube 2.0 and plywood elements were sealed with
Old Master’s Sanding Sealer (oil based), sanded is steps to 320 grit, then primed. The needle was then painted with
Dupli-Color chrome, the needle hub with blue, and the syringe top and barrel with white.
So, screw the three subsections together and what do you get? The completed ANTI-VIRUS nosecone. Oh, by the way, the blue tape on the syringe tip acts as a spacer so the white paint doesn’t get scratched when you screw the subsections together, it is completely concealed inside the needle hub.
Wow, that took some engineering and construction time.
So, how close did I come to the original OpenRocket design?
