|Scratch-Built Model Rocket
Part 2: Nose Cone
Made from a 3x5 card and 3 kinds of glue
|I start by making a mark in the middle of one long edge of a 3x5 index card. This is where the apex of the cone will be, and the mark reminds me of its location.|
|The upper edge of the card is folded over as shown to start the cone.|
|The cone is pre-rolled to something close to its final form. Note that the final flap wants to fly. It must be convinced to lay flat.|
|Unrolled to the first turn, a line is drawn to mark where the spray glue will and will not be allowed to go.|
|The far edge is pre-rolled on a thin rod. Guess a pencil would do, but this is a 1/8 inch dia. steel rod from some defunct tool. This gives it a bias toward curving, which will help make a smooth roll once the glue is applied.|
|Another card is used to mask the first section of the nose cone card. This is not absolutely necessary, one could just spray the whole card. I did that on the first few, but 3M Super 77 is sticky stuff, and rather inconvenient to have on one's fingers. Makes it hard to let things go.|
|The cone is re-rolled, this time with the glue. Since the final flap has been pre-rolled, it lays flat of its own accord. Be sure to check the inside and make sure the inner flap is pressed firmly against the cone.|
|Here is a more precise way to do it. Mark the overlap line as shown. Mask the card to the left side of the line, spray the other side, and roll. This will make a nicely-proportioned cone for this airframe.|
|The cone will be mated to a body tube. Here is a really good candidate, rolled at a slight angle.. Usually I try to roll them straight, so there is no taper. But in this case, a taper is a good thing, as it will provide a much larger gluing surface.|
|The dunce cap fits nicely on this tube, and stays put just from friction. I take that as a good omen.|
|Just so happens that this aluminum tube is a good fit for the
body tube. The Al tube is 1 inch outside diameter, 0.9 inch
inside diameter. It will be used to mark the cone.
|Cone is inserted in the aluminum tubing, the point centered, and the base marked.|
|I cut a little above the mark, to make sure the cone is a little larger than necessary. It's a lot easier to take more off than to add it back later.|
|A generous glob of white glue is applied to the end of the body tube, and smeared evenly.|
|Moment of truth. The cone is pressed onto the tube. Is is straight? Must find out quickly!|
|Apologies for the bad photo, but I had to do this fast. Sighting down the length of the tube, I note that the center of the point (bright dot) is not perfectly centered. So I adjusted it a bit.|
|But while the glue is still soft, I hold the tube loosely and
spin the assembly from the cone tip. Notice if it wobbles, and
how much. Adjust until there is no perceptible wobble, at which
point the cone is straight. Whew!
Excess glue is wiped off, and the assembly allowed to set for a half-hour or so.
|There is a bit of overlap, as planned. I must confess, I had already started sanding when it occured to me to take this picture - note abrasion on the left side.|
|Remember that aluminum tube and the marking? Well that isn't really necessary. You can just take a SHARP knife and cut away the skirt. It will be a bit rough, but we will fix it shortly.|
|The shoulder is sanded with 150 grit sandpaper to remove what remains of the skirt and make it all even.|
|More or less even, if a bit rough. Note that the overlap has been sanded to reduce its obtrusion.|
|The magic of wet-or-dry paper. Here I am using 400 grit to smooth the cone and its shoulder. This will remove the frass and make the whole thing pretty darned smooth.|
|But it is still porous. So I smear a layer of Elmer's glue all over the cone. This will seal and harden the surface. Let that dry for 15 minutes, and smear on another coat. That will make it smooth, glossy and much stronger. But not strong enough. It needs the third glue!|
|So the nose cone is stuck firmly onto the end of the body
tube. This might be OK for a pyrotechnic rocket that goes up and
blows up, but that's not what this is about. Proper recovery is
required, and that means the nose cone must come off to eject a
paarachute or streamer. So we will separate the cone from most of
Remember the silvery dowel? It's the one used to roll the body tubes. I will use it here to assist in cutting off the nose cone.
|The dowel is inserted into the body tube until it reaches the nose cone. This will support the far end of the body tube while it is being cut.|
|A long, sharp knife is laid on the body tube about 1/2 inch from the base of the cone, and rolled carefully back and forth to make a groove. Once a groove is established, more pressure can be applied as the knife is rolled, eventually cutting through the body tube.|
|Finally, the nose cone is set free. Note that the overlap has been sanded down and filled with glue-coats until it is barely visible.|
|For now, it is just a thin, fragle paper cone.
Compromised in places by sanding, but still intact. We will
make it strong with the third glue, epoxy.
A section of 3/4 inch dowel is cut to serve as a base.
|Some 5-minute epoxy is mixed up, perhaps a teaspoon. The entire interior of the paper cone is coated with this glue. I make sure that it coats the very tip of the cone to seal its small opening, and lingers in the shoulder where the body tube meets the cone. Any glue left over is dumped in the cone and spread around the perimeter, preparing for the next step:|
|Dowel is insertedin the cone, with 3/4 inch protruding. The picture is deceiving - I coated the end of the dowel with epoxy before inserting it, to make sure it is glued really well.|
|The nose cone assembly is stood upright on its base while the
epoxy cures. This is so it will drip down, reinforcing the
shoulder where the cone meets the tube and the paper is the thinnest.
This may cause the glue at the tip to drain down, opening it up again. If that happens, give it another drop of epoxy after this first application has set.
|The new nose cone assembly should fit the body tube nicely... that's where it came from! So even if the cut is uneven, or the tube is a bit out-of-round, you can rotate it back to the starting point, match the lines up, and everybody should be happy.|
|A screw-eye is added to give the shock cord something to hang onto. This is actually a different cone - note the paper base. It has a 1/2 inch wooden dowel for a core.|
|You can argue with the aesthetics. You can argue with the aerodynamics. But this is definately a cost-effective procedure... once you have bought the three glues!|