In this level-2 EZI-65 lesson, we will prepare the major pieces for assembly.

• Cut Body and Motor Tubes
• Fiberglass Body Tubes and Fins
• Prepare the Nose Cone
• Build the Motor Mount Assembly

Cut Body and Motor Tubes

We need to cut a 5 1/2" section of body tube (LOC BT-3.90 tubing) for the electronics bay. If you bought a whole tube, you'll only use a little of it. I purchased a second payload section from LOC so I decided to use half of it for my electronics bay.

There are several published techniques for cutting body tubes. The most common is: mark all around the tube, cut the tube longer using an X-acto blade or razor saw, and then sand down to the mark. This technique doesn't work well for me, especially with paper tubes. But, I have found a technique which is easy to use and produces finish results without sanding. As a woodworker, the answer to many cutting problems involves a jig. Borrowing from that tradition, I've created a simple tube cutting jig which I've used numerous times for phenolic and paper tubing (I have even cut Estes body tubing with it).

The jig is made with two 1x4" pine boards glued and screwed along one long end. At the right end (I'm right-handed), I attached a single edge razor blade so that it sticks out into the L shape about 3/16" (see picture). That's it! To use the jig, clamp a stop block the right distance from the razor blade so that you can rest the bottom of the tube against it. Then press the tube against the razor blade, using only moderate pressure, and rotate the tube with both hands. You should cut through a paper tube in 2-5 turns and a phenolic tube in 3-10 turns, depending on the thickness.

I first tried building this jig with the blade on an arm, but this didn't work as well. The main problem is that the spiral winding on paper tubes causes the razor blade to "wander," making it very hard to get clean cuts. If you decide to modify the jig, make sure the razor blade is firmly supported so that it can't flex at all. If you look carefully, you can see that I've actually mounted the razor blade with three screws.

Fiberglass Body Tubes and Fins

For paper tubes, you should always reinforce the ends by wicking some thin CA (Cyanoacrylate glue, see the INFOcentral Adhesives article) into the ends of the tubes. This gives them some strength, allowing sanding. Don't use too much, just saturate the ends. If the CA runs along the outside of the tube, you're using too much. I've found it is easy to get the right amount if you hold the tube at a downwards angle and press the CA nozzle against the egde as you squeeze.

(I will only cover the fiberglass process quickly here since there is an excellent INFOcentral article on Reinforcing Tubes.) All three body tubes (main airframe, payload section and electronics bay) should be fiberglassed for strength. I used a double wrap of 4oz. cloth followed by a single wrap of 2oz. cloth. The 4oz. cloth provides the primary strenth and the 2oz cloth has much smaller holes to fill/sand. If you're very skillful at fiberglassing, you can use an even lighter cloth than 2oz for the final wrap. All wraps should be done before the epoxy sets for the maximum bond strength. However, they can be done a couple of hours apart if you use a good epoxy system. (I strongly recommend West System 105 resin/206 hardner for fiberglassing. You cannot use the thick hobby shop epoxy for this.) Planning to take a break between wraps is a good idea. I find the fiberglass process very stressful: you're getting resin all over, trying to wrap the cloth tight, saturate it without getting excess resin drops, and not bond the tube to your support. Needless to say, prepare all your glass cloth and lay down your wax paper before mixing any resin.

Note that the body tube should be lightly, but thoroughly sanded with 100 grit sandpaper before fiberglassing. Don't sand through the outer paper wrap, but make sure all the surface sheen is gone.

How much cloth do you need to cut to cover a tube? Remember your high school geometry? The circumference of a circle is pd (p is 3.147 and d is the tube diameter). Our body tubes are 4" in diameter (circumference 12.54") so cut your cloth 2" wider than the tube length and 14" long for a single wrap or 26" long for a double wrap. (I like to use as little overhang at the ends as possible so the weight of the cloth doesn't sag and separate from the tube at the bottom while curing. You can also cut off most of the excess after applying the cloth, before leaving it to cure.) Don't worry about the edge being wavy (it's impossible to get it exactly straight), but make sure the cloth lays down flat against the tube at end of the wrap and try to cut off as many of the stray fibers as possible. Don't try to pull out the stray fibers!

We will also fiberglass the fins at this time. I have heard that the best way to do this is to wrap the cloth around one edge of the fins and onto both sides. This never works for me: I end up with a bubble somewhere along the edge where the cloth is wrapped, especially with heavier cloth. I like to do the fins in two stages, one for each side, and just use flat pieces of cloth. This also avoids having the fin stick to the wax paper since you're only trying to fiberglass one side at a time. For the fins I used a .56oz. "veil" as the final layer since it's easy to control the result on these small flat pieces when you do one side at a time. If you're careful, the fins will require no sanding on the face at all. (Primer can fill the tiny holes in the veil.)

1. cut out 12 pieces of 4oz. cloth and 6 pieces of lighter cloth 6" x 6" (or a little larger)
2. lay each fin on a piece of wax paper
3. paint one side of a fin with a generous coating of resin
4. lay on one piece of 4oz. cloth and spread out with your brush (you will usually not need more resin)
5. lay on another pieces of 4oz. cloth and spread out carefully
6. add a small amount of resin to any dry spots
7. lay on the final piece of lighter cloth and spread out carefully
8. add a small amount of resin to any dry spots, make sure you have no stray threadsor resin drops on the surface
9. (repeat #2-8 for other two fins) let all three fins cure and repeat for other sides

While the fiberglass is curing, we can work on the other major components...

Prepare the Nose Cone

Blow-molded plastic nose cones are a little difficult to work with, but you can get a good finish with some patience. The major problems I've had with them are:

• sanding causes them to get "fuzzy"
• primer doesn't stick well
• the molded-in shock cord mount breaks

First of all, clean off the flashing and mold marks with a razor knife. It's OK to cut a little into the plastic here, just make sure nothing sticks up over the surface. Once you've removed all bumps, flashing and mold marks, you need to wash the nose cone thoroughly to remove the mold release. Use hot water and abrasive soap and make sure you clean the whole cone, including the shoulder. Dry thoroughly.

Now you can fill the low spots in the cone and the gaps from the mold parting line. Note that wood filler doesn't stick the plastic. Use epoxy or plastic model filler. (Devotees of West System products will note the purple is 407 "low density fairing filler," which is easy to sand.)

To get the primer to stick to the nose cone, you need to sand it to generate a rough surface. (The fuzzing caused by coarser sandpaper cannot be removed by sanding with finer sandpaper, but repeated applications of primer and sanding can conquer the fuzz.) Also, it's best not to try to mask the nose cone; design your color scheme so the nose comes out all the same color to avoid having the masking tape pull the primer and paint right off. (You would not believe the trouble I had getting my V2 paint job to look halfway decent.)

To solve the problem of the weak shock cord mount, be sure to use a quick link to connect the shock cord, parachute and nose cone together. This way, the shock cord mount is only supporting the weight of the nose cone itself. The parts list for this project calls for four quick links, one for each end of each shock cord. This one is the most important.

Build the Motor Mount Assembly

Now we'll build the motor mount assembly. We're going to attach two of the centering rings to the motor mount tube, one at the forward end and one just above the fins. The third one will be added after the fins are attached.

We need to mount the eyebolt into the top centering ring. To do this, drill a 1/4" hole in one of the three centering rings. Bolt the eyebolt through the centering ring, with an SAE washer on both sides of C.R. and the nut on the bottom. I like to put some epoxy onto both sides of the hole in the C.R. before I do this and make sure there is some epoxy on the threads when I tighten down the bolt. You won't have access to this eyebolt once the rocket is assembled so make sure it stays.

The middle centering ring should be placed just above where the fins will mount. This will allow us to bond the fins to the C.R. itself. Also, we need to make sure this C.R. is mounted at right angles to the motor mount tube. To determine the position, measure from the aft end of the body tube to the top of the pre-cut fin slots. On my kit, this is 5 1/8". If you're going to use an Aero Pack retainer, you also need to allow 9/16" of the M.M.T. to stick out the back of the rocket. For me, the aft edge of the middle C.R. is located 5 11/16" from the end of the M.M.T. Draw a line around the M.M.T. at this point by wrapping a piece of paper around it, making sure the edges meet exactly and then draw along the edge of the paper.

Note for West System users: always paint a little unthickened epoxy on porous surfaces to be bonded before actually bonding them with thickened epoxy. The unthickened epoxy will wick into the porous material better and will fill the pores so that they don't pull the resin out of the thickened mixture. For bonding two porous surfaces, use 403 "microfibers" filler, otherwise use 404 "high-density filler."

Sand the full length of the outside of the motor mount tube with 100 grit sandpaper. Bond the top centering ring (with the eyebolt facing forward) near the top of the M.M.T. (1/4" to 1/2"). Use a generous epoxy fillet on both sides of the top C.R. Bond the middle C.R. just forward of the line you drew and use a generous fillet only on the forward side. Try to get the middle C.R. exactly perpendicular to the M.M.T. Make sure the aft edge of the C.R. lines up with the mark you drew. Double-check with a small square. (There is no fillet on the aft side of this C.R. so you can do this without ruining your tool.)