Some Techniques For Building From Plasticard

Having always built my rockets from scratch, and because plasticard is lighter, easier to work with and finish than balsa or cardboard, I've had a few years to try and get things right. In that time, I've found a few problems and a few neat tricks.

Here are the lessons I've learnt, by subject:

• Body Tubes
• Fins
• Nosecones
• Finishing
• General Tips
• Tools and Materials

Body Tubes

• The thickness of the plasticard determines the diameter of your body tube. Choose 0.01 inch for upto 50mm diameter. When glued into a tube, it will need minimal structure to make it properly circular.
• 0.02 inch can be used for upto 100mm and can be used down to about 40mm, but isn't really needed unless the rocket is over a 100mm.
• Plasticard appears only to be available in A4 or smaller sheets. One A4 sheet can give 2 lengths of D diameter and 1 standard engine-diameter tube, if measured carefully.
• 35mm film cases can be cut and lightly sanded, then glued between pieces of tube for much longer bodies.
• When making the tube, it is necessary to hold the plasticard in a tube shape. I do this using 2 film cases, cut to slightly different diameters, one which fits inside the tube and the other outside. Glue is then applied to a section of the tube and the film cases slide over and under the joint.
• There are 2 methods of joining edges of a tube together. Making the width exactly the same as the required diameter, the edges can be glued 'face on'. However, even a difference of 0.5mm is enough to severely ruin the effect.
• The easier method is to allow an overlap of 2-4mm, then sandwich the glue in the middle, and place a small amount along the top surface. When pushed together, the edges will melt together and form a much better tube shape, and a stronger join. It might be necessary to run a knife along the top edge, to leave it flush with the tube.

Fins

• Fins should be made of 0.02-0.1 inch plasticard, depending on the power of the model.
• To increase the contact area between the fin and body tube, glue a small 'rail' along each side of the fin, which gives three times as much contact area.
• When gluing plasticard, only use poly(styrene) cement. It gives a better joint than even epoxy and needs no surface preparation.
• On the flipside, if a fin is stripped, then it will probably take a piece of the body tube with it. Make sure the tip of the leading edge is secure.
• To give strength to fins, wait for a few hours for the poly cement to dry properly, then apply a fillet of bathroom sealant.
• If you have access to a bubblejet printer with a straight paper path, then fin designs can be printed directly, allowing spares to be created as necessary, and allowing them to be scaled up or down if necessary for other designs. The ink can rub off completely unless left for a few hours, but I normally cut while the ink is still wet. A damp piece of tissue can be used to remove in from the finished fin once it's cut out

Nosecones

• I've yet to make a decent nosecone from plasticard, either buy ones the right size, lathe your own (a CNC lathe will allow you to produce spare noses), or mould them from foam.

Finishing

• You can use just about any paint, or even some pens and markers. Opaque colours can be sprayed on directly, with no need for an undercoat or sanding.

General tips

• If you have applied too much poly cement to a joint, some of the plastic will melt and go gooey. Don't be tempted to prod it. Leave for 12 hours or so, to go solid. A small piece of 0.01 can then be cut out, glued on top, and cut back to a flush finish. When overpainted, it can't be seen.
• When sliding the outer shaper over a glued section of body tube, it normally pushes off some white gloop. This is a mix of poly cement and plasticard and is perfect for filling in small holes.
• When cutting, it is only necessary to score the surface. Even curved cuts can then be bent forward and back, and then popped out. This is especially useful for thick fins.
• Vast quantities of film canisters can make life easy, use them for staging, engine mounts, shaping the tube, sticking sections of tube together, mounting nosecones, etc. Crosshatch the surface with a knife before using poly cement to stick them in place.

Tools and materials

The following items are all kept to hand :

• A large stock of 0.01 plasticard, one or two sheets of other grades, upto 0.1 and scraps from other projects.
• A bottle of humbrol poly cement with a fine applicator, and a piece of wire to keep the applicator unblocked. The bottle can be refilled from the cheaper tubes
• A collection of film canisters. Any photo developer will normally have no problem finding thousands of them. Kindly decline their generosity (which most I've tried display) and take only a carrier bag of them. A junior hacksaw is sometimes useful to give them a uniform cross section.
• A Swann Morton no.4 scalpel and type 26 blades. When using a new blade, they are excellent, but there is no need to use a new blade for most work. You should stop using the blade when you have to exert pressure on it to cut properly, or if you break the tip back to the thick part. The rest of the blade is normally still sharp for other tasks.
• An X-Acto No 5 handle with a type 28 hook blade. Used for cutting the canisters and for thicker fins. My blade seems to have lasted for years, it doesn't need to be surgery-sharp, as long as the edge isn't ragged.
• A ruler with a perfect edge, or a steel rule if you don't use knives very much.
• Masking tape. Use it for holding things in place while they dry, and also for working out where to places fins. Also usable as a mask during painting
• A pencil or a liquid ink pen, to mark the card. Biros don't work properly, because the surface is too smooth.