Now that you have a design idea it's time to transfer the profile (side of the car) and plan view (top of the car) to your block of wood. The block included in your kit is usually close to 180cm in length but may vary a little shorter or longer. Be careful to measure the final overall dimensions of the finished car to ensure that your design does not violate the racing specifications.
Use scissors to cut out your car drawing and trace the outline onto the side of the wood. If you prefer, you may find it just as easy to copy or duplicate your lines on the wood directly. Use a dark pencil or ball point-point pen so that the lines are easy to see when you're cutting.
When cutting out the car shape stay as close as possible to the lines. The more accurate you are now the less you will have to sand later.
Sanding the wood body will eliminate any of the saw blade marks as well as any small blemishes in the wood surface. If you have access to a motorised belt-disc sander your work will be quickly done but for most of us a sheet of sandpaper and a block will do just fine. Start by using a rougher sandpaper (220 grit) and wood or rubber block on the rough portions of the wood car body. Gently smooth the edges and corners of the car while using a little more pressure on the flat areas. When you have the smoothed switch to the finer (400 grit) paper. It will provide an excellent surface for your final finish.
If you drill holes for your weight and then fill them you may need to sand these also
Weight
Your finished wood block along with the, wheels, axles and trim will not usually weigh much over 75 grams while the finished car is allowed to weigh in up to 150 grams (or 100 grams in the Restricted 100 Division). Don't even think about skipping weight addition if you want to be race competitive. The weight of your car overcoming friction is what will allow to you to win over other cars. You must make gravity work for you. Your car must overcome both breakaway friction and minimise air resistance and it will do this by being as heavy as allowed while presenting the smallest profile to the air-stream. That's why we wanted the low and skinny body design.
There are two basic approaches to adding weight to a derby car. The easiest is to attach pre-drilled and shaped lead weights to the outside of the car. Some of the commercial varieties are cast such that they provide a tapered shape and break-off ribs that permit convenient adjustment to overall weight after the car is assembled. It is best to attach this type of weight to the bottom of the car so the centre of gravity may be kept low. If you use this type of weight on the bottom of your car ensure that the weight doesn't hang down too far. It may not be obvious until race-day but the weight could drag on the track guide. This could prevent the car from moving off the starting line. Mortise or "hog out" a void in the wood on the underside of the car and then attach the weight inside the void.
The other method for adding weight involves the installation of weight internal to the body so that there is no additional wind resistance. This may be only a small advantage but it just might make the difference of a winning millimetre or two at the end of the track. Most car profiles will be narrower at the nose and provide little space for adding lead internally. There is an advantage in placing the weight in the back. The front wheels perform the function of guiding or steering and the less weight on these wheels the easier the car corrects itself when it strikes the guide strip. Fewer and shorter contacts with the guide strip means a faster car.
Internal Drilling
Each internally weighted car will have a little different cavity placement based on the wheel/axle position and amount of wood available to accommodate the weight. The hole or cavity for the lead weight must be large enough to accommodate the weight you using. You will need fewer holes for lead than you will for other materials. Plan on drilling at least 2 or 3 holes of 8-9mm diameter at a depth of 30mm each. Experience has shown that holes drilled from the side or back tend to work the best. Locate and drill the holes being careful not to drill all the through the wood. Also make sure that you are leaving enough wood around the hole to provide a margin of safety in your drilling operation.
There are many things that you might use to add weight to the car but you will find that lead will probably be used most often. It is the heaviest practical element available for its volume, it works easily and is commonly available in a number of forms. As options to lead you could try steel in plate, tubular forms or even common bolts. Other metals may be used but just as steel you will find them difficult to work and sometimes awkward to attach or insert.