Building a Pinewood Derby Car
The Cub Scout Pinewood Derby is probably the most popular "fun event" that a young Scout will participate. The recognition of the time spent building the car may
be seen as Pack prizes for the most colorful, most inventive, fastest, most
"radical" and as many other categories as one can imagine. In the San Diego -
Imperial council, the Cub with the fastest car in the Pack is eligible to
compete with all the other Cubs from the Packs at the San Diego 500 held at the
San Diego - Imperial Scout Fair. Every year, boys with their parent's help, build cars of every description to enter at the local Pack competition. The construction of the car is intended to be a parent and son project with the son doing the majority of the work. The parent should supply the advise and limited assistance with the more difficult tasks. Please remember above all that the Pinewood Derby is supposed to be fun for all. So get started early and take your time building and testing your car. Plan to
spend at least 4 to 6 hours building the car over several days. The experienced racers may spend many times this amount of time and it shows in the appearance and racing performance. The planning and construction of your car may be approached in many ways. This
information will serve only as a guide to some while providing good first-time information and pointers for others. The experienced wood craftsman will find the teaching experience a great project for a young man while the "Klutz" may find it just a little challenging. No matter, the time spent working and learning with your son should be a lot of fun.
If you're designing a car for speed here are the important points about car design to keep in mind.
o Sleek Shape o Maximum Weight o Smooth, Round Wheels o Polished Axles o Good Lubrication o Straight Running
On the other hand if your objective is to create a unique or personal design then think about these points.
o Model your car after something you like or adapt a theme from a Cub Scout or other recognizable object or character.
o Use color and finish as a way to get your car noticed. A bright red or yellow paint job with a high gloss finish is always an attention getter.
o Attention to the details of car construction shows in the final product
o Design on paper before you start cutting wood
Construction Step 1 - The Plan (or What are we Doing?)
You may already have an idea as to what your car should look like when you're done but in order to take this idea to a completed form you should have a plan. Take a little time to sketch out your idea on paper. If you haven't decided what you want to do you may want to check out some possibilities. Look at the profiles provided in this guide to get some ideas. Draw your design at full scale so you can transfer the profile and shape to the wood block later. Ready-made templates or car outlines can be purchased at Scout supply outlets, the Scout Shop or Scout mail-order catalog. These will help you transfer a predefined profile to your car but are certainly not required. You may want to take a look at the templates in this web site for some ideas.
Starting with a block of wood is like a hand full of clay. What are you you going to do with it? What kind of car do want to build? Well, there are several basic types of car classifications cars that are fast, cars that are fast to build and then there are character cars. Character cars are cars that model other types of cars or objects. Remember that a highly decorative car with characters, decals and
other trim will not be as aerodynamic as a "plain" car. The sleek low profile designs will tend to have less wind drag and therefore faster. The fast car is usually not a handsome car. Don't limit your design ideas but we'll talk about the plain, more aerodynamic designs and remember, you can paint car just about any way you you'd like.
Construction Step 2 - Gather Materials and Tools.
You will, of course, need the basic car kit that includes the wood block, axles, wheels and numeric decals. They cost $3.55 + applicable tax in the 2005 catalog. The kits produced since 1998 have unpredictable quality wheels in the kit and that may make it more difficult to produce a fast car every time. If you have Still have an older kit it may be used as long as it is the Grand Prix series racer kit. Do not substitute the wheels and axles from non-BSA kits into your car design. This will make it illegal in most races and you can be
disqualified. You will need the following tools and additional materials:
Safety
Glasses (for drilling, sanding etc.)
Coping Saw (A Powered Dremel Saw or Scroll Saw may also be used)
Small File (Mill or Fine Cut)
3/8"/10 mm Drill Bit (a Brad point bit gives you better hole positions)
Electric Drill Motor
Tracing Paper
Small Strip of Soft Cloth (like an old Tee Shirt)
80 Grit and 220 Grit Garnet Sand Paper
400 or 600 Grit Wet or Dry Paper
Metal Polish (for polishing the axle)
3/8"/10 mm Tubular Weight (Available from Scout Shop or plumber supply)
Wood Putty (or better yet - plastic auto body filler)
Sanding Sealer or wood Primer
Finish Paint (Either Spray or Brush on)
Decals and Decorations as Desired
This set of tools and materials will vary depending what you have available and the extent of work you have in mind.
Construction Step 3 - Cutting the Basic Car Shape.
Decide how you want you car to look. Again, you may want to refer to the templates in this web Site. When 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 7 inches (17.8 cm) in length but may vary a little shorter or longer. Be careful to measure the final overall dimensions of the finished car to insure that your design does not violate the racing
specifications.
Using your side profile drawing and a sheet of carbon tracing paper align the drawing to the block and carefully trace the outside lines of your car so that the image is transferred to the wood. If you prefer, you may find it just as easy to copy or duplicate your lines on the wood directly. Use a hard lead pencil or ball point-point pen so that the lines are easy to see when you're cutting.
Construction Step 4 - Wheel Mount Preparation.
Its been discovered over the years that cars with a longer wheelbase can be faster than shorter wheelbase cars.
With this in mind you may want to consider relocating the two axle slots in the car block toward the ends of the block. Perform this modification only if your pack or local rules permit it. The San Diego 500 rules do permit this change. Remember to set the wheel slots back at least half the diameter of the wheel so that it doesn't extend over the end of the car body. The overall length of the car (including wheels) cannot exceed seven inches. It is very important to cut the new axle slots exactly square to the sides of the block so that the axles provide a good alignment for tracking. An alternate method is to use a drill press to make the holes but in either method make sure that the final position of the axle isn't too high so that it creates a problem for the block dragging on the track's guide strip. Use a #43 (2.3 mm) drill bit. Insert the axles in each of the slots or holes so that you know they'll fit later. Install the axles at the top of the slots so that they have plenty wood under them. Now that we have opened the wood fiber remove the axles. We'll permanently install the wheels and axles after the paint has dried.
Construction Step 5 - Drilling Holes for Weight.
Your finished wood block along with the, wheels, axles and trim will not usually weigh much over 2.5 ounces (71 grams) while the finished car is allowed to weigh in up to 5.0 ounces (141.75 grams).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 minimize 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 or zinc 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 center of gravity may be kept low. If you use this type of weight on the bottom of your car insure 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 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 inch 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 withthe guide strip means a faster car.
Drilling the Car Body. 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 3/8" ( 10
mm) (or 7/16") diameter at a depth of 1 ½" (38 mm) 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 way 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.
Construction Step 6 - Adding the Weight.
There are many things that you might use to add weight to the car but you will find that lead and zinc will probably be used most often. These are the heaviest materials easily available for their volume. Lead works easily and is commonly available in a number of forms. As options you can use 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.
Warnings
Lead is toxic and should be handled as little as possible.
Use gloves and never put your hands in or near your mouth after handling it. Always wash your hands thoroughly after handling lead.
Do not use mercury at all! It is toxic, difficult to handle and should not be touched by Cubs or adults.
Weigh your car on accurate scales. Most household scales are not very accurate. If you have access to calibrated scales compare a known item weight on the calibrated scales to your home scale indication for that same item. Mark this reference for use later. Allow for scale inaccuracies by not adding to exactly the 5.0 oz. (141.75 grams) indication. It is better to be slightly light than to have to remove weight on race day.Consider also, while you may have an accurate scale your pack may not. It could be weighing items heavier than they actually are!
be seen as Pack prizes for the most colorful, most inventive, fastest, most
"radical" and as many other categories as one can imagine. In the San Diego -
Imperial council, the Cub with the fastest car in the Pack is eligible to
compete with all the other Cubs from the Packs at the San Diego 500 held at the
San Diego - Imperial Scout Fair. Every year, boys with their parent's help, build cars of every description to enter at the local Pack competition. The construction of the car is intended to be a parent and son project with the son doing the majority of the work. The parent should supply the advise and limited assistance with the more difficult tasks. Please remember above all that the Pinewood Derby is supposed to be fun for all. So get started early and take your time building and testing your car. Plan to
spend at least 4 to 6 hours building the car over several days. The experienced racers may spend many times this amount of time and it shows in the appearance and racing performance. The planning and construction of your car may be approached in many ways. This
information will serve only as a guide to some while providing good first-time information and pointers for others. The experienced wood craftsman will find the teaching experience a great project for a young man while the "Klutz" may find it just a little challenging. No matter, the time spent working and learning with your son should be a lot of fun.
If you're designing a car for speed here are the important points about car design to keep in mind.
o Sleek Shape o Maximum Weight o Smooth, Round Wheels o Polished Axles o Good Lubrication o Straight Running
On the other hand if your objective is to create a unique or personal design then think about these points.
o Model your car after something you like or adapt a theme from a Cub Scout or other recognizable object or character.
o Use color and finish as a way to get your car noticed. A bright red or yellow paint job with a high gloss finish is always an attention getter.
o Attention to the details of car construction shows in the final product
o Design on paper before you start cutting wood
Construction Step 1 - The Plan (or What are we Doing?)
You may already have an idea as to what your car should look like when you're done but in order to take this idea to a completed form you should have a plan. Take a little time to sketch out your idea on paper. If you haven't decided what you want to do you may want to check out some possibilities. Look at the profiles provided in this guide to get some ideas. Draw your design at full scale so you can transfer the profile and shape to the wood block later. Ready-made templates or car outlines can be purchased at Scout supply outlets, the Scout Shop or Scout mail-order catalog. These will help you transfer a predefined profile to your car but are certainly not required. You may want to take a look at the templates in this web site for some ideas.
Starting with a block of wood is like a hand full of clay. What are you you going to do with it? What kind of car do want to build? Well, there are several basic types of car classifications cars that are fast, cars that are fast to build and then there are character cars. Character cars are cars that model other types of cars or objects. Remember that a highly decorative car with characters, decals and
other trim will not be as aerodynamic as a "plain" car. The sleek low profile designs will tend to have less wind drag and therefore faster. The fast car is usually not a handsome car. Don't limit your design ideas but we'll talk about the plain, more aerodynamic designs and remember, you can paint car just about any way you you'd like.
Construction Step 2 - Gather Materials and Tools.
You will, of course, need the basic car kit that includes the wood block, axles, wheels and numeric decals. They cost $3.55 + applicable tax in the 2005 catalog. The kits produced since 1998 have unpredictable quality wheels in the kit and that may make it more difficult to produce a fast car every time. If you have Still have an older kit it may be used as long as it is the Grand Prix series racer kit. Do not substitute the wheels and axles from non-BSA kits into your car design. This will make it illegal in most races and you can be
disqualified. You will need the following tools and additional materials:
Safety
Glasses (for drilling, sanding etc.)
Coping Saw (A Powered Dremel Saw or Scroll Saw may also be used)
Small File (Mill or Fine Cut)
3/8"/10 mm Drill Bit (a Brad point bit gives you better hole positions)
Electric Drill Motor
Tracing Paper
Small Strip of Soft Cloth (like an old Tee Shirt)
80 Grit and 220 Grit Garnet Sand Paper
400 or 600 Grit Wet or Dry Paper
Metal Polish (for polishing the axle)
3/8"/10 mm Tubular Weight (Available from Scout Shop or plumber supply)
Wood Putty (or better yet - plastic auto body filler)
Sanding Sealer or wood Primer
Finish Paint (Either Spray or Brush on)
Decals and Decorations as Desired
This set of tools and materials will vary depending what you have available and the extent of work you have in mind.
Construction Step 3 - Cutting the Basic Car Shape.
Decide how you want you car to look. Again, you may want to refer to the templates in this web Site. When 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 7 inches (17.8 cm) in length but may vary a little shorter or longer. Be careful to measure the final overall dimensions of the finished car to insure that your design does not violate the racing
specifications.
Using your side profile drawing and a sheet of carbon tracing paper align the drawing to the block and carefully trace the outside lines of your car so that the image is transferred to the wood. If you prefer, you may find it just as easy to copy or duplicate your lines on the wood directly. Use a hard lead pencil or ball point-point pen so that the lines are easy to see when you're cutting.
Construction Step 4 - Wheel Mount Preparation.
Its been discovered over the years that cars with a longer wheelbase can be faster than shorter wheelbase cars.
With this in mind you may want to consider relocating the two axle slots in the car block toward the ends of the block. Perform this modification only if your pack or local rules permit it. The San Diego 500 rules do permit this change. Remember to set the wheel slots back at least half the diameter of the wheel so that it doesn't extend over the end of the car body. The overall length of the car (including wheels) cannot exceed seven inches. It is very important to cut the new axle slots exactly square to the sides of the block so that the axles provide a good alignment for tracking. An alternate method is to use a drill press to make the holes but in either method make sure that the final position of the axle isn't too high so that it creates a problem for the block dragging on the track's guide strip. Use a #43 (2.3 mm) drill bit. Insert the axles in each of the slots or holes so that you know they'll fit later. Install the axles at the top of the slots so that they have plenty wood under them. Now that we have opened the wood fiber remove the axles. We'll permanently install the wheels and axles after the paint has dried.
Construction Step 5 - Drilling Holes for Weight.
Your finished wood block along with the, wheels, axles and trim will not usually weigh much over 2.5 ounces (71 grams) while the finished car is allowed to weigh in up to 5.0 ounces (141.75 grams).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 minimize 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 or zinc 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 center of gravity may be kept low. If you use this type of weight on the bottom of your car insure 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 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 inch 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 withthe guide strip means a faster car.
Drilling the Car Body. 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 3/8" ( 10
mm) (or 7/16") diameter at a depth of 1 ½" (38 mm) 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 way 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.
Construction Step 6 - Adding the Weight.
There are many things that you might use to add weight to the car but you will find that lead and zinc will probably be used most often. These are the heaviest materials easily available for their volume. Lead works easily and is commonly available in a number of forms. As options you can use 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.
Warnings
Lead is toxic and should be handled as little as possible.
Use gloves and never put your hands in or near your mouth after handling it. Always wash your hands thoroughly after handling lead.
Do not use mercury at all! It is toxic, difficult to handle and should not be touched by Cubs or adults.
Weigh your car on accurate scales. Most household scales are not very accurate. If you have access to calibrated scales compare a known item weight on the calibrated scales to your home scale indication for that same item. Mark this reference for use later. Allow for scale inaccuracies by not adding to exactly the 5.0 oz. (141.75 grams) indication. It is better to be slightly light than to have to remove weight on race day.Consider also, while you may have an accurate scale your pack may not. It could be weighing items heavier than they actually are!