5KidsRacing's Cub Scout Pinewood Derby Build Instructions
The following set of pinewood derby car instructions are geared towards the Cub Scout/parent team with some basic knowledge about a derby car build. These instructions are written based on my experience using different tools, methods and products. There is a lot of information out there and this is my attempt to cut through all the false claims and bad products and tell you what really worked for me and my kids. First and foremost you should read your derby rules carefully and make sure the methods I am describing are legal in your particular derby race. Remember “If you can’t race, you can’t win”.
To use these instructions your track must be a center guided track. This means that your track has to have a 1/4” tall by 1-5/8” wide guide down the center of each lane which guides the cars and keeps them in their respective lanes.
If your rules allow the following components and techniques then you should be able to use the instructions, but please check your rules and then re-check them. Typically rules are written in very specific wording if a certain technique is not allowed. If your rules don’t say specifically that the following are not allowed then they are probably allowed. If you are in doubt please check with your Derby Committee person, better safe than sorry!
· Four wheels required but only three wheels have to touch the track surface
· Railrunning technique
· Negative canted rear wheels
· Positive canted front dominate wheel
· Standard or extended wheel base
· Graphite lube
· No test track to tune on
· Full weight BSA or BSA “box” wheels
· Aftermarket, BSA or BSA “box” axles
Throughout this set of instructions I will recommend products to be used for each step. Some will be from specific pinewood derby vendors and others will be general items you can buy from your local store or online.
· Railrunning – Setting up your pinewood derby car to run down the center guide. A railrunner is built such that one of the front wheels always contacts the center rail and guides the car straight down the track. The body will be built in such a way to keep all the other wheels off of the center rail.
· Negative Cant Rear Wheels – The axle hole is drilled at an angle so that when you install the axle the head is above the pointed end. When done correctly during movement, forward or reverse, the wheels will stay on the axle head and will not contact the car body.
· Front Dominate Wheel or “FDW” – This is the wheel that will run down the rail during railrunning.
· Positive Canted FDW – The FDW axle will be bent so that the car steering can be adjusted and then installed in the car with the head of the axle below the pointed end.
· Drift – When the cars FDW is adjusted the car will turn, the amount of turn over a certain distance is called drift.
· The "Silver Bullet" - This tool accurately allows a novice user to drill perfectly canted rear axle hole and a straight FDW hole. This is the first and most important step in building a fast car. (see DerbyDad4Hire.com)
· Center of Mass or “COM” –This is the balance point of you finished car. If you COM is too far in front of the rear axle centerline your cars weight will not stay on the track slope long enough, and if it is too far back the car will be unstable.
· An Good Drill Press
· Pair of Vise Grips
· Combination Square
· Forstner Wood Bits (1/8” up to 1” set works well)
· Some Kind of Saw (wood, mitre, coping, etc..)
· Misc. Grades of Sandpaper for wood
· 5 minute Epoxy
· Black Sharpie Marker
· Hammer or Rubber Mallet
· Regular Screwdriver
· 7/32" or 1/4" 4-Fluted End Mill Bit
· Bench type vise or Metal Adjustable Clamp
· Polished #43 Drill Bit or Small Metal Rod for Burnishing
· 91% Isopropyl alcohol (Walgreen’s)
· 6 to 8 ft x 2 ft wide board for tuning (shelving board from Lowe’s)
· 1/4” x 1-5/8” wood strip for tuning
Note: All of the purchased pinewood derby products listed below can be purchased from vendors on my recommended links page. If you have a question about which particular product I would recommend please contact me.
· The "Silver Bullet" or a pre-drilled body
· Wheels: Lathed BSA Wheels or BSA box wheels (Check your rules)
· Axles: Precision made .091, .092 or .093 Stainless Steel axles, BSA Speed Axles or
BSA Box Axles (Check your rules)
· Axle Polishing Kit
· Brasso Metal Polish for axles
· Novus 2 Plastic Polish for wheels bores
· Fluffy Pipe Cleaners
· Walgreens brand Q-Tips
You need to drill your body with the "Silver Bullet". There are no tools out there that will give you the results like the "Silver Bullet” does…. Period. It is the best money you will spend and should be the first PWD tool you buy. Bending axles to get a canted car is painful and doesn’t work very well for the novice builder. With a body drilled by the "Silver Bullet" and a good railrunning technique you have the foundation for a very fast car.
· Take your raw wood body and using a combination square draw lines for your axle centerlines. For a standard wheel base of 4-3/8” just copy the dimensions from the axle slots to the other side of the block. If your rules allow an extended wheelbase then place the back axle at 5/8” from the back of the block and the front axle 5-3/8” in front of the rear axle.
· Mark the height to drill the rears 1/8” up from the bottom of the block, mark the Front Dominate Wheel (FDW) (This is the wheel which will be railrunning) up from the bottom also 1/8” and mark the raised wheel for 5/32” up from the bottom.
· Use the "Silver Bullet" to drill the axle holes in the car body. The rears are drilled with negative cant… around 3 degrees and the front and lifted wheel holes are drilled straight. Make sure you use the correct drill bit for the different axles. Standard “out of the box” BSA axles and BSA clone axles are about .089” in diameter and require a #44 drill bit. Most good aftermarket of axles are .091” in diameter (at the pointed end) and require a #43 drill bit.
· Take your body with the finished drilled axle holes and put in 3 straight axles and 3 good wheels. I use a set of good, polished & straight axles. With the 2 rear good axles/wheels installed and the FDW good axle/wheel installed check and make sure when rolling the car straight forward and straight reverse that the wheels move out on the axle head. If the wheels go into the body of the car at any time during this test you must re-drill.
· Body axle hole drilling done!
There are many ways to weight a car, tungsten discs, tungsten rounds, tungsten cubes, lead, zinc, pennies, steel, etc.. Below I show some examples of typical weight placement for tungsten discs and cubes. Each type of weight has it's advantages and disadvantages. You have to decide what type of weight works for your skill level. One thing to note is that large tungsten discs typically cause you to have to cut the ends of your axles off.
· Before cutting your car profile drill and glue in your weight. I know this is a leap of faith because you want a certain “Center of Mass” (COM) for the car and you can’t figure that out without the body cut to shape, but you will just have to trust me here. I would rather not cut weight out after the profile of the car is cut and the body is weak. There is a possibility that the axles holes could shift and you don’t want that…. You should be able to add about 3-1/2 ounces of weight to the car and still have some weight left to tweak the COM and bring the weight up to 5 ounces at the end. If 3-1/2 ounces of weight here is too much then you have too much wood left in the car. For 3/8” tungsten rounds use a 3/8" diameter Forstner bit and for the 1" diameter disc use a 1" diameter Forstner bit. Drill the holes so the weight is flush with the bottom of the car. Glue the weights in with 5 minute epoxy. You can also at this point drill a few other holes in the rear of the car which you will place tungsten putty at the end to tweak COM and final weight. A drawing for example drill locations for the tungsten putty is shown below in the "COM Adjustment" section. I have also included a drawing to show where I would install the weight with regards to tungsten rounds and cubes below.
· Also, during this step drill 1/4”or 3/8” diameter holes in the bottom of the car to expose the axle ends. You can use this hole as an inspection hole for car check-in or to glue in the axles if they are loose. I like to use the holes to remove and install axles without pulling on the wheels or axle heads.
Cutting the Car Profile:
· Cut a profile that is at most ½” thick at the rear and taper it down to very little (1/32”) at the front. Sand it down in the rear until you see the top of the tungsten cylinders. I would keep the full width of the car… I haven’t had much luck with pointed thin cars.
· Mark and sand or cut off 1/16”-3/32” off of the DFW side of the car. This is cut back so your DFW runs the rail but the rear wheel behind the DFW doesn’t hit the rail.
Paint the car:
· Place painters tape over the axle holes and where the hubs will hit the body.
· Paint the car and let thoroughly dry.
If aftermarket axles are allowed then…
For goodness sakes use them! Use a .091, .092 or .093 diameter stainless steel aftermarket axle. the ones from my recommended vendors are super straight and offer a speed advantage. (see THIS page for part selection)
· Cut a "bend groove" in the FDW. Place a wheel on the axle and with a sharpie mark the location just past the inside wheel hub. Chuck the axle in a drill press and use a diamond needle file and on your mark cut a groove half way through the axle.
· Cut a “K-House” groove in the FDW head. This is just a regular screwdriver slot in the head used to adjust steering or drift. You can cut this with a dremel or a hack saw.
· Sand the axles with a good axle polishing kit. Take each grade of sandpaper and cut them into 1/4" strips. Chuck you axle in a drill press, hand drill or dremel and spin it at a medium speed. Starting with the coarsest grade and working to the finest use each paper with water and for 5 seconds each. Do not forget to also polish the underside of axle head area. Between grades wipe off the axle with a clean cotton cloth.
· Polish the axles with Brasso. Using a strip of cotton cloth use a peas sized amount of Brasso and poilish the axle for 20 seconds.
· Finish the axles by cleaning them with 91% Isopropyl alcohol and a clean cotton cloth while spinning them.
· Set the axles aside because they are done!
If aftermarket axles are not allowed then…
Use BSA "Speed Axles", these will be a speed advantage over “out of the box” axles. "Speed Axles" are typically axles that look like BSA axles, but are machined without flaws. (see THIS page for part selection)
· Follow the same instructions as above.
If only the axles out of the “Official Pinewood Derby Car Kit” you received are allowed then…
· Buy a set of replacement “out of the box” BSA axles and spin each of them in a drill press and select three straight axles. There are $20 tools out there that will straighten stock BSA axles, but for $1.95 you can get 10 and you should be able to find 3 straight ones in the 14 axles.
· While spinning in a drill press gently file off the ridges on the axle shaft, file off the burrs on the axle head and file a slight taper on the axle head with a good diamond needle file. Be careful not to reduce the diameter of the axle shaft!
· Follow the same instructions as above.
If aftermarket wheels are allowed then…
Use the lightest lathe turned wheels that meet your rules (see THIS page for part selection)
· I would not sand the OD or inner edge of the wheel at all, just leave these surfaces as you receive them!
· If the second step is not removed then use a 7/32” or 1/4" 4-fluted end mill bit and your drill press to remove the outer second step from the wheel (adults only using the 4-fluted end mill).
· If the inside hub is not re-coned then I would leave the inside hub alone instead of trying to re-cone it yourself.
· Polish the bore with the Novus 2 plastic polish and the Walgreen's Q-tip. Start by cutting the fluffy ends off of a Walgreens brand Q-Tip. Cut one end at a 45 degree angle, that willl be the end you insert into the wheel bore. Take the Novus 2 and squeeze a pea sized amount into the inside wheel hub. Take the Q-tip and mount the non-45 degree end into a cordless drill. If you are right handed, hold the wheel in your left hand and the cordless drill in your right. With the cordless drill turning very, very slowly insert the side of the wheel with the Novus 2 applied onto the 45 degree Q-tip end. Slowly work the wheel up the Q-tip shaft, then back down, (but not off the Q-tip), then back up, then all the way off the Q-tip. You will hear some squealing and that is good. This should take about 5 second each way for a total of about 20 seconds per wheel.
· Use the Novus 2 and polish the inner and outer hubs by hand with a clean cotton rag.
· Use Extra Fluffy Pipe Cleaner and 91% Isopropyl alcohol to clean the polish from the bores and inner and outer hubs. Very important to make sure this is done well. Then use a clean and dry Extra Fluffy Pipe Cleaner and compressed air to thoroughly clean the bore out.
· Wheel polishing is done!
If only the wheels out of the “Official Pinewood Derby Car Kit” you received are allowed then…
· Cut the OD and inner edge on a lathe to your rule specifications or…
· You can try and use a wheel shaver, but it takes some practice or…
· Research different methods online, but the new wheels are not too bad out of the box and you could end up making them worse…. Without a certain skill level required with the first two options I would just leave them in out of the box condition.
· Follow the same instructions as above to polish the bore and outer bore faces.
Graphite & Burnishing:
· Use Hob-E-Lub
· On the drilled, weighted and painted car body sand the spots that you covered with several grades of sandpaper until they are smooth. Next rub/grind graphite with your finger into these spots. Do this procedure several times until they are silver shiny with graphite.
· Take a #43 drill bit or small metal rod that is smaller than the wheel ID and polish the end of it just like you did for your axles. Insert the polished end into the bore and pour in some graphite. While holding both sides of the rod and while using some pressure roll the wheel back and forth on a clean, flat and smooth surface. While doing this use your fingers to rub graphite into each side of the wheel hubs. Do this 3-4 times adding graphite each time. You will probably get graphite all over the wheel tread… clean the graphite off the wheels tread and other places where you don’t want graphite with 91% Isopropyl alcohol at the end. There are other methods out there… feel free to experiment. Some burnish using an Extra Fluffy Pipe Cleaner full with graphite spinning in a drill press. I have done this with success. Recently some have used a q-tip stem full of graphite spinning in a drill with success. I would just advise against any method that may enlarge the wheel bore at all.
· Rub graphite on the inside edge of the DFW until it is silver shiny. This is the edge that will run down the rail.
· Weigh the finished body, wheels and axles… Add some Tungsten Putty to the scale until you reach 5 ounces (or a little under).
· Lightly put the wheels and axles in the car… don’t push them all the way in, just enough so they stay.
· Use a raw BSA car block and place your car on it until it is balanced. What is the distance from the centerline of the rear axles to the balance point? That is your COM. Place the Tungsten Putty on top of your car until you get a COM of about 5/8”-7/8”. Once you find this position measure the location.
· Remove the wheels and axles, turn the car over and drill some small holes to place the Tungsten Putty in the body at the location you measured. I would try and keep the weight centered left to right in the car. If you can’t then put more weight towards the side with the DFW.
· Re-weigh the car, wheels and axles and verify you are at 5 ounces (or a little under).
Bending the DFW Axle:
· Take the DFW axle and place the pointed end into a vise. Place a screwdriver in the bend groove and lightly tap with a hammer to bend the axle. Bend the axle so it just fits through the bore of the wheel which is about 3-4 degrees. This is not an exact science, if you underbend the axle a little bit then leave it, if you overbend a little then leave it. If you overbend so much that the axle will not fit through the wheel bore then you will need to bend it back a little. The only good way to bend it back is to clamp it back in a vise and tap on the axle head slightly. Be very careful not to put a bend in the area where the wheel bore rotates.
Installing Axles in the Wheels:
· Take a pair of needle nose vise grip pliers and grip a extra BSA axle by the head and top part of the shaft. This is not one of your good polished axles, it is just an extra axle that you are going to use to relax the wheel hole if necessary. Leave at least 3/4” of the end of the axle exposed. Insert the axle carefully in each of the axle holes. If it goes in nice and smooth with some resistance then that is good. If it is really tight then insert and remove the axle in the vise grips a few times to loosen the hole. You may even have to use a drill bit to clean out the hole a little. If the axle is loose just wet the tip of the nail and insert it into the hole, wait a second and rotate the axle around. The water will cause the grain to tighten, tightening the axle.
Lubing/Installing the Axles/Wheels:
· Place the FDW wheels on the FDW axle. Pour some graphite into the bore from both sides and tap the wheel to get it to migrate into the bore. Hold the axle top and with the wheel at a 45 degree angle spin the wheel for 10 seconds. After the 10 seconds the wheels should spin nice and straight without chatter or any unusual movement. Repeat this procedure 2-3 times. I am not a fan of timing how long the wheels spins, it is not an exact indicator of how well the wheel is prepped. I am more concerned about how it looks and sounds when spinning than how long it spins. Install the FDW in the body of the car. The axle is installed so the head of the axle is bent down. Be careful not to bend the axle during installation. Most gap tools are .030” thick, which is about the same as a credit card. I would make the gap much less, around .010” to .020”. If your car is drilled correctly, which it will be using the “Silver Bullet”, then you can run smaller gaps. Smaller gaps will minimize the amount of wobble in rough sections or the curved section of the track. The smaller the gap the harder it is to re-lube. With a small gap you re-lube the same way as with a larger gap. Hold the spot that you are going to lube vertical, pour some graphite in that area then tap the wheel slightly to work the graphite in the bore. Once you feel there is some graphite in the bore, which you will hear as a crunching sound when you rotate the axle a little, then spin the wheel for 10 seconds. Same procedure for the other side of the bore and all the other axles. With a small gap this will be harder and take more time, but I would avoid taking the wheels off of the car to re-lube.
· Place a rear wheel on a rear axle and perform the same process as above. With the rear wheels you can turn the axle when spinning it and find the spot where the wheel spins the best. Mark this spot with a sharpie and mount this spot DOWN when installing the axle in the body. Gap the same as the front.
· If your rules allow I would mount the lifted wheel solid… I wouldn’t let it turn. Put an axle in the wheel and push it all the way in so the wheel is locked against the body. Check and make sure the spacing between your two front wheels adheres to your rules (usually 1-3/4”) and adjust if necessary. Rub some graphite on the spot on the inner edge of the wheel where it can contact the rail.
· Take your tuning board and mark lines down it in 1” increments up to like 8”. Place your front wheel on the “0” line and let the car roll down the board. Turn your FDW axle in small increments using a screwdriver (I use a utility knife blade) until you get the car to drift 3-4” in 4 ft. For a smooth track (BestTrack) keep it closer to 3” and for a rough track (old wooden) keep it closer to 4”. You should also be taking note about how the car rolls. It should be nice and smooth, without chatter or strange sounds.
· Now take a ¼” thick x 1-5/8” smooth board (center guide) and place it down your tuning board. Take your car and run it down the board. Check the gaps between your rear wheels and the center guide. They should be about the same on each side.
Up to Race Day:
· I would re-lube the wheels a few times. Place graphite in the bore from each side, tap it down and spin the wheels for 10 seconds. Make sure the wheel tread is clean and free of debris. I clean them with 91% Isopropyl alcohol. To get graphite off the car body I use baby oil. Just use a very small amount of oil on a small cotton cloth and clean the graphite off. Then use a dry cotton cloth to get the residual oil off the car. Transporting the Car: · With all the time and effort spent on making a car please make sure it makes it to the derby in race ready condition. There is a simple and cheap method to build a carrying box for your car and it can be found here. GOOD LUCK!!!!
Transporting the Car:
· With all the time and effort spent on making a car please make sure it makes it to the derby in race ready condition. There is a simple and cheap method to build a carrying box for your car and it can be found here.