uh, oh. Cub Scout Pinewood Derby time is coming. Again.

[nicer20]

Heartiest Congratulations !!
Super Grandson Super Grandpa !!!!

[dbhost]

Hey LCHIEN my friend and his family are volunteering me to help out with the pinewood derby for their kids (Not scouts, but similar organization). Any tips for making the cars fast?

[LCHIEN]

Hey LCHIEN my friend and his family are volunteering me to help out with the pinewood derby for their kids (Not scouts, but similar organization). Any tips for making the cars fast?

The big things are wheels and weights

Get the weight as close to the maximum as you can, you are at the mercy of the "official weigh-in" scales s I make my cars exactly 4.995 to 5.000 oz with a couple of #6x1/2" wood screws in the bottom to back out if they go over, The PWD official blocks weigh about 3.5 ounces, the wheels and nails 0.5 oz. I usually cut away a lot of wood and put lead weights in the body so the COG is 1/2 inch in front of the rear axle - weight concentrated towards the back gives several advantages.

Wheels and nails: I follow the pack rules which usually call for using the kit nails as axles, and unmodified wheels (except for light sanding). I chuck them in a slow drill and use a file to take off any burrs under the head. I then use 220, 400, 1000 and 3000 grit sandpaper strips to polish the axle where the wheels ride. Check under a microscope -polished on left, unpolished on right.



The next thing is wheel alignment. I always use a drill press and a #44 drill bit. The back wheels go in .150" above the bottom of the car. I put in with a 2.5 degree angle from the vertical (SEE MY OTHER POSTS FOR THE JIG) so that the wheels have a slight camber but the tops of the wheels clear the body. The wheels will ride away from the body and and ride on the edge.
The front wheels I use the 3-wheel technique the rt front wheel I drill the hole perpendicular to the body but .050" higher than the left and rear wheels so that it does not actually ride on the ground. It only provides steering correction with the guide rail.
The left front wheel I drill the hole perpendicular to the body at the same height (.150") as the rears. But the magic is in the wheel prep. I slot the top of the head so its like a slotted screw head and can turn with a small screwdriver. Then I put it in a vise clamped just beyond where the wheel will be and put about a one degree bend in the nail using a small hammer, in line with the slot in the head. I do it by eyeball.
This is your steering axle...If you put the bend up (slot vertical) then the wheel is nominally straight and cambered 1 degree. If you turn the screw head CW or CCW 90 degrees you can affect the steering up to 1 degree right or left respectively. The more you bend the nail the more sensitive it becomes and hard to adjust. SO a degree by eyeball I find works well, usually my adjustment is no more than 10-20 degrees of the nail head. Then adjust the completed car so it tracks as straight as possible and does not spend a lot of energy rubbing against the guide rail. I made a 8-ft dual section of track with two pieces of 1-3/4" door-stop as a guide for testing rolling friction and straightness. About 3" of inclination is good to test rolling friction. Having a control car and a test car helps in seeing improvements. When you make a meaningful improvement to the test car then do the same for the control so you can keep comparing future improvements.



Back of the car (this guy did it by bending axles, but I drill my holes at an angle...easier to control with my jig):

Front:


You'll want to graphite dust the axles and wheel hubs well as a lubricant... and work it in really well.

The body being aero dynamic helps a lot... usually the winners seem to be thin 1/4" wedges with a lot of weight. My last car was 1/4" thick at the front and 3/8" at the back and drilled out. Wheels and nails weighted .5 oz, body weighed .7 Oz and the weights weighed 3.8 Oz!


I always chuck the wheels up and go over them gently with 220 grit on the tread area and the inside rim to make sure there are no burrs.


Of course appearance and originality are usually awarded. Here's a portion of the entries into the pack this year, to see some of the variety.
my grandson's is #25 and mine is 23 and 24 at the bottom



Finally remember its the kid's car. Show them some possible examples (google images, Pinewood derby car, or just google pinewood derby) shows a lot of examples. Googling how to make a fast PWD car gets a lot of results. But let them do the choice of design, let them cut the shape on the bandsaw, do the sanding and prep work and nail polishing, and painting. Explain to them the reasons why you do the things described above. The temptation to totally build the car yourself is why I enter a car in the family division...