sweet928

My sons scouts 1st pinewood derby is coming up. I have two weeks. Got the idea to ours as a 928. Problem is I have no clue how to carve wood. Any of you guys with kids ever have the same idea and offer any tips or pictures? I want to make it look as close to my OB as possible - planning to paint it the same petrol blue, etc.

sweet928

I just remembered someone here had generated a 3d model of a 928 a few months ago. Was wondering if I could get/send that electronic file to a CNC shop and have it CNC'd into wood? I don't know if that is a very costly idea or not but how cool would that be to have a pinewood 928!

Mrmerlin

isnt a pinwood derby car supposed to be done by hand??
and made out of a certain size piece of wood?
I would suggest to get a 928 model and then carve your wood till the bodies look the same there are some 1/24 scale models as well as 1/48 that you can use

deptotpr

Awesome! I raised three boys. I think none of my boys made their "own" derby cars. I think the event is for the dads? haha- Good Luck, cannot wait to see the finished product.

leperboy

There is a specific rule that is widely ignored that the cars must be done by the Scout. To help ensure this, our Pack has a Dads' division and a kids' division and the dads can go hog wild on their cars. I think having the block milled professionally is probably far beyond the spirit of the competition, though, and I'm not sure what the kid learns or gains from that.

The wood is soft and easy to shape. Last year I did a 1947 Allard. you need a rasp, a planer and sandpaper from 24 grit up to 200 grit. It just takes time but you can sand and slice it into whatever shape you want. I have a template for the top and sides that I glue to the wood to guide my wood removal.

Go to your local scout shop and they will have literally hundreds of dollars worth of stuff you can buy to enhance your car. Kits to polish the nails, side wood to widen your car body, special lead weights, graphite, wheel alignment kits, special sandpaper and wax for the wood, and so on and so on. It just takes time to do it well by hand.

Matt

sweet928

Yes, I already have the kit. It's a solid block of pinewood about 7" x 4" by 4". Four nails and four wheels. The rest is up to the Father/Son team.

I don't think they are "supposed" to be hand carved. Seems like most Dads use machines these days, but simple designs. There's so many sites that will sell you a machined, but off the shelf body -- that I'm feel "hand carved" Dad's are in the minority.

I figure the 928 "idea" is the originality, to justify a machined body. (I want to have it machined so it's perfect.) I want this to be a keeper, not a one time racer. I'll spend the father / son time putting the wheels on, painting it, etc. I even found a web site that sells light up LED kits for Derby racers. As you can see, I have lofty goals for this, but not much time.

If I hand carve this thing it will look like crap. If machining cost an arm and a leg, I guess I'll hand carve, but shudder to think what it's going to look like.

sweet928

I guess you have a point. Maybe I'll take a stab at it and try to hand carve this thing, but now I think it's going to be an ENZO. LOL. That would be good if there was a Dad's Division, as I really wanted to make an awsome machined 928. I'll bring it up at the next meeting. I just have a sneaking suspicion that we're going to be the only hand carved team.

jleidel

When I was a lad, we would use a band saw for the rough cuts, then go back with incrementally finer grain sandpaper to mold the specific shapes. If you're at all interested in speed, I would suggest the following:

- Invest in the round-style derby car lead weights [the size escapes me... 1/8"??]. Drill pilot holes in far rear of the car [as far rear as humanly possible]. You can back fill with sandable wood filler if you're going for a smooth look.
- deburr and polish the wheels using a polishing stone
- polish the axle nails
- [read the rule book first before doing this one], grind the wheel surfaces into points... reduces the rolling contact surface.
- reset 1 of the four wheels [preferably one of the front two] slightly higher [1/32" or so]. This, combined with a serious rear weight bias will reduce the overall rolling friction by running down the track on three wheels.

[my old man is a mechanical engineer... so pinewood derby time was a "learning" experience... drag coefficient equations in tow]

MattCarp

That is the best list of recommendations for the pinewood derby I've ever seen!

I'd say air resistance is negligible at these size/speeds...

Your recommendations on reducing rolling resistance make total sense (polish nails/wheels, go for three wheels, "V" the wheels), but the thing about adding weights. I thought objects all feel at the same speed regardless of weight (32 ft/sec^2)? What does the extra weight really do? Doesn't it increase the rolling friction?

pcar928fan

The best car I ever had (I think I got 3rd in the WHOLE COUNCIL!!!) my dad and I built together. It was FAST!!! Very fun! Got my Eagle back in '79 and my brother followed in '86 or '87...my dad and both of his brothers are Eagles too! I LOVED my scouting days. My brothers son is in Tiger cubs now so I figure if he stays in till he is a Boy Scout dad and I will get involved again and it will be a big family affair. I hope so anyway.

Steve Martin

If you hand carve this 928, you will at the end, appreciate it not only for what it became but for how it became. Others will notice it aswell. the 928 should be an easy carve, with all the roundness and no really sharp angles. the only tricky part to carve would be the rear spoiler(GET A DREMIL TOOL FOR THAT AREA). Spend the day with your boy on the porch( or in the garage) just looking at the car and creating your car. in the end, no matter how good or shabby it turns out, you'll have a masterpiece that you and your boy carved together and that is the time worth $1,000,000,000,000,000,000,000.....

Also, think 30 years into the future, when your now grown boy, shows up with a hand carved car out of a chunk of pine that he and your grandson carved one sunday afternoon. upon closer inspection of that car you notice the resemblence to the 928..........

you got tears yet?

dont cheapen the experience for your boy. You can go anytime and have a piece of good hardwood CNC'd into a nice 928 for your mantle. this is the bond time for father and son.....

Mrmerlin

weight at the back makes the cars the fastest, and it will also keep the one front wheel from dropping

leperboy

All good suggestions. Although, I hesitate to put the weights too far back because you want some downforce on the front wheels or it could skip the track. I put the weight directly in front of the rear axle. Also, at least in our Pack you are not allowed to narrow the width of the wheels. They have to be issued width.

One very important thing to remember is that if your son doesn't win, all he has to show for the derby is his car. So, try to make it cool. If your son is young, like six or seven, he may be more interested as something to play with than a competitive car.

My dad was an dynamics engineer with McDonnell Douglass and built the ugliest cars you'd ever see. I hated my cars. And, although they were mechanically sound, we never won anything. There are too many variables such as luck, stuff on the track, kids manhandling the car before the race. Anyway, I ended up with loser cars that also were too ugly to play with.

Now, the kite-flying contest... I have a first place for every year I entered.

Matt

Jerry Feather

Here is what I suggest you do:

Check the rules to see if you can add wood to the basic block of wood and if you can change the wheel base slots in the block. If you can do both then go the the hobby store and get some strips of balsa wood about half inch thick that you can use to build up the basic block because there is not enough wood in it to make a 928 and it is intended for an open wheel car, which the 928 is not.

Then take the basic block somewhere and have it trimmed down from the top so that it is only about 3/4 inch thick. This is so you can build it up with balsa wood for carving the 928 shape all in Balsa. You might also get an exacto carving kit, some paint and primer. Go to harbor freight and get a sanding block and some coarse,some fine, and some very fine sandpaper for it. You might get the carving kit here cheaper. Get a tiny file for metal--very fine.

Now, before we start the carving we need to do some engineering. The derby car's success will depend on a balancing of gravity, momentum and friction; and maybe a very tiny bit on aerodynamics. The aerodynamics are already set by the 928 design we are using so we can ignor that. The friction will depend on some work on the running gear which I will describe later. Gravity works equally on something light and something heavy, so the total weight of the car wont matter in that respect, but I think momentum is the biggest factor in this race. However, that can be a killer too. If the car is very heavy it will tend to go faster in the bottom straight because of momentum, but it will also take longer for gravity to get it started at the top of the ramp.

Therefore, what I suggest that you try is to add a little weight to the car but not much. I think the advantage of the weight on the straight is greater than the dissadvantage at the start. I suggest too that you be selective with the placement of the weight. I had my son put extra weight in the rear of his car simply because I could envision a downhill ski racer putting his weight to the rear to go facter. Maybe that is for a different reason, but that was why. We didn't get to experiment and you wont either, so roll the dice. I suggest you drill the rear of the basic block from back to front with two or three 1/4 inch holes from back to foreward of the rear axel or where it has been or will be located and then insert some chunks of quarter inch rod or bolt shanks pushed foreward to just over the axle. When you have them where you want them you want to put some glue in the hold them in place. You better check too about a weight restriction in the rules.

Now is the creative part you are looking for. Take a picture of you 928 from the side straight on. Print it on plain paper. Then put it is your copy machine and reduce it or expand it so the the size of the tires matches the size of the wheels in the derby kit. make a couple of copies. Then measure the wheel base in the picture you have copied th the right scale and see how close that comes to the wheel base of the derby kit. It it needs to be changed then cut new axle slots, or one of them and that will move the axle.

Next, compare the picture of the car which you have cut out of the paper by now, with the side of the basic block and see where you will need to add balsa wood to build the block up. Cut the balsa strips and glue them on the block with carpenter glue. Make the block so that you can glue the 928 picture on the side completely. Then cut the profile of the 928 out of the block all the way across. It should be like cutting it out with a band saw. If you have access to one do it that way, otherwise do it with you knife and coarse sand paper. Be careful to have the profile true at this point and do not be tempted to start rounding it out yet. This is important because when you start rounding you lose the profile reference.

After the block is "profiled" then you must carefully cut out the wheel wells to match the wheels from the kit. They will not match the 928 wells, but that is ok. No one will notice.

Now you can start to do the rounding with your knife and coarse sandpaper. The best way to start this is to profile it from the front and rear, then start rounding. You will be in the nature of a sculptur at this point, so your carving skill will be created here. If you mess it up, simply take the balsa off and start over or glue some more balsa on and fix your screw-up.

Finish the car with very fine sand paper and then primer it. sand the primer out with 450 or even 600 grit paper then paint it blue. Outline the windows with a knife carefully and then paint them with a small brush in silver.

Now for the running gear. Take the nails they provide for axles and put them in you electric drill and with the tiny file which they are turning, smooth the burrs off especially under the nail head. Then using very fine paper while they are turning smooth them up so they are shiny. When you run the car, and not too much before, put a tiny drop of machine oil on each axle.

Let me know if you need anything more.

Jerry Feather, FBA Certified
S4's (6)
KGJT

robot808

um, shouldn't it be a 50/50 weight distribution? i mean, if you're do this thing...