Woodworking Question - Drilling Holes

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GregGleason

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The Cub Scout Pinewood Derby is coming up soon and I am about to make the big cuts.

The design is simple, but requires lightening voids for weight distribution. If it were me, I would use my plunge router to hollow things out. But I want my children involved, so I am going to let them use the drill press to make the lightening holes.

Attached is a side elevation so you can see what is proposed (dimensions are in inches).

My question is a process one. I think it is best to cut the holes first, then cut the rest of the sloped wood away. Also, is it best to drill pilot holes for the bigger holes, and if so, what is the rule of thumb?

Greg

Car.Cut.Pattern.jpg
 
Greg- I would cut the holes first. 1) more surface area to steady and clamp to, plus it's prolly pretty square stock to start with. 2) the stress (pressure) of unrelieved wood chips during the plunge with spiral bits tends to bulge any thin walls you may wind up with. Pilots are good for layout. Drill partially and bring up to dispense chips. Wax or hard bar soap lubes the bit if it is really hard wood. (should be pine right?-that's soft.) Be sure to space your holes so you don't collapse the adjacent one if the walls are too thin. Use a sacrificial piece of wood under the body to produce clean holes and reduce breakout. YMMV...
 
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My question is a process one. I think it is best to cut the holes first, then cut the rest of the sloped wood away. Also, is it best to drill pilot holes for the bigger holes, and if so, what is the rule of thumb?

1. I would get some scrap wood and do some tests prior to using the actual contest piece of wood.

2. I used to drill pilot holes in wood when I was going to drill large holes. I would drill maybe a 3/16" pilot hole for a final 1/2" hole.

3. I don't understand your need to reduce weight. When I worked with these our cars were usually way below the weight limit so we added lead weights to make them heavier.

4. I know that lots of people do wedge designs, but you could achieve the same weight as the drawing you show with holes, by just making the piece of wood a little bit thinner.
 
Greg,

First of all congrats for wanting to have the young'uns involved in the project. I have parents (fathers) come into my store and use the test track for their cars and the kids aren't even allowed to touch the cars. Seriously.

Also, most cars need weight added to be competitive. Using the approved wheels and axles and using a wedge design I predict the car will only weigh around 2.5 to 3 ounces when finished 5 ounces is the max and I hear that 4.5 ounces is ideal for the tracks hey now use but have no idea why.

Good luck and more importantly, have fun.
 
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3. I don't understand your need to reduce weight. When I worked with these our cars were usually way below the weight limit so we added lead weights to make them heavier.

...

That's a good question. The physics of the race, as I have been learning, is taking as much as weight possible and concentrating it toward the rear, but keeping the CG in front of the rear wheels. So the weight will be added to get it to the 5oz limit, just most of it added toward the rear.

Greg
 
Max weight is always best, and in front of and above the front wheels. I've been involved with the pinewood derby for years and this has proven results.
Get graphite powder and too much is not enough.
Polish the nails, but don't make the wheels sloppy and wobble.
As for drilling holes, brad points work best with a backer on the exit side.
Slow speed on the drill press, advance slowly and back out frequently to help the chips fly out of the flutes.
The derby is one my favaorite things of the year. I try to do something different each year, even though I know what the winning combo is. Just not fair to the others, ya know?
 
Hehehe, Have you checked out the cost of the tungsten weights you are going to need to bring it back up to 5 oz? We got down the road on a similar design a few years ago and then I went to buy the weights and my jaw dropped.

Mostly my son went for show and not speed though. Helps to have a scroll saw. He did all the scrolling. On the piano I did route out the inside pocket and run some of the wires.

Lizzard1sm.jpg

Lizzard2.jpg

Piano1.jpg

Piano2.jpg
 
Hehehe, Have you checked out the cost of the tungsten weights you are going to need to bring it back up to 5 oz? We got down the road on a similar design a few years ago and then I went to buy the weights and my jaw dropped.

Mostly my son went for show and not speed though. Helps to have a scroll saw. He did all the scrolling. On the piano I did route out the inside pocket and run some of the wires.

I have been stocking up on the tungsten weights using the Hobby Lobby 40% off coupon. They are a bit pricey. :eyepop:

Those are amazing designs!

Last year we did fancy, this year it's speed.

Greg
 
Last year we did fancy, this year it's speed.

You can't do both?
Well I understand that there might be a little bit of aerodynamics involved with the fancier designs.

My daughter's church was doing a similar thing, but for the boys and girls. I helped her build cars, and I built some for me. The block of wood they give you will create an open-wheeled car. I wanted something more like a modern sports car so I found some 1/2" thick pieces of scrap wood, sawed wheel openings in them, and glued them to the sides of my block. Then I sawed and sanded the whole thing into the shape of a Ford GT. Another year I just bought a 1/24 scale plastic model kit and glued its body on top of the block of wood. That model was of a NASCAR car and had a lot of decals, so that car looked pretty good even though I recognize that it is outside of the rules.

Our track was a little bumpy so if the CG was too far to one end or the other the cars wouldn't track very well. I've read that the CG should be near the back end since this part is higher up the hill and gives you a better potential energy. But I think lubrication and attention to wheels are the keys to a fast car.
 
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