Derby Talk

Hi guys,
The wife is out if town so it's the perfect time to jump start the cars. After successfully drilling my axels holes I cut all 3 cars down on the bandsaw. All are 5/16 thick. Even so I came darn close to the raised FW on the first car and cut the others thicker. Also when routing out the rear weight pockets I had a lot of cracking around the axel holes. Had to put axels in place and wood putty up the chips. My plan is glue small wooded veneers squares over the pockets and put the weights in ASAP to strengthen. I even had one car show a hairline crack in the rear axel wood between weight pockets. Quickly added some CA glue and glued on veneer. Man this thin cars are fragile. Will they hold up on the track?
Noskills

If I am routing out weight cavities, I do it before I cut the block down. Helps a ton with the chipping and cracking.

Lately, we've just cut through the entire slab then cap it with 1/32" basswood. WAY easier.

For the fronts, you don't need that much difference between the two hole heights. You pick up some lift from the DFW when you steer it with a downward bent axle.

I cut the car to the thinness I want using my bandsaw, then I use the scroll saw and cut out my weight pockets. I put 1/64th birch plywood behind and in front of the axle slot, this prevents them from splitting out when I drill my axle holes, it provides a lot of strength. I then cover my weight pockets with 1/64th birch plywood and sand it smooth.

Part of the problem you may be having is a dull or cheap router bit. When I routed out a bunch of cars, I would start having the problems you are describing and most of it was due to a dull router bit. My first 4 or 5 cars would be clean and then I would have some that were too fragile. It also could be the router speed also.

IMHO I know a lot of people use a router bit in a dremel, I have not had a high level of success that way. When I bought a router table and a good router I was much happier. Some on here are much better wood workers than me, this is my own humble experience. Hope it was helpful and good luck.

Successful sequence:
1. Cut and sand body to 1/4"
2. Drill axle holes
3. Cut weight pockets with jig saw, leaving 1/4" to 3/8" wide around rear axle holes
4. Assemble and super glue 1/4" cubes in an L-shaped form lined with wax paper. Press cubes into sides and bottom of "L" to get tight bond and good alignment.
5. Check weight assemblies for fit; file/sand pockets as necessary.
6. Tape over axle holes
7. Assemble cubes into body with epoxy with wax paper form above and below
8. Sand top and bottom smooth, lightly sand around axle holes.

Hmm, can't say I had that much trouble with mine. No chipping whatsoever following Sporty's tutorial. Part of the trick with routing is to not make your routing channels too deep. Rout 1/8" deep at one time. Then increase your depth and rout the next 1/8." Take your time routing through the wood with a series of passes. Otherwise, you run the risk of burning up your bit and chipout.

My process:

1. I planed my entire blocks square
2. Then I drilled axle holes on both the top and the bottom of the block (gave me two cars out of a single blank)
3. Checked the axle holes to make sure they were square with the body
4. Took the blocks to the bandsaw and ripped 3/8" bodies out of the block
5. Drilled holes in the appropriate places to help prevent chip out when routing--see Sporty's How-To on Spoon car building
6. Used a very small router bit in my Dremel Mototool and routed the cavities, connecting drilled holes in corners making sure to test fit Tungsten cubes
7. At this point, I sanded the tops of the blanks down to the final thickness

Paul

I followed psycaz method. For an example, check Derby Evolution, Poplar Bodies Laser Cut, the "Inferno" Pinewood Derby car body. I glued the cap on after cutting the body. You then turn the car upside down and install the squares on the cap and 3 sides of wood. I finished off the back with glazing putty although there is very little finishing to do. I used vinyl gloves to protect my hands and a tweezers to cover the squares, one at a time, in the epoxy. Since epoxy dries so fast I installed the two back rows first and let it dry. You can then work on the two front rows. If you have a dremel there is a fine tooth saw blade available. By drilling a small hole in the corners it should be easy to make the cut outs. Glazing putty was then used to fill the crack between the cap and car body so it would look like it was all one piece.

Thanks all,
It could be my equipment, my technique and the wood. I did not get splintering on all blocks-one was pretty bad. I cut my blocks to 5/16 and then use a dremmel cutting bit (cylinder shaped) in my drill press to route out the pockets. I do drill holes around the perimeter I wish to cut. I tend to use the router to drill down then move horizontally to cut. I like Paul's idea of routing a thin bit at a time...makes sense.

Well after all I fixed the chipping with wood putty, the crack with CA glue, put in rear weights and 1/64 veener on top. All looks good. I then sand down to 1/4 in (my bandsaw leaves pretty good marks).

Will have some in progress shots soon,

Noskills

Seth,
For my thin car blues I use a full block router and blue painters tape on the end.
This a way I can make two cars with one block by cutting in new axle slots
cut into and sand it smooth on the belt sander.

If I start with BSA type pine, my traditional process is something like this:
- Check plumb of my table saw blade with machinist square, cut a test board and verify with cheap digital caliper;
- Trim the large blocks down to (3) 5/16" planks using my table saw with a very good blade and fence;
- Take side cuts on any planks that are too wide for my drilling tool;
- Go through even more work to get my drill press and drill block in perfect alignment;
- Check flatness of the planks, only prep them if the face which will be in contact with my drilling tool does not tip when I push all over from on top of it;
- Drill out weight pockets with a couple sizes of end mills (1/8", 3/16" mostly);
- Drill axle holes, verify satisfactory alignment with test axles and wheels.

Lately I am getting more used to starting with 1/4" slabs and in that case, cutting out the weight pockets and adding a 1/64" plywood top is best done before drilling.

Ideas above including the 1/64" plywood braces in front of and behind the axle area as well as planeing the blocks are very good.

At the end of the day, look at the time/cost/results and make your own decision.

Quadad-

Where do you find 1/64" balsa for the tops? I think 1/32" is the thinest balsa I can find at my local Hobby Lobby.


Birddog

birddog - most any hobby store should have 1/32" and 1/64" plywood (not balsa) in the same area as the balsa. Don't expect a lot of strength obviously from the 1/64" but it can do a few good things as can the 1/32".

Veneers are much easier:

Veneers are much easier:

Image

Resullivan,

Is that a car with an extended front end? (rears 5/8 from the end with standard wheelbase/)? I was not able to get 24 cubes into my cars of this built mostly as I did not hollow out the body and I left alot of weight for paint.

May I ask what kind of COM you put on this car and how much drift you use to keep it running smooth? My cars like this are at a COM of about 6/8th and will have 4 in over 4 feet.

Thanks,
Noskills

Noskills, if you set the toe at 2" over 4', will the car run faster? I think you race on an aluminum track and it probably is very smooth.

Noskills, if you set the toe at 2" over 4', will the car run faster? I think you race on an aluminum track and it probably is very smooth.

Speedster,
One would think so and its impossible for me to test. The best I can do is compare from build to build. The biggest difference I noticed in 3 cars we made with a drift of 4 in over 4 feet vs the 2 cars we build with a drift of 2 inches was consistency. The difference between best and worst time seemed to be lower with the higher drift. So many factors though its hard to say this means anything. And you are right we race on a 42 ft aluminum best track.

Noskills