This thread follows my earlier post about indenting the "RR" wheel...
The good news is that my cub scout won 1st place overall in the pack. He was happy, so that's all that really matters, except that from what I observed, the car was not a rail rider, despite our attempt to do so. I stood at the end of the track and observed the car wobble on the guide rail, although not as severely as the other cars.
Two cars were built... one for my cub scout, and one for my youngest son who participated in the sibling race. I observed the same wobble in the sibling car. The sibling car also won its two heats, but the races weren't timed, and the car only ran on 2 of the 6 lanes, so I am not sure how it truly performed. Car construction was intended to be the same. Brief summary...
The front left wheel was raised. The front right wheel had a positive cant (toe in) of 1.5 deg. The body of the car near the front right wheel was indented 1/32" of an inch. Both rear wheels had a negative cant (toe out) of 2.5 deg. The spacing between the body and the front right wheel was 30 thou and the spacing on the back wheels was 68 thou. We used the Pro-Axle Press in conjunction with the Pro-Rail Rider tool to bend the axles. I used the Pro-Body Tool to "true" the axle slots and used the Pro-Axle Guide to insert the axles. I used the Pro-Wheel Shaver to "lathe" the wheels.
After construction, we attempted to align the rear wheels on a granite counter-top. The cub scout's car rear wheels would promptly go out to the axle heads. We never were able to fully tune the sibling car rear wheels to do so. The back right wheel on the sibling's car seemed to oscillate on its axle when in motion. We were able to tune both cars to turn left at a rate of 3" over 6', although the sibling car seemed much less responsive to turning the front right rear wheel axle to achieve the desired turn rate.
1. Pro-Axle Press II/Pro-Rail Rider Tool - I didn't feel comfortable with the outcome. Despite being CNC-machined, the tools did not necessarily fit well with one another. After each moderate hammer strike, the Pro-Rail Rider Tool would recoil upwards. I'm not sure if the nail moved slightly during the process. The whole process did not seem accurate and repeatable.
2. Pro-Wheel Shaver XT II - Our pack has a rule that says the beading on the outer edge of the tire face has to remain intact. After ruining several tires, I realized that the blade of the Pro-Wheel Shaver itself was not a straight line. I'm not sure if it had been used before and repackaged or whether the blade was poorly manufactured, but the blade was rounding the tire tread near the beading. I don't think I ever truly "lathed" the inner rim of the tire that the car rode on.
I assume that the uncertainty in the bend of the axles combined with the outer edge of the wheel tread not necessarily being true were significant factors.
1. What are better options for axle bending? The Derby Worx Pro Axle Bender appears (from watching the video) to be a more desirable option from my perspective. It seems to eliminate the uncertainty than I noted in my observations, and it appears to give more flexibility in axle angle options. Is there something I am missing? I understand there are other methods using a screwdriver, but I'd rather the certainty and repeatability of a precision tool.
2. Has anyone else observed the same issues with Pro-Wheel Shaver blades? I intend to order replacement blades for next year, but am not looking to receive the same quality blades.
3. Would it be better in the near-term to increase the respective cants on the front right wheel and the rear wheels to achieve the desired outcome, considering we were unsuccessful the first time? I assume that increasing the rear wheel cant would result in a stronger tendency to ride the axle heads, and increasing the cant on the front right wheel will allow make the the car more responsive to slight changes.
4. Also, would increasing the turn rate of the car decrease the wobble? I had read that desired turn rate was 3-5" over 8'. I used a rectangular table surface (removed the legs) as the testing board. I elevated one end with a 2'x4' and then used wood shims to make it level it in the appropriate axis.
I am happy to answer any other questions about the car construction and will appreciate any feedback. Thanks!
1. Rail Rider - To minimize the rebound when striking the tool, put the Pro-Axle Press on a piece of wood (2x4) on he concrete. The wood will absorb some of the impact and minimize the rebound. Also, the Rail-Rider is sensitive to the diameter of the axle. So if you use BSA Nails and file the burrs and then polish, you can easily reduce the diameter such that the tool will not create enough of a bend. This can be corrected, by placing a strip(s) of paper (or strip of business card if needed) between the axle and the rail-rider. This paper "shim" replaces the lost diameter, allowing the tool to work properly.
2. Wobble - This can come from incorrect rear wheel alignment, or from not enough front wheel steering. When checking the alignment of the rear wheels, make sure the wheels stay on the axle head in both the forward and backward direction. A 3 inch drift or 6 feet is not enough. I recommend a minimum of 5 inches over 8 eight, and have had the best luck with about 8 inches over 8 feet. You've got to make sure that the amount of drift will keep the steering wheel tight against the rail regardless of the foibles of the track. The track may lean left, right, or alternating both ways, and the drift has to overcome this.
I would not use the wheel shaver. The cheapest way to get a good set of wheels is to buy a matched set of preferred wheels (2, 4, 8, 15 I think) from Maximum velocity for $8.95. His instructions tell you how to order. They come to you with a note "lightly sanded". You can also buy a 5198 Pro-axle bender $79.95 and from Derby Evolution one of Knotty Racing's "Wheel Runout gage" for $49.95. You can also build your own run-out gage per Instructions on page 64 of Troy Thorne's book, Build a Winning Pinewood Derby car.
That being said, I would narrow the car 1/16" behind the dfw. With your new axle bender, bend 3 nails to 1 1/2 degrees. Set the rear axles with Negative cant. Do not put any front wheels on the car. Keep the body of the car parallel to the surface and slowly roll the car forward and then backwards. The wheels should migrate to the axle heads and stay there. If they do not then a very minor adjustment should correct it. Hopefully the nails are in the slots as straight as you can possibly get them. I have no Proof of the following - if you cant the rear wheels to 2 1/2 degrees will the heavy cant hide a toe problem? I don't know. At 1 1/2 degrees I have found if there is toe misalignment it will show. You do not want the back wheels trying to steer the car. Insert the dfw with Positive cant and leave it with 1 1/2 degree bend. That's enough to keep the wheel on the rail and the adjustment is not overly sensitive. Set the drift to 2" in 4' to start. I think 1/4" x 1 1/2" Pine lattice strip is a stock size. That's close enough to the 1 5/8" wide strip of the Pinewood derby track. Buy a board for $4.00, screw the strip to it, raise the board 3 or 4" and test the car. Only the dfw should touch the guide strip. Insert the ndfw with a straight nail.
I set all wheels with the thickness of 2 credit cards so I can hold the nail head with the special pliers. After all adjustments are made I push the nails in to 1 credit card thickness.
My teams have 3 cars set up this way for racing on the 10th and 11th of this week. One car for a Sponsor race on the 10th and 2 cars set up for the Girl Scout race on the 11th. Tomorrow a friend and his Cub Scout and Girl Scout will be setting their 2 cars this same way. We'll see how we all do.
Check out what is said in the last post about gripping the wheel as well.
And a video on how to fix the blade in the xt2 wheel shaver if this what your seeing with your shaver.
Speedster - Yes, an aluminum track. My concern with pack rules wasn't warranted, so I could have indented a full 1/16" with no issue. Thanks for the tip on the pine lattice strip.
What do you use for your testing board (not the strip)? I have an older rectangular kitchen table which is rather level. I removed the legs, elevated one side, and then shimmed it level in the proper axis. I was concerned about buying a board that wasn't level which would have affected the testing (in my mind). This also why I tested over a 6 ft distance (length of table).
Thanks for the tip on the 1 vs. 2 credit card difference. I inserted the dfw's to a 30 thou spacing which caused some difficulties tuning them.
Whodathunkit - Thanks!
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- Railriding can be done with bent rear axles, but having a method of alignment is crucial. I would point you to Stan Pope's "camalign" system that uses weights to isolate performance of each rear wheel to make tuning a lot faster: http://stanpope.net/bentaxlealign.htm
- A tuning board is a necessity, both for testing alignment and setting drift. Mine's made out of a piece of smooth shelving board and a yardstick. It's a cheap build, but you need one.
- I don't bother with special tools to bend axles. A soft piece of pine, a pair of pliers and a bend measuring guide get the job done for scout axles.
- "Typical" RR recipes don't give enough bend on the DFW. I like to drill with about 5 degrees of positive camber and then bend the axle about 1.5 degrees for setting the drift and adding a little more positive camber.
Regarding the wheel shaver, I have pretty much given up on it. For Scout races, we buy a few tubes of wheels and try to find the ones with the tightest bores and the lowest amount of radial runout.