Learn to Build A Winner (Cont'd)

Woodshop 101 (Continued)

5. Wheel Alignment Techniques

Wheel alignment is a very critical step in preparation of the car. Wheel alignment is the last step. Once the wheels are aligned properly, NO changes should be made to the axles except for addition of graphite prior to racing.

This is my procedure for alignment. It is not necessarily the only way or the best way, but it can be accomplished with no unique equipment.

Goal:

Whether moving forward or backward, our Car must roll in a straight line, and its wheels should not try to move in or out on the axle.

Equipment:

a flat tabletop with some straight Line across it (the wood join line of a wood tabletop is satisfactory)
carpenters level or spot level
wedges (4) to adjust table
tweezers (to handle shims)
shims (20 or so) - 1/8" X 1/2" pieces of waxed paper
start and stop blocks wood
pencil and paper (work sheet)
sharp craft knife

Setup:

Use the wedges under the table legs to level the tabletop (side to side) and to raise one end of the table by 1/4". The result is that the straight Line on the tabletop runs slightly "down-hill". (A car which accelerates smoothly straight down this incline is probably "race ready".)

Place the start block at the upper end of the Line and the stop block at the lower end.

The table top should be clean and free of anything bumpy or sticky (e.g. dust, bread crumbs, peanut butter, jelly, and paste from the last den meeting.)

Wheel evaluation:

Before beginning alignment, check the wheels by removing them from the car and rolling them, one at a time, on the table top. They should roll straight and smoothly with little or no wobble. If a wheel veers or wobbles, it should be reworked or replaced.

Axle installation procedure:

Construct an "axle installation guide" by drilling or gouging a slight depression in a small block of wood. The wood can be 2 inch square of 1 inch pine. The depression should be about 1/20 inch deep. Adjust the depth of the depression so that the width of the car with axles installed is just a hair under the width limit, usually 2 3/4 inches. Place a reference mark on the face of the guide to show where the top of the car should be.

To install a wheel on the car, place the axle in the wheel and set them, point up, on the axle installation guide. Make sure that the nail head is in the depression. Rotate the axle until its "up" side is toward the reference mark on the face of the guide. Hold the car with its "top side" aligned with the reference mark and press the car body down on the axle until the body contacts the wheel hub. This will leave about 1/16" to 1/8" of "play". The "play" is used in the alignment evaluation (and left that way when alignment is completed.)

Recheck the axle orientation to assure that it did not twist during installation.

Preliminary Alignment:

This step uses one side of the car and the bottom of the car as a reference. If the side of the car has been tapered, then this step must be skipped or you must construct a temporary reference, e.g. a strip of wood tacked to the bottom of the car.

The purpose of this step is to observe the initial axle orientation and to accomplish initial axle alignment. To do so, the axles should be installed on the car without the wheels on them. The axles should be installed to the correct depth, so use the axle installation procedure above but place the wheel to the side of the axle so that it serves as a depth gage.

Align a "try square" against the reference side of the car approximately even with the front axles. Sight between the axle and the try square and observe whether they are parallel. It is easiest to verify by watching light disappear between the axle and try square blade as the combination is rotated slightly. The light should disappear across the entire length of axle simultaneously. If not, the axle is not parallel to the blade of the try square. Align the blade across the bottom of the car and perform a similar evaluation. Apply waxed paper shims to the outer 1/8 inch of the axle holes to bring the axles into alignment. To insert a shim, remove the axle without disturbing any shims that are in place, insert the new shim(s), replace the axle to correct depth, and fold the shim ends out of the way against the side of the car.

Repeat the process for the rear wheels, being sure to use the same side of the car as reference.

Note the count and locations of the shims needed.

Final Alignment Process:

Identify the dominant front wheel. Remove it.
(Most of the time, only one for the front wheels bears weight. That is the dominant wheel. To identify it place the car on a flat level surface and press down gently on the car near each front wheel. The dominant wheel will not give. The other will move down slightly until the axle contacts the wheel hub.)
Align the three wheels (see alignment step)
Reinstall the dominant front wheel
Align the dominant front wheel (see alignment step)
Clean up the loose ends (see Clean up)

Alignment step:

The following step is repeated until all of the wheels being aligned are "true", i.e. no wheel moves in or out on its axle.

Trial 1. Place the car behind the start block, front end down-hill. Pull the wheels to the outer end of the axles. Release the car, and observe and record the trial results. Observations in each trial should include whether (and in which direction) your Car turns, and whether (and in which direction) each wheel moves on the axle during its first few revolutions.
Trial 2. Place the car behind the start block, front end down-hill. Push the wheels to the inner end of the axles. Release the car, and observe and record the trial results.
Trial 3. Place the car behind the start block, back end down-hill. Pull the wheels to the outer end of the axles. Release the car, and observe and record the trial results.
Trial 4. Place the car behind the start block, back end down-hill. Push the wheels to the inner end of the axles. Release the car, and observe and record the trial results.

Interpret the trial results for each wheel as follows:

Car turns (before wheels move on axles). Action: Shim forward wheel accordingly. (Usually, try to resolve this aspect first. Once the car is rolling more-or-less straight in both directions, at least for short distances you can concentrate on how the wheels move on the axles. In addition to turning around the axle, they may move in or out on the axle, and that movement may or may not depend on the direction the car is rolling.)
Wheel IN-IN: Axle is canted down. Action: Shim up from bottom.

Condition observed: A wheel moves IN when the car rolls forward and IN when the car rolls backward. This means that "any motion causes the wheel to move in", and it indicates that something other than "steering" is causing the wheel to move...the cause is that the car's weight is pushing the wheel "out of the way" due to a downward sloping axle. To correct this, cause the outside end of the axle to raise (toward level) by shimming the axle up from the underside of the axle hole.
Wheel OUT-OUT: Axle is canted up. Action: Shim down from top.

Condition observed: A wheel moves OUT when the car rolls forward and OUT when the car rolls backward. This means that "any motion causes the wheel to move out", and it indicates that something other than "steering" is causing the wheel to move...the cause is that the car's weight is pushing the wheel "out of the way" due to a upward sloping axle. To correct this, cause the outside end of the axle to lower (toward level) by shimming the axle down from the upperside of the axle hole.
Wheel IN-OUT: Axle has toe-in. Action: Shim back from front.

Condition observed: A wheel moves IN when the car rolls forward and OUT when the car rolls backward. This means that "the car and the wheel are trying to go in different directions." In this case the axle orientation dictates that the wheel's line of travel will intersect with the car's line of travel toward the front of the car. To correct this, cause the outside end of the axle to move back by shimming the axle from the forward side of the axle hole.
Wheel OUT-IN: Axle has toe-out. Action: Shim forward from back.

Condition observed: A wheel moves OUT when the car rolls forward and IN when the car rolls backward. This means that "the car and the wheel are trying to go in different directions." In this case the axle orientation dictates that the wheel's line of travel will intersect with the car's line of travel toward the back of the car. To correct this, cause the outside end of the axle to move forward by shimming the axle from the back side of the axle hole.

("IN-OUT" means that the wheel moves IN on the axle as the car goes forward, and OUT on the axle as the car goes backward.)

Shimming:

Before inserting shims crimp them along their long axis.

If drilled holes are used for the axles, place an additional shim in the outer 1/8" of the hole and bend it flat against the car body. Assure that ALL shim material stays in place as the axle is being replaced.

If drilled axle slots are used for the axles, the outer end of the axle cannot be shimmed up. Therefore, if the outer end needs to be shimmed up, shim the inner end of the axle down.

Clean up:

Now that the Car runs straight and the wheels don't move in or out on the axles, those small tabs of shim material need to be removed. Use a razor blade or sharp craft knife to trim them away flush with the Car body. Blow out any loose pieces.

Now, recheck the wheel alignment by repeating the alignment Trials 1 through 4 to assure that all is well.

Exceptions:

Complete alignment usually takes about an hour. It is a process of successive approximation, and it may require successively finer changes as it progresses. If the alignment process does not "converge" after a reasonable number of shimming steps, look for some of the following:

Wheels are not "true", e.g. conical or out-of-round.
There are irregularities in the table top.
An axle is not right (e.g. bent).
Irregularities in one or more axles.

If one of the wheels will not align, consider entirely replacing or reworking that wheel and axle.

[Fig 17. Alignment Woorsheet]

6. Practices to Avoid

Melting Lead.

Molten lead is hot! And it cools off very slowly. Spilled on clothing, it quickly burns through to skin. Splashed on skin, it will cause serious burns. Spilled on the floor of your kitchen, it will burn through the floor covering and char, and possibly ignite, the floor boards. It is nasty stuff!

If that isn't enough, check this out! Lead, itself, is a poison that can, over time, cause harm. Lead often has additives, such as arsenic. Heating the lead in an enclosed space, like a kitchen, produces potentially dangerous gases.

Here is my suggestion: Acquire the lead already in small sizes of 1/2 to 1 ounce (a slug of lead 3/8" x 1 1/4" weighs about an ounce). Another idea is to buy lead sheet (it is used in the roofing business as flashing around vent pipes, etc.) and cut it with tin ships into small pieces of about 3/4" x 1 1/4". Either way it can be shaped with a hammer to fit the cavities you cut in your Car.

If you must melt, assure that the location and ventilation is good. Wear protective clothing, Minimize the risk by casting enough for your entire pack. A mold for casting lead slugs can be made from two pieces of 2" x 1/4" angle iron. Clamp them together to form a "T". Drill two 1/4" holes and use bolts to hold the pieces together. At each corner of the "T", drill a 1/4" hole and use four three inch bolts with 2 nuts each to form legs. Clamp the pieces together at several places and drill down the joint (from the top center of the "T") with a 3/8" drill to a depth of about 1 1/2". Space the holes about 1/2 to 5/8" apart on centers. Two 24" pieces of angle iron can be used to cast 40 or more slugs in one pouring, enough for a whole den.

[Fig 18. Casting form]