DMSBD Tech Tips

Construction Tips for a First-Time Car Builder
Article 2:
Spindle Polishing - by Ian Carsten

The following is a quotation from the AASBD’s “Lets Go Racing” stock car assembly plans/rules. “You may polish the axle spindles with very fine grit sandpaper.” Now you know it is legal to do so, but the plans never tell you why or what benefits you’ll realize. Here is why you should polish your spindles.          

Many racers feel that the wheel bearings need to be free to move somewhat on the axles to reduce bearing binding. Most of this movement is a back and forth sliding motion lengthwise along the spindle. This can happen since the bearing recesses in the two halves of the wheel are almost never in perfect alignment as assembled. This causes the two bearings to be on slightly different axes. So when the wheel rotates, the two bearings fight each other. Also, some bearing assemblies wobble as they roll due to manufacturing errors.

What happens is, the inner and outer portions of one or both of the two steel rings that form the bearing’s raceways are not concentric to each other as manufactured. Consequently, as the bearing turns, the inner ring wobbles forcefully relative to the outer ring. The outer ring is press fit very firmly into the wheel hub, so it can’t move relative to the wheel. This is the reason that you will see some wheels wobble as they rotate. However, there is some clearance between the hole in the inner ring and the spindle, which is very slightly smaller. So when such a wheel rolls under a weight load, one or both of the inner rings is forced to squirm back and forth along the spindle. Also, there could be some small amount of rotation of the inner ring on the spindle as well. Bearing engineers refer to this as bearing creep.

You can easily simulate this to hear the effects of the two bearing assemblies pushing against each other. Place a z-glass wheel on a 1/2-inch diameter steel rod, hold it horizontally, and give the wheel a good spin. Note what it sounds like. Now, with the wheel still spinning, hold the bar with one hand on each side of the wheel. Press your thumbs down against the bar and slide your thumbs inward until they rest against the non-rotating inner rings of the bearings. Now, press your nails inward firmly against the inner rings. The bearings get pretty noisy while you apply pressure. That is what happens as 1/4 of your car’s weight bears down on the wheel if the bearings are not aligned in the same wheel or if one or more of the bearing assemblies wobbles as it turns.

Such wheels with misaligned or wobbly bearings generate increased rolling resistance, and that limits the speed of your car. By polishing and lubricating your spindles, you can reduce rolling resistance as much as possible, and that can result in very slightly greater speed.

To reduce rolling resistance, racers polish the 1/2-inch diameter spindles with very fine emery paper; usually beginning with 600 followed by successively finer grades, such as, 800, 1200, 1500, and 2000. And, they often follow this up with aluminum polish, which contain an extremely fine polishing abrasive. They then clean off all the residue, and oil or grease the spindles. This allows the bearings to move about slightly on the spindles with as little resistance as possible if the bearings are wobbly or are not perfectly aligned in the same wheel.

There are different opinions on spindle polishing. Here are some things to consider before you begin. Raw spindles measure approximately 0.497-inch diameter. Spindle polishing necessarily removes some material, but very little need come off. A very finely polished spindle may still measure 0.496-inch diameter. A very efficient way to polish a spindle would be to chuck the square stock in a 4-jaw chuck on a sufficiently large engine lathe and then polish it by letting the lathe supply the rotation. However, since most of us don’t have access to industrial-size machine tools, here is a recipe that works quite well.

Although it is possible to polish spindles on axles that are mounted on the floorboard, it is more convenient to do so before mounting them. You will need a table or workbench that you can c-clamp the axle to while you work on the spindles as well as two c-clamps large enough to clamp the axles to the table. You must have abrasive cloth or paper of the wet-or-dry type in grades 600, 800, 1200, 2000. You can most easily obtain suitable abrasive paper at paint supply houses that cater to auto body paint/repair shops. You may also want a jar of aluminum polish to finish the job. Mother’s Aluminum Polish, available in the automotive department of any K-Mart or similar store works well. Also needed are some soft rags, which can be cut into strips and discarded afterwards. And, you will want a can of oil that lets you dispense a few drops at a time.

Place the axle so that the entire length of one spindle hangs well off of the tabletop. You will want to position the first c-clamp to hold the square stock firmly down against the table. The clamp must not interfere with the spindle. Now clamp the other end of the square stock to the table. This job will get your hands dirty and oily, so wear an apron or some old clothes you don’t mind getting greasy. Also, you should keep some disposable rags handy for wiping off your hands as well as the residue from the spindle that the polishing operation will generate.

Now you are ready to start polishing. If you could see the lathe-turned surface of the spindles sufficiently magnified, you would notice the surface is composed of a series of hills and valleys left by the point of the tool bit as it removed metal. You first want to start with 600 paper to quickly remove and level the tops of the “hills”, and that must be done evenly all the way around the spindle to keep it circular. You start by cutting a strip about as wide as the spindle is long. Put a couple of drops of oil on the spindle and wrap the paper around the top of the spindle. The oil helps flush away small particles of metal as they are abraded from the surface of the spindle, keeping the abrasive free to keep cutting. It also helps produce a better surface finish than water, which is used when using this material for auto body painting.

You pull one end of the paper down while allowing the other end to move up, keeping a modest tension on the paper. You simply move your hands up and down just as if you were polishing shoes with a polishing cloth.

You should devise a way of keeping track of how much time or how many back and forth strokes you have made. Counting 1,2,3… with each down stroke of your right hand works well. You should try about 200 strokes. Then stop, clean off the spindle, oil it again and give it another 200 strokes and clean the spindle again.

Now loosen the clamps and rotate the axle 90 degrees clockwise. Repeat the polishing steps in the above paragraph. Repeat this until all four sides have received 400 stroke cycles with 600 paper. Inspect the spindle closely. You should have removed most of the high ridges and the remaining tool marks left if the spindle should look much less noticeable. If you are not satisfied, you can give each side of the spindle another 200 strokes until it looks like it is starting to become smooth.

Then you repeat the process with 800 grade. Bear in mind that each successively finer grade of paper will remove metal at a slower rate than the previous grade, and will probably require correspondingly more strokes to smooth the spindle to the next level of fineness. After you have finished with the finest grade of paper, it is time to polish the spindles with the aluminum polish. You simply smear a little dab of the aluminum polish on the spindle and use a strip of rag in pretty much the same manner that you used the abrasive paper. The difference is, you don’t use any oil, and since the abrasive is much finer and softer, you can, and should bear down with considerably more force to obtain the proper results.

You’ll notice that the aluminum polish goes on as a fine white paste, but after you have worked it against the spindle for a bit it leaves a jet black residue on the cloth. You will have to reapply the paste often and try to keep using a fresh part of the rag because when it gets clogged with the black residue, it won’t polish anymore. Every little while, you should stop and buff the spindle with a clean rag with no paste on it. It shouldn’t take too long before it shines almost like a mirror. You don’t have to worry about taking off too much stock with the aluminum polish because its action is so gentle, it would take an extremely great amount of polishing to produce a measurable change the diameter of your spindle.

When you are satisfied with the degree of polish on the spindle, you can turn it around and work on the one on the other end. It will probably take you two to three hours to finish one spindle. Therefore, you will probably want to polish the next spindle after you’ve taken a break or at another time. It is rather labor intensive, but unless you have access to a lathe, this is probably the way it will have to be done. Your fastest competitors are already doing this, so if you don’t do it as well, you’ll be racing at a slight disadvantage.

This concludes Article 2: Spindle Polishing.

Proceed to Article 3: Preparing Rear Axle & Front Kingpin for Triangulation

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