According to Dr Jobe and other experts on the physics of these cars, total friction does not go up or down when the size of the instantaneous contact area is increased or decreased; the total friction stays contact. So there is no direct beneficial effect, contrary to intuition. The effect (if any) is indirect and secondary, from how it affects lubrication over time.*5 J's* wrote:We are not allowed to grooved axled in our Pack so I have no experience with grooved axles and graphite. I would say if grooves provide an advantage it would be quite small and the risk for messing up the surface is too great of a risk. I would not do it.Ynot wrote:Can I put a groove in the axle for less contact surface and to allow for graphite or is this no longer a good idea. I saw this in Meades book. I've also seen multiple grooves per axle somewhere online. Is this better or worse?
In league racing I use Krytox oil and groove these axles - but I can tell you from experience it's real easy to mess up a good axle, and once grooved you have to be REAL careful to not bend an axle. A slight unintentional bend and you will lose any benefit gained from the grooves. My two cents anyway...
If the groove has sharp, right-angled shoulders, those edges could scratch the soft plastic of the wheel bore and mess things up badly.
If the groove has broad gently-sloped shoulders, that means that some of the active touching axle surface has a different diameter than the rest, which could add a kind of internal canting that you don't want; it changes as the wheel migrates left and right across the axle.
The groove makes it hard to do an even job of polishing the axle after cutting the groove; the shoulders will get eroded more during polishing.
Grooving could also send the wheel inward where it rubs continuously against the car body, or outward where it rubs continuously against the nail head.
If grooving is (sometimes) beneficial, I guess it is from leaving a thin ring of unwiped surface on the inside of the wheel bore. Loose graphite flakes can hide there until accidentally redistributed by the car handlers between races, or redistributed by left/right wheel wanderings during a race. But excess loose graphite is not good in the early races; what you want is worked-in graphite smoothly covering all friction surfaces (the entire bore, and the bottom edge of the axle).
In the past, I've re-applied graphite just before check-in, by dabbing in graphite with a small watercolor paint brush and then spinning the wheels manually while holding the car upright, and then knocking off the excess. I'm now thinking that it would be better to hold the car upside down while doing that manual spinning, so that the bores are rubbing against the same side of the axle that will be facing towards the track and bore during racing.