I know what Marco meant, as I've had off-line discussions and debates to quite a degree.
Marco believes that by freeing up backing plate rotation, there's a chance that the backing plate will spin unabated, ramping up rotation to an un-stabilizing and potentially damaging or dangerous level. The damage or danger occurs if the machine is throttled up prior to placing it in contact with the paint surface.
Although nobody I've ever met starts the machine prior to setting against the paint, this was apparently a concern (for other parts of the world).
As to the percentage shift...
I believe that Marco is trying to say that IF the backing plate were allowed to ramp up its rotation, the rotational ACTION delivered to the paint surface would be DOMINANT over the orbiting action, meaning the rotation would have a larger EFFECT on the paint as compared to the orbital motion. This is an understandable assumption, but one that I believe to be incorrect.
Again, my disagreement is based upon what I understand Marco to mean.
Why do I disagree? Here's why:
Imagine setting a random orbital machine on a table, backside down (this means that the backing plate's face would be visible because it would be facing upward). Next, place a level atop the backing plate, and adjust the machine so that the backing plate is set to perfectly horizontal. Lock the machine down so that it remains level, even when running.
IF our machine utilized "perfect" or "drag-free" sealed bearings (a super-low friction bearing that has very low or NO internal resistance), and such a bearing was used to support the backing plate mounting pad, then in theory we could spin the backing plate with a push of the hand, and it would continue to rotate for a very long time. For this discussion, let's identify such a bearing as a high quality bearing.
If my reasoning is correct... until a lot of weight or pressure or force was placed atop the backing plate, the bearing would remain un-loaded. Only the weight of the backing plate, internal friction (and I suppose gravity) would slow rotation of the plate.
Now things get interesting.
If you turn on the machine, you might expect to see the backing plate immediately start to rotate. The fact is, a high quality bearing (as we've defined it) will remain un-loaded or drag-free, just as it was with the machine turned off. So... rather than rotate, the plate would remain still or nearly still, at least until the minute amount of friction present between the balls or needles inside the sealed bearing touch the internal race of the bearing (the race is essentially the "track" that the bearings ride in under a light load, or on under a heavy load). Keep in mind that the bearing's lubricating fluid can place force against the bearing, effectively "driving" or pushing against the bearings.
Wow, tough to write that part (probably not very clear).
Basically, the backing plate is not going to rotate all that much, even though you might have expected it to.
NOW, what if you unlocked the still-running machine from the table, held it in your hands, and started to violently tilt and shake the machine? How would these motions affect backing plate rotation?
Well... the backing plate's mass would place a load on the bearing because as you tilted and shook the machine in all sorts of directions, the backing plate's momentum would fight against your sudden and rapid directional changes (the backing plate would attempt to continue on the path it was traveling, but its mounting stud would guide it in the direction the machine was traveling).
Due to the loading of the bearing, the backing plate would start to spin! If you then stopped the machine and installed a foam buffing pad onto the backing plate, and then re-started the machine again (and resumed your violent tilting and shaking of the machine), you would see an increase in rotation because the added weight and leveraging of the pad would increase the load placed against the bearing.
What do you suppose would happen if you decided to place the still-running machine against a painted panel? Would the backing plate and pad stall, or start to rotate?
It depends. If the pad was placed in LIGHT contact with the panel... AND there was enough drag created by the pad as it contacted the panel, then rotation would slow. As long as the bearing wasn't loaded to a higher degree, internal bearing friction would remain very low (so there would be very little interaction or contact between the internal bearing, and bearing race). We still have to realize that there's some fluid dynamics present, so the bearing's lubricating fluid could affect rotation (increasing it).
What if you placed un excessive amount of pressure against the machine in hopes of squashing the pad and loading the bearing?
At some point, backing plate rotation would stall. But, if you continued to add pressure AND the machine's motor did not bog, THEN you would see the backing plate ramp up its speed, at least until the bearing's internal friction became too high (at which point the bearing would become inefficient, and would slow or fail).
Where does this lead? No seriously.. I'm lost now.
Oh yeah!
If the goal was to scrub excessive backing plate rotation during free-spin in a free-air situation, I doubt the premise was a good one. I think the goal was to scrub backing rotation while the plate was under load, during use. After all, it is a fact that when the LHR 21ES is used at high speed, it can become unstable.. If the machine is tilted, or the pad encounters some sort of bulge or flared section of a panel, the machine's large offset can cause the pad to grab and steer the machine onto its side. Although this instability is not a big or notable issue when using thin or pliable pads, it certainly becomes an issue when using a tall or inflexible pad (such as the Rupes blue pad, or a closed cell dense foam cutting pad).
Oh my gosh, it's late and I'm punchy. I hope at least some of this makes sense.
Good luck deciphering it all!
