As long as the rpms and the orbital movement is the same, the same throw, the movement between the pad and the paint will be the same no matter how efficiently those rpms are delivered. The reason we like to keep the rpms up on our bicycles is that it takes less power per revolution to create a given amount of power output at higher rpms than lower. So, the stress on our muscles has more peaks but the peaks are lower and therefore easier to maintain. This principle is nice to know but I don't see a correlation between bicycles and polishers as far as this conversation is concerned, unless you're pointing out that a larger throw machine is like using a higher gear, which will require more peak power per rpm. I would agree with that but again, no matter how efficiently or inefficiently those rpms are delivered, as long as they are delivered, the outcome at the point of contact should be the same.
Yes, I agree that if the tool is generating the same orbits per minute under load (and a similar rotational rate, although 70% or more of the movement comes from the orbital action at the edge and far more near the center) then the results are going to be similar. The pad doesn't really care what is pushing it across the paint, but this could be said for any style of polisher.
I understand your confusion in my point because I apparently deleted a paragraph before hitting reply. The point is that two tools will not deliver the same movement across the paint because of the differences in efficiency. The point about the bicycle is to drive home the point that it isn't necessarily the power the tool delivers, but rather how efficiently it delivers the movement to the paint. Random orbital action requires less power to drive the pad because of the increase in leverage (driving a small orbit vs. a large rotation). It takes surprisingly little power to move a pad in a 21mm orbit vs. rotate an 8 inch pad, even if the results are similar.
The pattern of a dual action machine does not repeat from revolution to revolution because orbits per revolution are not a whole number. You can see the pattern shift if you turn the machine upside down and watch the pad.
You have to forgive my inner geek, but these are the discussions that I absolutely love to engage in. I take it we are similar peas from the same pod.
A forced rotation polisher will produce the same pattern as a function of its gear drive. The pad will slither in an out like a snake slithering in a circle. It will always produce the same distance between the outer peaks and the shape of the inner arch of the movement will always be the same.
It is an assumption you make that the number of orbits per rotation are not always based on a whole number. This is completely dependent on gear ratio inside the tool. Some tools will produce an even number of orbits per rotation while others may not - it is dependent on the design of the tool. If it is not a whole number, then the same, always repeating pattern is still scribed (same distance between peaks, same length between peaks, same shape of the arches between peaks), but the pattern will appear to rotate slowly. However the pattern itself remains identical, and the rotation of that pattern remains constant, so it is still creating a repeating, non-random movement.
That's why a dual action machine can create a swirl free, pattern free finish
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I'm not sure I would agree with that statement. The reason why a gear driven tool is far better at producing a surface that is free of visible scratches, compared to the linear motion of a rotary, is because the scratches imparted to the surface tend to cross hatch in an infinite number of angles as the tool is moved across the paint.
On a rotary tool, the motion is always the same, but the curvature of the angle becomes sharper as the center of the pad passes over (for anybody reading this, think of the curvature of the earth, which appears flat because of its large diameter vs. the curvature of a dime) and then immediately shifts to the opposite direction as the center passes over a spot, and continues to open up as the pad passes over the paint. This is why holding the pad flat (on a rotary) helps to eliminate visible scratches.
On a gear drive tool, the repeating U-shaped pattern becomes far more pronounced as the pad passes over a spot, then opens back up past the center. This helps to cross hatch and disperse the scratches, resulting in a pattern that our eyes struggle to see.
While some rotation of the pattern would help, most gear driven tools orbit on a whole number, and rely on the movement of the pad across the paint for the cross hatching to occur. Thank you for the thought provoking discussion.
