# Quantitatively evaluating ROSs

• posted on December 24, 2004, 4:46 am
After reading several articles with their own subjective evaluation of ROSs, I decided to apply a simple numeric test to compare two of them and I was surprised by what I found. I hope you find this interesting and useful to decide your next ROS purchase.
The fairly straightforward logic goes like this:
1. Unlike disk sanders, each grit particle on an ROS moves in a more or less circular orbit, and ALL of them move in the same orbit (as long as the pad is not spinning wildly)
2. Call the orbit diameter "D" and the OPM (orbits per minute) "R". Simple math tells you that each particle travels a distance of pi*D inches per orbit, and pi*D*R inches per minute, or pi*D*R/12 feet per minute.
3. To compare, say, the Ridgid R2610 with the PC 97366 and with a belt sander, consider this: - the R2610 has R=1/4 and R (max) = 10000 in aggressive mode. This gives the particles a speed of 655 feet/min - The PC97366 has R=3/16 and R(max) of 6000, giving it just 295 feet/min.
Incidentally, the amperage on both is about the same too. Startled? I sure was.
-Ram
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• posted on December 24, 2004, 5:45 am

But what do the numbers tell? Do they factor in the dust collection ability and its effect on finish? Orbits under a given pressure? Does a longer stroke = better finish or just faster cutting? Factor in weight and comfort in the hand as that becomes very important when sanding a lot of surface. Is the ROS with the highest feet/min the best?
I think some more testing is needed to show a correlation between your numbers and actual results in various situations.
As for the amperage, no, I'm not startled It is not the amps, but what you do with them that counts.
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• posted on December 24, 2004, 6:24 am
ramkumar snipped-for-privacy@hotmail.com wrote:

That is really interesting, I am going to be very interested to see where this thread is going to go.
The intial knee-jerk reaction is to ignore the amperage for now as Edwin stated, "it's what you do with the amperage." The R2610 doesn't have a gearbox, the PC doesn't have 'self powered' dust collection. I know both machines really well. I'm thinking if there is some way to test these machines in a scientific way. Repeatable. The mechanical impedance 'z' is important as well. I was given a Craftsman 1/2 sheet sander once. The body was so light, that the paper remained mostly stationary and the body vibrated like nuts. So even though the amperage and stroke distance were there, there sure as hell wasn't any sanding going on. So the non-moving mass is a very important item. (The PC has a completely different weight distribution than the Ridgid.) The bulk of the non moving mass is much further removed from the centre of the paper on the PC than the Ridgid. There is a lot of shit going on all at the same time.
Cool
Rob
And on the same principle as filing aluminum, you can skid over with a courser cut than a finer one, I have noticed that on acrylic, in some cases, a 180 grit paper cuts better (more aggressively) than a 120.
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• posted on December 24, 2004, 6:47 am

I suspect the brushes on my now-dead PC 333 have done me a pre-mature insult. I've discovered that the variable speed settings on the Bosch ROS that replaced it sure cause a (MUCH) bigger difference in sanding capacity than I ever suspected/expected possible (the slower the speed the more aggressive the surface material removal -- with the same grit paper). Surely the difference caused by 8-hole ventilation (Bosch) vs 5-hole (Poorly Capable) ventilation can't be suspect here!
Help me see what you're talking about :-/
--
Enjoy life and *do* well by it
-- it might well be the only chance you get :-)
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• posted on December 24, 2004, 2:21 pm

I believe that all goes down the tubes when you actually set the ROS sander down on the wood and begin sanding. Orbits decrease significantly when the sander is actually working.