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View Full Version : orbits/revolutions...the difference


rolled1
09-05-2009, 03:09 PM
As the title suggests and following on from the previous thread about the clark orbital sander.I'm currently looking for a rotary to go along with the DA but dont understand the difference between RPM and OPM..
some rotary's are quoted with speeds of 600-3000rpm and other's with 4000-7000 orbits per min. is there a way of converting orbits to revolutions?
sorry for the long thread but I alway's assumed a revolution and orbit were 1 and the same,perhaps someone can elaborate for me??

andy monty
09-05-2009, 04:26 PM
As the title suggests and following on from the previous thread about the clark orbital sander.I'm currently looking for a rotary to go along with the DA but dont understand the difference between RPM and OPM..
some rotary's are quoted with speeds of 600-3000rpm and other's with 4000-7000 orbits per min. is there a way of converting orbits to revolutions?
sorry for the long thread but I alway's assumed a revolution and orbit were 1 and the same,perhaps someone can elaborate for me??



this help?

http://i235.photobucket.com/albums/ee41/DaveKG/PadMotion.jpg

taken from Dave KG's guide

http://www.detailingworld.co.uk/forum/showthread.php?t=63859

rolled1
09-05-2009, 04:48 PM
I've already come across that diagram but does'nt really explain why some rotary's have figures in RPM and other fixed orbit rotary's(not DA's)quote figures in OPM which seem to be a lot higher

VIPER
09-05-2009, 05:56 PM
A rotary's figures should only ever be in RPM as the pad spins on a fixed axis.

The confusion comes when some DA/Random Orbit machines also quote their specs in RPM when strictly speaking they should quote in OPM (some do).

The actual revolutions per minute of a DA machine, when used for polishing, is determined by the pad, polish and mostly the pressure against the car. It will normally be anything from 1 rev per second upwards, (or 60+ RPM to keep the figures like for like) but it's largely irrelevant, it's the amount of times the plate is oscillating per minute that's doing the work, the pad only needs to be kept rotating relatively slowly.

rolled1
09-05-2009, 07:14 PM
A rotary's figures should only ever be in RPM as the pad spins on a fixed axis.

The confusion comes when some DA/Random Orbit machines also quote their specs in RPM when strictly speaking they should quote in OPM (some do).

The actual revolutions per minute of a DA machine, when used for polishing, is determined by the pad, polish and mostly the pressure against the car. It will normally be anything from 1 rev per second upwards, (or 60+ RPM to keep the figures like for like) but it's largely irrelevant, it's the amount of times the plate is oscillating per minute that's doing the work, the pad only needs to be kept rotating relatively slowly.

Yeah I understand but some sander/polisher's which might be suitable for car polishing? have their figure's quoted in OPM....see link
http://www.machinemart.co.uk/shop/product/details/cros2-contractor-150mm-random-orbital-sander

VIPER
10-05-2009, 12:24 AM
Yeah I understand but some sander/polisher's which might be suitable for car polishing? have their figure's quoted in OPM....see link
http://www.machinemart.co.uk/shop/product/details/cros2-contractor-150mm-random-orbital-sander

I can't really see what you're getting it in all honesty :confused: There are only 3 types of polisher you use on a car - a rotary is always measured in RPM and is purely a measurement of how fast the unloaded plate spins. A DA/Random orbit should be measured in OPM and is a measure of each one of those ellipses on the diagram above - it doesn't spin that fast on the car as it's not directly driven, it's induced spin by the random nature of the action (think of twirling a hula hoop around your waist) and it's possible with sufficient pressure to get it stop spinning completely. Then the 3rd is a combo of both (like a Flex) which has a random orbit but is directly driven by a gear from the motor rather than the 'induced' spin from a traditional DA.

If you're asking specifically about that Clarke DA machine then it's perfectly fine for car polishing as I've got one and a few other have as well. As long at it's got a speed range of approx 4k - 10k then on the lower of the various speeds it's fine. In fact I've used mine on the highest speed a few times, meaning an OPM of 7k but it still only spins the pad at about 2 revs per second.

rolled1
10-05-2009, 12:31 PM
Sorry but I did'nt realise that machine was a DA..I've already spent 150 on a G220 which I had have seen that previously! I'm looking for a rotary but getting a bit confused over all the figure's,just dont want to spend my hard earned cash on a machine and then find out that it's totally unsuitable for the job:thumb: