Polisher type
Free-spinning dual-action polishers: how they move and stall
On a free-spinning random orbital polisher the plate orbits and rotates freely, so rotation can slow or stop under friction. Throws, plates and limits.
Also listed as random orbital polisher, free-spinning DA, RO polisher
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Short answer
On a free-spinning dual-action (random orbital) polisher the backing plate orbits and is free to rotate. RUPES explains that if friction stops the rotation, the motion simply becomes orbital, which is why these machines can stop spinning on curves or under pressure without a fault. They still remove paint: Milwaukee warns that too much pressure, the wrong angle or improper motion may cause swirl marks or burning.
Key facts
- Motion
- The plate orbits and is free to rotate; if friction stops rotation, the motion becomes purely orbital[1]RUPES says rotation speed is independent of the orbit count.
- Orbit throw
- Model-specific: 12 mm (RUPES HLR75), 15 mm (RUPES LHR15ES, Milwaukee 2684-20, FLEX XFE 15), 21 mm (Milwaukee 2685-20)[2][1][3][4][5]
- Backing plate / pad size
- 125 mm / 5 in (RUPES LHR15ES, Milwaukee 2684-20); 6 in (Milwaukee 2685-20); 75 mm (RUPES HLR75)[1][3][5][2]
- Speed range
- RUPES LHR15ES 2,000-5,000 rpm; Milwaukee 2684-20 2,650-5,100 rpm; 2685-20 2,400-4,500 rpm[1][3][5]Each maker's own figure.
- Example models
- RUPES BigFoot LHR15ES; Milwaukee M18 FUEL 2684-20 and 2685-20; FLEX XFE 15 150 18-EC[1][3][5][4]
- Suited to
- Auto Care HQ says dual-action machines are considered safer for beginners than rotaries[6]An explainer's view, not a measurement. It does not make any polisher safe on every paint.
- Cautions
- Too much pressure, the wrong angle or improper motion may cause swirl marks or burning[7]Milwaukee's polisher manual warning, written for its random orbital polishers.
Watch out for
- Stalling is how the motion works. RUPES says that when friction stops the plate rotating, the motion becomes orbital. On curves or with heavy pressure, expect rotation to slow.
- It can still burn paint. Milwaukee's manual warns of swirl marks or burning from too much pressure, the wrong angle or improper motion.
- Plate and pad rules differ by maker. Milwaukee says the backing plate should match the pad diameter on its 2684-20/2685-20, while RUPES pairs its 125 mm LHR15ES plate with 130-150 mm foam pads. Follow your tool's maker.
What fits
Product details below are the seller's own description unless a source is shown. Pick the variant named for each item.
15 mm corded random orbital polisher
FLEX FC3321-Z 120 V brushless random orbital polisher (15 mm)Choose the FC3321-Z listing that includes the 5 in (FT333) and 6 in (FT334) backing plates.
Sold on Amazon: check 'Ships from' and 'Sold by' on the Amazon offer before you buy, and look for a North American certification mark on the tool's nameplate.
Check price on Amazon Opens amazon.com15 mm cordless random orbital polisher (FLEX 24V)
FLEX FX3321-Z 24V brushless cordless random orbital polisher, 15 mm (tool only)Choose the FX3321-Z tool-only listing; battery and charger are sold separately.
It runs on FLEX 24V packs, so pair it with genuine FLEX batteries and a FLEX charger. As with any Amazon pick, check 'Ships from' and 'Sold by' on the Amazon offer before you buy.
Check price on Amazon Opens amazon.com
Compare with forced-rotation and rotary machines, or by throw: 15 mm long-throw and 21 mm long-throw.
Questions
Why does my dual-action polisher stop spinning?
On a free-spinning machine the plate is free to rotate, and RUPES says that if friction stops the rotation the motion simply becomes orbital. Curves, pressure and pad contact all add friction.[1]
Can a dual-action polisher burn through paint?
Yes. Milwaukee's polisher manual warns that too much pressure, the wrong angle or improper motion may cause swirl marks or burning.[7]