Sanding is the step everyone wants to skip and nobody can. It is also the step where the wrong tool costs you the most time, because a sander that removes material slowly turns a twenty minute job into an afternoon, and a sander that removes material too aggressively leaves swirl marks you then have to sand out by hand.
Two machines dominate the general purpose end of the category, and they work on genuinely different principles. Understanding that difference, plus how grit progression actually works, resolves most sanding frustration. The goal is not a smooth looking surface. It is a surface where every scratch left behind is finer than the finish can reveal.
How Random Orbit and Sheet Sanders Differ
A sheet sander, often called a finishing sander or palm sander, vibrates a flat pad in tiny orbits or straight back and forth. The pad is rectangular, it takes a piece cut from a standard sandpaper sheet, and it reaches into square corners. Because the motion repeats along a fixed path, the scratch pattern is regular, which means any scratch coarse enough to see will show up as an obvious repeating mark.
A random orbit sander spins a round pad while simultaneously moving it in an orbit, and the two motions are not synchronized. No point on the abrasive follows the same path twice in a row. That randomness is the entire point: it breaks up the scratch pattern so the surface reads as uniform rather than lined. Random orbit sanders also remove material considerably faster than sheet sanders at the same grit, because the combined rotation and orbit produce a longer effective cutting stroke.
The trade offs follow from the shapes. Round pads cannot reach into a corner, so a random orbit sander leaves the last inch of an inside corner untouched. Sheet sanders handle corners but work slowly and are prone to visible scratch patterns on anything that will take a clear finish. Cordless machines such as the Milwaukee 2684-20 M18 Fuel random orbital tool show how far the random orbit format has moved toward untethered work.
Grit Progression and Why Skipping Steps Backfires
Every abrasive grit leaves scratches sized to itself. The job of each successive grit is to remove the scratches left by the previous one and replace them with finer ones. That is the whole mechanism, and it explains why skipping grits wastes time rather than saving it.
If you jump from 80 grit straight to 180, the 180 paper has to remove deep 80 grit scratches using an abrasive that removes material slowly. You will spend longer at 180 than you would have spent doing 120 and then 180, and you will probably still leave some 80 grit scratches behind that appear the moment finish goes on. The conventional guidance is to move no more than one step at a time in the common sequence: 80, 100, 120, 150, 180, 220.
Where you start depends on the surface. Rough sawn or badly uneven stock starts at 60 or 80. Milled lumber that just needs cleanup starts at 100 or 120. Previously finished surfaces being refinished depend on how much coating has to come off. Where you stop depends on the finish. For paint, 120 to 150 is usually sufficient, since paint fills fine scratches. For clear finishes on hardwood, 180 to 220 is typical. Sanding beyond 220 before a water based or film finish can actually reduce adhesion by burnishing the surface closed.
Reaching What the Round Pad Cannot
Almost every real project has areas a random orbit sander cannot touch. Inside corners, narrow rails, carved profiles, and tight recesses all need something else, and reaching for a sheet sander is not always the answer.
An oscillating multi tool fitted with a triangular sanding pad handles inside corners well, because the point of the triangle gets fully into the corner and the oscillating motion is gentle enough to control. Tools like the Ryobi P343 oscillating tool take standard sanding pads and assorted grit sheets for exactly this purpose.
For contoured or very small areas, a rotary tool with sanding drums and flap wheels reaches into curves and interior cutouts that no flat pad can follow. Compact models such as the Dremel 8240 rotary tool cover this detail range. The practical workflow is to do the broad surfaces with the random orbit sander, then switch to the detail tools for the edges, and finally hand sand with a block along the grain at the final grit to unify the surface.
Dust, Pad Condition, and Common Mistakes
Dust extraction is not a comfort feature. Dust trapped between the abrasive and the workpiece acts as a lubricant that prevents cutting, and it also causes the paper to clog and glaze. A sander connected to a vacuum, or at least running with a functioning dust bag and clean pad holes, cuts noticeably faster and consumes less paper. Aligning the holes in the disc with the holes in the pad matters for the same reason.
Three habits cause most poor results. Pressing hard is the first: it slows the orbit, generates heat, and creates the swirl marks people blame on the machine. Let the tool’s weight do the work and move it slowly across the surface, roughly an inch per second. Second is running worn abrasive. Once a disc stops cutting, it burnishes rather than sands, and burnished wood takes finish unevenly. Third is neglecting the hook and loop pad. A worn pad lets discs shift and detach, and a pad with a damaged edge leaves marks. Pads are replaceable consumables on most machines.
When the sanding is finished and a painted or clear coated surface needs refining further, machine polishing takes over from sanding. That is a separate discipline with its own tools, and the polishers and buffers category covers it. For sanders themselves, the random orbit sanders category is the place to compare pad sizes and orbit specs.
Key Takeaways
- Random orbit sanders remove material faster and avoid repeating scratch patterns.
- Sheet sanders reach square corners but work slowly and can leave visible lines.
- Each grit exists to remove the previous grit’s scratches, so skip no more than one step.
- Stop around 120 to 150 for paint and 180 to 220 for clear finishes on hardwood.
- Dust extraction speeds cutting and extends abrasive life significantly.
- Pressing hard causes swirl marks; let the machine’s weight set the pressure.
- Use an oscillating tool or rotary tool for corners and contours the round pad misses.
Frequently Asked Questions
Why does my random orbit sander leave swirl marks?
Usually excessive downward pressure, which slows or stops the pad’s free rotation and turns the random pattern into a repeating one. Worn or clogged abrasive and skipped grits are the other two common causes. Reduce pressure, replace the disc once it stops cutting, and confirm you did not jump more than one grit step. Moving the sander too quickly across the surface can also contribute.
What orbit size should I look for?
Orbit diameter, sometimes listed as orbit or oscillation size, typically ranges from about 1/8 inch to 3/16 inch on 5 inch machines. A larger orbit removes material faster and leaves a slightly coarser finish at the same grit. A smaller orbit refines more finely and is better suited to final passes. For general work a mid range orbit handles both roles adequately.
Should I sand between coats of finish?
Usually yes, lightly, with fine abrasive around 220 to 320 depending on the product. The purpose is to knock down raised grain and dust nibs rather than to remove material. Use very light pressure, check the finish manufacturer’s guidance for recoat windows, and remove all dust before the next coat. Some finishes specify no sanding within a stated recoat window.
Can I use a random orbit sander to remove paint?
It works, though paint clogs abrasive quickly and heat can turn some coatings gummy. Use a coarse grit, keep the sander moving, and expect to change discs often. Abrasive designed to resist loading helps considerably. Be aware that paint in older buildings may contain lead, in which case sanding is the wrong approach entirely and testing should come first.
