I'm looking for a sander and as I browse through the various offerings I can see that most manufactures offer both a sheet sander and a random orbit sander. Aside from the shape of the sanding surface, are there any functional differences between the two? What scenarios does each type excel at?
One other consideration that the others didn't mention. Square sheets of sandpaper (Sheet sander) are cheaper than the hook/loop pads for orbital sanders. So if you go through a lot of sandpaper you might save some money with a sheet sander, assuming a job where either tool will work.– JohnFxJan 30, 2022 at 17:21
In addition to Rob's answer, the motion of both sanders is a bit different.
Sheet sanders tend to move back and forth in a straight line, with small variation side to side.
A random orbit sander has an eccentric cam mechanism that makes the sanding disc move in a circular but not round fashion. I'd best liken it to the old spir-o-graph toy- it's 'orbiting' around the central point, but it's not a simple circle. You get less noticeable scratches this way.
As to the difference in application.. sheet sanders excel at getting into corners and edges, but can cause grooves because the sheet only moves in one direction.
An RO sander is great for wide open spaces, where if you use a successively finer grit, you end up with a nice smooth surface. But it doesn't get into inside corners very well. My RO sander also has holes in the pad, which facilitates sanding dust removal with a shop vac. (I'm not sure if modern sheet sanders have a dust collection port, but none of mine do.)
My sheet sander has a lever that allows you to set it for either back and forth sanding, presumably parallel with the grain, or orbital for more aggressive sanding. As you might expect, the back and forth (oscillating) motion produces a surface ready for finish. The orbital motion (not to be confused with random orbital) produces, upon close inspection, many tiny, but visible circular scratches which have to sanded out, either by hand (quite easily) or by setting the sander to oscillate.– Ast PaceJun 4, 2015 at 1:24
@ASTPace - nice! My sheet sanders are all old enough to be called 'vintage', so I'm a bit out of the loop there. Jun 4, 2015 at 14:09
Modern sheet sanders (at least mine) does have a dust port. You just mount the paper, and press it down on the tray that came with the sander and it will punch holes in the right places.– JohnFxJan 30, 2022 at 17:19
Sheet sanders usually take 1/4 or 1/2 sheet of sandpaper held in place with 2 clamps, though some can also take hook-and-loop paper. As Graphus pointed out, most models today have dust collection. Many models come with a hole punch in order to perforate standard sheets of sandpaper with the appropriate pattern of dust collection holes, but for some you must buy the hole punch separately. Sheet sanders themselves are relatively inexpensive and the paper is also very inexpensive on models which use normal sandpaper, compared to sanders that use hook-and-loop sanding media.
Random orbit sanders typically use round sanding disks held in place with hook-and-loop (velcro), and have holes in the both the sanding media and the sander's pad for dust collection. A random orbit sander costs the same or more than a sheet sander with more or less the same specs, and the sanding discs cost more than normal sandpaper. You have to be somewhat careful when buying media, because there are 2 "standard" but basically incompatible hole patterns, 5-hole and 8-hole. Although 5-hole sanders are not as commonly sold today, you can still find 5-hole sanding discs. Festool has its own proprietary hole patterns, called Jetstream and Multi-Jetstream. Mirka has its own line of Abranet sanding mesh which, as mesh with many small holes already, doesn't require any particular hole pattern and can attach to any hook-and-loop sander.
Dust collection not only reduces the amount of dust in the air and all over the place, but it also allows the sandpaper to work more efficiently by preventing a layer of wood dust from building up between the sanding media and the workpiece. The resulting airflow across the sanding media's surface also helps against excessive heat buildup, which will melt and destroy the plastic hooks (for the hook-and-loop fastening) on the bottom of the sander's pad.
As TXTurner and LeeG pointed out, the two types of sanders also produce different scratch patterns. Sheet sanders can reach into corners which a random orbit sander cannot do with its circular pad.
Sheet sanders use a linear or orbital (circular) motion, and some can be switched between the two. Random orbit sanders use an eccentric circular motion which is intended to create a less visible scratch pattern, but some higher-end models can also be switched into a gear-driven orbital mode for more aggressive sanding.
I've found that the universal hole patterns don't perform as well for dust collection on my 8-hole ROS.– DoresoomJun 3, 2015 at 21:07
Good answer but not sure about this bit "Sheet sanders ... usually don't have dust collection except in high-end premium models" This may be different in different markets but in the UK even budget models can (usually?) have dust collection. Some even also provide a two-part perforation accessory to make up your own paper with the necessary hole pattern to allow it.– GraphusJun 4, 2015 at 6:03
@Graphus hey, you're right; they've made some nice improvements since I last looked at them. Thanks for the correction; I've updated my answer.– rob ♦Jun 4, 2015 at 13:13
Random orbit sanders rotate and oscillate to give scratch pattern that is harder for the eye to discern. Sheet sanders typically just have some random oscillation. RO sanders can be more aggressive.
Both sanders can support dust collection (see Festool), but typically sheet sanders do not have provisions for dust collection, and RO sanders almost always do.
The larger sheet sander (1/2 sheet) are great for finishing a large, flat surface. Sheet sanders also work well for sanding into corners, something you cannot do with a round RO sander.