Orbital sander technique
An orbital sander rewards patience and punishes force. The whole craft is a ladder of grits climbed one rung at a time, a hand that moves steadily and presses hardly at all — and dust control taken as seriously as the finish.
The guidance below is workshop practice, labelled as such; the dust-control section is the exception, where every fact carries a reference to the Health and Safety Executive's wood dust guidance and resolves to the ledger at the foot of the page. Where this article and your machine's manual disagree, the manual wins.
§1 The ladderThe grit ladder, one rung at a time
Sanding is a sequence of scratch patterns, each grit erasing the coarser scratches of the one before and leaving finer scratches of its own. This site's tools work along the ladder40 · 60 · 80 · 120 · 150 · 180 · 240 · 320 — a workshop rule of thumb, the same one theSanding Disc Estimator publishes as its constants, not a standard. Two habits make any ladder work:
- Start as fine as the surface allows. The starting grit answers to the surface in front of you — sawn or weathered stock needs a coarse start, planed or pre-sanded stock can begin much further up. Starting coarser than the surface needs digs scratches you then spend three grits removing.
- Climb rung by rung. Skipping a rung leaves the previous grit's scratches at the bottom of the new grit's pattern, invisible until a finish makes them permanent. Each grit's job is only to remove the scratches of the one before; that job done, move on — polishing away at one grit flattens the abrasive, burnishes the wood and gains nothing.
- Stop where the finish wants. There is a point beyond which further grits close the surface against the finish you plan to apply. The estimator's own targets stop at 150 for painted work, 180 for a standard clear finish and 240 for fine work — rules of thumb again, adjustable in the tool.
How many discs a job needs at each rung is arithmetic, not intuition — theSanding Disc Estimator plans the sequence for your surface and finish and counts the discs, spares included and labelled.
§2 The handMovement and pressure
A random orbital sander is designed to do its cutting under little more than the weight of the machine and a guiding hand. Pressing harder does not cut faster: it slows the pad's orbit, turns random scratching into deep looping scratches, heats the disc so it clogs, and wears the abrasive in patches. If the machine is not cutting fast enough, the answer is a coarser grit or a fresh disc — never more force.
- Keep the pad flat on the work; tilting onto an edge digs a gouge in one pass.
- Move in slow, steady, overlapping passes, letting each pass lap well over the last, and cover the surface in an even pattern rather than orbiting your attention around the spot that looks worst.
- Racing the machine across the surface leaves it no time to erase the previous grit's scratches; a slow, deliberate rate of travel is the single easiest upgrade to most people's sanding.
- Start the sander on the work (or lower it running with care) and lift it before you stop it, so a spinning-down pad never sits parked on the surface.
- Between grits, vacuum the surface or wipe it clean — grit carried forward scratches below the new grit's pattern.
§3 SwirlsWhere swirl marks come from
The little pigtail swirls that appear under stain or lacquer have a short list of causes, and all of them are avoidable: skipped rungs on the ladder; pressing hard enough to stall the random action; tilting the pad; dust or a shed abrasive grain trapped between disc and work; a worn disc cutting unevenly; and moving the machine too fast for the grit to finish its work. The defence is the routine above plus one habit at the end: inspect the surface in low, raking light — a lamp laid nearly parallel to the work shows every swirl and missed patch before the finish does, while there is still time to drop back a grit and erase them.
§4 DustDust control — the HSE-sourced part
Fine sanding dust is the most dangerous dust a small workshop makes, and an orbital sander makes little else. This section is not workshop folklore: each fact below is the Health and Safety Executive's published guidance on wood dust.
- Wood dust can cause serious health problems, including asthma, and hardwood dust can cause cancer, particularly of the nose.1
- Sanding is a very dusty job that may need additional protection: a suitable face mask as well as dust extraction.1
- Never sweep up wood dust and never clear it with compressed air — both simply put the finest dust back into the air you breathe.1
- Clean up with an industrial vacuum cleaner of at least dust Class M.1
In practice that means the sander runs connected to extraction through its dust port, a suitable mask goes on before the trigger is pressed, and the machine's own perforated pad and hood do their work with a hose attached rather than a clip-on bag alone. The estimator's page carries the fuller HSE-sourced dust panel, including exposure limits and extraction examination requirements, alongside its disc arithmetic.
§5 RoutineThe routine, in one list
- Read the surface and choose the starting grit it needs — no coarser.
- Connect extraction, put the mask on, and start on the work.
- Slow overlapping passes, flat pad, the machine's weight only.
- Finish each grit everywhere before moving one rung up; vacuum between rungs.
- Check in raking light before calling any grit done.
- Clean up with the Class M vacuum — never the brush, never the airline.1