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How to use a variable speed angle grinder

Updated: 22 October 2026

The first cut is a length of steel clamped to a bench in a UK garage. How to use a variable speed angle grinder starts before the dial. You unplug, you match the disc to the maximum speed marked on the tool, you keep the guard and the side handle on, and you stop if the switch will not kill the disc. This page is that sequence. It does not rank the nine listings in the [angle grinder with speed control comparison](/hub/tools/angle-grinder-with-speed-control). Products Compared used public UK guidance and the fault reports in those amazon.co.uk files on 21 October 2026. We did not run the tools.

The first cut is a length of steel clamped to a bench in a UK garage. How to use a variable speed angle grinder starts before the dial.

Our top picks

Bosch Professional Bosch GWS 9-115 S 230 V

Best overall

Bosch Professional Bosch GWS 9-115 S 230 V
8.6/10about £77.00
View offer
TEENO TEENO 1000 W 125 mm

Alternative

TEENO TEENO 1000 W 125 mm
5.4/10about £32.99
View offer
KATSU Tools KATSU 115 mm 750 W

Best value

KATSU Tools KATSU 115 mm 750 W
6.3/10about £24.99
View offer
On this page
  1. 1.Unplug and read the disc
  2. 2.Guard, handle, and the right wheel
  3. 3.Set the dial, then let it run up
  4. 4.When you put it down

Unplug and read the disc

Electrical Safety First’s domestic advice is to unplug the grinder before you change the wheel, before you press the spindle lock. Clamp the work, wear goggles, keep both hands on the tool, and point sparks away from anything that burns. Run a new disc for at least 30 seconds with nobody in line with it. The speed you care about is the maximum marked on the grinder, not the step you intend to use. FEPA says the machine must not run a wheel above the wheel’s own maximum. In this set that printed maximum is 11,000 rpm on the KATSU and 12,000 rpm on several 125 mm listings. The two Bosch amazon files do not print an rpm band, so you read the plate on the tool. If the listing never printed a voltage, do not assume a 13 A plug. That check is in the buying guide.

Guard, handle, and the right wheel

Bosch Professional’s UK proper-use notes say the guard stays on and is adjusted to sit between you and the wheel. A broken guard is replaced before use, not removed so a pad will fit. The side handle stays on. One UK review of the 110 V Bosch said the auxiliary handle was missing from a torn box. That is a delivery fault to stop for, not a reason to run the tool one-handed. FEPA says you do not grind with a cutting wheel, and you do not twist the tool in the cut. If you need to dress a weld flat, fit a grinding disc or a flap disc rated for the tool’s maximum, and keep the guard. DEWINNER and LiunxDromic list a wood saw blade. That line is not a method. TEENO’s pack line names two cutting discs, two grinding discs, a guard and a wrench. Check each disc’s rpm mark against the 12,000 rpm maximum on that listing.
Bosch Professional Bosch GWS 9-115 S 230 V

Testsieger

Bosch Professional Bosch GWS 9-115 S 230 V
8.6/10about £77.00
View offer

Set the dial, then let it run up

For a cutting disc in metal or stone, the Bosch GWS 9-115 S manual points to the top of the range. That is a guide for that model family, not a number the amazon raw files print, and not a lab result on the budget six-speed dials. KATSU says demanding work wants the higher speeds, because low speed cuts power. Set the dial before you start. Hold the tool with both hands, let a new disc run up away from the work, and bring it to the cut without twisting. A listing that prints 2,000–12,000 rpm has not promised that 2,000 rpm still cuts 3 mm steel. Paint, a wire cup or a wool pad is a different job.

When you put it down

Put the tool down when the switch will not stop the disc, when the tool starts itself, when the head is loose, or when a disc leaves the spindle. In the TEENO file, two of the six UK blocks say the switch did not stay off or the tool turned itself on. In the shared POSENPRO block, a switch stopped after about 45 seconds. In the TOPWAY file, the head came away from the housing. In the LiunxDromic file, the disc jumped off the axis on switch-off, and a spindle lock seized on the first change. Unplug, and stop. This page will not describe a repair. At work, mounting wheels for other people is trained work under HSE’s HSG17 and PUWER. A householder who has never changed a disc should get a competent person for that first fit. Also stop for a damaged cable, a damaged RCD, or a live site you are not equipped for.

Common questions

Do I unplug before the spindle lock?
Yes. Electrical Safety First says to unplug before the wheel comes off. The lock only lets you turn the nut once the tool cannot start. A lock that will not press, as in one LiunxDromic report on the first change, is a reason to stop. Do not hold the spindle with pliers while the plug is in.
Can I take the guard off to polish?
No. Bosch’s proper-use guidance keeps the guard on and adjusted, and a broken guard is replaced before use. A pad that fits only with the guard off is the wrong pad. Sparks and a shed wire still leave on the open side, including on a low dial.
What rpm must the new disc show?
At least the maximum marked on the grinder, not the dial step you hope to use. Where this set prints a maximum, it is 11,000 rpm or 12,000 rpm. Both Bosch amazon files print none, so you use the plate on the tool. A disc rated below that maximum is not suitable for a quick cut.
Which way do I set the dial for a cutting disc?
At the top of the range for metal or stone, which is the Bosch manual’s guide for the GWS 9-115 S and is labelled as that guide. KATSU says demanding work wants the higher speeds because low speed means lower power. The disc must still be rated for the tool maximum. Pads and wire cups are a different job.
What if the switch does not stop the disc?
Unplug at the plug, without putting a hand near the wheel. Do not keep cutting while you flick the switch. UK reviews here already describe a TEENO that would not stay off, a TEENO that started itself, and a POSENPRO switch dead after about 45 seconds. The tool stops there.
Is a wood blade in the kit a normal cutting disc?
No. DEWINNER and LiunxDromic bullets list a wood saw blade beside metal discs. A toothed blade is not a bonded cutting disc. Keep wood off this tool. Use a metal cutting or grinding disc only if its own rpm mark meets the grinder’s maximum.
Does a side handle have to stay on?
Yes. Both hands are the domestic advice, and the handle gives the second hand a place. If the handle is missing, as one 110 V Bosch reviewer reported, you do not start one-handed. TEENO’s pack line says one handle while a bullet mentions two, so you count what is actually in the box.

Related pages

Polishing with an angle grinder

Best angle grinder with speed control

Angle grinder with speed control

110 V or 230 V angle grinder for a UK socket or site

Variable speed angle grinder buying guide for the UK

Sources

Public UK sources from the research digest, used for this page in October 2026. Prices, stars and review counts are from the nine amazon.co.uk listings captured on 21 October 2026. HSE site-voltage guidance and PUWER apply at work. They are not a certificate for a domestic grinder. Restart protection and the 2,800–11,000 rpm band are Bosch manual facts, not amazon bullets.

  1. HSE, HSG17 Safety in the use of abrasive wheels (retrieved 21 October 2026)
  2. HSE, Electrical supplies for construction sites (retrieved 21 October 2026)
  3. BSI, BS EN IEC 62841-2-3:2021+A11:2021 (retrieved 21 October 2026)
  4. FEPA, EN 12413 bonded abrasives safety leaflet (retrieved 21 October 2026)
  5. Electrical Safety First, Angle grinders (retrieved 21 October 2026)
  6. GOV.UK, UKCA and CE marking in Great Britain (retrieved 21 October 2026)
  7. Bosch, GWS 9-115 S manual (retrieved 21 October 2026)
  8. amazon.co.uk listings for the nine ASINs (retrieved 21 October 2026)