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How to use a DeWalt impact driver

Updated: 22 October 2026

The first screw sinks, cams out, or stalls when the bit is loose or the mode is a guess. How to use a DeWalt impact driver starts with the battery off, a 6.35 mm impact bit seated, and the lowest mode the body actually has. The steps cover the DCF887, DCF850, DCF840, and DCF870. Which body to buy is the [buying guide](/hub/tools/de-walt-cordless-impact-driver/sub/de-walt-cordless-impact-driver-buying-guide). Prices stay on the [DeWalt cordless impact driver comparison](/hub/tools/de-walt-cordless-impact-driver). Listings and manuals were read for 20 October 2026. This is not a lab test. A qualifying purchase can earn a commission at no extra cost to you.

The first screw sinks, cams out, or stalls when the bit is loose or the mode is a guess.

Our top picks

DeWalt DeWalt DCF887N

Best overall

DeWalt DeWalt DCF887N
9.2/10about £59.95
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DeWalt DeWalt DCF850N

Best value

DeWalt DeWalt DCF850N
8.0/10about £98.43
View offer
DeWalt DeWalt DCF840N

Alternative

DeWalt DeWalt DCF840N
6.1/10about £78.00
View offer
On this page
  1. 1.Fit the bit before the battery goes back on
  2. 2.What the modes actually do
  3. 3.Drive it in a straight line and stop
  4. 4.When it is behaving, and when to stop using it

Fit the bit before the battery goes back on

Lock the direction switch in the centre, or take the battery off, before you change a bit. These drivers take a 6.35 mm hex shank. Round drill bits do not fit. One DCF887 buyer returned the tool for that reason and said the driver itself was fine. Use impact-rated bits. A DIYnot thread about a weak DCF887 turned out to be a slipping holder, and the same holder slipped in a combi as well. On the DCF840, push a 6.35 mm hex bit in until it locks. Pull the collar away from the tool to release it. Do not pull the collar to insert the bit. The DCF850 and DCF870 use a drop-and-load change, and the battery-off rule still applies. If the bit walks before the screw moves, reseat it.

What the modes actually do

The DCF887 manual lists three bands: 0–1000, 0–2800, and 0–3250 rpm, up to 3800 impacts per minute. Precision Drive pauses as the head seats, then impacts slowly. If the fixing will not move, select mode 2. Reviewers say mode 1 is too soft and mode 2 is too fierce, so many feather the trigger on mode 2. The DCF850 has the same three modes, and mode 1 draws the same complaint. The DCF840 has no dial: 0–3200 rpm and 0–4200 ipm, so the trigger is the control. On the DCF870, reviewers call the first speed very quiet. The data plate is still 56 Nm.
DeWalt DeWalt DCF887N

Testsieger

DeWalt DeWalt DCF887N
9.2/10about £59.95
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Drive it in a straight line and stop

Keep your forearm in line with the screw. Cam-out comes from a worn bit, the wrong recess, or the tool leaning off the axis. Mode 3 will countersink a head you meant to leave flush. Ease off as the head meets the timber. For a run of boards, pilots and the flush stop are on the decking page. About 205 Nm on the DCF887 and DCF850, and 192 Nm on the DCF840, are maximum figures, not the torque of every screw. Specified bolts still want a torque wrench. A fixed electrical installation stays with someone qualified to certify it. Declared sound pressure runs from 88 dB(A) to 96 dB(A). Those are emission figures. At home, ear protection is still the practical response.

When it is behaving, and when to stop using it

A pause as the head seats, on mode 1, is Precision Drive. A tool that reverses itself is a different thing. One DCF840 review describes the driver spinning the wrong way, then the correct way, still unrepaired. Separate DCF850 reviews describe a cut-out and a sticky direction switch. Those are single UK reports, and mode 2 does not cure them. Stop and go back to the seller. The Consumer Rights Act 2015 lets you reject faulty goods, generally within 30 days. Do not open the gearbox. As a rule of thumb, time to the 2.5 m/s² action value is under ten minutes at the DCF850's 18.5 m/s². That is not a site survey and not medical advice. A clutch, rather than a lighter mode, is on the versus page.

Common questions

How do I change the bit?
Take the battery off or lock the direction switch in the centre. Push a 6.35 mm impact-rated hex bit in until it locks. On the DCF840 you pull the collar away from the tool to release it, and you do not pull the collar to insert the bit. The DCF850 and DCF870 use a drop-and-load holder. Round bits do not fit. If the screw cams out immediately, reseat the bit before you blame the mode.
What is Precision Drive for?
On the three-speed bodies it is the light mode that drives like a screwdriver, pauses as the head seats, then impacts slowly. Use it for small screws where a full impact would bury the head. If the fastener stalls, the DCF887 manual says select mode 2. The DCF840 has no mode dial, so you only have the trigger. The pause is normal. A tool that reverses itself is not that pause.
Why does mode 1 stop on a long screw?
Mode 1 is the light band, 0–1000 rpm on the DCF887. A long timber screw can sit there without the blows you expected. Fit an impact bit, then select mode 2 and feather the trigger. A slipping bit holder can imitate the same stall, as in the DIYnot case where the holder, not the motor, was the fault.
Why did the screw head sink?
The mode was too high, the trigger stayed on after the head met the timber, or there was no pilot where the board needed one. Mode 3 will countersink a head you meant to leave flush. Back the screw out if the surface is still sound, drop a mode, and ease off earlier on the next one.
The tool will not impact. Is it broken?
On mode 1, a stall can be Precision Drive or a light setting doing what the manual describes. Reseat the bit and try mode 2 before you call it a fault. It is a fault if the direction reverses itself, if it cuts out in normal use, or if the switch is sticky. One DCF840 review and two DCF850 reviews describe those patterns. Stop, and use the seller under the Consumer Rights Act rather than stripping the gearbox.

Related pages

Best DeWalt impact driver

DeWalt cordless impact driver

DeWalt cordless impact driver buying guide: length

DeWalt impact driver for decking: screws, not pilots

DeWalt impact driver vs combi drill: screws or holes

Sources

Public UK sources from the research digest, used for this page in October 2026. Prices, stars and review counts are from the four amazon.co.uk listings captured on 20 October 2026. Noise and vibration action values apply at work. They are not a certificate that a domestic driver is silent or safe for all-day use.

  1. DCF887 instruction manual (retrieved 20 October 2026)
  2. DCF850 instruction manual (retrieved 20 October 2026)
  3. DeWalt UK, DCF840N-XJ bare unit (retrieved 20 October 2026)
  4. DeWalt UK, DCF850 compact kit (retrieved 20 October 2026)
  5. HSE, hand-arm vibration calculator (retrieved 20 October 2026)
  6. HSE, noise for employers (retrieved 20 October 2026)
  7. GOV.UK, Supply of Machinery (Safety) Regulations 2008 (retrieved 20 October 2026)
  8. Consumer Rights Act 2015, section 23 (retrieved 20 October 2026)