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How to use a Forstner bit

Updated: 2026-10-23

A 40 mm Forstner bit burns, grabs or tears the exit if you treat it like a twist drill. Set a slow speed, clamp the work, clear the chips, and keep the bit out of an impact driver. Which listing to buy is on the [40 mm Forstner bit buying guide](/hub/drilling-and-accessories/forstner-bit-40mm/sub/forstner-bit-40mm-buying-guide). Prices stay on the [40 mm Forstner bit comparison](/hub/drilling-and-accessories/forstner-bit-40mm). These steps were matched to the machine notes on those amazon.co.uk listings on 20 October 2026. The speeds below are a rule of thumb, not a British Standard, and there is no lab cut behind them.

A 40 mm Forstner bit burns, grabs or tears the exit if you treat it like a twist drill. Set a slow speed, clamp the work, clear the chips, and keep the bit out of an impact driver.

Our top picks

TA-VIGOR TA-VIGOR 40 mm, carbide tip

Best overall

TA-VIGOR TA-VIGOR 40 mm, carbide tip
7.0/10about £9.46
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HSAWBIT HSAWBIT 40 mm, hex

Alternative

HSAWBIT HSAWBIT 40 mm, hex
6.3/10about £12.99
View offer
ASNOMY ASNOMY 40 mm, carbide tipped

Rank 3

ASNOMY ASNOMY 40 mm, carbide tipped
8.5/10about £11.89
View offer
On this page
  1. 1.Set the speed before you touch the wood
  2. 2.Clamp, then choose the machine
  3. 3.Depth and chips
  4. 4.Eyes, and when to stop

Set the speed before you touch the wood

A 40 mm rim scrapes a circle about 126 mm around, so spindle speed is a high edge speed. Katz-Moses publishes about 250 rpm in hardwood and about 500 rpm in softwood for bits from 1 3/8 inch to 2 inch. Popular Woodworking starts near 600 rpm above 1 3/8 inch and watches for chips, not smoke. If the rim browns, slow down before you push harder. Do not copy a 35 mm cup speed of about 1,000–1,500 rpm onto this bit. That layout is on the 40 mm or 35 mm hinge-hole page.

Clamp, then choose the machine

Clamp the work before the rim meets the surface. A loose board becomes a lever. ASNOMY says sizes above 40 mm are better in a fixed drill, or in a vice if you use a hand drill. One reviewer switched to a press after a grab. Another said a hand drill was easy, so follow the listing's warning. Both DTGN pages say use a press above 35 mm so the centre does not wander. TA-VIGOR lists a bench drill, a vertical drill or a CNC router, not a hand drill. HSAWBIT allows a hand drill and still has a review of softwood that jumped. A hex shank does not stop the rim walking. Keep the bit out of an impact driver. HSAWBIT states that ban.
TA-VIGOR TA-VIGOR 40 mm, carbide tip

Testsieger

TA-VIGOR TA-VIGOR 40 mm, carbide tip
7.0/10about £9.46
View offer

Depth and chips

Pull the bit out, let the chips fall, then go back in. A packed hole burns the bottom even at a sensible speed. ASNOMY states 60 mm of depth and the green DTGN bit states 64 mm. That is not a reason to bury the shank. TA-VIGOR says inject water on hardwood. No review here confirms it, so keep electrics clear of the water. A through-hole needs a backing piece. A flat bottom versus a hole-saw plug is on the Forstner bit versus hole saw page.

Eyes, and when to stop

Wear eye protection. The Health and Safety Executive treats flying particles as a reason for it at work, and HSAWBIT says the same. Hand the job to a fitter when you cannot clamp the work, when you are drilling a run of doors, or when the board is a fire door. The DTGN listings exclude concrete, steel, ceramic and glass.

Common questions

How fast should a 40 mm Forstner bit spin?
Use a rule of thumb, not a standard. For this diameter, published workshop figures are about 250 rpm in hardwood and about 500 rpm in softwood, or a start near 600 rpm if you judge by the chips. You want shavings, not smoke. A 1,000–1,500 rpm figure published for a 35 mm hinge cup is too fast to copy onto a 40 mm rim. If the edge browns, slow down before you push harder.
Can I use a cordless hand drill?
Yes on some of these listings, and only with the work clamped. HSAWBIT allows a hand drill. ASNOMY prefers a fixed machine above 40 mm. DTGN says use a press above 35 mm. TA-VIGOR does not list a hand drill. Reviews include both an easy hand-drill cut and a grab that ended the attempt. If the centre walks on scrap, move to a pillar drill.
Can I use an impact driver?
No. HSAWBIT states the ban, and the hammering action is the wrong motion for a scraping rim. A hex shank on these bits is a drill-chuck shape. Where the hex is given as 8.5 mm, it is wider than a 6.35 mm quarter-inch quick-change holder. Use a drill or a drill press, in rotation only, not hammer mode.
Why does the wood burn?
The rim is dwelling or spinning too fast, or the flutes are packed with dust. HSAWBIT reviews describe a flat rim that overheats in hardwood and leaves fibres that need sanding. Drop to the slower end of the rule of thumb, pull the bit out to clear chips, and ease the feed. A blunt edge from a cheap bit will burn even when the speed is right, which a scrap cut shows before you touch the finished piece.
How do I stop the bit walking?
Clamp the work and let the centre point seat before the rim cuts. DTGN's listing says a press above 35 mm keeps the centre from wandering. A loose door in one hand and the drill in the other is how reviewers describe a jump off the mark. If it has already walked, do not chase it. Plug the scar or move the centre and start again on a press.
Should I wear eye protection?
Yes. Chips leave a 40 mm rim hot and fast, and HSAWBIT's listing tells you to wear eye protection. The Health and Safety Executive treats flying particles as an eye hazard in the workplace. The same glasses belong on a home bench, including when the bit is in a drill press. They do not replace a clamp or a slow speed.

Related pages

Pillar drill

Forstner bit 40mm

Best 40 mm Forstner bit for the job in front of you

Check a 40 mm Forstner bit listing before you order

40 mm or 35 mm Forstner hinge hole on a cabinet door

Forstner bit vs hole saw when you need a flat bottom

Sources

Public UK sources from the research digest, last checked on 20 October 2026. Shelf prices and star lines are the amazon.co.uk figures in the product display for this comparison.

  1. HSE: PPE overview (retrieved 20 October 2026)
  2. Consumer Rights Act 2015, section 19 (retrieved 20 October 2026)
  3. Bosch Professional UK, 40 mm Forstner bit 2 608 577 019 (retrieved 20 October 2026)
  4. Hart Wholesale, Blum 71B3550 (retrieved 20 October 2026)
  5. Furnica, 35 mm hinge cup guide (retrieved 20 October 2026)
  6. Katz-Moses Tools, Forstner speeds (US shop, rule of thumb) (retrieved 20 October 2026)
  7. Famag Tool UK, classic 40 mm Forstner bit (retrieved 20 October 2026)
  8. amazon.co.uk listings for the ASINs in this comparison (retrieved 20 October 2026)