How a bit is built
Every bit has three parts. The shank is the plain end the chuck grips. The body carries the flutes that lift chips out of the hole. The point or tip starts the hole and decides how clean its rim is. Bosch describes its brad-point bits in exactly those terms: a centering tip for an accurate start, extra-wide flutes for fast chip removal, and a cylindrical shank for three-jaw chucks.
The cutting diameter and the shank diameter are separate numbers. Many larger bits run on a reduced shank: Freud's 1/2 in carbide Forstner bit has a 5/16 in shank, and its 1/4 in bit a 5/32 in shank. Others need a bigger chuck than their smallest sizes suggest, as Diablo's Forstner bits, which require a 3/8 in minimum chuck. What the chuck must hold is the shank, within the chuck's stated capacity.
Choosing a bit by the hole
| Hole you need | Bits made for it | What the maker says |
|---|---|---|
| Small round holes and pilots | Twist, brad point | WEN prefers brad point bits in wood and allows metal-piercing twist bits |
| A clean hole that will show | Brad point | Bosch: a centering tip and smooth, clean holes in soft and hard wood |
| Flat-bottomed, overlapping or angled | Forstner | Freud: flat-bottomed, pocket and overlapping holes, guided by the rim |
| Fast larger holes through framing | Spade, auger, self-feed | Bosch and Milwaukee: tips that pull the bit through the wood |
| Large holes through thinner stock | Hole saw on an arbor | Milwaukee: a pilot bit in the arbor centres the saw |
| A seat for a screw head, or a plug | Countersink, counterbore, plug cutter | Fuller: sized to the screw gauge, plugs matched to counterbores |
Each claim is its maker's, for its own bits. The full sheet, with every bit drawn, is the chart of drill bit types. No type is best for every hole.
Square holes are not drilled. A mortise is cut by a bit turning inside a square hollow chisel, in a mortiser or a mortising attachment its maker matches to the machine, or chopped by hand; the joint itself is covered in the mortise and tenon guide.
Equipment notePaid link
16-piece Forstner bit set, 1/4 to 2-1/8 in
Freud PB-100
For the flat-bottomed, pocket and overlapping holes in the table above: Freud's PB-100, sixteen Forstner bits from 1/4 to 2-1/8 in in 1/8 in steps, by Freud.
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Which tool each bit belongs in
- Drill presses. Bosch lists its brad-point bits for portable drills and drill presses, and Freud and Diablo their Forstner bits for both. WEN's drill-press manual says not to use auger bits, which can lift the work off the table and spin it.
- Drills only. Bosch lists its spade bits for corded and cordless drills and its auger bits for rotary drills/drivers. Bosch says the spade bit's fully threaded tip pulls the bit through the wood by itself.
- Impact drivers. DEWALT's DCF887 takes 1/4 in hex accessories only and says to use impact accessories only, because others may break; Milwaukee's 2953 manual says it is intended for drill and driver bits. Read the manual for the driver you have; impact drivers sets the two side by side.
Safety— Shank, chuck and capacity
Fit only a shank the chuck is rated for: 13 mm on DEWALT's DCD777, 5/8 in on Powermatic's PM2800B and WEN's 4214. A cutting diameter larger than the chuck is normal on a reduced-shank bit; a shank larger than the chuck is not something to adapt around. Seat the shank to the depth the manual gives — about 3/4 in for DEWALT, about 1 in for Powermatic — and never let the jaws close on the flutes.
Sizes, screws and speeds
- Diameters. Fractional, number, letter and metric bit sizes are matched across systems on the drill bit size chart.
- Screw holes. Clearance and pilot holes for wood screws, from a countersink maker's chart, are on the pilot hole chart; screw diameters and heads by gauge on the wood screw size chart.
- Speeds. No universal speed table exists. Powermatic gives a rule — smaller drills faster, softer materials faster — and WEN a table for its own machine that gives no bit type. Both are set out in the drill press guide.
Before drilling with a bit
- Bit type chosen for the hole, not the nearest bit to hand
- Shank within the chuck's capacity, seated as the manual says
- Bit allowed in this tool by its maker
- Sharp, straight and clean
- Work clamped, with scrap behind a through hole
- Speed set for the bit, the size and the wood
The drilling pages
- Tools: drills and drivers, impact drivers and drill presses.
- Technique: drilling clean holes with each bit and using a drill.
- Charts: drill bit types, drill bit sizes, wood screw sizes and pilot holes.
- Choosing: drill bits and a drill press, by their makers' specifications.
- Holding the work: clamps.
Sources
Every statement about a bit's use, size or shank is its maker's for its own bits; another maker's bit of the same type may differ. Where makers disagree about which tool a bit or accessory belongs in, each is named. No bit was tested.
- 1.
Brad Point Drill Bits. Bosch.
Used for: A brad-point bit's centering tip for exact positioning and accurate starts, extra-wide flutes for fast chip removal, a cylindrical shank for three-jaw chucks, and use in portable drills and drill presses; shank diameters of 1/8 to 3/8 in.
- 2.
Daredevil Standard Spade Bits. Bosch.
Used for: Spade bits with spur-and-reamer tips that pre-cut the wood and a fully threaded tip that pulls the bit through; for corded and cordless drills; 1/4 to 1-1/2 in on a 1/4 in shank.
- 3.
Daredevil Auger Bits. Bosch.
Used for: Auger bits for rotary drills/drivers, 6-1/2 in long for work between studs, 1/4 to 1-1/2 in, with decreased-pitch tips.
- 4.
PB-100 Forstner Bit Set and carbide Forstner bits. Freud.
Used for: Forstner bits for flat-bottomed, pocket, angled and overlapping holes, located by a centre spur and guided by the outer rim; for hand-held drills and drill presses; carbide bits on reduced shanks (1/4 in on 5/32 in, 1/2 in on 5/16 in).
- 5.
FB-007 High-Speed Steel Forstner Bit. Diablo (Freud).
Used for: High-speed steel Forstner bits requiring a 3/8 in minimum chuck, for drill presses and hand-held drills.
- 6.
SELFEED Bit 2-1/8" (48-25-2122). Milwaukee Tool.
Used for: Self-feed bits for repetitive large holes, with a centre feed screw that pilots the bit and pulls it through and a hex shank for the drill chuck.
- 7.
HOLE DOZER Small Arbor with Cobalt Pilot Bit (49-56-7110). Milwaukee Tool.
Used for: A hole saw arbor with a pilot bit; the small arbor takes saws up to 1-3/16 in.
- 8.
Countersinks, Counterbores, Tapered Drills, Plug Cutters catalog (PDF dated 2006), page 4: Recommendations for Wood Screw Predrill Sizes and Lengths. W. L. Fuller, Inc., 2006.
Used for: Countersinks set on taper point drills that predrill, clear the shank, countersink and counterbore for one screw size in a pass, and plug cutters matched to the counterbores.
- 9.
Model 4214 12-inch Variable Speed Drill Press manual (2015), as hosted by a retailer. WEN Products, 2015.
Used for: Brad point bits preferred for wood in its drill press, metal-piercing twist bits usable, auger bits not to be used; a wood speed table by bit size with no bit type given; backup material under the work.
- 10.
Operating Instructions and Parts Manual, 18-inch Variable Speed Drill Press, Model PM2800B (Rev. E1, 04/2019), as hosted by Purdue University. Powermatic, 2019.
Used for: Speed set by material, hole size, drill type and quality of cut, smaller drills faster, softer materials faster; a 5/8 in chuck; sharp bits for the best and safest performance.
- 11.
DCD777 Cordless Drill/Driver instruction manual (English). DEWALT.
Used for: A 13 mm keyless chuck; accessories inserted about 3/4 in; sharp bits only; a backup block for thin material.
- 12.
DCF887 Cordless Impact Driver instruction manual (English). DEWALT.
Used for: An impact driver chuck that accepts 1/4 in hex accessories only, and impact accessories only, since non-impact accessories may break.
- 13.
M18 FUEL 1/4" Hex Impact Driver 2953-20 Operator's Manual (as hosted by a distributor). Milwaukee Tool.
Used for: An impact driver intended for use with drill and driver bits.
About this guide
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