Wood boring bits compared: spade vs Forstner vs hole saw
Once a hole in wood passes about 1/2 inch, twist bits stop being the right tool and the question becomes which boring bit to reach for. The three families do not really compete: a spade bit is a flat paddle that plows through framing lumber fast, a Forstner bit is a rim-guided cutter that leaves a clean flat-bottomed hole, and a hole saw cuts a ring for big through-holes. This page compares them head to head, prints the size ranges and RPM ceilings with sources, and ends with the decision table. For the full size ladders, see our dedicated Forstner bit sizes and hole saw sizes pages; for why RPM falls with diameter, the drill press speed chart.
The one-paragraph verdict
Pick the bit by the hole, not the habit. Rough through-holes in construction lumber, drilled fast and never seen: spade bit [1] [5]. Visible or precise holes, flat bottoms, angled or overlapping holes, hinge cups: Forstner [1] [7]. Holes past 2 inches, or through thin stock such as doors and panels: hole saw [1] [9]. Cost follows the same line: spade bits are the cheapest per size, Forstner bits sit in the middle, and hole saws buy cups plus an arbor [3] [9].
Spade bits (paddle bits)
A spade bit is a flat blade with a center point and two cutting spurs at the edges, shaped like a paddle. The geometry is deliberately crude: the point walks less than a twist bit's chisel edge, the spurs score the hole wall, and the flat body scrapes the rest out of the way. The result is a hole drilled quickly through clean wood, with a rougher wall than any rim-shearing cutter leaves, and noticeable tear-out where the bit breaks through the back face [1] [5]. A backing board clamped behind the work keeps the exit side respectable.
Sizes and set contents, from catalog data: the Irwin Speedbor 6-piece set runs 3/8, 1/2, 5/8, 3/4, 7/8, and 1 inch [3] [4], and 13-to-14 piece sets span 1/4 to 1-1/2 inches, typically bundled with a 6 inch quick-load extension for boring through wall plates and studs [4] [8]. That extension trick is the spade bit's structural advantage: the shank is a flat bar, so long extensions and flexible shafts exist that no Forstner design matches. Speed-wise, spade bits run faster than Forstner bits at the same diameter but are still diameter-limited: WorkshopCalc's boring table caps them at about 500 RPM by 2 inches [1], and Bosch prints a 1,500 RPM maximum right on the shank of its Daredevil spade bits [5] [6].
Forstner bits
A Forstner bit is guided by its rim, not its center: a sharp outer ring shears the hole wall clean while interior cutters and a center spur clear the middle. That is why it produces the flat-bottomed, square-shouldered holes that cabinetmaking runs on, and why it can drill overlapping holes, holes at an angle to the face, and holes on the edge of a board without wandering [1] [7]. The price of the geometry is speed and heat: the large contact area means RPM must fall as diameter rises, from about 1000 RPM at 1-1/4 inch down to 500 at 2 inches and above [1] [2], and past roughly 1-1/4 inch the work belongs on a drill press with the stock clamped.
The full inch and metric size ladders, set contents, and the per-diameter RPM table live on our Forstner bit sizes page. The number worth memorizing here is 35mm: every standard European concealed cabinet hinge presses into a 35mm cup, which makes 35mm the single most important Forstner size in furniture work and the reason nearly every metric set includes it [7] [8]. The 1-3/8 inch bits marketed at cabinetmakers are the imperial stand-in, but 1-3/8 inch is 34.9mm, not 35; for a true hinge cup use the metric bit or the cup will bind.
Hole saws
A hole saw cuts an annulus: a ring of teeth around a hollow cylinder, driven by an arbor with a pilot drill that guides the start. Because it removes only a ring of material instead of the whole disc, the power demand stays low enough that diameters from 3/4 to 6 inches are practical on a handheld drill, which no Forstner design can say [1] [9]. The hole is a through-hole by definition; there is no flat bottom, the kerf walls are rougher than a Forstner's, and the plug has to be pried out of the cup. Wood-specific saws have deep gullets for chip clearance; bi-metal saws cross over into metal at much lower RPM. In softwood, a 2 inch saw runs around 450 RPM [1] [9]. Diameters for specific jobs, deadbolts and conduit and door locks, are tabulated on our hole saw size chart, and the arbors and mandrel threads that mount every cup are charted on our hole saw arbor size chart.
Size and speed summary
| Bit family | Diameter range | Typical RPM at 1 in / 2 in | Bottom | Sources |
|---|---|---|---|---|
| Spade bit | 1/4 to 1-1/2 in (sets), individual larger | about 1500 / 700 | Flat but rough | [1] [4] [5] |
| Forstner bit | 1/4 to 3 in | about 1000 / 500 | Flat and clean | [1] [2] |
| Hole saw | 3/4 to 6 in | about 750 / 450 | None (through-hole) | [1] [9] |
The RPM figures are top-end softwood numbers from the WorkshopCalc boring chart, cross-checked against EngineerFix's press guidance (2 inch Forstner: 500 RPM max in softwood, as low as 250 in hardwood) [1] [2]. In hardwood, knock each figure down 30 to 50 percent and let scorch marks be the warning that you did not [1] [2].
Which bit for which job
| Job | Winner | Why | Sources |
|---|---|---|---|
| Cable or pipe hole through studs and joists | Spade bit | Fastest per hole, cheap, works on long extensions | [1] [4] [5] |
| European hinge cup | 35mm Forstner | Flat bottom, exact 35mm diameter, clean rim | [7] [8] |
| Dowel joints, pocket holes, partially-depth holes | Forstner | Only family that leaves a repeatable flat bottom | [1] [7] |
| Angled or overlapping holes | Forstner | Rim guidance cuts without walking off a center punch | [1] [7] |
| Deadbolt or door knob hole (2-1/8 in through a door) | Hole saw | Thin stock, big diameter, low torque demand | [1] [9] |
| Holes over 2 in in thickness over 1 in | Hole saw | Forstner contact area overheats; the ring cut stays cool | [1] [2] |
| Many repeated production holes in lumber | Spade bit | Speed per hole dominates; wall quality irrelevant | [1] [5] |
Related
For the full Forstner inch and metric charts: Forstner bit sizes. For hole saw diameters by task and arbor sizes: hole saw sizes. For the RPM logic and press pulley mapping: drill press speed chart, and for handheld bands the drill speed chart. If the hole is really a screw clearance question, start at the pilot hole chart instead.
Sources
- WorkshopCalc, Drill Speed Chart reference: Forstner and spade bit speed chart by diameter, wood twist-bit bands, 2 inch hole saw approximately 450 RPM in softwood (workshopcalc.com/reference/drill-speed-chart)
- EngineerFix, Drill Press RPM Chart: 2 inch Forstner maximum 500 RPM in softwood, 250 in hardwood; slow-speed reasoning (engineerfix.com/drill-press-rpm-chart-what-speed-should-you-use/)
- Grainger, IRWIN Speedbor 88886 6-piece spade bit set listing: decimal equivalents 0.375, 0.5, 0.625, 0.75, 0.875, 1 in, carbon steel, hex shank (grainger.com/product/4XL03)
- Amazon, 14-piece spade bit set listings: 1/4 to 1-1/2 inch span with 6 inch quick-load extension (amazon.com)
- HomeFixated, Bosch Daredevil spade bit review: 1,500 RPM recommended maximum printed on the shank, 17 sizes plus extra 1/4 and 5/16 (homefixated.com/bosch-daredevil-spade-bits/)
- Bosch Tools, Daredevil spade bit product line page: speed, life, and ease-of-use positioning (boschtools.com/us/en/daredevil/)
- AIMS Industrial, Forstner Bit Guide: 35mm as the European concealed-hinge cup standard, clean flat-bottomed holes, selection and speed guidance (aimsindustrial.com.au/blogs/product-guides/forstner-bit-guide)
- CherryPicks, Forstner drill bits roundup: metric TCT sets including 35mm for hinge work (cherrypicksreviews.com)
- Zhonghuan Tools, Drill Bit RPM Chart by Material and Diameter: large-bit guidance, 2 inch hole saw approximately 450 RPM softwood (zhonghuantools.com/en/resources/drill-bit-rpm-speed-chart)