Once a hole grows past about half an inch, a standard twist bit becomes slow, heavy work that overloads the drill. The best drill bits for large holes either remove only a ring of material or use a reduced shank, so an ordinary chuck can still power a big diameter without stalling.
What to Look For
Large holes generate a great deal of cutting force, and that force rises quickly as the diameter grows. A full-diameter twist bit would need enormous torque and a shank too big for most chucks to hold. The smarter approach is to either cut just the rim of the hole and leave a solid slug behind, or to use a bit whose shank is stepped down to fit a standard drill. Match the tool to the material, the material thickness and the depth of the hole, because what works in thin sheet is not what you want in a thick steel plate. A hole saw that flies through plywood, for instance, is the wrong choice for a deep hole in solid steel where an annular cutter or reduced-shank bit belongs.
The Best Type of Bit for Large Holes
For thin material and general work, hole saws cut a clean circle while removing minimal material and putting little load on the drill. For clean, precise large holes in steel, annular cutters are outstanding and remarkably fast. For solid large-diameter holes in metal driven from a normal chuck, Silver & Deming reduced-shank bits are the classic answer.
- Hole saws: best for wood, plastic and sheet metal; they cut a rim and leave a slug.
- Annular cutters: fast, accurate large holes in steel with low thrust and clean walls.
- Silver & Deming: reduced-shank bits let a standard chuck drill big solid holes.
- Pilot & speed: use a pilot where required and run large diameters slowly to control heat.
Wood Versus Metal
In wood, hole saws and large auger bits handle doorknobs, recessed lighting cans and pipe runs cleanly and quickly. In metal, annular cutters and reduced-shank bits are far safer and cleaner than trying to force an oversized twist drill, which can grab violently and twist the tool out of your hands. Always clamp the workpiece and, on a press, never hand-hold metal. American-made cutters and Silver & Deming bits give the concentricity and durability that big holes demand.
Getting the Size Right
Confirm the finished diameter before you buy, because hole saws and cutters are sold by the size they cut rather than by a shank size. Read the size you actually need off your fixture, fitting or conduit, and remember that a pipe or conduit trade size is not the same as the hole diameter it requires. Getting this wrong means an expensive cutter that is a hair too small or too large for the part. Our conversion charts help you translate fractional, letter and millimetre sizes so the big hole you cut is exactly the one the job calls for.