How to Turn Your Drill Into a Core Drill

Written by jeff lockshin
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How to Turn Your Drill Into a Core Drill
Turn your hammer drill in to a core drill. (drill image by Vladislav Gajic from

When you need to drill large holes in concrete, brick, block, wood, or porcelain, it is not necessary to rent or buy a core-drilling rig. You can turn a lightweight rotary hammer drill or standard 3/8 variable speed drill into an effective core-drilling machine. Insert a core bit in your drill chuck, and core drill holes up to six inches.

Skill level:

Things you need

  • Rotary hammer drill
  • Standard variable speed 3/8 electric drill
  • Core bit assembly
  • Core bit adaptor
  • Core bit cup

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  1. 1

    Purchase a core bit adaptor and core bit cup(s). Adaptors are designed with a shank and a shaft. The shank is either a spline or slotted drive system (sds plus) for a rotary hammer drill chuck. Round shank adaptors are available for the keyed or keyless chuck on a standard 3/8 inch electric drill. The adaptor shaft is externally threaded 5/8-11 or 1 1/4-7 to accept a matching internally threaded core bit cup. Core bit cups range in size from one to six inches. They are interchangeable so that you can unscrew one size off the shaft and screw another onto the drill. Core bit adaptors and core bit cups are available at hardware stores and online.

  2. 2

    Select the correct adaptor shank for your hammer drill by determining if the chuck is spline or sds plus. You can find this information on the drill or in the drill instruction manual. Insert the shank of the adaptor into the chuck No tightening of the chuck is required since sds and spline chucks are self-locking. Screw a core bit cup on the threaded portion of the adaptor. You now have a core-drilling machine.

  3. 3

    Insert a one-piece core bit into your rotary hammer drill in the same manner as the core bit adaptor. Your drill is now set for core drilling. One-piece core bits are designed with a spline or sds shank and a brazed or welded core bit cup on the end of the shaft. They are available in single sizes only because the core bit is fastened to the shaft, and cannot be removed.

  4. 4

    Open the keyed or keyless chuck of a standard 3/8 variable speed drill rated for a minimum of 300 rpms. Place the round shank of your core bit adaptor in the chuck and tighten. Round shank core bit adaptors are made for and only to be used in a standard keyed or keyless chuck. Mount the core bit cup on the end of the adaptor shaft. Your now have a core drill. Because of the low torque rating for a standard drill, never attempt to drill a core hole over two inches.

Tips and warnings

  • A core bit adaptor allows you to change core bit sizes by screwing them on or off the shaft.
  • Core bits are available either carbide or diamond tipped.
  • Shaft extensions can be used with core bit adaptors and assemblies for drilling through extra thick material or structures.
  • 5/8 inch adaptor shafts are used for core bits up to 1-1/2 inch to 1-1/4 inch adaptor shafts are available for mounting larger core bits from 1-5/8 inch up to 6 inch.

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