Most UK tradespeople already own an SDS rotary hammer drill — either SDS Plus for general use or SDS Max for heavy-duty applications. Both can be adapted to run diamond core bits using a ½″ BSP adaptor, avoiding the cost of a dedicated core drill machine. The question is not whether this is possible but where the limits are, and why those limits matter when the job demands more than the adaptor can safely provide.
SDS Plus vs SDS Max: The Fundamental Difference
SDS Plus (also written SDS+) is the standard rotary hammer shank used in most compact and medium rotary hammers — machines in the 700W–1100W class. The shank diameter is 10mm. SDS Max uses a 18mm shank and is found in heavy-duty demolition and chiselling machines from 1500W upward. The larger shank cross-section transmits substantially more torque.
For core drilling, torque is the critical variable. A 107mm diamond core bit cutting through brick cavity wall generates significantly more rotational resistance than a 52mm bit through soft block. As diameter increases, the required torque rises faster than linearly — doubling the bit diameter roughly quadruples the torque demand.
SDS Plus Core Drill Adaptors
An SDS Plus to ½″ BSP adaptor — such as the DART SDS Plus Core Drill Adaptor — fits into the SDS Plus chuck and provides the ½″ BSP female thread that standard diamond core bits require. The adaptor converts the hammer rotation to rotation-only by locking out the hammer function in the chuck.
Practical limit for SDS Plus: 52mm maximum bit diameter in brick or soft block.
Beyond 52mm, the torque demand of the core bit exceeds what an SDS Plus chuck and adaptor interface can reliably transmit. The shank may slip, the chuck may heat, or the adaptor can work loose mid-cut. For 38mm and 52mm bits cutting through standard brick or calcium silicate block, SDS Plus is an effective and low-cost approach.
SDS Plus adaptors should not be used with the hammer function engaged under any circumstances. Diamond core bits are rotation-only. Hammer mode with an SDS drill destroys diamond segments immediately.
SDS Max Core Drill Adaptors
An SDS Max to ½″ BSP adaptor fits SDS Max machines and handles the higher torque of the larger shank and motor. The DART SDS Max Core Drill Adaptor is the most common UK version.
Practical limit for SDS Max: 65–82mm maximum bit diameter in standard brick. Up to 107mm in soft masonry with a capable machine.
A high-power SDS Max machine (such as the Bosch GBH 5-40 DCE at 1100W) can drive a 107mm core bit through standard brick without issues. In denser material — engineering brick, concrete block, hard mortar courses — the same combination will struggle and may overheat the adaptor or stall mid-cut.
SDS Max adaptors are a legitimate mid-ground for occasional use on 65–82mm holes in brick and block, where buying a dedicated core drill machine is hard to justify on frequency grounds.
When to Use a Dedicated Core Drill Machine
A dedicated diamond core drill machine — with a ½″ BSP chuck, fixed rotation-only operation, integrated water connection, and motors from 1050W to 1800W — is required when:
- Bit diameter exceeds 82mm in hard material: Engineering brick, dense concrete block, or any C25+ concrete requires the motor torque and clutch control of a dedicated machine. The Hilti DD 110-D or Bosch GDB 350 WE are the correct tools for this range.
- Reinforced concrete is present: Rebar contact creates sudden torque spikes that an SDS drill with adaptor cannot safely absorb. A dedicated machine's torque-limiting clutch prevents dangerous kickback.
- Wet coring is required: Dedicated machines have integrated water inlets. Running water cooling through an SDS drill adaptor is impractical and ineffective.
- High volume or daily use: SDS drills are not designed for continuous rotation under the sustained load of core drilling. Repeated use beyond the 52mm/soft-material limit accelerates motor wear and chuck damage.
Adaptor Size Selection at a Glance
| Bit Diameter | Material | SDS Plus | SDS Max | Dedicated Machine |
|---|---|---|---|---|
| 38–52mm | Standard brick / block | ✓ Suitable | ✓ Suitable | Not required |
| 65–82mm | Standard brick / block | ✗ Not suitable | ✓ Suitable | Recommended |
| 107mm | Standard brick / block | ✗ Not suitable | Marginal — soft only | ✓ Required |
| 107mm+ | Concrete / reinforced | ✗ Not suitable | ✗ Not suitable | ✓ Required |
UK Adaptor Products
The most widely available SDS-to-BSP adaptors in the UK are:
- DART SDS Max to ½″ BSP adaptor — standard fit for most SDS Max chucks; includes pilot pin for core bits. Available from most UK tool merchants and online.
- SDS Plus to ½″ BSP adaptors — several unbranded and own-brand versions from tool merchants. Confirm the SDS Plus shank engagement length before purchasing — shorter shanks can slip in the chuck under load.
Both types require that the SDS drill's hammer mode is disabled before use. Some drills have a mechanical lock to prevent hammer operation — check this is engaged. Running a diamond core bit with hammer on, even briefly, will destroy the bit segments within seconds.
For full accessory selection including extension rods and pilot drills, see the accessories guide. For dedicated machine options when the adaptor approach reaches its limits, see the core drill machines guide. For general setup and technique, see how to use a diamond core drill.
