With an angle grinder the high starting RPM with most models may cause the core bit to walk and a starter or centering bit or a jig (board with a hole pre-drilled for the size of the core bit) is recommended for core bits 3” and larger. With centering bits, their long length is susceptible to runout at the high RPM’s of fixed speed angle grinders and a rubber “stabilizer” is recommended to keep the bit centered. The centering bit is used just to start the hole boring with the core bit and after the first 3/8” is cut the bit can be easily removed and the boring operation continued to completion.

A Centering Bit assembly with a 5/8"-11 adapter, 11" carbide tipped centering bit and hex wrench is now available for $44.95. Optionally a rubber stabilizer square is also available.

The centering bit with stabilizer square is ideal when using large diameter core bits with high RPM angle grinders or boring in any surface where the core bit is inclined to walk while starting the hole. At very high RPM the centering bit is subject to runout and the stabilizer plate keeps the centering bit in the center of the core bit. Once the hole is started the centering bit and stabilizer plate can be quickly removed while the core bit remains attached to the drill and then continue with the hole boring.

**Hole Pro makes no endorsement for any of the power tools listed below. This information is provided as a guide when determining the tool needed to drive one of the Blue Boar dry cutting Diamond Core Bits.
Power Tools
Max Hole Size

Unitec ED 1300

12 Amps
0-2000 RPM

Unitec 2001 P

15 Amps
2-speed gearbox
0-800 & 0-1570 RPM

Cardi 9150

15 Amps
3-speed gearbox
700/1860/2380 RPM

Makita GA7021

15 Amps
6000 RPM

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