Internal Grinding
Internal grinding finishes bores to tight diameter, roundness and finish, often after hardening, using a small high-speed wheel inside the bore. It is used for bearing housings, bushes, gears, sleeves and dies where bores must hold a few microns.
What it is
The part is held in a chuck and rotated while a small grinding wheel on a long quill rotates at high speed inside the bore. Straight, tapered and blind bores, as well as internal faces, can be ground.
Internal grinding follows boring or reaming, and after heat treatment it restores the bore size and roundness that hardening distortion disturbs.
Typical applications
- Bearing seats in housings and gears
- Hardened bushes and sleeves
- Die and punch guide bores
- Hydraulic cylinder and valve bores (short)
- Tapered bores for tool holders
Suitable materials
- Hardened and case-hardened steels
- Alloy and tool steels
- Stainless steel
- Cast iron
Points to consider
- Long, small bores limit wheel stiffness; deep bores may be better honed.
- Blind bores need a relief groove at the bottom for the wheel to finish.
- Grind bore and face in one setup when squareness matters.
- Leave around 0.1–0.3 mm on diameter for grinding after hardening.
Frequently asked questions
When is internal grinding needed?
When a bore must hold a tight tolerance and fine finish, especially after hardening, such as bearing seats and guide bores.
What is the difference between internal grinding and honing?
Internal grinding sizes bores accurately and can grind faces too. Honing is better for long bores, improving roundness, straightness and finish with a cross-hatch pattern.
Can blind bores be ground?
Yes, with a relief groove or undercut at the bottom so the wheel can clear the end of the bore.