Many customers ask: “It’s just a hole—why not use a drill for speed instead of requiring the more complex reaming process?”
The answer lies in the difference between “creating a hole” and “finishing a hole.”
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Here are some reasons why conventional drilling alone cannot achieve H7 tolerance:
- Run-out (deviation): A drill bit tends to wobble or slightly deviate from center as it enters the material, resulting in an out-of-round or non-straight hole.
- Surface finish: The cutting edges of a drill leave relatively rough tool marks. For H7 requirements, the surface must be smooth like a mirror for bearing or shaft fitting—something drilling cannot achieve.
- Dimensional inaccuracy: Drill bits often cut slightly larger than their nominal size (over-size) due to heat and vibration.
This is exactly where reaming becomes necessary to correct what drilling leaves behind:
- Micrometer-level accuracy: H7 tolerance typically allows only about +0.015 mm to +0.02 mm (depending on size). A reamer, with multiple cutting edges distributed around its body, minimizes vibration and ensures highly stable cutting.
- Geometric correction: It improves the roundness and straightness of the pre-drilled hole.
- Ultra-fine surface finish: The reaming process acts like a polishing cut, producing a smooth surface that perfectly meets tight fit requirements.
Therefore, machining an H7 hole is not just about changing the tool—it is a tightly controlled process. Drilling is for making a hole; reaming is for achieving proper fit. If you need a mechanical component to operate smoothly, without vibration, and with long service life, an H7 reamed hole is a fully worthwhile investment.
Contact us now for consultation and a quotation.
