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Precision CNC Lathe Part Manufacturing and ISO Tolerance Guide | ARK CNC

At ARK CNC, in our facility in Bayrampaşa, Istanbul, we produce high-precision metal parts for various industries using state-of-the-art C-axis capable CNC lathes. In industrial manufacturing, especially in critical sectors such as aerospace, medical, and special machinery manufacturing, it is not enough for a part to simply come off the lathe; it must fully comply with specified dimensional tolerance standards.

In this technical guide, we will examine the most commonly used tolerance standards in precision metal part manufacturing processes, how these tolerances are indicated in technical drawings, and our methods for maintaining micron-level precision in CNC turning operations.

What is Tolerance and Why is it Important?

In engineering, tolerance refers to the acceptable deviation amount of a part from its design dimension (nominal dimension). Perfect manufacturing is inherently impossible; therefore, tolerances ensure that parts seamlessly integrate with each other during mechanical assembly and perform their function flawlessly.

ISO Tolerance Standards Used in Precision Metal Part Manufacturing

The most common internationally recognized standard in the industry is ISO 286 (Geometrical Product Specifications – Dimensional Tolerances) system. This system clearly classifies the permissible deviation amount according to the part's dimension and intended use.

Hole Basis Tolerances (H7, H8 etc.)

Typically defines internal hole dimensions in female form. For example; a hole with H7 tolerance offers a narrow deviation range, almost above the nominal dimension, at micron level, ensuring compatible operation with the shaft.

Shaft Basis Tolerances (g6, h6 etc.)

Typically defines external shaft diameters in male form. For example; g6 tolerance is positioned slightly below the nominal dimension and is preferred in tight fit or controlled clearance fit applications.

Tolerance Indication and Examples in Technical Drawings

In engineering drawings, tolerances are shown using two basic methods for clear understanding by the manufacturer:

• Direct Deviation Limits: For example, when values of $+0.02 / -0.01$ are given for a nominal dimension of $20\text{ mm}$; a measurement range of maximum $20.02\text{ mm}$ and minimum $19.99\text{ mm}$ is accepted.

• Tolerance Class Code: The indication $20\text{ H7}$ refers to the use of the micron precision range belonging to the H7 class in the ISO standard table.

ARK CNC: Tolerance Precision in CNC Turning Operations

Maintaining micron-level tolerances is possible not only with a modern machine park but also with years of engineering experience. The basic methods we apply in our facility to maintain critical tolerance classes such as H7 are:

• Thermal Stabilization: Thanks to the advanced cooling fluid and temperature control systems in our machines, we minimize the thermal expansion of the part during long-term manufacturing.

• In-Process Quality Control: With the intermediate measurement controls we perform during machining operations, we instantly detect and intervene in possible dimensional deviations.

• Precision Cutting Tool Selection: With the correct carbide insert and rigid tool holder combinations, we maximize both surface roughness and dimensional stability.

Get Expert Support for Your Projects

You can rely on our experience since 2003 for your parts with complex geometries and subcontracting manufacturing projects requiring tight tolerances. To examine our machining capabilities, you can visit our Services page; by sending your technical drawings in STEP, IGES or DXF format via the Contact Form you can receive a professional price quote within 24 hours.