Granite Air-Bearing Guideways: Design and Inspection Questions Before Ordering

When ordering a granite air-bearing guideway, an overall drawing and a general request for “high precision” are not enough. Buyers should also define the bearing arrangement, functional surfaces, mounting interfaces, inspection requirements, and scope of supply.

Air bearings operate using a pressurized air film between the bearing and its opposing surface. For this reason, the guide surface is part of the bearing system—not simply a structural support. Surface finish, local flatness, and interruptions such as holes or seams require consideration during design.

This guide explains the questions OEM engineers and procurement teams should resolve before requesting a quotation for a custom granite air-bearing guideway or assembly.

1. Define Exactly What You Are Ordering

The term “granite air bearing” can describe different products. Before comparing quotations, identify which components and services are included.

Your project may require:

• A granite base with precision air-bearing guide surfaces.
• A granite beam or guideway component.
• A granite component with mounting inserts and interfaces.
• A granite and air-bearing mechanical assembly.
• A complete motion system with drives, feedback devices, and controls.

These are different supply scopes.

For example, a quotation for a granite guideway should not automatically be interpreted as including air-bearing pads, pneumatic equipment, motors, encoders, or final motion testing.

A clear RFQ should state:

The required supply scope includes the granite guideway, installed threaded inserts, and dimensional inspection documentation. Air-bearing pads, pneumatic equipment, motion controls, and final system integration are supplied by the customer.

Adapt this statement to your actual project, and ask the supplier to list any exclusions separately.

2. Identify the Air-Bearing Design and Its Requirements

Provide the selected air-bearing manufacturer, model, and relevant application drawings whenever available.

If the bearing has not yet been selected, identify this as an open engineering item rather than asking the granite supplier to assume a universal guide-surface specification.

Air-bearing design guides address local flatness, surface finish, preload, guideway interruptions, and air-supply requirements. These requirements must be considered together for the selected bearing arrangement.

Useful information includes:

Where the bearing manufacturer and machine designer specify different requirements, resolve the difference before approving the granite drawing.

3. Mark the Guide Surfaces Clearly

A granite component may include several types of surfaces, but not all of them serve as air-bearing guide surfaces.

Identify:

• Load-carrying guide surfaces.
• Lateral guide surfaces.
• Mounting surfaces.
• Reference datums.
• Support contact areas.
• Clearance surfaces.
• Areas outside the bearing travel envelope.

For each guide surface, show where the bearing operates and how that surface relates to the other functional features.

This is particularly important when a moving assembly uses more than one face of a granite beam or guideway. The drawing should communicate the required relationships between those faces, not just their individual dimensions.

A marked-up drawing is often more useful than a general note stating “all surfaces high precision.”

4. Separate Local Flatness from Full-Length Geometry

Local flatness concerns the area beneath the bearing at a given position. Full-length geometry concerns the guide surface or feature over a larger measurement extent.

Both deserve attention, but they answer different questions.

New Way’s application guide explicitly defines local flatness in relation to the bearing footprint and discusses it in relation to the designed air gap. This illustrates why guide-surface requirements should be linked to the selected bearing design rather than copied from an unrelated project.

For your RFQ, identify separately:

• Local flatness requirements and their evaluation area.
• Full-surface flatness, where applicable.
• Straightness of specified features or measurement lines.
• Parallelism between guide surfaces.
• Perpendicularity between relevant faces.
• The datum system used for inspection.

Do not use one unspecified “accuracy” value to cover all these characteristics.

Likewise, do not assume that a granite component’s straightness result is automatically the straightness of motion of the completed stage. Component inspection and system performance testing should be specified as separate acceptance activities.

5. Specify Surface Finish Without Ambiguity

Air-bearing guide surfaces need a defined surface-finish requirement, not merely a polished appearance.

Bearing manufacturers provide guidance for the surfaces used with their products. New Way, for example, discusses surface finish as part of guide-surface design and notes its importance when operating with small air gaps.

When specifying surface finish, state:

• The required parameter, such as Ra or Rq.
• The unit of measurement.
• The applicable measurement standard or procedure.
• The surfaces and areas to which the requirement applies.
• Any reporting requirements.

Avoid copying a finish value without its parameter and units. A note such as “finish 16” is incomplete.

Use the requirement approved for the chosen bearing and application. A recommendation from one bearing supplier should not be presented as a universal specification for every air-bearing system.

6. Review Holes, Slots, Seams, and Surface Interruptions

Mounting features can become functional concerns when they lie within a bearing’s travel path.

Air-bearing manufacturers discuss holes, grooves, and seams because these features can affect bearing operation. Their acceptability depends on factors including bearing design, feature size, and the available supporting area. New Way’s guidance recommends avoiding guideway seams where possible.

Before releasing the drawing, check:

• Does any bearing pass over a hole, slot, or recess?
• Is there a joint or seam within the travel area?
• Are inserts located inside a functional guide surface?
• Could a feature create a raised edge?
• Has the bearing supplier reviewed unavoidable interruptions?

Do not assume that a feature is acceptable simply because it is small relative to the entire granite base.

Show the bearing travel envelope on the drawing so that potentially conflicting features can be identified during technical review.

7. Describe Loads, Supports, and Installation Interfaces

Provide a drawing or sketch showing how the granite component is supported and how loads are applied.

Include:

• Support locations and contact areas.
• Payload and its operating positions.
• Bearing locations.
• Drive and actuator interfaces.
• Mounting inserts and fastening details.
• Relevant operating forces and moments.
• Assembly and alignment interfaces.

If acceptance measurements must be made under a particular support or loading arrangement, state this explicitly.

Also identify whether the supplier is responsible for the granite component alone or for establishing alignment within a larger mechanical assembly.

This makes the quotation more precise and reduces the chance that different parties work to different assumptions.

8. Agree on Air Supply and Cleanliness Responsibilities

Even when the supplier provides only the granite component, air-supply responsibilities should be clear at the system level.

Air-bearing design guidance addresses air cleanliness, filtration, pressure, and flow requirements. New Way’s guide specifies air relatively free of particulates, water, and oil, while its design overview discusses selecting appropriate filtration and flow capacity.

For a project inquiry, identify:

• The party selecting the pneumatic equipment.
• The required supply conditions specified by the bearing manufacturer.
• Whether regulators, filters, tubing, and monitoring devices are included.
• The party responsible for commissioning and operating procedures.
• Any cleanliness requirements during assembly and delivery.

Use the selected bearing manufacturer’s requirements rather than applying a generic pressure or filtration value to every project.

9. Separate Component Inspection from System Acceptance

Before ordering, create two lists: what will be checked on the granite component, and what will be checked on the assembled system.

Not every project includes all three levels.

The acceptance scope should match the supplier’s contractual responsibility. If a complete motion system is not included, its performance should not be implied by a component inspection report.

For each required test, agree on:

• The characteristic being evaluated.
• The measurement method.
• The applicable tolerance.
• The setup and relevant conditions.
• The report format.
• The party performing the test.

10. What Should the Inspection Report Include?

Specify the documentation you need during quotation, not after manufacturing is complete.

Depending on the agreed scope, request:

• Part identification and drawing revision.
• Inspected features and datum references.
• Applicable acceptance limits.
• Recorded measurement results.
• Measurement locations or layout.
• Relevant support and environmental conditions.
• Instrument identification.
• Measurement uncertainty and conformity decision rule, where required.

Ask the supplier to distinguish actual measurement results from nominal drawing values.

If you require a surface map, raw data, or a particular report format, include that requirement in the RFQ.

RFQ Checklist for a Granite Air-Bearing Guideway

Use the following template to prepare your inquiry:

Subject: RFQ — Custom Granite Air-Bearing Guideway

Dear ZHHIMG Team,

Please review the attached drawings and provide a quotation for the following project.

Application:
Part number and drawing revision:
Quantity:
Required supply scope:
Overall dimensions:
Air-bearing manufacturer and model, if selected:
Bearing arrangement and travel envelope:
Payload and load distribution:
Guide-surface geometry requirements:
Surface-finish requirements:
Mounting inserts and interfaces:
Support arrangement:
Inspection and documentation requirements:
Assembly and system-testing responsibilities:
Delivery destination:
Requested schedule:

Please identify missing information, technical exceptions, and assumptions included in your quotation.

Discuss Your Granite Air-Bearing Project with ZHHIMG®

ZHONGHUI Group supplies precision granite components and granite assembly solutions for precision equipment applications.

For an air-bearing guideway inquiry, send your current drawings, bearing specifications, travel requirements, loading information, and inspection criteria.

If the project is still in development, clearly identify which requirements are confirmed and which remain open for review. This provides a stronger starting point for defining the granite component, the supply scope, and the acceptance plan.