During the development phase of ultra-precision equipment, many customers focus on the overall machine function design and underestimate the definition of precision for granite frames. Problems such as inconsistent dimension benchmarks, ambiguous tolerance logic and undefined precision boundaries are often discovered after drawings are submitted for machining. This will cause finished products to fail to match core components such as linear motors, optical modules and air bearings, resulting in rework, schedule delays and extra costs. As the benchmark substrate of the whole set of equipment, ZHHIMG® ultra-stable granite frames require a complete, measurable and traceable geometric precision system defined in the early customization stage, rather than simply marking length, width and thickness. Only by confirming all dimensional and precision indicators in the early stage of the project can the material advantages of granite, including low deformation and high damping, be fully exerted to guarantee the long-term nano-level operating performance of the equipment.
1. Outline dimensions and weight limits: basic conditions for machining and hoisting
The first set of indicators to confirm in customization is not precision, but overall outline specifications, maximum single-piece weight and boundary dimensions, which determine raw block selection, machining plans, transportation and hoisting schemes. It is necessary to confirm the total length, total width, total thickness of the frame, as well as the outline dimensions of each step, avoiding slots and hollow structures. Meanwhile, confirm the net weight of finished products and the positions of hoisting stress points. For large-span granite frames, different outline contours will change internal stress distribution. If the maximum outline dimension is not confirmed in advance, issues such as insufficient raw stone, insufficient machine travel and overload of workshop hoisting load may occur. The core of this step is to distinguish nominal dimensions and machining allowance for blanks. The allowance shall consider material consumption in rough grinding, fine grinding and nano-level manual finishing, so as to avoid material shortage during fine machining.
2. Geometric precision of reference surfaces: defining the metrology origin of the whole equipment
All precision of granite frames depends on reference surfaces, which is the most critical and easily overlooked part in customization projects. First, the main reference plane shall be agreed with the customer, and the flatness of the reference plane, evaluation interval and acceptance criteria shall be defined. Flatness cannot be described by a general value only. It needs to be confirmed whether it is the overall full-area flatness or local sectional flatness, and which metrology standard is adopted, such as DIN, ASME or GB. Besides flatness, the straightness of reference surfaces shall be confirmed. For long gantry frames and ultra-long beds, straightness is critical for stable movement of guide rails and linear motors. Surface roughness of reference surfaces also needs confirmation. Roughness directly affects air bearing operation, guide rail fitting and assembly friction characteristics. Scenarios including optical inspection, semiconductors and CMM require greatly different roughness values.
3. Mutual position precision: parallelism, perpendicularity and angular tolerance
When the frame is equipped with multiple groups of reference surfaces, vertical facades and step surfaces, the positional tolerance between surfaces becomes the key confirmation item. Parallelism is mostly applied to upper and lower reference surfaces and mounting surfaces of double guide rails; perpendicularity is used for vertical facades and main reference surfaces, such as mounting surfaces of gantry columns and assembly facades of optical brackets. Many equipment assembly failures originate from undefined perpendicularity tolerance between surfaces in the early stage. If the frame has inclined surfaces or V-shaped positioning grooves, angular tolerance and measurement benchmark of angles shall also be confirmed. For position precision, measurement methods shall be clarified: full-area scanning by laser interferometer or multi-point sectional sampling, so that both sides reach an agreement on inspection methods and avoid disputes over acceptance standards.
4. Dimensional precision of mounting features: threaded holes, pin holes, positioning slots and counterbore holes
All assembly features on granite frames are interfaces connecting metal modules, guide rails, linear motors, air bearings and optical platforms, whose precision requirements differ greatly from outline dimensions. It is necessary to confirm coordinate dimensions of each hole, position tolerance of holes, aperture tolerance and hole depth tolerance. Positioning pin holes usually require high position tolerance, while threaded holes need confirmation of bottom hole precision, hole chamfer and thread depth. For positioning slots, T-slots and counterbore holes, slot width, slot depth, slot straightness and parallelism of slots relative to reference surfaces shall be confirmed. It is necessary to distinguish high-precision positioning holes and ordinary fixing holes. Tolerance of ordinary fixing holes can be relaxed, while positioning pin holes and air bearing mounting holes must have strict position tolerance, otherwise module alignment will be difficult during later assembly.
5. Precision of splicing structure (for multi-section split frames)
Many large gantries and ultra-long inspection beds cannot be manufactured as a single monolithic block and require assembly of multiple granite components. For split spliced frames, splicing-related precision must be confirmed separately in the early stage. It is necessary to confirm flatness of splicing surfaces, fitting gap between splicing surfaces, total length after splicing, overall straightness and coplanarity of reference surfaces after assembly. Meanwhile, confirm position precision of splicing positioning pins and splicing benchmarks. Granite splicing is not simple docking. Stress release and height difference control at seams directly affect long-term stability of the whole machine. Without defined splicing precision in advance, tiny steps may appear at splicing seams after commissioning, which will hinder operation of guide rails and sliding tables. 
6. Precision acceptance boundary, environmental conditions and metrology traceability requirements
Precision values cannot be separated from testing environments. This is critical for customized ultra-precision granite. In the early stage, confirm environmental conditions for precision inspection: testing temperature, temperature uniformity, anti-vibration conditions, and whether the component is in a free and unconstrained state during precision measurement. The same flatness indicator will show different results when measured in an ordinary workshop versus a constant-temperature vibration-isolated workshop. Meanwhile, both parties confirm acceptance measuring instruments, sampling points for inspection and traceability requirements of metrology certificates. All testing instruments can be traced back to national metrology institutes. The valid period of precision shall also be confirmed, distinguishing static factory precision and allowable precision drift of equipment in long-term service. Deformation expectation caused by material stability shall be included in the early scheme, so customers will not equate short-term factory precision with permanent invariance.
7. Deformation indicators under load: precision prediction under dynamic working conditions
Apart from static geometric precision, high-end inspection and semiconductor equipment also require confirmation of deflection deformation indicators of the frame under rated load. Under the preset installation load and module weight specified by customers, the maximum subsidence and bending deformation allowed on the reference surface of the frame shall be simulated and confirmed in the early design phase. Although granite features high rigidity, large-span frames still produce tiny deformation after loading. Confirming load deformation indicators in advance helps customers complete overall machine structure compensation design and guarantee inspection precision of equipment under loaded working status.
Conclusion
Confirming dimensional and precision indicators in the early customization of ZHHIMG ultra-stable granite frames essentially converts the overall precision requirements of equipment into geometric indicators of granite components that can be machined, measured and accepted. Most precision disputes in projects arise from confirmation of only length, width and thickness in the early stage, without systematic definition of benchmarks, position tolerances, hole precision, splicing standards and acceptance environments. Completing full-set precision confirmation at the early project stage, ZHHIMG can lock the full set of frame precision indicators from raw block selection, machining plans, grinding processes to metrology acceptance, relying on global metrology standards and mature granite machining technology, and provide stable and reliable benchmark carriers for ultra-precision inspection, semiconductor and laser optical equipment.
Post time: Sep-28-2026