CNC Turning & Milling · Robotics
Holding P6/H6 Fits and 0.015 mm Coaxiality on a 7075-T6 Robot Gearbox Planet Carrier
A 3,300-part production order used soft-jaw turning, a 12-position milling fixture and ZEISS CMM inspection to control precision fits and 0.01-0.02 mm GD&T across front, rear and rotational features.
At a Glance
- Material
- 7075-T6 aluminum
- Process
- Soft-jaw CNC turning, 12-position fixture milling and ZEISS CMM inspection
- Application
- Industrial robot reduction gearbox
- Production volume
- 3,300 parts
- Precision fits
- P6 pin holes, H6 bore and h6 register
- GD&T requirements
- 0.015 mm position and coaxiality; 0.01-0.02 mm perpendicularity
From the Production Drawing
The Requirement, in the Engineer's Own Notes
The production drawing ties precision fits and cross-face GD&T controls to datums A and B. The order header, revision details, dates, drawing number, part code and personnel information have been excluded from this published excerpt.
01
The Challenge
This 7075-T6 second-stage planet carrier combines different feature systems on every accessible side. The front carries a dense ring of threaded and through holes around a machined internal profile; the rear combines a square central boss, four larger holes and a deeper pocket; the outside diameter adds radial features and rotational interfaces. Two four-hole P6 patterns, an H6 bore and an h6 register are related through datums A and B, alongside 0.015 mm position and coaxiality controls and 0.01-0.02 mm perpendicularity limits. Those relationships had to survive turning, milling and repeated re-fixturing across a 3,300-part production order, not only on a single showpiece.
02
OUJI's Approach
OUJI split the rotational and multi-face work into controlled operations. Soft jaws located the part for CNC turning of the outside diameter and concentric features. The parts then moved to a dedicated 12-position fixture plate for batch milling. Using the same locating architecture across twelve fixture stations standardized how each part was seated and clamped instead of rebuilding the setup for every workpiece. After machining, the datum-related diameters and geometric characteristics were checked on a ZEISS coordinate measuring machine, with the programmed report documenting both the measured value and its tolerance band.
03
The Result
The published ZEISS CMM report records nine checked characteristics on the inspected part, with all nine inside their stated limits. Cylindricity measured 0.0019 mm against a 0.0100 mm limit. Perpendicularity measured 0.0013 mm and 0.0051 mm against 0.0100 mm and 0.0200 mm limits. Coaxiality measured 0.0014 mm and 0.0015 mm against a 0.0150 mm limit. The 70 mm register measured 69.9900 mm within a 70.0000/+0.0000/-0.0190 mm report band, and the 24 mm bore measured 24.0123 mm within a 24.0000/+0.0150/-0.0000 mm band. These values document the inspected part; they are not presented as a capability study for all 3,300 units.
Production Sequence
From Soft-Jaw Turning to Documented CMM Results
The photographed route follows the same part through rotational machining, repeatable batch fixturing, dimensional inspection and final front-and-rear review.
The 12-position fixture standardizes locating and clamping across a batch of twelve parts. It does not remove every setup transfer, so the cross-operation datum relationship is verified again by CMM after machining.
01 · CNC turning
Locate the rotational features in soft jaws
Soft jaws support the outside diameter while the lathe establishes the concentric turned surfaces and register geometry. The photographed intermediate state shows the hole-ring face while the part is still held in the turning setup.
02 · Batch milling
Standardize locating across twelve fixture stations
A dedicated fixture plate holds twelve workpieces at once for sequential milling. Reusing the same locating architecture reduces part-to-part setup variation while the front, rear and radial milled features are completed in controlled operations.
03 · CMM inspection
Measure the datum-related geometry on a ZEISS CMM
The inspection program checks the controlled diameters together with cylindricity, perpendicularity and coaxiality. Parts are staged beside the machine while the probe runs the programmed measurement sequence.
04 · Recorded results
Compare every measured value with its report limit
The published report excerpt contains the nine checked characteristics and their tolerance bands. All nine are shown within tolerance. Program name, part code, order metadata, operator and date have been excluded from the image.
05 · Finished geometry
Review the completed front and rear feature systems
The two finished views show why the process cannot be treated as one simple flange operation: the dense front hole ring and internal profile are paired with a different rear pocket, boss and four-hole geometry while sharing the same functional datum structure.
Sources & technical references
- ISO 286-1:2010 — ISO code system for tolerances on linear sizes — ISO (International Organization for Standardization)
Defines the tolerance and fit code system used by the P6, H6 and h6 designations referenced in the production drawing.
- ISO 286-2:2010 — Tables of standard tolerance classes and limit deviations — ISO (International Organization for Standardization)
Provides the standard tolerance classes and limit-deviation tables for holes and shafts.
- GB/T 1804-2000 — General tolerances for linear and angular dimensions without individual tolerance indications — Standardization Administration of China
The production drawing applies class m to dimensions without an individual tolerance.
- GB/T 1184-1996 — Geometrical tolerancing; geometrical tolerance for features without individual tolerance indications — Standardization Administration of China
The production drawing applies class k to geometrical features without an individual tolerance.
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