CNC Turning · Robotics · Brass
Machining a Graphite-Lubricated High-Strength Brass Robot Joint Bushing to Ø16 h7 / Ø8 H7
A small ZCuZn25Al6Fe3Mn3 bushing combined graphite lubrication inserts with an Ø16 h7 outside diameter, an Ø8 H7 bore and 0.01 mm datum-related geometric controls.
At a Glance
- Material
- ZCuZn25Al6Fe3Mn3 high-strength brass with graphite inserts
- Process
- CNC turning, qualified external graphite insertion, final precision turning and OD inspection
- Application
- Robot joint bushing
- Precision fits
- Ø16 h7 OD (0/-0.018 mm) and Ø8 H7 bore (+0.015/0 mm)
- GD&T requirements
- 0.01 mm perpendicularity to A and coaxiality to B; GB/T 1184 class H
From the Production Drawing
The Requirement, in the Engineer's Own Notes
The published excerpt retains only the product views, critical dimensions, datum indicators and tolerance frames. The drawing identifier, title block, order and customer information, dates, approvals and personnel details have been excluded.
01
The Challenge
The drawing uses a 5:1 scale because the bushing is physically small, yet it combines two precision fit features: an Ø16 h7 outside diameter with a 15.982-16.000 mm limit range and an Ø8 H7 bore with an 8.000-8.015 mm range. Individually specified 0.01 mm perpendicularity and coaxiality controls reference datums A and B, while unspecified geometric tolerances follow GB/T 1184 class H. The part also cannot be completed as a simple turned blank. Graphite has to be inserted as a specialist lubrication process, after which the returned intermediate requires final machining to bring the OD to size and cut the protruding graphite flush with the finished surface without losing the intended insert geometry.
02
OUJI's Approach
OUJI kept the machining, route control and final acceptance under one project plan. Initial CNC turning was completed in OUJI’s Mazak turning cell. The graphite insertion stage then went to a qualified specialist partner, consistent with OUJI’s vetted-partner model for processes that require dedicated expertise. After the graphite-filled intermediate returned, OUJI performed the final precision turning operation that established the Ø16 h7 outside diameter and brought the exposed graphite level with the finished mating surface. The returned condition and finished condition were reviewed side by side, and the final outside diameter was checked directly with a digital micrometer.
03
The Result
The photographed inspection records an outside-diameter reading of 15.992 mm. That value is inside the drawing’s Ø16 h7 range of 15.982-16.000 mm and sits 0.008 mm below the upper limit. This is evidence for one inspected part and one outside-diameter feature only. It is not presented as proof of the Ø8 H7 bore, a batch-wide inspection result or a statistical capability study.
Production Sequence
From CNC Turning to a Verified Graphite-Insert Surface
The photographed route separates the in-house machining stages from the qualified specialist process, then closes the loop with a direct check of the finished outside diameter.
A qualified external process means the specialist partner performs the graphite insertion while OUJI remains accountable for the routing, returned condition, final machining, inspection and delivery.
01 · CNC turning
Machine the small brass blank in a Mazak turning cell
OUJI turns the high-strength brass blank and prepares the geometry required before graphite insertion. The photograph documents the small part at the Mazak turning cell; unrelated reference information visible elsewhere on the machine is not used as dimensional evidence for this case.
02 · Specialist graphite process
Route the lubrication inserts through a qualified partner
A specialist partner completes the graphite insertion stage. The photographed intermediate shows the part after that process returned to OUJI, with graphite still protruding beyond the brass surfaces; it does not depict the partner’s proprietary operation itself.
03 · Final precision turning
Size the Ø16 h7 OD and machine the graphite flush
The returned intermediate is precision turned to the final outside-diameter limit while the protruding graphite is cut level with the mating surface. The side-by-side photograph makes the state change visible: rough graphite projections before the operation and clean elliptical inserts in the finished surface afterward.
04 · OD verification
Check the finished outside diameter against the h7 limits
A digital micrometer records 15.992 mm on the inspected finished part. The value is compared directly with the drawing range of 15.982-16.000 mm; no claim is made here for the unphotographed bore inspection or for an entire production batch.
Sources & technical references
- ISO 286-1:2010 — ISO code system for tolerances on linear sizes — ISO (International Organization for Standardization)
Defines the ISO tolerance and fit code system used by the H7 bore and h7 outside-diameter designations 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 H to geometrical features without an individual tolerance.
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