Custom CNC Machined Robot Torque Sensor Mounting Ring with 0.01mm Flatness Grade in 6061-T6 Aluminum

Dongguan Changxinda Precision Technology Co., Ltd. has manufactured custom robot components to drawing since 2008. The plant operates 4-axis and 5-axis machining centers, turn-mill combined lathes and precision CNC lathes, staffed by more than 90 people, with 50 to 60 percent of production exported to robotics, automation, medical, automotive and aerospace buyers. Every part on this page is a non-standard item: your drawing, your material callout, your inspection requirement.

This page covers the torque sensor mounting ring — a thin circular flange that sits between a robot joint output and the sensor or the arm segment above it. The ring itself looks unremarkable: a flat face, an outside diameter, a bore and a bolt circle. What makes it difficult is that the sensor reads strain through it. Any flatness error, any variation in wall thickness, any residual stress that relaxes after machining becomes hysteresis and drift in the torque signal — and a robot that cannot repeat its own force readings cannot be trusted with a delicate assembly task.

Ring-shaped parts are turned, then the hole pattern is milled from a single datum. The order is not optional, because every re-chuck on a thin ring introduces a new distortion.

• Blank preparation: the ring is cut from plate or bar with 3 mm allowance per side, then rough turned on both faces and on the outside diameter, leaving 0.5 mm of stock for the finishing operation.
• Stress release: rough turned rings are released from the chuck and allowed to stabilise before finishing. On a 4 mm wall ring this step removes the ovality that would otherwise appear only after the part is unclamped.
• Soft jaw finishing: finish turning is done in aluminium soft jaws bored to the ring diameter, so clamping force is distributed around the full circumference instead of being concentrated at three points.
• Bolt circle in one set-up: the hole pattern is milled in a 4-axis operation from the finished bore and face, so the position of every hole is generated from one datum. Drilling the pattern before the faces are finished is a common cause of bolt circle runout.
• Deburr and mask: holes are chamfered in the program, then the sensor contact face is masked before anodizing, since a coated face changes the stack height of the joint.
• Matched sets: when a ring is supplied with its mating flange, both parts are machined in the same batch from the same stock, so the fit is proven before shipping rather than at the customer assembly station.

The declared capability for this part family is 0.01 mm flatness on the sensor contact face, 0.01 mm roundness on the bore and outside diameter, 0.01 mm position on the bolt circle, and 0.01 mm parallelism between the two faces.

• Flatness measured on a granite surface plate with a dial indicator, then confirmed on the CMM across a grid of points rather than at three spots.
• Wall thickness checked at eight positions around the circumference, since uneven wall is the main source of thermal drift in service.
• Bolt circle position verified as true position against the drawing datum, not as a centre-to-centre distance.
• Surface roughness on the sensor contact face held at Ra 0.8, with a roughness trace included in the first article report when requested.
• Anodized rings are re-checked after coating, because coating thickness variation is itself a flatness error on a thin ring.
• Metrology room at 20 °C, CMM resolution 0.001 mm, first article report with a ballooned drawing.

Torque sensor interfaces are rarely standard across robot platforms, so the ring is treated as a fully custom part.

• Outside diameter 40 mm to 200 mm, wall thickness from 3 mm, bore and pilot diameters to your fit.
• Bolt circle from 4 to 16 holes, M3 to M8 or through holes, with counterbores or spot faces as required.
• Materials: 6061-T6 and 7075-T6 aluminum, 304 and 316L stainless steel for higher stiffness or corrosion resistance.
• Finishes: clear anodizing, black anodizing, hard anodizing, chromate-free conversion coating, with selective masking on functional faces.
• Laser marking of part number, batch and serial on a non-functional face for traceability.
• Supply as a matched ring and flange set, or as a kit with dowel pins, screws and O-rings packed together.
• Drawing input in STEP, IGES, X_T, DWG, DXF or PDF, or a sample ring for measuring and modelling.
• Prototype quantity from one piece, no tooling charge, design feedback returned within 24 hours.

Robot projects move in phases, and the torque ring usually sits on the critical path of a joint assembly. The schedule is quoted from the process route so that it holds.

• A named project engineer per order, with weekly status updates and photographs of work in progress.
• Written notice at least 5 working days before the ship date if any step is at risk, including the anodizing subcontract step.
• Shipping by express, air or sea, door to door, with rings protected by foam and packed flat so the faces cannot be damaged in transit.