Five-Axis CNC Machined Aluminum Wrist Housing
Wrist housings machined on five axes from 7075-T6 billet, with compound-angle bores positioned to ±0.02 mm, bore axes angled to ±0.02°, 4 mm walls and coplanar mounting pads within 0.02 mm. Paired housings are matched in weight within 5 g.
- Compound-Angle Bores in One Set-up
- Bore Position ±0.02 mm
- Walls Held at 4 mm
- Balanced Within 5 g
*Send the kinematic model and the bearing drawing, not just a 2D print. The bore intersection point is what sets the robot repeatability, and a print usually dimensions each bore from a different face.
Wrist Housing Overview
A wrist housing carries two intersecting bearing bores at compound angles, and the distance between those axes is the robot accuracy. It cannot be machined in three axes without losing that relationship.
The billet is roughed on five axes leaving 1 mm, stress relieved, then finished in a single five-axis set-up so both bores, the pads and the motor flange stay in one coordinate system before the part is released.
7075-T6 Aluminium Billet
7075-T6 is used because the walls are 4 mm and the housing sees reversing loads at the wrist. Its strength lets the lightening pockets go deeper without the bore distorting under bearing preload.
6061-T6 or 6082-T6
6061 is chosen for a low-load wrist where cost matters more than stiffness, and 6082 where the housing is welded to a fabricated forearm instead of bolted.
Below 4 mm wall the bearing bore goes oval when the bearing is pressed in; the fix is a thicker wall or a steel insert, not a harder alloy.
Wrist Housing Specifications
Five-axis machining data for wrist housings, with the bore, angle and wall values that decide whether the arm repeats.
| Specification | Machining Data | Specification | Machining Data |
|---|---|---|---|
| Product | Robot Wrist Housing / Compound-Angle Housing | Machining Process | 5-Axis Simultaneous CNC Milling, Boring |
| Material | 7075-T6 Aluminium Billet | Envelope | Up to 260 × 200 × 180 mm |
| Bore Diameter | Ø 30 – 110 mm, H7 | Bore Axis Angle | Any Compound Angle, ±0.02° |
| Bore Position | ±0.02 mm in X, Y and Z | Bore Roundness | 0.015 mm |
| Wall Thickness | 4 – 10 mm | Web Thickness | 3 mm Minimum |
| Flange Face | Square to Bore 0.02 mm | Mounting Pads | Coplanar 0.02 mm |
| Balance | Within 5 g Between Paired Housings | Surface Finish | Ra 1.6 µm Bores, Ra 3.2 µm Blends |
| Customization | Cable Passages, Motor Flange, Dowel Holes, Lightening Pockets | Lead Time | 8 – 10 Days Sample, 18 – 25 Days Batch |
| Inspection | CMM Bore Axis and Position, Roundness, Pair Weighing | Packing | Foam Cradle per Housing, Pair Boxed |
Key Features of Our Wrist Housings
Both axes cut in one set-up, roughed then stress relieved.
Both Bores in One Five-Axis Set-up
The wrist and forearm bores are finished without re-fixturing, so the axis intersection stays within 0.02 mm and the kinematic model matches the real arm.
Rough, Stress Relieve, Finish
The part is roughed to 1 mm, taken off the machine and stress relieved, then finished. Skipping that step moves the bores 0.03 mm overnight.
Walls Held at 4 mm
Wall thickness is checked with an ultrasonic gauge at six points after finishing, because a 3 mm wall goes oval under bearing preload and the wrist loses stiffness.
Pads Coplanar to 0.02 mm
The mounting pads are finished in the same set-up as the bores, so the housing bolts down without shims and the motor flange stays square to the axis.
Wrist housing that has to hold its axis?
Surface Finishes for Wrist Housings
Bores and pads are fits, the body is visible and the pockets are hard to coat evenly.
| Finish | Main Purpose | Finish | Main Purpose |
|---|---|---|---|
| Hard Anodizing | Wear resistance on the bore and pads | Type II Anodizing | Colour on the visible body |
| Masked Bores | Bores stay at H7 after coating | Bead Blasting | Even matte before dye |
| Laser Marking | Axis reference and serial | Chromate Conversion | Conductive finish for earthed arms |
| Anodizing Build | 25 – 50 µm on Wear Faces | Vapour Blasting | Satin Blends Between Pockets |
| Bore Plugs | Removed After Coating | Pad Protection | Taped Coplanar Faces |
| Balance Mark | Dot on the Light Side | Assembly Clean | Ultrasonic Before Bearing Fit |
*Hard anodizing builds 25 to 50 µm and will take up the H7 bore. Bores are masked with expanding plugs and the pads are taped, otherwise the bearing will not go in and the pad will not sit flat.
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Machining Process for Wrist Housings
Both bores are cut in one five-axis set-up, so the wrist axis and the forearm axis intersect where the kinematic model says they do.
01. Kinematics and Bearing Review
Check the axis intersection, the bearing fits and the motor flange, then build the five-axis model from those rather than from the 2D print.
02. Rough on Five Axes
Rough all faces and pockets leaving 1 mm, keeping the part on a dovetail so it can be turned over without losing the datum.
03. Stress Relieve
Take the part off, stress relieve it and let it settle, because 80 % of the material has been removed and the bores will move otherwise.
04. Finish Bores and Pads
Finish both bores, the pads and the motor flange in one five-axis set-up, checking the axis intersection on the CMM before unclamping.
05. Match, Anodize, Verify
Weigh and match the pair, mask the bores and pads, hard anodize, then re-check the bore size and the pad coplanarity.
Send the kinematic model and the bearing fits, and we will quote a wrist housing with both axes cut in one set-up.
Wrist Housing FAQs
Because the two bearing bores intersect at a compound angle. In three axes the part has to be re-fixtured between bores, and each re-fixture adds 0.02 to 0.04 mm to the axis intersection error.
0.02 mm in X, Y and Z, measured on the CMM with a mandrel in each bore. That is the number that shows up as repeatability at the tool centre point.
Yes, for any housing where more than 60 % of the billet is removed. Without it the bores move 0.03 mm in the first 24 hours and the part is scrap.
4 mm as standard and 3 mm in a local web. Below 3 mm the wall deflects under bearing preload and the bore goes oval even though it was round on the CMM.
By weight within 5 g and by bore position within 0.01 mm of each other, so a left and right wrist behave the same under the same servo tuning.
Yes, bores and pads are masked as standard. If a coated bore is needed it is machined undersize and honed after anodizing to the finished H7 size.
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