Harmonic-drive housings, joint brackets, link arms and motor mounts machined on sixteen five-axis centers, so load-carrying bores and mounting faces come off one setup instead of three.
A joint that measures correctly on the bench can still run rough under load. The causes below are the ones we meet most often when a customer brings us a redesign.
Each bore can sit inside its own limit and the pair still misses coaxiality. The bearing then sits cocked, preload becomes uneven, and one side of the joint runs hot. Machining both bores from one datum is the direct fix.
Diameter alone does not describe a bearing seat. A three-lobed bore that averages to nominal will pinch the outer race. We check form on seats rather than only size, and we say so when the drawing is silent about it.
A flange that is not square to the bore is flat on the surface plate and wrong in the assembly. When the bolts are tightened the housing is pulled, and the axis tilts with it.
Twisted links and drifted bores show up as position error at the tool centre point, not as a failed part. By then the joint has been rebuilt twice and the servo has been compensating for geometry.
The geometry of a robot joint is simple. What decides whether it lasts is how the bores relate to each other and what the bearing seats actually measure.
This is the main reason joint work comes to five-axis centers. The bracket is held once and the rotary axes bring each bore to the tool, so both bores share a datum and a spindle axis. Where a bracket is too large for the rotary table, we machine a reference face first and use it for every later operation.
The same logic applies to the output flange and the motor pilot. Cut them in the setup that cuts the bore and the relationship between them is machine-made, not fixture-made.
A bearing seat is a system of diameter, roundness, taper and surface finish. Two of those are on most drawings; the other two decide whether the joint feels tight at speed.
Seats that carry a pressed or preloaded bearing are finished to Ra 0.2–0.8 μm and checked for form, because a lobed or tapered seat can be exactly on diameter and still load the race unevenly.
For most arm joints the material question is a stiffness question. 7075 gives the highest stiffness for a given section, which lets you thin the walls and still hold position under load. 6061 costs less and machines faster, and it is the right default where stiffness is not the limiting factor.
Titanium enters when the load concentrates at a small joint and steel inserts are not acceptable. It cuts far more slowly, so the design has to justify it, usually by removing a part rather than by making one part stronger.
Every component below is quoted against one question: which feature decides how the joint behaves in service?
| Component | Critical feature | Why it decides how the joint feels |
|---|---|---|
| Harmonic-drive housing | Inner bore and its concentricity with the output flange | Any eccentricity becomes a once-per-revolution ripple in the output motion |
| Joint bracket or yoke | Bore alignment between the two arms and squareness to the mounting base | Offset bores tilt the axis, and the servo compensates for it all day |
| Link arm | Parallel faces and end bores | Bent or twisted links show up as position error at the tool centre point |
| Motor mount | Pilot bore concentric with the bolt circle | A pilot that is off centre shifts the rotor and loads one bearing harder |
| Cable guide and cover | Wall thickness and running clearance | Thin covers rub through where clearance was assumed rather than measured |
Part families that arrive with a robot joint project, from a single prototype to a production set.
Thin-wall housings with an internal bore, a flange and a bolt pattern that all have to agree with each other.
Two-arm brackets where bore alignment decides the preload, machined in one setup or against a machined reference face.
Long parts where parallel faces, end bores and weight relief have to be produced without inducing twist.
Pilot bores, bolt circles and mounting faces made concentric in one operation instead of three.
Steel load-path parts in 17-4PH, 4340 or hardened grades, turned and milled to the fit you specify.
A complete joint set quoted as one order, so the parts are machined to the same revision and arrive together.
| What we hold | Where it applies | How it is verified |
|---|---|---|
| ±0.005 mm / ±0.0002 in | Bores, seats and faces called out on the drawing | Measured on the finished part, with results reported on request |
| Ra 0.2–0.8 μm | Bearing and sliding seats | Compared against the surface callout on the drawing |
| Ra 0.8–1.6 μm | Mating faces and seals | Checked where the seal or gasket type makes finish critical |
| Roundness and taper on seats | Any bore carrying a pressed or preloaded bearing | Form measured, not inferred from a diameter reading |
| One datum per part | Related features cut in the same setup | Reported as a feature-to-feature relationship rather than separate dimensions |
Joint work is judged in service, not on the delivery note. These are the numbers we work to and the checks behind them.
Our stated machining tolerance, held on the features you call out and on the dimensions the drawing leaves open, with ±0.0002 in as the imperial equivalent.
Fine finishing reaches Ra 0.2–0.8 μm, which is what a pressed or preloaded bearing needs from its housing.
Enough capacity to hold a joint set in one setup rather than splitting it across machines and datums.
Medical and laboratory robotics run under the same quality system as our medical device work, alongside ISO 9001:2015.
Related features are cut in one setup, so the relationship between a bore and its flange is decided by the machine, not by a fixture.
One joint is a normal order and runs on the same equipment as a production set, with the same inspection.
Housing, bracket and link machined to one revision so the set assembles without selective fitting.
Rotor, stator sleeve and output flange parts where concentricity sets the vibration level of the drive.
Pins, dowels and steel inserts for load paths that cannot run through aluminium.
Small actuated joints machined under ISO 13485 process control, with dimensional documentation available.
Yes, and that is the main reason this work comes to five-axis centers. The bracket is held once and the rotary axes bring each bore to the tool, so both bores share one datum and one spindle axis.
Where a bracket is too large for the rotary table, we machine a reference face first and use it for every later operation, which keeps the same relationship without the single setup.
We machine to ±0.005 mm / ±0.0002 in, which covers the seats you call out and the dimensions the drawing leaves open. Send the bearing part number and we will work to the recommended housing fit.
If the seat needs a specific roundness or taper, mark it, because that is what we will measure and report.
Rough with stock left on, let the part settle, then finish with light passes and short tools so cutting forces stay low. Finishing happens after the last clamp change, so a wall that relaxes slightly is not clamped back into shape and then released at inspection.
We machine the parts and can quote light assembly such as pressing bearings, installing dowels or fitting inserts, where that takes work off your line.
For most robotics customers we supply machined and inspected parts with the fits already verified against the mating components.
STEP, STP, IGS, IGES, STL or X_T for the model, and DWG, DXF or PDF for the drawing with the functional dimensions marked. If the joint is one part of an assembly, send the neighbouring parts too, because clearance problems are usually visible in the assembly and invisible in a single part.
Yes. One part is a normal order with no minimum quantity, machined on the same five-axis centers as production work. If the prototype will be tested to failure, tell us and we will quote it in the production alloy rather than a stand-in material.
Say which faces stay visible. We plan clamping around them, keep finishing cuts for after the last fixture change, and quote the finish you asked for as a separate line so you can see what it costs.
Anodizing, bead blasting, polishing and as-machined finishes are all available on joint quantities.
Quotation and a free DFM analysis within 12 hours, production starting within 24 hours of approval, and parts shipping in 3–5 days. Orders that include anodizing or heat treatment are scheduled with those steps included from the start, not added afterwards.
We will tell you which faces we would machine in one setup, where the risk sits in the current design, and what it costs to take that risk out. Uploads stay confidential and an NDA is available.
Single-setup machiningForm checked, not only sizeReports on requestNo minimum order
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