Where the accuracy actually comes from
A folded base frame is not an accurate surface. A machined pad is. Where a linear rail, a servo mount or a bearing housing bolts to a frame, the accuracy is established after welding — weld oversize, then machine the pads — and that sequence has to be in the plan before the first frame is cut.
Where no machined interface exists, the part is a structure and should be dimensioned as one: overall size, squareness, and the positions of bolt-on features under general tolerance. Specifying a precision tolerance on a welded frame does not buy accuracy, it buys inspection and rejection.
| Interface | How accuracy is achieved | What the drawing must say |
|---|---|---|
| Linear rail or profile rail mount | Machined pad after welding, or a separate ground plate | Flatness, parallelism and a datum |
| Servo / gearbox mount | Machined face or a separate mounting plate | Position tolerance to the rail datum |
| Robot cell base | Leveling provisions plus a machined reference | The reference plane and how it is measured |
| Guarding panel | Folded frame with a defined opening | Mesh or polycarbonate, fixings, tool access |
| Operator station | Folded and formed ergonomics | Reach, viewing angle, hinge and lock detail |
| Conveyor / indexing frame | Structure with adjustable feet | Adjustment range rather than a fixed tolerance |
Guarding is a design task, not a panel
A guard has to prevent access to a hazard, be inspectable, and come off for maintenance without needing a ladder and two people. That combination usually means a folded frame with defined apertures, a mesh or clear panel retained in a rebate rather than bonded, and hinges or quarter-turn fasteners on the side that gets serviced.
The interlock is the other mechanical consequence. Where a guard carries a safety switch, the switch needs a mounting surface and an actuator with a defined alignment range, so the guard and the switch have to be designed together. Retrofitting an interlock to a finished guard normally means a new guard.
- Decide which surfaces are machined and which are structural, and say so on the drawing.
- Design the guard for one-person removal, from the side where maintenance actually happens.
- Allow for cable routing to sensors, switches and actuators before the geometry is frozen.
- Check that every fastener can be reached with the tool a technician will bring.
Materials, finish and vibration
Frames are normally steel, folded sheet with returns and gussets for most machines, square tube where the span is long or the load heavy. Aluminium appears where mass matters — moving axes, robot end effectors — and then the joint design changes with it.
Finishing is usually powder coat for the frame and bare or anodised for machined reference surfaces, which have to be masked. Where a machine vibrates, thread-locking and fastener retention matter more than thickness; a bolted joint that loosens is a design problem, not a stiffness problem.