When a machined part misses tolerance, it can be tempting to blame the CNC machine, the tooling, or the program. In reality, it can come back to the setup: how the component is located, clamped, supported and referenced while it’s being cut. That’s workholding — and it can be one of the biggest factors behind repeatable accuracy, predictable lead times, and parts that assemble first time.
 
At Universal Fabrications, our approach to precision CNC machining (milling, turning and post-machining of complex fabrications) starts with a straightforward principle: if you can’t hold it properly, you can’t machine it properly. It’s a practical discipline that becomes even more important as parts get larger, more complex, or more critical to the final assembly.

Common CNC Machining Issues – How Workholding + Real-World Expertise Prevents Them

“It’s difficult to assemble” – parts don’t “pull up”, holes don’t line up, interfaces fight each other

Assembly fit problems can occur even when individual features measure within tolerance. The root cause is often datum control and feature-to-feature relationships across multiple operations — features aren’t being machined from the same functional references, or they can shift during re-clamping.

Universal’s approach: The machining route is planned around the functional datums that drive fit. Workholding is engineered so those datums are protected across every operation. Where appropriate, a dedicated fixture is designed and manufactured in-house so components load consistently and critical interfaces machine true to the same reference every time.

“There is Chatter, taper, poor surface finish or inconsistent bores”

These symptoms can occur when there is insufficient rigidity — either the part can flex, or the clamping method can allow micro-movement under cutting load.

Universal’s approach: Controlled support points, correct clamping pressure, and predictable tool access. On turning, that can mean the right jaw/collet strategy; on milling, it’s often about supporting thin walls and avoiding distortion from over-clamping. Universal also manufactures its own fixtures, so complex parts aren’t forced through a “generic” setup. This is especially relevant on precision bores, bearing locations and powertrain-type geometries where finish and geometry directly affect performance.

“Distortion caused by clamping” – especially on thin sections and large flat faces

Distortion can occur when clamping forces “pull” a component into shape while it’s held, then it relaxes after machining, and the part moves out on flatness, parallelism or squareness.

Universal’s approach: Workholding that supports the component in its natural state, spreads clamping loads, and sequences machining to reduce stress-release effects. Where required, fixture design is used to support critical faces and keep the part stable without brute force. This often shows up on lightweight structures, large faces that must seal, and parts with thin-wall features where “holding it harder” can make it worse.

“Machined weldments/fabrications won’t sit flat”

On weldments, movement can occur due to residual stress, distortion, and part-to-part variation. Datums can shift between “as welded” and “as machined”, so a textbook approach can struggle on real components.

Universal’s approach: Treat the weldment like a real object — define functional datums, control clamp-induced distortion, and machine critical interfaces in stages to stabilise geometry. Where needed, dedicated fixtures are designed to support the frame consistently while machining mounting faces, bearing locations, alignment features, or sealing surfaces. This is a familiar challenge across defence structures, construction/plant frames, and engineered assemblies where multiple interfaces must align cleanly without fettling.

“Inconsistent results across batches” – first-offs are okay, then variation creeps in”

Variation can occur when the loading method, clamping, or re-clamping is inconsistent — or when too many variables sit in the setup rather than the process route.

Universal’s approach: Standardised workholding (often fixture-based), a controlled loading method, and a stable process route — turning good first-offs into reliable production output. This becomes critical when moving from prototype into repeat production, where delivery rhythm and consistency matter just as much as tolerance.

Machining Support

Universal’s machining platform supports the workholding-led approach above across milling, turning, and post-machining of fabricated assemblies:

Send drawings for a quote

If you need precision CNC milling, CNC turning, or post-machining of fabrications/weldments, send your drawings and Universal Fabrications will propose a manufacturing approach that protects accuracy, repeatability and lead time — starting with the workholding strategy that makes the machining succeed.