CNC Parts for Medical Devices: Tolerance Labeling Mistakes That Cause Rework

Created on 09.29

For mechanical engineers, design engineers, and procurement managers in medical device R&D (e.g., diagnostic instruments, orthopedic tools, biotech equipment), rework on CNC parts is a costly nightmare. It delays regulatory compliance, hikes production costs, and risks missing critical new product launch timelines. One of the top culprits? Avoidable tolerance labeling mistakes. Below are the most common errors—and how to fix them—plus how Marigold Rapid (

www.marigold-rapid.com) keeps your medical CNC parts on track.​

1. Not Labeling Reference Datums​

Tolerances only make sense with a clear reference datum (a fixed point/surface for measurement). For example, if you design a CNC-machined bracket for a blood analyzer but skip datum labels, machinists can’t align the part correctly. This leads to misfits during assembly—forcing rework to adjust holes or mounting points.​

Fix: Always mark 1–3 reference datums (e.g., “Datum A: Bottom Surface”) on CAD files, especially for parts that attach to other medical components.​

2. Over-Tolerancing Non-Critical Features​

Medical devices need precision—but over-specifying tolerances on non-key features wastes time and causes rework. For instance, an orthopedic instrument’s handle (a non-functional cosmetic part) doesn’t need a ±0.005mm tolerance (reserved for surgical tips). Tightening tolerances beyond what’s necessary leads to frequent rejects, as even small deviations trigger rework.​

Fix: Prioritize tolerances: Use tight specs (±0.01mm) for critical parts (e.g., sensor housings) and looser ones (±0.1mm) for non-essential features.​

3. Ignoring Material Thermal Expansion Tolerances​

Many medical CNC parts (e.g., autoclave-compatible components) undergo high-temperature sterilization. If you ignore thermal expansion in tolerance labels—for example, using a fixed ±0.02mm tolerance for a stainless steel part that expands 0.05mm when heated—the part will be out of spec post-sterilization, requiring rework.​

Fix: Add thermal expansion allowances (e.g., “+0.03mm for 121°C sterilization”) based on the material (stainless steel 316L, titanium alloy).​

4. Missing Geometric Tolerances​

Size tolerances (e.g., “10mm ±0.01mm”) aren’t enough—medical parts often need geometric tolerances (flatness, perpendicularity) to function. For a 输液 pump’s seal housing, skipping a “Flatness: 0.02mm” label can lead to leaky seals, as the uneven surface fails testing. This forces rework to grind the surface flat.​

Fix: Include geometric tolerances for parts that need alignment, sealing, or movement (e.g., “Perpendicularity: 0.01mm for Shaft Hole”).​

How Marigold Rapid Prevents Tolerance-Related Rework​

At Marigold Rapid, we specialize in medical device CNC parts—so we catch tolerance mistakes before they cause rework. As a one-stop full-process integrated manufacturer, our DFM (Design for Manufacturability) team reviews your CAD files for free, flagging missing datums, over-tolerancing, or unaccounted thermal expansion.​

Our fast response means you get feedback in 24 hours—no delays to your medical R&D timeline. Backed by SGS certification (ISO9001 and 13485), our machining process adheres to medical tolerance standards, ensuring parts meet specs on the first try. Whether you’re designing orthopedic components or diagnostic instrument parts, we flexibly adapt to your tolerance needs—zero rework, zero headaches.​

For medical device teams tired of tolerance-related rework, Marigold Rapid is your reliable partner. Contact us today to review your CNC part designs!