Low-Volume CNC Machining for PC Medical Device Housings

When a medical device needs dozens of finished plastic housings, the manufacturing choice is not always straightforward. Injection molding may eventually offer the right economics at higher volumes, but the tooling investment can be difficult to justify for an initial batch.

For this medical equipment project, the requirement was 60 PC (Polycarbonate) bottom covers for early market introduction and product trials in the United States.

The covers were CNC machined from customer-supplied CAD data, carefully sanded and finished with white paint. These were not raw engineering samples—the customer needed finished housings that could be installed on actual product units.

Project Details

A Flat Housing with Substantial Internal Machining

The bottom cover has a relatively low overall profile, but the internal geometry makes it more involved than a simple flat panel.

As shown in the part, there are broad recessed sections at different depths, a large rectangular opening, raised circular features, perimeter mounting holes, smaller holes and slots, and several local steps.

These details matter when evaluating a CNC machined medical device housing.

Large pockets account for substantial material removal, while smaller mounting and locating features still need to remain in the positions specified on the drawing. The perimeter geometry also has to correspond with the rest of the equipment enclosure.

This is why a plastic housing cannot be evaluated from length, width and material alone. Internal geometry, machining depth, openings and functional features can have a greater influence on machining time and process planning.

Why CNC Machining Was Chosen for 60 Sets

At 60 sets, the customer needed more than a few prototypes, but the project had not yet reached the point where an injection mold made economic sense.

The units were intended for market promotion and trial use. Keeping the manufacturing route flexible was therefore valuable.

With PC CNC machining, the covers could be produced directly from the current CAD model without first investing in production tooling. If early product feedback resulted in a change to a mounting point, opening or internal clearance, the design and machining program could be updated for a later batch.

CNC machining was not selected because it is always cheaper than molding. It was selected because it suited the quantity, design maturity and current production stage.

For buyers looking for 50–100 finished plastic housings, that distinction can be important.

Machining a Large Polycarbonate Bottom Cover

With a footprint of roughly 400 × 300 mm, the part is larger than many typical CNC machined plastic components.

Broad recessed areas and multiple feature depths mean that machining sequence and workholding need consideration as material is progressively removed.

Polycarbonate also benefits from appropriate cutting conditions. Tool condition, cutting parameters and heat control influence the quality of edges around openings, holes and smaller features.

The objective is not to apply the tightest possible tolerance everywhere.

Instead, the drawing determines where dimensional control matters most—for example, mounting locations, mating areas, internal clearances and other features that affect assembly.

This approach keeps the machining requirements tied to the actual function of the cover.

Sanding Matters Before White Painting

The machining process creates the required geometry, but the finished cover also has a cosmetic requirement.

Before white paint is applied, the relevant surfaces need careful sanding.

Tool paths and local transitions that are barely noticeable on raw PC can become much easier to see beneath a uniform painted finish. Broad surfaces are particularly sensitive because small inconsistencies can stand out once the coating is applied.

At the same time, sanding needs restraint.

Mounting holes, edges, locating features and mating areas should retain their machined geometry. Aggressive manual finishing around these locations can improve appearance while unintentionally affecting fit.

For medical equipment plastic housings, surface preparation therefore has two jobs: create a suitable base for painting and preserve the functional geometry already established by CNC machining.

From a Machined Part to a Finished Housing

Inspection changes once the cover has been painted.

Before finishing, attention is mainly on the drawing-defined features: holes, pockets, openings, mounting locations and other functional dimensions.

After painting, the broad white surfaces, edges, recessed regions and local transitions also need to meet the specified cosmetic requirement.

Paint buildup around functional areas needs attention as well, particularly where another component will mount or locate.

The customer was purchasing 60 finished medical device bottom covers, not unfinished machined blanks. Machining, manual surface preparation and painting therefore had to work as one manufacturing sequence.

Repeatability Matters More at 60 Pieces

A two-piece prototype order and a 60-piece finished housing order create different production demands.

Once the first parts establish the machining and finishing approach, the same critical features and appearance standard need to carry through the remaining batch.

For this project, the workflow was kept practical:

Drawing Review → PC CNC Machining → Feature Inspection → Sanding → White Painting → Appearance Check → Protective Packing

The process itself is not unusual. The important part is maintaining control as the housings move from machining into manual finishing and painting.

That is what makes this project better described as low-volume plastic housing production rather than simply prototype machining.

When Does CNC Machining Make Sense Before Tooling?

This manufacturing route can be worth evaluating when:

• the initial requirement is measured in dozens rather than thousands;
• the product design may still change after early market feedback;
• tooling investment is difficult to justify at the current volume;
• PC or another engineering plastic is required;
• internal features need accurate machining;
• the exterior needs a finished painted appearance.

There is no universal quantity where CNC machining becomes better or worse than injection molding. Part geometry, material, finishing, tooling cost and expected future volume all influence the decision.

In this case, machining 60 PC covers allowed the customer to put finished products into the market first and leave the injection-molding decision for a later production stage.

RFQ Information for Medical Plastic Housings

For a custom medical device plastic housing, a useful RFQ should include more than the overall size and quantity.

The most helpful information is:

3D CAD + 2D Drawing + Material Grade + Quantity + Critical Tolerances + Assembly Interfaces + Cosmetic Surface Requirements + Paint Color / Finish

For a bottom cover, identifying critical mounting holes, mating areas and visible surfaces helps us understand where machining accuracy matters most and where additional attention is required during finishing.

That gives us a clearer basis for evaluating both the CNC work and the finished housing requirement.