Plastic Enclosure Machining: What Designers Need to Know About Materials, Tolerances and Corner Radii

MACHINING HIGH-PERFORMANCE PLASTICS

Virtually every standard enclosure will need machining to create apertures for controls, LEDs or a display – or for extra ventilation. Perhaps extra PCB mounts will need to be added (or pillars may need to be removed to create space).

Advances in CNC machining make it possible to achieve incredibly precise cuts and finishes on customized plastic enclosures. This has enhanced accuracy, quality and consistency – particularly on plastics that have traditionally been more difficult to machine.

Plastics can be both easier and harder to machine than metals, depending on the characteristics of the polymer and the machining process involved. Thermoplastics may be softer and lower density than metal but they also present unique challenges.

One such drawback is plastics’ tendency to melt, deform or warp due to heat build-up. They can soften, melt or become discolored when subjected to excessive heat during machining. ABS or ASA can easily warp or smear when exposed to excessive cutting heat. As plastic begins to weaken, it can stick to the cutting tool or create unwanted burrs. This makes it harder to remove material cleanly – potentially affecting the precision of the machining.
 
So it pays to partner with an experienced enclosures manufacturer like OKW that carries out all machining and other customization work in-house. One trusted supplier is fully accountable for quality and consistency from start to finish.

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TOLERANCES FOR MACHINING PLASTIC ENCLOSURES

Deviations from the nominal dimensions and the subsequent processing of our parts depend on the manufacturing or production processes used. DIN ISO 20457 applies for injection molding.

This international standard replaces the older DIN 16742. It is crucial in ensuring consistent quality. Tolerance group TG 6 applies for our thermoplastics. If the parts are mechanically processed, DIN ISO 2768m always applies.

All dimensions < 1.18"/30 mm to the reference edge of the case have a tolerance of ±0.012"/0.3 mm. All other parts – unless specified – are against DIN ISO 2768m T1. At the same time, the tolerances of the basic parts must be taken into account.

For linear measures, tolerances range from ±0.004"/0.1 mm for nominal dimensions of 0.020"/0.5 mm to 0.236"/6 mm to ±0.020"/0.5 mm for dimensions from 4.724"/120 mm to 15.748"/400 mm. For angular measures, the tolerances range from ±1° (nominal dimensions up to 0.293"/10 mm) to ±0.16° for 4.724"/120 mm to 15.748"/400 mm. Different prices apply, based on the tolerance(s) being specified.

Download our guide to machining tolerances (PDF) >>

SPECIFYING CORNER RADII

For radii, tolerances range from ±0.008"/0.2 mm (nominal dimensions 0.020"/0.5 mm to 0.118"/3 mm) to ±0.079"/2 mm for dimensions from 1.181"/30 mm to 4.724"/120 mm. Alternatively, you can specify R=0 (sharp edge) punched for an additional charge.

Aesthetics play a significant role in the selection of corner radii, especially for consumer-facing products. Rounded corners typically have a more sleek, modern and polished appearance, while sharp corners can make an enclosure appear harsh or less finished. Smooth, rounded edges are often chosen for aesthetic reasons in consumer electronics, medical devices and high-end appliances.

The size of the enclosure also impacts the desired radius. For smaller enclosures, slightly larger radii might be necessary for a smooth, ergonomic look. Larger enclosures may benefit from more moderate radii that still maintain a smart appearance.

Softer plastics are easier to machine with smaller radii, while harder or tougher plastics may require larger tools and radii to avoid excessive tool wear or material deformation. Achieving a precise radius – especially for small corners – may be more challenging with certain plastics due to material properties such as brittleness or tendency to chip. Larger radii tend to be easier to machine consistently, especially in higher-volume production runs.

Smaller corner radii can be difficult to finish cleanly in some materials, especially if they are prone to smearing, chipping or melting during machining. Larger radii tend to have better surface finishes, as there is less heat generated and less material deformation during the cutting process.

Designers may choose a specific corner radius to align with the brand’s aesthetic identity. For example, a brand that prioritises sleek, contemporary designs may choose larger radii for a softer look.

Softer plastics such as ABS are generally more forgiving and can handle smaller radii without cracking or breaking. These materials can often tolerate sharper corners, though larger radii are often preferred to enhance aesthetics and reduce stress concentrations.

More rigid plastics such as ASA+PC and PMMA can be more prone to cracking, especially under stress or impact. For these materials, larger corner radii are recommended to reduce the risk of stress concentrations and to improve impact resistance.

Contact us to discuss your machining requirements >>

REQUEST A SAMPLE

At OKW, we know that specifying the right enclosure is essential for the functionality, presentation and protection of your electronics. That’s why we offer free samples of our plastic enclosures – allowing you to test and assess them before making a commitment.

By requesting a free sample, you can evaluate how well your chosen enclosure meets your specific requirements, ensuring it is the right size, shape and design for your project. You’ll have the opportunity to assess its ease of use, compatibility with your components, and its ability to withstand environmental conditions. Additionally, you can test how well it works with your assembly process.

Take the guesswork out of your decision-making and be confident in your choice. With a free sample, you’ll be able to experience the quality, durability and practicality of our enclosures firsthand, so you can be sure they meet your exact specifications.

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REGISTER FOR 3D MODELS

Download a 3D model (x_t, stp, sat) of your chosen enclosure and evaluate how well it will house your components. Customize the design in your CAD software to ensure that all the mounting points, holes and features align perfectly with your project’s needs.

The 3D model also lets you experiment with the aesthetics and functionality of the enclosure in a virtual environment, testing different configurations and features. It’s an efficient way to optimise your design – ensuring everything works seamlessly before you proceed to manufacturing.

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