Finishes Like other plastics in the PE family, HDPE is highly resistant to coatings. It resists adhesives for much the same reason and, as such, needs to be bonded via plastic welding. HDPE is most often available in white, but can occasionally be found in other colors. We recommend leaving HDPE parts in their "as-machined" state for the reasons mentioned above.
As Machined: The challenges of CNC machining in HDPE are similar to those experienced with other engineering plastics. The machined surface of HDPE has a matte finish. Bead Blast: For a more uniform surface finish, the part can be bead blasted with fine glass beads to remove tooling marks and increase the matte appearance. However, bead blasting plastics may cause uneven surfaces or may damage finely detailed features.

Cost-saving Design Tips CNC machining in HDPE can produce lightweight and low-cost components. Below are some additional cost-saving tips to make production more economical.

Sub-assemblies: HDPE is purchased as sheet or bar stock in varying sizes. Designing parts as separate components that can then be assembled into the final whole is often a good idea. As mentioned above, HDPE does not work well with adhesives but can be welded. Alternatively, mechanical fasteners can be used to bolt components together. Tolerancing: Due to its tendency to expand heavily when exposed to heat, achieving extra-tight tolerances in working with HDPE can be challenging. We recommend only calling out tolerances tighter than +/- 0.010" when necessary to reduce the increased scrap, cost, and lead times associated with tight tolerances on plastics like these.