Materials · Plasticsintermediate~2 min read

HDPE, and why CHIP does not give PVC settings

Short answer

HDPE cuts easily with a sharp single flute, leaves a slightly fuzzy edge, and almost nothing sticks to it, including glue and paint. PVC releases hydrogen chloride gas if it gets hot enough to decompose, which is corrosive to your lungs and your machine, and its dust is an irritant regardless, so CHIP does not publish settings for it.

HDPE

High density polyethylene. Sold as sheet, as cutting board material, and as marine board under names like Starboard. It is tough, waterproof and food safe, which makes it genuinely useful for jigs and anything that gets wet. For outdoor signs buy a marine board grade such as Starboard, which has UV inhibitors compounded in; plain HDPE sheet chalks and goes brittle in sunlight.

Machines

Easily. Low cutting forces.

Edge finish

Slightly fuzzy or stringy. Sharp tools help a lot.

Chips

Long and stringy. They wrap around the bit.

Glue and paint

Almost nothing sticks to it. Plan mechanical fastening.

Movement

Expands and contracts noticeably with temperature

Cutting it

Single flute, very sharp. A dull bit smears HDPE rather than cutting it.
Moderate RPM, generous feed. Same logic as acrylic: thick chips, low heat.
Watch for chips wrapping the tool. Long stringy chips catch on the bit and get dragged back into the cut. Good extraction and an air blast help.
Expect a burr. HDPE leaves a soft fuzzy edge that is easy to trim with a knife or a scraper, and hard to remove by sanding because it just melts and smears.
Hold it down well. It is slippery and tape does not grip it reliably. Mechanical clamping or screws in the waste area are safer.

UHMW behaves similarly, a little tougher and a little more slippery. Both are excellent for shop fixtures and wear parts.

PVC

CHIP does not publish machining settings for PVC

PVC releases hydrogen chloride gas when it gets hot enough to decompose. The well documented hazard is laser cutting, and a router cut that overheats or chars heads the same way. Sign shops rout expanded PVC every day, so treat this as CHIP's editorial choice rather than a claim that routing it is unsafe. The gas, when it forms, is corrosive to your airway and it is also corrosive to the metal parts of your machine and your dust collection. The risk is worse in an enclosed shop, and worse still if the material gets hot enough to char. Because there are good alternatives for nearly every use, CHIP treats PVC as a material to substitute rather than a material to optimise.

What to use instead:

If you wanted PVC for	Use instead
A white, weatherproof sign substrate	HDPE sheet, or aluminium composite panel
A rigid printable panel	Aluminium composite panel, or an outdoor rated plywood with a good finish
A machinable white plastic part	HDPE, UHMW or acetal depending on the requirement
Lightweight indoor lettering	Acrylic, or painted MDF

Expanded PVC foam board, sold under trade names, is the same polymer and the same concern applies. If you have material you cannot identify and you suspect it is PVC, the safe assumption is that it is.

Other plastics, briefly

Polycarbonate. Extremely tough, does not shatter, and it machines badly: it tends to produce a burr rather than a chip. Very sharp single flute tooling and a fast feed.
Acetal (Delrin). Machines beautifully, holds tight tolerances, an excellent choice for mechanical parts. More expensive.
Nylon. Tough, absorbs moisture which changes its dimensions, and it is stringy to cut.
Foam PVC, foam board, and styrene. Soft and easy, but see the PVC note above for anything vinyl based.