Last week I read a “how-to” where it said to use a dull razor blade to scratch and cut plastic sheet materials. I suppose I can see where that recommendation came from, but it’s wrong. For scoring plastic sheet goods for hand-separation, nothing beats a plastic scoring knife.
Clarification: the “score and snap” method can only be used to create controlled breaks in certain plastic materials, such as acrylic, styrene, and construction laminates. Many plastic materials cannot be scored and snapped and must be cut using other means. If in doubt, check with your plastics supplier.
Here’s how scoring a plastic sheet works:
- Lay out your cut line.
- Use a straightedge and scoring knife to cut a narrow and shallow groove in thin plastic sheet materials (e.g. 1/8″ acrylic). (Thicker plastic sheets might need to be cut via other means.)
- Make multiple passes to deepen the groove if needed.
- Place the plastic sheet, groove-side up, over a hard edge, such as a tabletop, with the groove slightly beyond the edge.
- Optional: Clamp a flat block over the sheet, preferably with a hard edge as well
- Bend the overhang with a quick and even motion.
- *SNAP*. The groove will deepen as a crack propagate throughout the thickness of the sheet, separating it into two pieces with straight and relatively clean edges.
The process is similar as with cutting glass, but with plastic it’s usually okay to make multiple passes with the scoring knife.
Scoring can be accomplished with utility knife blades and other such instruments, but a scoring blade is really the best way to do it.
There are three main types of plastic scoring knives:
- Fixed-blade utility knife
- Retractable knife
There might be slight design differences, but scoring knives – at least all the ones I’ve used – all feature triangular blades with strong points. You might see sharpened edges, but it’s the flat inside of the pointed blade that is mainly used for scoring.
The flat sharpened edges are used for deburring or cleaning up of freshly separated edges.
Disposable Plastic Scoring Knife
You can generally find these inexpensive scoring knives at plastic supply centers. The blades are a little on the thin side, but they’re cheap and widely available.
Buy Now(via Tap Plastics)
Fixed-Blade Plastic Scoring Knife
Stanley’s 10-519 fixed blade scoring knife comes with a standard non-retractable fixed-blade knife with a 11-942 plastic scoring blade. The design actually works great, but the combo is hard to find and replacement blades even harder. There is a relatively new identical-looking Stanley Bostitch version, but I haven’t tried it yet.
I keep mine in its original plastic-covered retail display card since the blade is quite sharp and sticks out with no form of protection. Just something to keep in mind.
If you already have a fixed-blade knife, Stanley blades can be secured in the same way as regular utility knife blades.
Some fixed-blade knives are one-piece designs, such as the Hyde 45730 (via Amazon).
Retractable Plastic Scoring Knife
Retractable plastic scoring knives, such as this Olfa PC-L, are a good compromise between rigidity and convenience. Replacement blades are widely available, and Stanley now makes a new knife handle (model STHT10192) that is compatible with Olfa PB-800 replacement blades.
Buy Now(via Amazon)