How To Cut HDPE

While HDPE (high-density polyethylene) is highly durable, it is not difficult to cut. You can cut this plastic polymer in a similar way to wood, provided you account for its tendency to melt. Fortunately, it is pretty easy to cut HDPE successfully if you use the appropriate tool blades and cutting techniques.

How Do You Cut HDPE?

Cut thin HDPE sheets on both sides with a utility knife, then snap along the cut line. When cutting thick pieces of the polymer, use a power saw blade with large teeth and a gentle rake angle to prevent the plastic material from melting during the procedure.

Cutting Thin HDPE Sheets With A Utility Knife

It is quick and simple to make straight cuts in thin sheets (¼ inches or less) of HDPE with a utility knife. It’s also ideal if you’re aiming lengthwise like how you cut a vinyl siding.

Step 1: Measure And Mark

If you plan to make a straight cut, use a ruler to measure the HDPE sheet 

Take a scribe tool and scratch the intended cut line on both sides of the sheet, using the ruler as a guide. You could also scribe the piece of polymer with the tip of the utility knife to create a light scratch mark.

Step: 2 Position The Sheet 

Lay the sheet on a firm, flat work surface. Make sure the piece is stable.

Secure the ruler to the sheet with a long-tailed clip to allow you to hold the sheet in one hand while you use your other hand to slice the workpiece with the utility knife.

If the sheet is quite large, it is advantageous (but not essential) to secure it to the work surface with small clamps. Clamping will keep the piece stable (and allow you to hold the ruler while cutting).

Step 3: Perform The Cut 

Pass the utility knife blade along the length of the workpiece in a single movement following the marked line. Apply light pressure for the first few passes. Once a scored groove forms, press the blade more firmly to cut deeper into the workpiece. 

Cut the sheet until the blade is about 1/3 of the way through. 

Next, flip the sheet over and repeat the cutting process on the other side of the sheet. 

In most cases, however, you will likely need to make partial cuts on both sides of the sheet, and then snap it along the cut lines (see below). 

Note that if you are cutting HDPE sheets that are particularly thin (some are only 1/32 inches), you can conceivably cut right through them with the utility knife. 

Step 4: Snap The Sheet Along the Cut Line 

Align the cut line with the edge of the work surface. Then press down on the overhanging side of the sheet with a strong, quick downward movement to snap it off. 

Step 5: Smooth The Cut Edge (If Necessary). 

If the cut edge looks a little jagged and untidy, you can create a smooth finish with a carpentry file, sandpaper, or a combination of both. Note it is slightly more challenging to file and sand HDPE compared to wood.

When working with high-density polyethylene, select a file with a coarse face.

To sand HDPE, you can start with coarse grit sandpaper, for example, P80 to P120, before using finer grit finishing sandpaper such as P220, P320, or P400. 

Cutting Thick HDPE Board And Lumber With Power Saws

When cutting thick HDPE boards and composite lumber, power saws are optimal. Power saws that are often used to perform this task include:

• Circular saw, which is also ideal for cutting laminate countertop
• Table saw, which is also efficient in cutting plexiglass
• Band saw, which can cut wood and metals
• Jig saw, which is perfect for curved cuts

Sawing thick HDPE effectively requires an understanding of how the plastic material reacts to heat. This knowledge is critical because it enables wise choices about appropriate saw blades and cutting techniques.

HDPE is a thermoplastic, which means it gets soft and malleable when exposed to heat and hardens again as it cools. Its melting temperature is low compared with other commonly-used plastic polymer materials, and it melts at roughly 266⁰F (130⁰C) though this varies depending on the product.

It’s low melting point makes it a tricky material saw through neatly. Friction from the saw blade creates heat that can melt the cut edge of the HDPE. If the plastic starts melting, it impedes the movement of the blade (a problem called gumming), and the edges of the cut fuse together once it cools.

Fortunately, one can prevent these problems by using suitable saw blades and sawing techniques. If you’re using a table saw, there are the best table saw blades to choose from.

Step 1: Choose A Tool And Blade

Decide which power saw you plan to use. Next, choose a blade for the saw. 

Selecting the right kind of blade is critical when cutting HDPE. It is ideal to use specialized ‘plastic non-melt’ blades if possible, but wood saw blades also do the job. Carbide cutting discs are preferable. Clean, new blades are essential. 

The primary factor to consider is the tooth geometry of the saw blade and its effect on heat. Some saw blades generate less heat than others due to their tooth shape, size, and configuration. 

So, if you want to minimize heat build-up while cutting HDPE, and thereby avoid the associated problems of gumming and fusing, choose saws whose teeth have the following characteristics:

• Large-sized teeth
• Low teeth-per-inch rating (between 40 and 60 TPI)
• Gentle rake angle (low or negative) 

Power tools, especially circular saw blades with large saw teeth and low TPI rating allow more heat to escape as they cut through the HDPE, compared with fine-toothed cutting discs. The benefit of saw blades with a gentle rake is that their teeth are less likely to get stuck in the polymer because they cut less deeply than blades with a larger, aggressive rake angle.

A popular power saw blade for HDPE is the Diablo metal cutting disc (10 inches), which has a degree rake angle of minus 5 and 60 teeth per inch. More broadly, rip saw blades are great for cutting because they have less rake than cross-cut blades. 

Step 2: Measure And Scribe The Cut Line

Measure the piece of HDPE board or lumber and scribe the line where you plan to make the cut.

Step 3: Position The Workpiece

When using a hand-held power saw, place the HDPE workpiece on a stable, flat surface. Check that the scribed line extends sufficiently beyond the edge of the work surface to allow the blade to pass unobstructed.  

Depending on the situation, it might be worthwhile to take the additional precaution of securing the material with clamps so it does not shift while being cut.  

When using mounted saws like table saw, lay the workpiece leaning it snugly against your reliable table saw fence (to ensure the blade will cut in a straight line).

Step 4: Wear Protective Gear

Observe the general safety precautions for power saw use. It is prudent to wear protective goggles, cut-proof gloves, and a mask so you can cut the HDPE safely.

Step 4: Perform The Cut 

Switch on the power saw and start moving the blade through the workpiece. Pay attention to the following techniques for reducing heat build-up and preventing the plastic from melting and sticking to the cutting disc.

Always cut slowly because this helps minimize the friction and subsequent heat generated as the blade cuts the HDPE. For this reason, it is advisable to adjust the tool’s router speed so the blade rotates more slowly.

Another crucial tip is to avoid pushing the blade too far through the other side of the workpiece because this increases the chances of the tool becoming stuck. You should only allow the teeth of the cutting disc to penetrate out the back of the material (but not the face of the blade). 

As you cut, make sure you brush off or vacuum away the dust the saw generates, as it can gum up the blade. 

Misting the blade with water (mixed with a drop of dish soap) is an excellent way to simultaneously lubricate and cool the contact point between the blade and the HDPE. 

After every one or two cuts, switch off the power saw and clean the cutting disc to remove HDPE dust particles that would otherwise cause it to get stuck. 

Step 5: Smooth The Cut Edges

Finally, file or sand the edges of the cut to produce a smooth finish (as described earlier). Sand it just as you normally do after cutting an MDF.

Frequently Asked Questions 

Conclusion

Thin sheets of HDPE are easy to cut with a utility knife (either cutting right through the material or scoring and snapping it). Cut thick HDPE board and composite lumber without melting it by cutting slowly using a power saw whose cutting disc has large, sparsely-arranged teeth and a gentle rake angle.