Cutting on top of concrete will dull your utility knife blade more quickly. While the blades are easy to switch out, you can protect your blade a bit by laying a large sheet of cardboard (like an unfolded moving box) underneath the hardboard.
Continue your pencil lines over the edges of the board, so that you can see them when you flip the board over. A large T-square will work in place of a straight edge. You can try to make curved and shaped cuts, but it takes some practice to master cutting freehand with a utility knife. You might have greater success with a jigsaw.
Don’t stop-and-start while cutting with a utility knife. Complete the whole cut in one motion whenever possible. Maintain firm pressure on the straight edge so it doesn’t shift out of place while you’re cutting.
After the second or third pass of the blade, you can remove the straight edge if you wish. The channel should be deep enough to keep your blade moving straight along the cut line.
Make sure the pencil lines are in the exact same spot on both sides of the board. Use the pencil lines that you ran over the edges of the top side of the board to help guide the placement of the cutting line on the underside.
To finish the cut, run your blade along the corner you’ve created on the underside of the board—after a pass or two, you’ll have cut through the board. This is a similar process to cutting through a sheet of drywall with a utility knife.
Use a tape measure and a straight edge to make accurate, straight cut lines. Run your pencil lines over the edge of the board, so you can see them when you flip the board over. Remember the old adage: measure twice, cut once!
The teeth on power saw blades can splinter the surface of the hardboard as they cut up through the underside. The tape helps protect against this. Tape works best if you’re cutting straight lines or gentle curves. If you’re making sharper curves or more intricate cut patterns, clamp a sheet of particle board to the underside of the hardboard, as described in the hand saw directions in this article.
If you’re using a table saw, lay the board (without clamps) on the saw’s cutting table, aligned properly with the slit where the saw emerges during cutting. Limiting vibration is critical to smooth, accurate cuts with less splintering. Spring clamps—which you squeeze to open and release to tighten—and C-clamps—which you screw and unscrew to tighten and loosen—are both good choices here.
Use your saw’s instruction manual—or check the manufacturer’s website—for information on choosing and changing saw blades. When using any type of power saw, wear eye protection and hearing protection, wear long sleeves, remove all dangling jewelry and clothing, and tie back any long hair.
When using a jigsaw, start with the blade at the edge of your cut line, squeeze the trigger to start the saw, and guide it slowly and evenly along the cut line. A jigsaw is your best option for making curved or shaped cuts. When using a circular saw, you’ll also want to line up the blade at the edge of the cut line and squeeze the trigger to slice through the board. Make sure not to press down on the saw—allow it to glide freely as it cuts. When using a table saw, use the fence and both hands to guide the wood through the stationary, spinning blade that lifts up from the slit in the table. Work slowly and carefully, and use a pusher instead of your guide hand as it approaches the saw blade.
For an extra smooth finish, follow up with fine-grit (240 or higher grit) sandpaper.
Use a pencil, measuring tape, and straight edge to mark your cut lines, and use at least two spring clamps or C-clamps to secure the board firmly to a stable, flat workbench. See the section of this article on cutting with a power saw for more details on measuring, marking, and clamping down hardboard. A handsaw’s teeth rip into the underside of the hardboard when you cut. Putting the particle board on the underside will spare the hardboard from the brunt of the ripping motion of the saw’s teeth, thereby reducing splintering.
A piece of 1 in × 3 in (2. 5 cm × 7. 6 cm) dimensional lumber is a good choice here.
Even a smooth, straight cut with a handsaw will leave some rough edges on the hardboard. Smooth them out by passing medium grit (60-120-grit) sandpaper over the cuts several times, then follow up with fine-grit (240-plus grit) sandpaper if needed.
