The choice of utility knife design relies on the fabricator's choice. Comfort is key. Black blades contain a higher amount of carbon steel and will hold a sharper edge.
- Never cut towards yourself.
- A sharp blade is safer than a dull one.
- Never leave the blade open when it’s not in use.
- Be aware of where the knife will be after the cut. There may be bystanders there.
- Inspect your blade before and after use.
- Dispose of all used blades in a “sharps” container.
A good rule for the amount of blade to expose: “Only leave the blade out as far as you are prepared to have it in you”. (Maassen, 2011)
Standard segmented utility knife blades are made of steel and scored at regular intervals to facilitate a crisp and straight break when the user desires a sharper blade.
This is the bulk of the knife. The body of the knife often includes a variety features, which may be included depending on the manufacturer: An end cap with or without a small groove in which to insert the used tip of the blade and protect the user when snapping it off, A lanyard hole to hang the knife on a peg when not in use or insert a thong and fob to make retrieving from a pocket or pouch easier, A blade storage channel for extra blades, A blunt metal tooth to open paint cans or break tape on boxes being opened, A bladed slot for cutting string or cord, Any number of ingenious features they can imagine.
The size of the blade determines the size of the knife. There are three common segmented blade sizes: 9mm, 18mm and 25mm. Of these three the 18mm is the most common size. Thinner knives are more flexible but more susceptible to breaking.
The blades most commonly supplied with a utility knife are fabricated from tool steel, an alloy that provides good strength and has an ability to keep an edge. These are also the most commonly purchased replacement blades. A “black blade” is also sold, containing more carbon which will allow the blade to maintain a sharper edge.
There are three common locking systems used:
Ratchet lock - screws out to unlock and screws in to lock the blade in place.
Slide lock - has a second tab on the slider that when slid back from the main tab wedges the breaks into the corrugated channel sides to hold the blade in position.
Press-lock - most unsafe locking mechanism. Constantly engaged and locked until depressed by the user.
The segment being kept must be at least halfway to ¾ of the way within the end of the knife body. Keeping the scored side facing down toward the bench, apply downward pressure at roughly 45 degrees to the bench until the blade snaps. Warning, the use of pliers to snap blades can cause the blade to shatter and fracture.
All segmented blade type utility knives have their blades replaced from the butt end. There is usually a mechanical stop along the slider channel for ratchet locking knives and an end cap on slide-lock and push-lock knives that inhibit the accidental removal of blades. Once the ratchet is undone sufficiently or the cap removed (some are loose where others are hinged) the slider and the remains of the blade can be carefully slid out the back of the knife handle.
A non-segmented blade utility knife comes in a plethora of configurations. They fall into three basic groups: Fixed, Folding, and Retractable. Each of these groups utilizes the same double-ended blades. These blades come in numerous different modified shapes designed for specific uses, but for P&O a straight blade is ideal. Like the segmented blades, original and replacement blades are made from tool steel, high-carbon blades are also available.
Relatively new on the market, folding utility knives are becoming increasingly popular. When folded, they offer the user a much smaller unit to store. They often come with clips for storing on a belt or pocket edge. They also offer a quick and tool-less system for changing out worn blades.
Usually fabricated from aluminium for sturdiness and to reduce over-all weight, the handle contains the locking mechanism and a channel for safely stowing the blade and blade holder when folded. The handle is usually constructed of layers of metal either screwed or riveted together.
The blade holder secures the blade and is comprised of various parts that ensure the blade remains stationary within the knife. The user should become familiar with the function of these parts and recognize when they are misaligned or broken to avoid injury.
Without a functioning lock these knives are a serious hazard to the user. It is paramount that the lock be fully engaged, “clicking” into place, when opening the knife for use. These knives tend to have a release on the back of the handle, which once depressed releases the blade holder to be folded. An alternate locking system uses the pivot as the lock and pressing the pivot laterally disengages the lock.
Most folding knives have a way of grabbing the blade to flip it open. Pen knives, like the “Swiss Army®” knives, have a small groove in the side of the blade for a fingernail. Other locking blade knives have a thumb tab or a pin to pull the blade out. Folding utility knives could employ any of these.
Often referred to as a box-cutter. It’s most common configuration has a bi-valve cast metal handle held together with a screw.
Two-piece cast metal bodies (usually zinc) that interlock and are held together by a screw mid-handle. The screw is most often a slot/Philips combination. The internal fixations include; guides for the blade, a channel and corrugated ridge for the locking retractor and button, a countersink and threaded hole for the screw, and often a cavity for storing spare blades.
This is similar to the press-lock system mentioned previously but is more crude in both its construction and function.
Ensure the blade is fully retracted. To gain access to the blade, unscrew the handle’s screw. The spring in the locking mechanism may be unsecured which will cause parts to erupt during disassembly. Lift the side that the screw was just removed from. The old blade should be in a carrier with a nub in one of the slots in the blade. Flip the blade or replace the blade, prying it out with a flat head screwdriver if necessary. Ensure the nub is in one of the blade slots or the knife will not work correctly and may not fit back together. Reassemble the handle and re-secure the screw.