Guarding common machines: presses, saws, grinders, conveyors and robots

The principles in this course apply to every machine, but certain machines appear again and again in injury reports. This lesson looks at how the general principles apply to the most common ones, and at the specific standards that cover them. It is an overview for recognizing hazards and good practice, not a design manual: each machine type has detailed standards that a competent person must follow.

Power presses and press brakes

Power presses punch, form, draw and stamp sheet metal using a ram that closes a die. They cause a large share of amputations in manufacturing. Mechanical presses are driven by a flywheel through a clutch. Full-revolution clutch presses, an older design, cannot be stopped once a stroke starts until the crankshaft completes its revolution; part-revolution clutch presses can be stopped at any point in the stroke. Hydraulic presses use a cylinder and can usually be stopped at any point. Press brakes bend long sheets and are often hand-fed, with the operator holding the workpiece close to the dies.

CSA Z142, Code for power press operation: health, safety and guarding requirements, covers power presses in Canada, and some provinces refer to it. Point-of-operation safeguarding options include fixed die enclosure guards, interlocked guards, light curtains (only on presses that can stop mid-stroke), two-hand controls and, on some older presses, pull-back or restraint devices. Press brakes increasingly use laser-based systems mounted on the ram that detect fingers just below the punch and stop or slow the closing motion.

The most important rule for presses is that no part of the body should ever need to enter the die area during the stroke. Feeding with hand tools, automatic feeds, chutes and ejectors keeps hands out. Where hands must load parts, the safeguarding must ensure the press cannot close while they are there. Setup and die changes are high-risk tasks that need die blocks, lockout and safe procedures.

Saws

Saws cut by contact with a sharp, fast-moving blade, so any contact with the blade causes serious injury. Each type has its own hazards and guards.

Kickback deserves special mention. On a table saw, the rear of the blade, which rises toward the operator, can catch a workpiece that pinches it and throw it back at high speed. A riving knife, a curved blade that sits just behind the saw blade and rises and falls with it, keeps the kerf open and greatly reduces kickback. Push sticks and push blocks keep hands away from the blade when ripping narrow pieces.

Abrasive wheels and grinders

Bench and pedestal grinders are found in almost every shop. Their main hazards are wheel breakage, which can throw fragments at very high speed, contact with the wheel, and the workpiece being caught between the wheel and the work rest and pulling the hand in. Guards and adjustments are simple but critical.

Provincial regulations and the widely used ANSI B7.1 safety code for abrasive wheels set out the main rules: keep the wheel enclosed in a guard strong enough to contain fragments, keep the work rest adjusted close to the wheel, commonly within about 3 mm (1/8 in), so work cannot be wedged between them, keep the adjustable tongue guard at the top of the opening close to the wheel, commonly within about 6 mm (1/4 in), never exceed the maximum speed marked on the wheel, ring-test vitrified wheels for cracks before mounting, and stand to the side when starting a new wheel. Check your provincial regulation for exact requirements.

Conveyors

Conveyors move material through almost every warehouse, plant and mine. Because they run continuously and often unattended, people work near them all day, and they are frequently involved in entanglement, nip point and crushing injuries. Hazards include belt-to-pulley nip points at head, tail, snub and take-up pulleys, chain and sprocket drives, rollers, transfer points between conveyors, screw conveyors, and the material itself falling or jamming.

CSA Z432 and provincial regulations require guarding of conveyor nip points and drives. Many Canadian operations also follow ASME B20.1, the North American safety standard for conveyors. Key practices include fixed guards on all pulleys, drives and nip points within reach; pull-cord emergency stops along accessible lengths; guards on return rollers in walkways; covers on screw conveyors that cannot be removed while running; crossovers rather than climbing over conveyors; and lockout before clearing jams or cleaning belts.

Belt cleaning and tracking adjustments are classic conveyor hazards. Workers are tempted to scrape build-up from a running belt or adjust a tracking roller while watching the belt run. Engineering solutions include belt cleaners and scrapers that work without human contact, tracking adjustments placed outside guards, and guards with inspection windows. Where a task truly requires the belt to move, it should be done at slow speed with specific procedures, not by reaching past guards.

Robots and cobots

Industrial robots move fast, with great force, and can move unexpectedly as they follow programs. CSA Z434, which adopts ISO 10218 with Canadian deviations, covers industrial robot safety; the new 2025 editions of ISO 10218-1 and -2 absorbed the earlier collaborative robot technical specification ISO/TS 15066. Traditional robot cells use perimeter fences with interlocked gates, light curtains or scanners at openings, and reduced-speed teach modes with enabling devices. Collaborative applications allow people and robots to share space, using speed and separation monitoring or power and force limiting, but they still require a risk assessment of the whole application, including the tool and the parts being handled. ROB-450 and HSE courses on robotics cover this in depth.

Other common machines

CNC machines and automation

Computer numerically controlled machines are usually supplied with interlocked enclosures that stop the spindle and axes when the door opens. Their hazards shift toward setup, tool changes, programming errors that cause crashes, and the temptation to override door interlocks to watch a cut or speed up setup. Many CNC injuries involve a door interlock that has been defeated. Modern controls provide safe setup modes with reduced speeds and hold-to-run controls so the door does not need to be bypassed.