Operators of lathes are one of the largest machine worker populations in the United States, estimated to account for over 140,000 machinists. Of this population, approximately 3,000 suffer lost-time injuries annually in the United States. Some of these are fatal. These accidents occur in large industrial settings and factories, as well as in much smaller machine shops. No lathe operator is immune from an accident.
Operating a manual metal lathe, in particular, presents a number of hazards. For one, the lathe’s rotating parts easily can catch hair, jewelry and clothing, entangling the operator and resulting in severe and life altering injuries. Entanglement is also a risk whenever lathe operators use emery paper to sand or polish a rotating shaft. Without warning, the paper may wrap itself around the shaft, entangling the operator’s gloved hand, hair or loose clothing at over 300 RPM. Second, flying hot metal chips and coolant present serious risks if the machine’s guards or the operator’s PPE does not protect them effectively. Other risks include a work piece kicking back at the operator, slip-and-fall accidents due to coolant spilled on the floor, and parts or materials, such as chuck keys or unsecured work pieces, being projected at high speed and striking the operator and nearby employees. There have been lathe accidents recorded due to something as minor as the flashing effect of fluorescent light that can make a spinning lathe appear to have stopped.
Research shows there are numerous factors that can lead to a lathe accident. At the top of the list are malfunctions due to defective machinery, the failure to install proper safeguarding, mistakes due to the lack of employee training, poor lighting, and not providing proper PPE.
What does a metal lathe do?
A manual metal lathe is a precision turning machine that rotates a metal rod or irregular-shaped material while a tool cuts into the material at a preset position. Similar to a wood lathe, the metal lathe normally consists of a headstock and base that houses one or more spindles on which a work holding device or “chuck” can drive the stock while cutting tools remove metal, producing mainly cylindrical and conical shapes.
Operator Training & PPE
First and foremost, lathe operators must be trained and held accountable for following safe work practices. This is essential in avoiding injury. Examples of lathe machine safety precautions include not wearing loose clothing, rings and other jewelry, keeping long hair pulled back while operating a lathe and keeping hands and fingers away from rotating parts. As mentioned earlier, these practices are important because rotating parts will catch loose or dangling items and pull the operator into the machine, causing serious injuries or death.
OSHA makes it the responsibility of the employer to provide training that addresses safe start-up and shutdown as well as proper machine operation, speed adjustments and work piece placement, control and support. Employers must also equip lathe operators with proper PPE that includes safety glasses or other suitable eye protection, earplugs, protective footwear, and close-fitting clothing.
Safeguarding Standards for Lathes
There are no OSHA regulations specifically for lathes. Instead, OSHA considers lathes to be a 1910.212 machine, saying to the employer, “One or more methods of machine guarding shall be provided to protect the operator and other employees in the machine area from hazards such as those created by point of operation, ingoing nip points, rotating parts, flying chips, and sparks” … but 1910.212 requirements are vague because they cover such a wide variety of machinery. Therefore, a reference to something more detailed, like the “appropriate standard” ANSI B11.6-2001, Safety Requirements for the Construction, Care, and Use of Lathes, is required for specific safeguarding alternatives. Section 5 of this standard contains the safeguarding requirements on metalworking lathes.
An important standard that ANSI B11 standards reference is ANSI/NFPA 79, Electrical Requirements for Industrial Machinery. It provides detailed information for the application of electrical/electronic equipment, apparatuses, or systems supplied as part of industrial machinery, including lathes. This standard addresses such issues as requirements for operator controls, emergency-stop devices, disconnect switches, motor starters, and protective interlocks.
Of course, even properly installed safeguarding equipment can’t protect a machinist who “works around” the safeguarding, lifting a guard, for example, to accomplish a task. Thankfully, most shields can be interlocked with the machine’s electrical system to prevent operation when they are not in place. Swinging a shield from its protective position will break its electrical connection and cut the power, forcing a quick coast down.
A lathe has several points of operation that present hazards. Each requires specialized safeguarding equipment. Below we address each of these hazards and what can be done to avoid accidents.
1. Safeguarding the Chuck
The chuck area is by far the most dangerous area on a lathe. From a practical standpoint, a rotating chuck cannot be fully enclosed — unlike gears, sprockets, or chains that usually are completely covered, often by the OEM. However, that same lathe manufacturer may not provide safeguarding at or near the point of operation although, according to 6.21 of ANSI B11.6, manual lathes must be safeguarded with a chuck guard and chip and coolant splash shields as required. In this case the employer is responsible.
Hinged chuck-shields are one of the most common methods to protect lathe operators from the rotating work-holder. Their purpose is to prevent an operator from inadvertently coming in contact with the chuck, which often results in entanglement, serious bodily injury or even death. Chuck shields are commercially available from numerous providers. They may be constructed of metal, polycarbonate, or some combination of materials. When not in use, they need to be swung up out of the way, so most are hinged. Same for during set-up.
Although U.S. Safety Standards and Regulations do not require chuck-shields to be interlocked, some European and Canadian manufacturers offer that feature. With electrically interlocked shields, when the lathe chuck shield is lifted up, the positive contacts on the microswitch open, sending a stop signal to the machine control. The machine will not start up again until the emergency stop button has been reset.
A common complaint against chuck shields is that they limit visibility due to light reflecting off the shield, or that obstruct their view to the work piece. To overcome these problems a clip-on lamp is sometime installed yet these can easily overheat. A far better solution is newer shields featuring built-in bright LED lighting that yield better visibility without shadows or heat build-up.
2. Sanding Belt Holder
Hand sanding and polishing metal shafts on the lathe with an emery cloth has resulted in numerous injuries. Emery cloth and gloves can easily be caught on the shaft, pulling the operator’s hand and arm on the shaft. An automatic sanding belt holder enables lathe operators to sand, polish and debur hands-free, keeping them a safe operating distance away from the spinning shaft and preventing entanglement. It typically fixes to existing tool-case turrets.
American National Standards Institute (ANSI) standards state that an emergency-stop or “e-stop” is required on any machine that will tolerate a quick stop. Some lathes have a true e-stop built in to halt operation in less than a second, but most require several seconds to cease functions. An electronic motor brake can improve coast-down time, in some cases from 15 seconds to 3 seconds, which can make a significant difference in an emergency.
Per NFPA 79, the e-stop must be a red with a yellow background, and have a mushroom-shaped button with a manual latch that keeps it down once it is pushed to prevent machine operation by the regular controls. Once the e-stop is engaged, the latch keeps it down until a manual quarter-turn releases the latch and allows the machine’s controls to again command the machine’s actions. Kick plates or grab-wires that go across a machine can facilitate an emergency shutdown if there is potential for an operator’s hands to be caught.
E-stops need to be readily accessible. An e-stop button should be within easy reach at each location on the machine that requires operator interaction. When more than one individual is involved, each person should have his or her own e-stop.
4. Chip/Coolant Shields
The long stringy chips produced when turning steel can wreak havoc on an operation and production. Edges of the chips are scorching hot and extremely sharp putting the operator at risk for injury, as well. Chips can strike the operator in the upper body or accumulate on the floor creating a slip-trip hazard.
As protection against chips, coolants, lubricant and sparks, lathes should be equipped with a chip and coolant splash guard, also known as a carriage safety guard. This type of guard can be electrically interlocked like a chuck shield, and gives added protection to the operator from direct contact with rotating components. Coolants are often overlooked as a hazard yet workers often are exposed through inhalation, ingestion, skin contact, or absorption through the skin, leading to burns and irritations. Without a chip/coolant shield, operators can also be at risk of inhalation of airborne substances such as oil mist, metal fumes, solvents, and dust.
It is rare for an OEM to include this type of shield on a new lathe. Again, it is the responsibility of the employer to install it before the lathe is put into commission.
5. Chuck Wrench
According to feedback from OSHA Compliance Officers and Insurance Loss Control Inspectors, one of the most common lathe accidents results from the misuse of standard chuck wrenches furnished by lathe manufacturers. When the lathe is not being used, a typical – and very unsafe storage place for the chuck-wrench is in the chuck. At some point in time, the operator turns the lathe on without checking to see where the chuck wrench is located, which projects it across the shop floor. Spring-loaded, self-ejecting chuck wrenches are a solution to this problem because they won’t stay in the chuck by themselves, helping to prevent a potential ejection hazard at machine start-up.
7. Magnetic Motor Starters and Disconnects
When updating an older lathe it is required practice to bring it up to code with current electrical standards like NFPA 79. This will require the installation of a motor starter and disconnect those only locks in the OFF position. When adding a motor starter, ensure it is magnetic to provide drop-out or “anti-restart” protection.
8. Telescopic stainless-steel sleeves
Although slow moving, horizontal rotating components in a lathe can entangle an operator and crush body parts with their tremendous torque. Installing telescopic stainless-steel sleeves will seal off their pinch-points plus protect the components from metal chips and other destructive contaminants. Unfortunately, operators complain that these devices are time consuming to install, need to be removed and cleaned regularly, and cause a loss in carriage travel. However, when compared to preventing a life-changing injury, these complaints are trivial in comparison.
9. Other Precautions
As with any machine, provision for Lockout/Tagout is always important with lathes. Danger and warning signs, depicting specific hazards on lathes, are also strongly recommended.
10. Conduct Machine Safeguarding Assessments
Machine Safeguarding Assessments are a critical step in any machine safeguarding process as outlined by ANSI B11, especially for companies deploying older or refurbished lathes. It is not unusual for lathes built in the 1940s to still be in active service, having been resold several times over the decades.
Odds that an older lathe is up to today’s safety standards are highly unlikely. Employers are often lulled into a false sense of security because a serious accident hasn’t occurred, or they may simply assume that the lathe they purchased, whether new or used, came equipment with all necessary safeguarding. The only way to take the guesswork out of compliance issues in your shop is a machine safeguarding assessment conducted by a qualified third-party, to help keep operators safe, machines productive and processes online. They will assign each machine a Risk Rating of 1 to 27, with 27 being the worst, based on three considerations: Severity of Injury, Exposure Frequency, and Avoidance Likelihood. When conducted by professionals, your machine safeguarding assessment will be delivered with a compliance report and a safeguarding project proposal that will detail the timing, costs and specific equipment required to bring machinery up to current standards.