Chapter 10 Part 1: Manual Lathes

SAFETY

Safety needs to be the first concern with any piece of equipment in a machine shop. The lathe is often the most dangerous machine in the shop. It will generally have larger motors with more horsepower than any other equipment. Machinists using the lathe need to follow all the standard safety rules of the shop in addition to knowing the specific potential hazards they may encounter.

Rotational Hazard

Lathes are often the most powerful machines in a machine shop and require the utmost respect. The rotational hazards on a lathe are often the most dangerous, and the ones that every operator needs to be aware of. The spinning chuck of the lathe is much larger, many times more powerful, and often has protruding components. These aspects make it more capable of grabbing fingers, hands, and clothing to maim the operator. Other spinning components of the lathe that can cause injuries are the lead screw and feed rod. The lead screw and feed rod are long, often spinning, components that run the full length of the lathe. An operator who is unaware of these components could easily get loose clothing or aprons tangled in them. Once they grab ahold of something, they rapidly winch it in, possibly injuring the operator. It is a good practice to disengage the feed rod and lead screw if they aren’t being used.

Sharp Hazard

Lathes produce some of the most dangerous chips in the machine shop. Stringy chips can be long and unwieldy. If stringy chips come in contact with the operator and get wrapped around the spinning chuck, they could cause deep cuts or pull the operator into the machine. Short chips are also sharp, flying in straight lines away from the point of contact, often right at the operator. It is advisable to stand out of the way of these chips and for the operator to keep their hands behind their back. Cutting tools are also a sharp hazard on the lathe. An operator can easily be cut by a cutting tool while making machine adjustments if they are not careful.

Pinch points

The spinning handles on a lathe could create pinch points while under power feed conditions. The operator could also get pinched between the carriage and the headstock of the machine while under power feed. Being aware of the surroundings at all times is a must while using the manual lathe.

Fire Hazards

Under certain conditions, the lathe may produce large volumes of hot chips. Oily rags and paper products can easily catch fire if exposed to these chips. The operator must keep the area clean of combustibles.

MACHINE MAINTENANCE

Machine maintenance is a term for the periodic upkeep of a piece of equipment. Most machines have a section in the operator’s manual that covers the scheduled maintenance for that particular machine. As an operator, a couple of things that must be done daily on most machines are to lubricate and clean the equipment.

Lubrication

At the beginning of each use, the lathe should be inspected and properly lubricated. The headstock, quick change gearbox, and apron all have sight glasses that need to be checked before each use. If they are found to be low, the appropriate oil should be added to bring them up to the acceptable level. The machine operator’s manual will have specifics on the oil for each. The ways and other points of contact need lubrication before and during use. These lubrication points are often in the form of oil cups or ball oilers. In addition, the ways for the carriage and tailstock may also need oil applied directly to their surfaces. The correct oil for each machine and application can be found in the operator’s manual.

Cleaning

General machine cleaning should be performed at the end of each use, or in the event of heavy machining operations, whenever the amount of chips becomes dangerous to the machine or the user. Cleaning a lathe is best performed from top to bottom with a brush. Gently sweep all chips downward into the chip pan below, then clean out the chip pan. After all chips are removed, the machine should have all the oil removed from the ways of the machine and have the carriage and tailstock parked on the right side. If the oil isn’t removed, over time it will build up, dry, and create a coating that is difficult to remove and will cause difficult operation and decrease accuracy. Compressed air should never be used to clean a lathe. Compressed air can blow chips and debris under seals and into the precision mating areas of the machine, damaging them and ruining the machine’s accuracy.

Machine components

It is important that all lathe operators are familiar with the components of the machinery they are using. Getting to know the equipment, features, and functionality will help the machinist perform work in the safest and most efficient manner, as well as give them the industry-specific nomenclature necessary to effectively communicate with coworkers. One of the first things to consider when looking at a lathe is its size, or capacity. Lathes are sized by the diameter of work that can be turned, referred to as the swing, and the length of work that can be held between the spindle and tailstock. A common lathe size designation might be a 1340. This number designation means that a 13” part can be turned over the bed, and it could be 40” long in between the spindle and the tailstock.

Bed

The bed is the main structural component of the lathe. It runs horizontally, and most other components are attached to it. The bed contains the waysof the machine. The ways are precision flat or angular surfaces that give the machine its accuracy. The moving components that make up the linear movement of the lathe ride on the ways. The bed also supports the feed rod and lead screw.

Headstock

The headstock is attached to the left hand side of the bed. It contains the motor, spindle, and all the gearing required for machine speed changes. Some smaller machines may require the operator to change belt pulley positions or adjust a variable speed dial to alter speed. In the headstock, the spindle rotates on bearings.

Spindle

The spindle is located in the headstock and is driven by gears, shafts, belts, and pulleys attached to the motor. The nose of the spindle is where workholding devices are attached. Spindle speeds are generally altered by changing gears or occasionally by adjusting the power of a variable frequency drive. On latches equipped with power feed capabilities, the spindle will have gearing connected to it that provides power to the quick change gearbox, directly linking the two.

Motor

The motor is mounted to the backside of the lathe under the headstock. The motor has a pulley attached to it that is used to drive one or more belts to provide power to the lathe. Lathe motors come in different sizes, depending on the size and rigidity of the lathe. Industrial sized lathes often have 3 phase motors as opposed to the single phase motors found on smaller hobby machines.

Gears

The gears of the lathe are found inside the headstock, inside the quick change gearbox, inside the apron, and as a way to connect the headstock to the quick change gearbox. Some smaller lathes may require the operator to manually change one or more gears between the headstock and the quick change gearbox in order to alter the range of feeds the lathe is capable of.

Carriage

The carriage rides directly on the ways of the bed and is used to make axial movements of the lathe. The carriage supports both the cross slide and the compound rest. The carriage can have its movement locked to stabilize it during radial machining operations. The carriage handwheel is connected to gears that provide motion to the carriage by meshing with a rack gear mounted to the side of the bed. On imported lathes, the rack is often metric, making one full turn of the handwheel an uncommon length of measurement.

Often when machinists are moving machine components, they are thinking of making movements in 3D space. The way the operator keeps track of the 3D movements is by using the Cartesian coordinate system. The carriage moves the tool left and right along the Z axis of the three dimensional coordinate system.

Cross slide

The cross slide is mounted on the carriage and is used to make radial movements on the lathe. The cross slide supports the compound rest that sits above it. The cross slide often has a lock on the side to stabilize it while making axial cuts. The cross slide handwheel turns a screw that provides .200 change in part diameter for each revolution. It is important to recognize that the graduations on this handwheel are a reflection of the amount to be removed from the part in diameter, and not a linear distance. The cross slide moves the part in and out along the X axis of the three dimensional coordinate system.

Compound rest

The compound rest is mounted on top of the cross slide and is used to make angular movements. The compound rest has a lock that is used to stabilize it when not in use. The handwheel of the compound rest turns a screw that creates .100 of linear movement for every revolution. Unlike the cross slide, the movement of compound is direct movement and not based on diameter.

Tool post

A tool post is used to secure the cutting tool. It is mounted on top of the compound rest by way of a single nut that tightens it in place. Tool posts come in many different styles; however, the quick change toolpost is the modern standard in industry and is favored for its ease of use and adjustment.

Apron

The apron is attached to the underside front of the carriage and houses the hand wheel for the carriage movement as well as the gearing for the power feed components. Attached to the front and side of the apron are many knobs and levers. These include the carriage handwheel, a lever to engage the carriage to the feed rod, the half nut lever to engage the garage to the lead screw, a threading dial for timing the start of threads, and the lever used to turn the lathe in forward and reverse.

Quick change gearbox

Most industrial-sized lathes are equipped with a quick change gearbox that is inside the casting just under the headstock. The gearbox is directly linked to the rotation of the spindle by a train of gears. The gearbox transmits the rotational movement of the spindle through the feed rod and lead screw for the power feed functions located in the apron.

Tailstock

The tailstock is a movable component positioned on the right side of the lathe bed. It is used to perform all the standard hole making processes of a drill press, as well as adding extra support to long pieces of work. A handwheel moves the quill in and out to perform these actions. Depths of cut can be gauged by a simple scale on the quill, or more precisely by graduations on the handwheel, often .100 in a revolution. It is easily slid along the bed on its own ways, and is secured in place using the locking lever in order to stabilize it during use. When the tailstock is used to support work, the quill can also be locked in place using the smaller locking lever, preventing it from retracting under pressure.

Digital Readout (DRO)

A digital readout (DRO) is a device that uses electronic scales to show the position of the machine digitally through a readout box. The DRO of a lathe keeps track of two axes. X is the in and out movement of the cross slide, and Z is the side to side motion of the carriage. X positive is defined as the direction away from the operator, and Z positive is to the right of the operator. The readout can be easily zeroed at the push of a button, basically performing the action of zeroing the handwheel collars. They can also be set to whatever value the operator needs. The DRO has a few advantages over the traditional graduated collars:

The operator does not have to keep track of multiple rotations of the handwheel. On large projects it is easy to get lost. The DRO keeping track of all the operator’s movements is very helpful.

The readout doesn’t change unless the carriage or cross slide moves. This means that the task of considering backlash when changing cut directions is eliminated.

DROs have a finer resolution than graduated collars. The collars of the cross slide are often .002 in diameter for each graduation. On the carriage, the collar is often graduated in .005 increments. Most DROS have a resolution of .0005 or smaller. This makes it much easier to hold tight tolerances.

Modern DROs can do many different efficiency tasks that will not be covered in this text. An operator should consult their DRO operator’s manual for full details.

One disadvantage of a DRO is the cost. They cost several thousands of dollars to purchase and take hours of time to install. This is sometimes a larger cost than some smaller companies are able to incur. For this reason, all machinists should make sure they know how to operate equipment with graduated collars.