GROUP 1
LATHE MACHINE
Definition
A lathe machine is a machine tool that removes the undesired material from a rotating workpiece in the form of chips with the help of a tool that is traversed across the work and can be feed deep into the work.
It one of the most versatile and widely used machine tools all over the world.
This is also known as the ‘Mother of all Machines’. Nowadays, Lathe Machine has become a general-purpose machine tool, employed in production and repair work, because it permits a large variety of operations to be performed on it.
The Lathe Machine consists of following Main Parts:
- Bed
- Headstock
- Tail stock
- Carriage
- Saddle
- Cross Slide
- Compound rest
- Tool Post
- Apron
- Chuck
- Feed rod
- Lead Screw
- Spindle
Bed:
The bed of the lathe machine is the base on which all the other parts of the lathe are mounted. The bed is made from cast iron or nickel cast iron alloy and is supported on broad box-section columns.
Its upper surface is either scraped or grounded and the guiding and the sliding surfaces are provided.
The bed consists of heavy metal slides running lengthwise, with ways or v’s forced upon them. It is rigidly supported by cross griths.
The three major units mounted on a bed are:
1. Headstock
2. Tailstock
3. Carriage.
The scrapped or the ground guiding along with the sliding surfaces on the lathe bed ensure the accuracy of the alignment of these three units.
Headstock:
The headstock is present on the left end of the bed. The main function of the headstock is to transmit power to the different parts of the lathe.
It supports the main spindle in the bearing and aligns it properly. It also houses a necessary transmission mechanism with speed changing levers to obtain different speeds.
Accessories mounted on the headstock spindle are:
- Three jaw chuck.
- Four jaw chuck.
- Lathe center and lathe dog.
- Collet chuck.
- Face Plate.
- Magnetic chuck.
Tailstock:
The tailstock is a movable casting located opposite to the headstock on the way of the bed.
The basic function of the tailstock is:
- To support the other end of the work when being machined.
- To hold a tool for performing operations like drilling, reaming, tapping, etc.
It consists of the dead centers, the adjusting screws, and the handwheel. The body of the tailstock is adjustable on the base which is mounted on the guideways of the bed and can be moved.
Carriage:
Carriage is located between headstock and tailstock. The basic function of the carriage is to support, guide, and feed the tool against the job during operation.
It consists of 5 main parts:
- Saddle
- Cross Slide
- Compound rest
- Tool Post
- Apron
Saddle:
It is an H-shaped casting mounted on the top of the lathe ways. It provides support to cross-slide, compound rest, and tool post.
Cross Slide:
Cross slide is provided with a female dovetail on one side and assembled on the top of the saddle with its male dovetail.
The top surface of the cross slide is provided with T slots to enable fixing of rear tool post or coolant attachment. Carriage basically provides a mounted or automatic cross-movement for the cutting tool.
Compound Rest:
Compound rest is present on the top of the cross slide. It supports the tool post and cutting tool in its various positions. Compound rest is necessary for turning angles and boring short tapers and forms on forming tools.
Tool Post:
The tool post is mounted on the compound rest. It is used to hold various cutting tool holders. The holders rest on a wedge which is shaped on the bottom to fit into a concave-shaped ring (segmental type),
Which permits the height of the cutting edge to be adjusted by tilting the tool. It is fixed on the top slide. It gets its movement by the movement of the saddle, cross slide, and top slide.
The three types of tool post which are commonly used are:
- Ring and rocker tool post: It consists of a circular tool post with a slot for accommodating the tool or tool holder.
- Quick change tool post
- Squarehead tool post.
Apron:
The Apron is fastened to the saddle and hangs over the front of the bed. Apron consists of the gears and clutches for transmitting motion from the feed rod to the carriage, and the split nut which engages with the lead screw during cutting threads.
Two types of Apron are extensively used:
- Incorporating drop worm mechanism.
- Friction or dog clutches.
Chuck:
Chuck is basically used to hold the workpiece, particularly of short length and large diameter or of irregular shape which can’t be conveniently mounted between centers. It can be attached to the lathe by screwing on the spindle nose.
Four different types of chucks are most commonly used in Lathe:
- Independent or four-jaw chuck
- Three jaw or universal chuck
- Collect chuck and
- Magnetic Chuck
Independent or four-jaw chuck:
It is used for irregular shapes, rough castings of square or octagonal in such jobs, where a hole is to be positioned off the center. It consists of four jaws and each jaw is independently actuated and adjusted by a key for holding the job.
Three jaw or universal chuck:
It consists of three jaws that move simultaneously by turning a key and the workpiece automatically remains in the center of the chuck opening. It is used for holding a round, hexagonal bar or other symmetric work.
Collet chuck:
It is mostly used in the places where production work is required such as in Capstan Lathe or automats. It is used for holding the bars of small sizes (below 63mm).
Magnetic chuck:
They are of permanent magnet type or electrically operated. In Lathe, it does not have widespread use.
Feed Rod:
Feed rod is a power transmission mechanism used for precise linear movement of the carriage along the longitudinal axis of the lathe. In some lathe machines instead of feed rod lead screws are used.
Lead screw:
The lead screw is used mostly in the case when the threading operation is to be performed on a lathe. As we know for threading operation requires rotational movement of the job (workpiece) and the linear movement of the tool (tool post).
So rotation of the job is obtained by the chuck and the desired linear motion of the tool-post (as the lead screw drives the saddle when it is engaged) is provided with the help of a lead screw.
Spindle:
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