LATHE PARTS-CARRIAGE AND TOOL POST

Lathe parts- carriage and tool post

.the function of a carriage

. the parts of a carriage

. commonly used types of tool post

. features of different types of tool posts

Carriage is the feature of a lathe that provides the method of holding and moving the cutting tool. It can be locked at any desired position on the lathe bed. It consists of two major parts namely, apron and saddle.

Apron

The apron is botled to thee  front of the saddle. It contains mechanisms for moving and controlling the carriage. The main parts of an apron are:

-traversing handweel

-feed lever

-feed selector

-lead screw engagement lever

Saddle

It is a 'H' shaped casting having 'V' guide grooves at the bottom face, corresponding to the lathe bed-ways for mounting on the lathe bed and for sliding.

Parts of a saddle

Cross -slide

The cross -slide is  mounted on the top of the saddle, and it provides cross movement for the tool. This is fitted at right angles to  the bed and is moved by means of a screwed spindle, fitted with a  handle. A graduated collar, mounted on the screw rod along with the hand wheel, helps to set the fine movements of the cross-slide.

Compound rest

The compound rest is fitted on the top and to the front of the cross-slide. The compound rest  can be swivelled horizontally through 360°.

Top slide

The top slide is fitted on the top of the compound rest. It supports the tool post which holds the cutting tool. The top slide provides a limited horizontal movement for the cutting tool.

By swiveling the compound rest, the top slide can be set at an angle to the cross-slide.

Usually the compound rest is set in such a way that  the top slide is at right angles to the cross-slide.

TOOL POST 

The tool post holds and fimly supports the tool  or tools. The tool post is fitted on the top slide.

The commonly usee types of  tool post are

-American type tool post or single way tool post indexing type tool post  or squre tool post

-quick change tool post.

Single way tool post

It consists of a circular tool post bdy and a pillar with a slot for accommodating the tool or tool-holder. A ring base, a roker arm(boat piece) and a tool -clamping screw complete the assembly of this type of tool post.

The tool is positioned on the boat piece and clamped. The centre  height of the tool tip can be adjusted with the help of the rocker arm and the ring base. Only one tool can be fixed in this type of tool post. The rigidity of the tool can be fixed in this type of tool post. The rigidity of the tool is less as it is clamped with only one bolt.

Indexing type tool post

It is also called as squre tool post or a four-way tool post. Four tools can be fixed in this type of tool posts, and any one can be brought into the operating position, and the square head is clamped with the help of the handle lever.By loosening the handle lever, the next tool can be indexed and brought in to the operating position. The indexing may be manual or automatic.

The advantages

Each tool is secured in the tool post by more than one bolt, and, therefore, the rigidity is more.

Frequent changing of the tool for different operations need not be done as all the four tools can be clamped at the same time.

The disadvantage is thet skill is required to set the tools, and it takes more time to set to the centre height.

Quick change tool post

Modern lathes are provided with this type of tool posts. Instead of changing the tool, the tool holder is changed in which the tool is fixed. This is expensive and requires a number of tool-holders. But it can be set to the centre height easily, and has the best rigidity for the tool.