Capstan lathe is one of the types of semi-automatic lathe. In semi-automatic lathes machining operations are done automatically. Functions other than machining like loading and unloading of job, positioning of tools coolant operations are done manually.
The base part of the lathe is the bed. It is made of cast iron. Guide ways are provided on the top of the bed. Cross slide and turret head are mounted on the guide ways. The bed should be strong and rigid to withstand loads force and vibrations during machining process.
The headstock assembly is permanently fastened to the left end of the bed. Headstock of capstan lathe is similar to that of ordinary lathe. But it is heavier in construction . a powerful motor of 30 to 2000rpm speed is fitted.
The four main types of headstocks are
· Step cone pulley driven headstock.
· Direct electric motor driven headstock .
· All geared headstock.
· Pre-selective headstock.
3.TURRET HEAD AND SADDLE
The turret head is mounted on the ram fitted with turret slides longitudinally on the saddle. Turret head has a hexagonal block having six faces with a bore for mounting six or more than six tools at a time. The threaded hole on these faces are used to hold the tools. The actuation of ram is done by hand or power. An adjustable stopper is used to control the forward movement of the ram. Ram is returned to its initial position in order to index the cutting tool. The tools are indexed to 60 by rotation of circular plate which is indexed automatically along with the turret head. For bringing the next tool into cutting position a mechanism called Geneva mechanism is used.
It is an H shaped component fitted across the lathe bed. It moves along the guide way. It can be moved anywhere along the bed and locked to the required position. In capstan lathe the turret head is mounted upon the ram which slides upon the saddle.
There are two type of cross slides they are
· Reach over type
· Slide hung type
Reach over type
The cross slide has two tool posts having totally four faces of square turret for mounting the tools. Tools are indexed by an angle of 90. While indexing, the motion of each tool is controlled by stop bars.
Slide hung type
This type of cross slide is entirely supported on the front and has no rear tool post. This enables a greater swing capacity to hold large diameter workpiece.
Work piece is held in collet or chucks which is actuated hydraulically or pneumatically. All the needed tolls are held in the respective holes on the turret head. According to the sequence of operation the tool is moved with the help of turret head.
· Drilling, boring, turning, reaming, threading tools are mounted on the turret head.
· Forming, chamfering, knurling tools are mounted on the front end of the turret.
· Parting tool is mounted in inverted position on the rear end of the turret.
After completing each operation the turret head is moved back to its initial position which indexes the tools automatically.
· Rate of production is higher.
· Different ranges of speeds are obtained.
· More number of tools can be accommodated.
· Chucking of larger work pieces can be done.
· Operators of less skill is required hence lowers the labour cost.
· Higher rigidity so can withstand heavy loads.