SLOTTING ATTACHMENT IN DRILLING MACHINE
SYNOPSIS
There are number of machine tools producing round and taper holes. But many engineering components require square and non-circular holes. At present square and other non holes are produced using CNC machines or spark erosion or slotting machines. But there is no quality machine tool to produce square and polygon holes at minimum cost. Thus we made an attempt to design and fabricate an attachment for drilling machine which would produce square and polygon holes much more easily than the current method. This will be very useful to seat bolt heads etc.
This attachment can be though of an inversion of the “Cam and Ball mechanism. This attachment can be fitted either in drilling machine or vertical milling machine. A complete design for this attachment for a size of maximum 20mm square and polygon holes has been successfully done and tested using an upright drilling machine. For different sizes of holes less than 20mm the tool can be changed. Similar designs can be made for any size and any number of sides to avoid lot of setting time and pre-machining procedures involved in current methods and very useful in case of mass production.
INTRODUCTION
Coimbatore is a highly industrial city. This is mainly due to entrepreneurship of local peoples. As there is no public sector undertaking. The small-scale industries though have lathe and other general-purpose machine tools; they find it difficult to get a good finished square and polygon shaping the components. For producing square and polygon holes we have slotting and broaching machines. But it is slow process, the cost is high and setting time is more. A lot of time and manual work is involved in these methods.
So this project “FABRICATION OF SLOTTING ATTACHMENT IN DRILLING MACHINE” is very much useful, if it is provided with good quality form tools of different shapes and sizes. Hence a need exists for attachment which can produce non-circular holes at minimum cost. Thus an attempt is made to design and fabricate such an attachment.
WORKING PRINCIPLE
To obtain a hole of desired shape, first the maximum size of hole that can be inscribed in it is drilled using a conventional drill bit. Now without changing the job and spindle settings, the taper shank of shaft is introduced into the spindle. When spindle rotates the shaft receives the drive and transmits it to the sleeve. The other end of the sleeve is connected to the main shaft which is made up of mild steel 15 mm shaft. The bevel gear and cam mechanism is used to transfer the rotary motion in to the reciprocating motion.
Thus the stub reciprocates three times per revolution of the sleeve. The downward stroke is the cutting stroke. Thus the tool reciprocates with small amplitude and high frequency. The stroke length is equal to distance between the upward and downward movement of the crank shaft. ADVANTAGES
The accuracy of shape.
Comparatively less labour cost than other methods.
Less physical and mental fatigue.
Bolts and nuts can be easily seated.
Machining time is less.
DISADVANTAGES
Not so effective for very hard materials.
Feed should be given intermittently.
Overload should be avoided.
Chips remain in the hole.
When this unit was completed and tested using an Upright Drilling Machine vibrations where experienced due to the radial play of the internal parts. Thus the square could not be machined with that much accuracy. Thus to overcome this defect a thin walled cylindrical hollow sleeve has been introduced between the casing and sleeve. The cylindrical sleeve and the internal parts have very less clearance just to allow them to rotate and no radial play. Thus the vibrations have been arrested. The material used of the sleeve is Mild Steel.
OTHER APPLICATIONS
This drilling machine attachment shall be utilised for other purposes other than machining form holes. This unit eliminates the presence of slotting machine in machine shop. Of course it may not be useful for all the jobs that a slotter can perform. This is because of lack of rigidity that a slotter has. But for small job works like machining a keyway etc can be very well performed by using a suitable tool bit fixed in the tool holder using a bar. Now moreover by giving a very high RPM and minimum feed the frequency of reciprocation can be increased. When this high frequency reciprocation are applied on the job through an abrasive slurry, a hammering effect takes place on the work piece and any complicated shape in the tool can be produced in the job as a female part of the tool. The abrasive slurry consists of mixture of water and abrasive particles. This slurry and work piece is enclosed in a container.