How to Drilling and Boring Operation in Lathe Machine -Fitter Online Note

 Drilling and Boring Operation in Lathe

Introduction to drilling 

1- Frequently, holes will need to be drilled using the lathe before other internal operations can be completed, such as boring, reaming, and tapping. 

2- Although the lathe is not a drilling machine, time and effort are saved by using the lathe for drilling operations instead of changing the work to another machine.

3- Before drilling the end of a work piece on the lathe, the end to be drilled must be spotted and then center drilled so that the drill will start properly and be correctly aligned. 

4- The headstock and tailstock spindles should be aligned for all drilling, reaming, and spindles should be aligned for drilling, reaming, and tapping operations in order to produce a true hole and avoid damage to the work and the lathe. 

5- The purpose for which the hole is to be drilled will determine the proper size drill to use. 

6- That is, the drill size must allow sufficient material for tapping, reaming, and boring. 

7- The correct drilling speed usually seems too fast due to the fact that the chuck, being so much larger than the drill, influences the operator's judgment.

Method of holding drills in tailstock 

1- Methods of supporting the twist drill in the tailstock can vary Straight shank drills are usually held in a drill chuck, which is placed in the taper socket of the tailstock spindle. 

2- Combination drill and countersinks (center drills), counter bores, reamers, taps, and other small shank cutters can also be supported in this way.

3- Tapered-shank twist drills may be held directly in the tailstock tapered spindle as long as a good fit exists. 

4- If the drill shank is not the correct size, then a drill socket or sleeve may be used in the tailstock spindle.

5- A twist drill holder is used to support large twist drills with the tailstock center.

6- The drill is inserted into the holder and the tailstock center is placed in the center hole which is located at the rear of the drill holder.

7- The holder will rest on the cross slide or compound rest and must be supported by hand until it is held secure by pressure between the tailstock and headstock. 

8- When using this method, never withdraw or loosen the tailstock spindle while the lathe is rotating or the work piece can be thrown out at the operator. 

9- Always stop the machine before attempting to withdraw the twist drill.

10- Another method of supporting a large twist drill in the tailstock is to fasten a lathe dog to the drill shank and support the rear of the drill with the tailstock center in the center hole in the tang of the drill.

Drilling operations

1- Drilling is the production of cylindrical holes of definite diameters in work pieces by using a multipoint cutting tool called a drill. 

2- The drill chuck is mounted in a tailstock spindle and the feeding on the drill to work is done by rotating the tailstock hand wheel. 

3- To start the drilling operation, compute the correct RPM for the drill and bet the spindle speed accordingly. Ensure the tailstock is clamped down on the lathe ways. 

4- The feed is controlled by turning the tailstock hand wheel. 

5- The graduations on the tailstock spindle are used to determine the depth of cut. 

6- If a large twist drill is used, it should be proceeded by a pilot drill, the diameter of which should be wider than the larger drills web. 

7- Use a suitable cutting fluid while drilling.

8- Always withdraw the drill and brush out the chips before attempting to check the depth of the hole. 

9- If the drill is wobbling and wiggling in the hole, use a tool holder turned backwards to steady the drill.

10- Always use a drill that is properly ground for the material to be drilled. 

11- Use care when feeding the drill into the work to avoid breaking the drill off in the work. 

12- Drill should never be removed from the work while the spindle is turning because the drill could be pulled off the tailstock spindle and cause injury or damage.

Boring 

1- Boring is the process of enlarging and truing an existing drilled or core hole with a single point cutting tool. 

Necessity of boring a hole 

1- To enlarge a drilled hole larger than the drill size as drills are available in standard sizes only. 

2- To obtain concentricity of the hole. 

3- To maintain accuracy of the hole. 

4- To remove the error formed by drilling, and to facilitate the reaming operation. 

5- To obtain better surface finish. 

Boring tools and holders 

1- Boring is an internal operation performed on the drilled or cored holes. 

2- The cutting edge of a boring tool is ground similar to the left hand plain turning tool.

3- But the operation being performed is form right to left.

Enlargement of holes 

Drilling 

1- The operation of drilling consists of producing a hole in an object by forcing a rotating drill against it. 

2- The same result is carried out in some machines by holding the drill stationary and rotating the work as on the lathe. 

3- A dial test indicator magnifies small variations in sizes by means of a pointer on a graduated dial. 

4- This direct reading of the deviations gives an accurate picture of the conditions of the parts being tested.

Boring 

1- It is the operation of enlarging a hole that has already been drilled or bored with a single point tool. 

2- It also rectifies the error of drilling, if any.

Counter Boring 

1- It is the operation of enlarging one end of a drilled hole. The enlarged hole is connected to the original one and it is flat at the bottom. 

2- It is done to set bolt head and nuts below the surface.

Spot Facing 

1- To finish off a small surface around a drilled hole is known as spot facing. 

2- It is carried out to give a proper seating to bolts and nuts.

Counter Sinking 

1- The top of the drilled hole is beveled to accommodate the conical seat of a flat head screw and countersunk rivets. 

2- The operation is called countersinking.

Reaming 

1- It is the operation of enlarging a machined hole to proper size to a smooth finish. 

2- A reamer is an accurate tool and is not designed to remove much metal. 

3- Allowance for reaming should not exceed 0.015 inches.

Tapping 

1- It is the operation of forming internal threads by means of a tool called tap. 

2- To withdraw the tap, the arrangement is made by either a reversible motor or tapping attachment.

Trepanning 

1- It is the operation of producing a hole by removing metal along the circumference of a hollow cutting tool.

2- This operation is performed for producing large holes. 

3- Fewer chips are removed and much of the material is saved while the hole is produced.

Grinding 

1- This operation may be performed in a drilling machine to finish a hardened hole. 2- The grinding wheel is made to revolve with the spindle and is fed up and down. 

3- A suitable grinding wheel may be selected for surface grinding operation. 

4- Grinding can also be done to corręct out of roundness of the hole. 

5- The accuracy in grinding operation is quiet high about ± 0.0025 mm.

Types of boring tools 

1- The following are the different types of boring tools. 

1- Solid forged tools. 

2- Boring bars with bits. 

3- Brazed tool. 

4- Throw away bits inserted in special holders. 

Solid forged tools 

1- The solid forged boring tool is generally made of high a left hand turning tool. 

2- They are light duty tools and are used on small diameter holes.

3- They are held in special tool holders which are mounted in the tool post. 

4- Occasionally tungsten carbide or high speed steel tips are brazed to low carbon bars, for economy. 

Advantages 

 1- Available with square and round shank. 

 2- Enables to mount on the tool post easily. 

3- Re-grinding is easy. 

4- As the tool is integral, alignment is easy. 

5- Can be easily forged to the required shape and angle.

Boring bars with inserted bit 

1- The boring bar tool-holder is mounted in the tool post and is used for heavier cuts than those for the forged boring tool.

2- Square tool bits are set at angles of 30°, 45°, 90° in the broached holes in the bar. 3- The boring bars may be plain type or end cap type. 

4- The cutting tool of the plain type is held in position by a set screw. 

5- Cutting tool of the end-cap type is held in position by the wedging action of a hardened plug. 

6- The round or square section tool bits may be inserted in boring bars, the size depending on the diameter of the bar. 

7- The tool bit may be square to the axis of the bar for plain boring or at an angle for facing shoulder , or threading up to a shoulder. 

8- The bar is held in a split or 'V' block holder.

Advantages 

1- Used for heavy duty boring operation.

2- Used for deep boring operation. 

3- Tool changing is faster, thereby re-sharpening time is avoided. 

4- Cost is less because boring bar is made out of low carbon steel. 

5- Boring tools can be set square to the axis of the boring bar or at an angle very quickly.

Boring operation in lathe 

1- Boring is the operation of enlarging the previously drilled hole with the aid of single point cutting tool called boring tool. 

2- If the hole is enlarged only through a certain length then it is referred as counter boring.

3- For non-tapered holes, the cutting tool moves parallel to the axis of rotation.

 

4- For tapered holes, the cutting tool moves at an angle to the axis of rotation.

5- Geometries ranging from simple to extremely complex in a variety of diameters can be produced using boring applications. 

6- Boring is one of the most basic lathe operations next to turning and drilling. 

7- Lathe boring usually requires that the workpiece be held in the chuck and rotated. 

8- As the work piece is rotated, a boring bar with an insert attached to the tip of the bar is fed into an existing hole. 

9- When the cutting tool engages the workpiece, a chip is formed. 

10- Depending on the type of tool used, the material, and the feed rate, the chip may be continuous or segmented. 

11- The surface produced is called a bore.