Introduction to Grinding and Drilling in Basic Workshop Technology

Introduction

1.            The process of removing material from a piece of work by means of rotating abrasive wheel is known as grinding. Grinding wheel is mounted on the spindle and rotates on it. Metal is ground by the action of number of cutting edges coming into contact with the work piece.

2.         Types of Grinding Machines       (Refer Fig 1, 2 & 3)

(a)       External Cylindrical Grinding Machine

(b)       Internal Cylindrical Grinding Machine

(c)        Surface Grinding Machine      

Fig 1 External Cylindrical Grinding Machine

Fig 2 Internal Cylindrical Grinding Machine

Fig 3 Surface Grinding Machine

3.         Classification.         These machines are classified by the type, size of machine and special features as specified by the manufacturers.

4.         Purpose:       The purpose of grinding machine is:

           

(a)       To shape hard steel or metal which cannot be machined.

(b)       To obtain high degree of surface finish.

(c)        To obtain high degree of dimensional accuracy.

(d)       To overcome the inaccuracies in the previous machined surfaces.

(e)       To sharpen cutting tools.

(f)        To give correct geometrical shape to a product.

5.         Classification of Grinding Wheels.        Grinding wheels are classified by abrasive material, type of bond, grit or grain size, grade, structure, shape  and size of the wheel (Refer Fig 4 and Fig 5).

Fig 4 Grinding Wheel

(a)       Abrasive.      It is the actual cutting element of the grinding wheel. It is extremely hard and tough by nature. When it is fractured, many sharp edged corners are formed. Metal is removed by these multiple sharp cutting edges. These are of two types.

                        (i)         Natural:         Emery, Corundum and Quartz

                        (ii)        Artificial:        Silicon carbide and Aluminium oxide

(b)       Bond.             It is an adhesive that holds the abrasive in the form of wheels. These are of three types:

                       

(i)         Vitrified  

(ii)        Silicate  

(iii)       Elastic

(c)        Grade.            This is an indicator of degree of hardness of the wheel or tenacity of the bond to hold the grain in the grinding wheel.         

(d)       Grit or Grain.            Grit or grain is the size of the abrasive particles. It is designated by a number, which is the number of meshes or openings per unit length of sieve through which the abrasive grains would pass. 

Fig 5 Grinding Wheel

(e)       Dressing of Wheels.          Grinding wheels are dressed when these wheels lose the cutting ability.  These are dressed with either a wheel or diamond dresser.

Drilling

           

6.            Basic Operation.     Drilling is an operation through which circular holes are produced by means of drill.

7.         Purpose/ Use.  Drilling machine is used for following operations:

(a)          Drilling                       (b)       Reaming

(c)        Boring                     (d)       Counter Boring

(e)       Counter Sunking     (f)        Spot Facing

(g)       Tapping

8.         Types of Drilling Machines

(a)       Portable Drilling Machine.            It is a very small, compact unit carrying a small electric motor. It is commonly used for drilling holes in those components which can not be transported (Refer Fig 6).

Fig 6 Portable Drilling Machine

(b)       Upright Drilling Machine.    It is also known as standard, vertical or pillar drilling machine. It is used for heavy work and has rapid reversing mechanism for withdrawal of drills. These machines are manufactured in various sizes having drilling capacities upto 75 mm diameter. (Refer Fig 7)

Fig 7 Upright Drilling Machine