Basically there are three different methods by which centreless grinding can be done on different types of jobs.
Method # 1. Through-Feed:
This is simplest method and is applied only to plain parallel parts such as roller pins and straight long bars which are difficult to grind by ordinary cylindrical grinding method. In this case, controlling wheel is first positioned for the proper diameter, i.e. the gap between the regulating wheel and grinding wheel is adjusted equal to the desired diameter of the workpiece and then the job is fed and passed through the wheels.
The machine can remove upto 0.38 mm of stock on the diameter in one pass. The rate of longitudinal feed = π x diameter of regulating wheel x r.p.m. of regulating wheel x sin (angle of inclination of regulating wheel, usually 1° to 6°). This relationship does not consider effect of slip. For finish grinding, high speed of regulating wheel combined with less inclination are used and vice versa.
Advantages:
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(a) The operation becomes automatic by employing continuous magazine feed for longer bars and hopper for small jobs.
(b) No holding of the workpiece is required except the work support and hence the long bars can be ground easily without any deflection being produced.
Disadvantages:
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(a) This process is only used in case of straight cylindrical parts. If there is a head on the workpiece or it is tapered one, then this process cannot be used.
(b) Form grinding operation cannot be carried out by this process.
Method # 2. In-Feed (Plunge-Cut-Grinding):
This method of grinding is used when the workpiece is of headed, stepped or taper form. In this case there is no axial movement of the workpiece as the length of grinding has to be controlled.
The only movement occurring during the process is the rotating movement. During the process the workpiece is placed on the work-rest against an end stop and then the control wheel is advanced towards grinding wheel by some lever arrangement, and grinding continued till the workpiece is reduced to the required diameter.
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The regulating wheel is given a slight inclination of the order of 1/2° in order that the workpiece may remain tight against the end stop. If this inclination is not given to the controlling wheel, then there are chances that workpiece may fall down during the process. The length of the workpiece that can be ground is limited to 30 cm. By this process form grinding can also be done.
Method # 3. End-Feed:
This process of centreless grinding is used for headed components which are too long to be ground by the infeed method, i.e. when the length of workpiece is greater than the width of the grinding wheel.
The work is fed as in case of in-feed method and after a certain portion of length of workpiece has been ground, the axial movement takes place until the whole of length has been ground. It is also used for tapered work. Usually both grinding wheel and regulating wheel are trued to obtain the required taper.
