Internal Diameter (ID) Grinder Guide

What Is an Internal Diameter Grinder?

An internal diameter (ID) grinder, often referred to as an internal grinding machine, is grinding equipment that embodies the concept of internal grinding. It is primarily used to grind bores and holes and may be considered one of the most widely used grinding methods in the industry.

Internal grinding machines are used to accurately finish straight, formed, or tapered holes. You can find a variety of models of ID units in the market, the operation of which works very similarly to that of a lathe. It is essentially a kind of boring operation in which the workpiece is held by a work-holding device (usually a chuck or collet), and revolved by a motorized headstock. A separate motorhead is positioned in the same direction as the workpiece revolves around the grinding wheel. The workpiece can be fed in and out of the machine, and also positioned for depth of cut.


Types of Internal Grinding

Internal grinding is a very common machining method amongst the grinding processes. It can work different kinds of holes, including blind holes, step holes, etc. on parts of the machine. Despite being one of the most complex grinding methods, internal grinding machines remain to be widely used in machining. 

Internal grinding can be classified into three types: the center type, centerless type, and planetary type:


● Center type internal grinding:

This type of grinding has the workpiece around the centerline of the spindle box during the process. Mostly conventional internal grinding machines and universal cylindrical grinding machines embody this kind of grinding mechanism. They are especially suitable for grinding the inner holes of gears, flanges, sleeves, etc.


● Centerless type internal grinding:

As a renowned counterpart of center-type grinding, centerless grinding machines do not have center holes or need to use a work-holding device. During centerless grinding, the workpiece sits on a work rest blade and is supported by a second wheel (i.e., regulating wheel). The grinding wheel rotates as the workpiece is pushed down to the blade and pressed against the regulating wheel. The regulating wheel rotates in the same direction as the grinding wheel and controls the longitudinal feed of the workpiece when set at a slight angle.


● Planetary type internal grinding:

As the name suggests, the workpiece is fixed and the grinding wheel revolves around its own axis at high speed. Planetary internal grinding machines are primarily used for grinding workpieces that are exceptionally larger and inconvenient to rotate.


Internal Grinding Methods

Internal grinding can be further divided into two methods: longitudinal and cut-in method:


● Longitudinal Grinding:

This grinding method works very similarly to the cylindrical longitudinal grinding method. During the grinding process, you are required to first determine the diameter and the shaft of the grinding wheel based on the diameter of the hole and the length of the workpiece. The long shaft is more robust, and the length of the shaft only needs to be a little bit larger than the hole. 


● Cut-in Grinding:

Cut-in grinding resembles the cylindrical cut-in grinding method and is particularly suitable for grinding workpieces with short inner holes. During the grinding process, the long shaft has good rigidity, and the grinding wheel is easily blocked and blunt when the parts are fed continuously. The grinding wheel should also be dressed in time. During finish grinding, the lower cutting speed is usually used. 


Selecting Internal Grinding Wheels

Choosing the right grinding wheel may just be the one most important task for your internal diameter grinding machine. Here is a simple guideline to follow:


1. Selecting the diameter:

You have to make sure that the diameter of the grinding wheel is not too large, or the contact arc between the wheel and workpiece will increase. This leads to increased grinding heat that can be difficult to cool off and remove the debris. You also do not want the diameter of the grinding wheel to be too small because it will be difficult to achieve the desired ground speed. This will result in increased thickness and the load of the abrasive grains. 


2. Selecting the width:

Selecting the right width for the grinding wheel is also important. If the width is too narrow, the grinding wheel becomes susceptible to wear, and this is definitely not ideal for the efficiency of production as well as reducing the surface roughness. And if the width is too wide, it increases the grinding force by which the long shaft of the grinding wheel may be prone to deformation. Therefore, always choose the appropriate width when grinding the inner hole. 

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