Cylindrical GrinderA cylindrical grinding machine is typically used to grind the OD (outside diameter) of cylindrical shaped parts so as to reduce these parts to a very exact size and, at the same time, improve their surface finish. Typically, parts are turned on a lathe to a size slightly larger than the finished size desired, then put on the cylindrical grinder to finish it to the exact size required and improve the surface finish of the part removing any turning marks left by the lathe. Grinding parts is necessary in some cases because of the extremely close tolerances required in some applications such as valve seats, hydraulic seals, bearings and machine tool spindles.
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Cylindrical grinders are constructed similar to an engine lathe in that the part is held between centers, or, in the case of short parts, in a chuck or collet. The metal cutting is done with a rotating grinding wheel instead of a single point tool (on a lathe). The principle difference is the precision achievable with a grinding machine is several orders of magnitude better than what can be achieved with a lathe. Also, surface finish is dramatically improved. While lathes leave cutter marks on the work piece, grinders are capable of erasing those marks and leaving behind either a mirror finish or a brushed look. The difference between mirror finish and brushed look is the choice of the grit in the grinding wheel selected for the job. A fine grit wheel will produce a mirror finish and a coarse grit wheel will give a brushed look to the metal.
Grinding machines are used because they can produce parts of unbelievable accuracy. Typical inexpensive grinders can repeatedly produce parts accurate to 10ths (.00010in) and higher quality, better made machines can typically hold tolerances to as close 25 millionths (.000025in).
Like most machine tools cylindrical grinders come in a variety of types and can be equipped with a myriad of options. There are three basic types of cylindrical grinders the plain type, the universal type and the angle head type. Plain cylindrical grinders are for straight grinding of cylindrical parts. The angle head grinder has a grinding wheel head mounted at an angle usually fixed at 30 degrees. This enables the angle head grinder to produce shoulders, tapers and face areas of the part that may require it. The universal cylindrical grinder is the machine most often found in tool room settings. These machines are the most versatile of the three types. On a universal grinder, the wheel head swivels, the work head swivels and the table swivels. This enables the operator to do just about an operation on the part tapers, shoulders, faces, etc.
The list of possible options for cylindrical grinders is beyond the ability of this short article to cover in full, but some of the more important ones are:
Hydraulic Table Traverse: Some machines are totally manual and the operator must turn a hand wheel to move the table (and part) back and forth hydraulics automate this motion.
ID attachments: provides the ability to grind an inside diameter of a part
Plunge: provides the ability to plunge the grinding wheel into the rotating part without traversing the table; a shape can be dressed into the wheel and ground into the part this way
Spark Out: This is a timer that lets the machine linger after a certain size is achieved for a set amount of time until there are no more sparks and grinding is totally complete and ideal size is achieved.
Dressers: Machines can have various methods or attachments for dressing the wheel; all grinders need some method to true the wheel after a certain amount of use.
Tarry: Like spark out, the table moves to the end of its travel range and sits still for a while. Tarry can be set for both ends of travel; RH & LH
Auto Infeed: Lets the operator walk away and the machine feeds the wheel into the work automatically until the desired size is achieved
Rapid Wheel Advance and Retract: Eliminates dead time waiting for the grinding wheel to approach the work and retract back to home position at the end of cycle.
CNC Controls: Typically automate all machine functions, including dressing the wheel. Most often found in production shops.
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