Grinding and grinding machines

CHAPTER I

TYPES OF GRINDING MACHINES

History of the Universal Grinding- Machine

The universal grinding machine has had so great an influence on modern machine shop methods, and has done so much to raise the standard of workmanship and to increase the economy of production that a few words relating to the history of the development of this machine may be of interest.

The origin of the modern universal grinding machine is found in the crude grinding lathes of the early sixties. Mr. Joseph R. Brown, senior member of the firm now known as the Brown & Sharpe Mfg. Co., was intimately connected with the development of these grinding lathes into the universal grinding machine. The grinding lathe, as first built at the Brown & Sharpe Mfg. Co.'s works, was intended for the accurate and economical manufacture of the company's own products, and there was no idea of putting the machines on the market. In this respect the origin and development of the grinding machine was very much like the origin and development of the universal milling machine. The first work for which the grinding machines were designed was for grinding needle bars, foot bars and shafts of the Wilcox & Gibbs sewing machines. The first machine was built in 1864 and 1865, and one of these early machines is still in use in the Brown & Sharpe works. Cylindrical grinding, however, was done at the Brown & Sharpe works as early as 1862, this being indicated by the existence of drawings of a back-rest, dated September 22, 1862, which contains the essential features of a solid grinding machine back-rest of to-day.

These early machines were not grinding machines in the present meaning of the word, but were grinding lathes using, to a considerable extent, the parts of a 14-inch Putnam lathe. A great number of these were sold both in this country and abroad. Mr. Brown, however, realized the need of building a new machine designed especially for grinding, and is 1868 the design for such a machine was made. This design shows a machine containing most of the essential elements of the universal grinding machine of to-day. None of these machines were built at this time, however, on account of the pressure of other matters, and it was first in 1874 that working drawings were made for a complete machine containing practically all the features of the modern universal grinding machine. The first of these machines was exhibited at the Centennial Exposition in Philadelphia, 1876. The judges at the Centennial Exposition were especially impressed with this universal grinder.

The development of the grinding art since the Centennial Exposition has brought out many improvements and refinements, but the essential and is distinctly a manufacturing machine. It is adapted for grinding plain straight and taper work, and all work that can be revolved on two dead centers. These machines are made especially heavy and represent the highest development of machines of their class.

In Fig. 3 is shown a grinding machine of a heavier type than the two previously shown. This machine is built by the Norton Grinding Co., Worcester, Mass., and is known as a 20- and 32- by 168-inch self-contained grinding machine, the name being derived from the fact that the machine swings 20 inches', except in the gap indicated, where it will swing 32 inches. "This particular machine is motor-driven, the motor being of 20 horsepower capacity for large and heavy work. The foot-stock is arranged for sensitive adjustment in order to secure straight work. The grinding wheel used in this machine is 24 inches in diameter by 4 inches face. One of the principal features- of the machine is the gap arrangement, the gap being 44 inches long. The plates shown under the grinder bed are intended to be carefully embedded to straight-edge and level in the foundation of the machine. Wedges are used under the machine resting on these plates. These wedges are adjusted with two nuts, one on either side of the projecting end of the wedge, the nuts being operated on threaded studs fixed in the base of the machine. Both the plates and the wedges are machined to insure broad permanent contact. The total length of this machine is 22 feet, and it weighs 25,000 pounds.

In Fig. 4 is shown the Bath duplex internal grinding machine. When this machine was placed on the market in 1909 it represented an entirely new departure in internal grinding machines. This machine places internal grinding on as practical a basis as that which external grinding has achieved during the past decade. The principal advantage of the Bath duplex grinder is that the arrangement of the grinding spindles and the work-holding head, or heads, makes it possible to gain considerable time in the grinding and gaging of internal work. Two pieces can be ground on the machine simultaneously, and it is not necessary to shift the reciprocating slide in order to gage, insert or remove the work. It is possible to use two grinding wheels at once, one operating from each end of the work. It is also possible to use a number of grinding wheels mounted on a supported spindle between the two grinding heads and to quickly grind the inside of a sleeve or bushing by having one wheel after the other enter the work, the previous wheel, of course, leaving the work before the next one enters. This saves considerable time, as it makes it unnecessary to reverse the reciprocating table for each cut.

The novel feature which, in particular, distinguishes this machine from older designs is that the grinding wheels and spindles pass in through the back end of the head-stock spindle as shown in Fig. 4 r instead of running into the head-stock spindle from the front.

In Fig. 5 is shown a large face grinder designed and built by the Diamond Machine Co., of Providence, R. I. This machine is designed for the general run of surface grinding operations in the ordinary machine shop. It consists, as seen from the illustration, of a reciprocating table sliding on a long bed. The table carries the work back and forth in front of the face of a large ring emery wheel. The longitudinal table movement is obtained by an open and crossed belt reversing mechanism in the back of the machine, which is connected to the table rack by heavy gearing. The mechanism used is similar to that of a planer. Machines of this type can be profitably applied to such operations as the finishing of machine columns, pipe flanges and a great number of similar pieces requiring a plane surface, but not a high degree of accuracy.


CHAPTER II - PRINCIPLES OF GRINDING

The development of the grinding machine has made rapid progress during the last few years, and the process, of grinding is more and more recognized as having both economical and technical advantages, as compared with the old methods of obtaining finish. This is especially true regarding plain cylindrical grinding, and this is due chiefly to the fact that the machines for this kind of grinding are easier to build, and in general more efficient, than machines for other kinds of grinding. It is probably true, however, that there is more misunder- standing among engineers and workmen in regard to cylindrical grinding than in the case of any of the other mechanical arts. Nearly every operator has a different theory, and each maker of grinding machines has his own method of grinding.


Relative Time Required for Finishing by Turning and Grinding

It has often been claimed, by people who have had long and thorough experience in regard to this subject, and whose testimony, therefore, must be considered as having weight, that time can be saved in finishing a cylindrical piece of work by taking a roughing cut with an ordinary cutting tool, leaving about from 0.008 to 0.010 inch of metal, and grinding off this amount instead of taking a second cut in the lathe and finishing the piece by filing.