Tips and tricks
Production grinding
PRODUCTION GRINDING
BY FRED B. JACOBS
Editor of Abrasive Industry and Author of Abrasives and Abrasive Wheels
Published by The Penton Publishing Co. Cleveland, Ohio, 1922
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PREFACE
Production grinding is widely practiced to meet the demand for cutting and finishing repetition machine parts in large multiples. In the automobile, motor truck, agricultural and similar industries, production grinding has increased output and has effected economies never before attained by other machining methods. Large production and precision are not generally associated as being practically obtainable, but the cutting of metals by grinding makes this possible. The operations illustrated and discussed in this work represent the highest development of production and precision grinding practice. Every method presented has been subjected to the test of successful commercial manufacture involving big output accurately produced at proportionately low costs. A large part of the data contained herein originally was published in Abrasive Industry, but in its classification for the purpose of this text-book a careful selection of methods was made to insure the inclusion of every phase of production grinding. As a reference work for abrasive and grinding engineers, grinding room foremen and operators it will serve as a standard of the best latter-day practice. It points out how many classes of work can be ground advantageously and it will prove of great value in determining efficient production methods in specific instances.
CONTENTS
- Grinding Marmon Automobile Parts
- Packard Parts Are Ground Accurately
- Grinding Oakland Automobile Parts
- Chevrolet Grinding Operations
- Ford Parts Ground in Large Quantities
- Accurate Production of Tractor Parts
- Chilled Iron Cam Grinding Methods
- Quantity Production of Ball Bearings
- Roller Bearing Production Methods
- Making Ritter Dental Parts
- Finishing Large Paper Mill Rolls
- Grinding and Corrugating Chilled Iron Rolls
- Accurate Auto parts Regrinding Work
- Milling Cutter Production Methods
- Die Grinding Operations in a Steel Plant
- Precision Grinding Work of Other Days
PRODUCTION GRINDING
GRINDING MARMON AUTOMOBILE PARTS
While quantity production of high-grade automobiles has been a specialty of the Nordyke & Marmon Co., Indianapolis, for many years, methods of production have been revolutionized as a result of experience gained by building two types of aircraft engines during the war, the Hall-Scott and Liberty. As soon as contracts were awarded for these engines, the company built and equipped a modern 1-story brick and cement fireproof structure 800 x 635 feet, equipped it with modern machine tools and started to manufacture aircraft engines on a large scale. Those who are not familiar with the degree of accuracy insisted upon in engines of this type do not realize the enormous difficulties encountered in building these units on a quantity basis.
Many lessons were learned, sometimes through costly experiment, to be sure, but the motors were built and some of them were in service over the battlefields of France. Where accuracy is desired, the grinding wheel plays the important part. Almost innumerable time studies at this plant have proved beyond doubt that grinding processes in the manufacture of automobile parts is not only the most accurate method to use in producing parts in quantities, but at the same time it is the most economical. Accuracy of fit in automobile construction has been a characteristic of hand-made foreign cars, tool-room built engines and racing cars, but it is only within recent years that automobiles have been built on a production basis that are equal in accuracy of fit to these hand made products.
The object of this chapter is to describe briefly some of the more important grinding operations at the Marmon plant.
As stated previously, this factory is housed in a 1-story structure. This eliminates trucking from one floor to another and at the same time insures adequate lighting facilities. The shop is divided into different departments, or jobs, each department being devoted to the manufacture of one unit only. Each department has all the machine tools and other equipment necessary to finish the unit to which it is devoted. Thus there is no grinding job, milling job, drilling job, etc., in fact grinding machines are scattered all over the shop, being located in the different departments wherever they are needed. This necessitates the installation of a large number of machine tools, but it results in increased efficiency as trucking from one department to another is reduced. Machines are so installed in each department that the work progresses in as nearly a straight line as possible.
Some of the more important grinding operations now will be considered. The main bearings are fitted without the use of liners. The object of this practice is to present an unbroken surface for bearing and lubrication. The bearings are bearing metal cast in place in a cast iron shell. The shells are roughed-out on the turret lathe and then lined with bearing metal. The next operation is to cut them nearly in two so as to form two halves. The cut is made off center so that a full half bearing results. The other half is discarded. Before separating the bearing, however, the outside is carefully ground to the desired diameter to fit the crank case, as shown in Fig. 1. As it is not practicable to force the comparatively soft bearing metal on a tapered arbor for grinding, a special arbor is employed. This arbor is provided with collars that grip the cast iron liner at the sides. This is an important grinding operation as the contour thus formed is used as a locating point in a subsequent operation. The bearing shown in Fig. 1 is the main center bearing. Its housing is provided with flanges, the insides of which are finished in the grinding operation. The other two main bearings do not have flanges. Thus the grinding of these parts is a simple operation. In grinding these parts, they are held to extremely close limits as the surface thus formed must fit the accurately bored seats in the crank case. The wheel used for this operation is crystolon, 24, combination grit, K grade, operated at normal speed.
After grinding, the bearing is cut apart and the flat surface for the joint on the section that is to form half a main bearing is carefully scraped to a bearing. This scraping brings about two important results. First, it assures an oil-proof joint and again it forms a surface from which the operator tests the top of the bearings to make sure that the joint is to be just midway between the circle representing the outside of the cast iron bearing shell. The bearing is tested for accuracy under a dial test indicator, reading to 0.0001-inch, and the limit of tolerance on the half bearings is 0.0001-inch. Extreme accuracy is necessary for it must be borne in mind that the object is to make two separate halves of a circular piece that will form a true circle when assembled. Any mechanic will appreciate the difficulties encountered in working on two separate halves that must assemble into a perfect part. Were it not for the fact that the grinding machine is used to form the outside contour, such extreme accuracy would not be possible. By grinding these units, however, production costs are reduced to a minimum.
DOWNLOAD FREE BOOK: Production grinding
Many lessons were learned, sometimes through costly experiment, to be sure, but the motors were built and some of them were in service over the battlefields of France. Where accuracy is desired, the grinding wheel plays the important part. Almost innumerable time studies at this plant have proved beyond doubt that grinding processes in the manufacture of automobile parts is not only the most accurate method to use in producing parts in quantities, but at the same time it is the most economical. Accuracy of fit in automobile construction has been a characteristic of hand-made foreign cars, tool-room built engines and racing cars, but it is only within recent years that automobiles have been built on a production basis that are equal in accuracy of fit to these hand made products.
The object of this chapter is to describe briefly some of the more important grinding operations at the Marmon plant.
As stated previously, this factory is housed in a 1-story structure. This eliminates trucking from one floor to another and at the same time insures adequate lighting facilities. The shop is divided into different departments, or jobs, each department being devoted to the manufacture of one unit only. Each department has all the machine tools and other equipment necessary to finish the unit to which it is devoted. Thus there is no grinding job, milling job, drilling job, etc., in fact grinding machines are scattered all over the shop, being located in the different departments wherever they are needed. This necessitates the installation of a large number of machine tools, but it results in increased efficiency as trucking from one department to another is reduced. Machines are so installed in each department that the work progresses in as nearly a straight line as possible.
Some of the more important grinding operations now will be considered. The main bearings are fitted without the use of liners. The object of this practice is to present an unbroken surface for bearing and lubrication. The bearings are bearing metal cast in place in a cast iron shell. The shells are roughed-out on the turret lathe and then lined with bearing metal. The next operation is to cut them nearly in two so as to form two halves. The cut is made off center so that a full half bearing results. The other half is discarded. Before separating the bearing, however, the outside is carefully ground to the desired diameter to fit the crank case, as shown in Fig. 1. As it is not practicable to force the comparatively soft bearing metal on a tapered arbor for grinding, a special arbor is employed. This arbor is provided with collars that grip the cast iron liner at the sides. This is an important grinding operation as the contour thus formed is used as a locating point in a subsequent operation. The bearing shown in Fig. 1 is the main center bearing. Its housing is provided with flanges, the insides of which are finished in the grinding operation. The other two main bearings do not have flanges. Thus the grinding of these parts is a simple operation. In grinding these parts, they are held to extremely close limits as the surface thus formed must fit the accurately bored seats in the crank case. The wheel used for this operation is crystolon, 24, combination grit, K grade, operated at normal speed.
After grinding, the bearing is cut apart and the flat surface for the joint on the section that is to form half a main bearing is carefully scraped to a bearing. This scraping brings about two important results. First, it assures an oil-proof joint and again it forms a surface from which the operator tests the top of the bearings to make sure that the joint is to be just midway between the circle representing the outside of the cast iron bearing shell. The bearing is tested for accuracy under a dial test indicator, reading to 0.0001-inch, and the limit of tolerance on the half bearings is 0.0001-inch. Extreme accuracy is necessary for it must be borne in mind that the object is to make two separate halves of a circular piece that will form a true circle when assembled. Any mechanic will appreciate the difficulties encountered in working on two separate halves that must assemble into a perfect part. Were it not for the fact that the grinding machine is used to form the outside contour, such extreme accuracy would not be possible. By grinding these units, however, production costs are reduced to a minimum.
DOWNLOAD FREE BOOK: Production grinding
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