Tips and tricks
Grinding and lapping
GRINDING AND LAPPING
TOOLS, PROCESSES AND FIXTURES
By JOSEPH V. WOODWORTH
1907; HILL PUBLISHING COMPANY; NEW YORK
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A Practical Treatise and Toolmakers Reference Work upon Precision Grinding and Grinding Processes, the Preparation and Use of Abrasives, Lapping Processes and Methods, the Construction and Use of Laps, and the Design, Construction and Application of Fixtures for Grinding Accurate Repetition Parts of Steel and Iron; together with the Automatic Hardening and Tempering of Interchangeable Tool Steel Parts of Delicate Structure and Percentages of Carbon, Necessary in Steels used for Various Tools and Parts, and which are Afterward Subjected to Grinding and Lapping Processes
PREFACE
In the pages following are shown engravings and half-tones of tools, machines, grinding fixtures, laps and lapping devices and arrangements, and combination fixtures for presenting duplicate work to grinding operations from the simplest to the most intricate in modem use; and we have endeavored to not only describe how to use them, but to describe and illustrate how to design and construct them as well, in a clear practical manner, so that all grades of metal-working mechanics may be able to understand thoroughly how to design, construct and use them for the economic production of the marvelous variety of machine parts and tools required to-day to perform the stupendous labor of our wonderful civilization.
Many of the tools and devices described and illustrated in this volume we designed and used ourselves; others were designed under our personal supervision; while others have been selected from published articles written for the technical press under our own name and various pen names. For many other descriptions and illustrations we are indebted to the kind courtesy of the editors of American Machinist, and Machinery, respectively, and here extend our thanks and sense of deep obligation to these journals for the privilege of using extracts and illustrations of articles which have appeared in their columns. For a large number of practical "kinks" and "points" we acknowledge our indebtedness to the numerous concerns with which we have been connected, and to the fellow workers with whom we have associated.
The sections on "Hardening and Tempering of Tool Steel Parts of Delicate Structure, which Require to be Ground and Lapped Afterwards," and "Carbon Percentages in Hardened and Ground Steel Tools and Parts," are so near akin to the general subject of this work, that they have been given a place so that the mechanic interested in grinding and lapping may become thoroughly familiar with the practice necessary to create the necessary fundamental conditions in parts which are required to be hardened, ground and lapped to interchangeable dimensions. We have endeavored to keep all obsolete matter out of this treatise, and to make every process, method, tool and device described represent the very highest that has been attained in the development and application of each type shown. With the object in view of giving to the present-day mechanic a volume treating of the design, construction and use of grinding and lapping, tools, fixtures and processes through which he may insure the increasing of the output and its efficiency, and at the same time lower the cost of production, we beg to submit this book for the approval of those for whom it was written.
Many of the tools and devices described and illustrated in this volume we designed and used ourselves; others were designed under our personal supervision; while others have been selected from published articles written for the technical press under our own name and various pen names. For many other descriptions and illustrations we are indebted to the kind courtesy of the editors of American Machinist, and Machinery, respectively, and here extend our thanks and sense of deep obligation to these journals for the privilege of using extracts and illustrations of articles which have appeared in their columns. For a large number of practical "kinks" and "points" we acknowledge our indebtedness to the numerous concerns with which we have been connected, and to the fellow workers with whom we have associated.
The sections on "Hardening and Tempering of Tool Steel Parts of Delicate Structure, which Require to be Ground and Lapped Afterwards," and "Carbon Percentages in Hardened and Ground Steel Tools and Parts," are so near akin to the general subject of this work, that they have been given a place so that the mechanic interested in grinding and lapping may become thoroughly familiar with the practice necessary to create the necessary fundamental conditions in parts which are required to be hardened, ground and lapped to interchangeable dimensions. We have endeavored to keep all obsolete matter out of this treatise, and to make every process, method, tool and device described represent the very highest that has been attained in the development and application of each type shown. With the object in view of giving to the present-day mechanic a volume treating of the design, construction and use of grinding and lapping, tools, fixtures and processes through which he may insure the increasing of the output and its efficiency, and at the same time lower the cost of production, we beg to submit this book for the approval of those for whom it was written.
CONTENTS
- GRINDING; CONDITIONS, RULES, METHODS, PROCESSES, MACHINES AND ATTACHMENTS FOR ACCURATE GRINDING; USE AND PREPARATION OF ABRASIVES
- LAPS AND LAPPING; CONSTRUCTION AND USE OP TOOLS AND PROCESSES FOR FINISHING GAGES, TOOLS, DIES AND MACHINE PARTS TO ACCURATE DIMENSIONS
- CONSTRUCTION, USE AND OPERATION OF GRINDING FIXTURES AND JIGS, FOR FINISHING REPETITION AND ARTICLES OF METAL, SMALL HARDENED AND TEMPERED STEEL PARTS AND SPECIAL WORK
- THE HARDENING AND TEMPERING OF INTERCHANGEABLE TOOL STEEL PARTS OF DELICATE STRUCTURE WHICH REQUIRE TO BE GROUND AND LAPPED AFTERWARD
- PERCENTAGE OF CARBON CRUCIBLE STEEL PARTS AND TOOLS SHOULD CONTAIN, TEMPER COLORS TO WHICH THEY SHOULD BE DRAWN, AND DEGREES OF HEAT FOR GIVING THEM PROPER TEMPERS
- LAPS AND LAPPING; CONSTRUCTION AND USE OP TOOLS AND PROCESSES FOR FINISHING GAGES, TOOLS, DIES AND MACHINE PARTS TO ACCURATE DIMENSIONS
- CONSTRUCTION, USE AND OPERATION OF GRINDING FIXTURES AND JIGS, FOR FINISHING REPETITION AND ARTICLES OF METAL, SMALL HARDENED AND TEMPERED STEEL PARTS AND SPECIAL WORK
- THE HARDENING AND TEMPERING OF INTERCHANGEABLE TOOL STEEL PARTS OF DELICATE STRUCTURE WHICH REQUIRE TO BE GROUND AND LAPPED AFTERWARD
- PERCENTAGE OF CARBON CRUCIBLE STEEL PARTS AND TOOLS SHOULD CONTAIN, TEMPER COLORS TO WHICH THEY SHOULD BE DRAWN, AND DEGREES OF HEAT FOR GIVING THEM PROPER TEMPERS
SECTION I - GRINDING; CONDITIONS, RULES, METHODS, PROCESSES, MACHINES AND ATTACHMENTS FOR ACCURATE GRINDING - USE AND PREPARATION OF ABRASIVES.
GRINDING, TEMPERATURE AND WATER
It will be conceded by practical men, that the most important thing relating to the successful grinding of machine parts and articles of metal is the question of temperature, and it is possible that this is the reason why this method of removing material and finishing duplicate work is not more extensively used. Grinding without water gives very unsatisfactory and discouraging results. It is only within the past few years that makers of grinding machines have done much in the matter, as the revised conditions of machines of late design indicate.
An idea of the development that has taken place to date may be gained when it is understood that the first grinding machine built by those pioneers in the field - Messrs. Brown & Sharpe - had nothing but a tin of water below the wheel to catch the dust. A suds can over the wheel was an improvement, then a very small pump and tank were adopted. The largest machine we know of holds a hogshead of water, and delivers 50 gallons of water per minute at the grinding surface or point. Some condemn the plan of using water continuously, arguing, with reason, that upon using the water over and over again the lubricant becomes greasy and dirty, so much so in fact as to interfere with the wheel's efficiency. They condemn the use of soda for similar reasons, and advise a continuous supply from the public mains. The best results have been gotten from pure, clean water, and soda would never be used in the best shops were it not for fear of rusting the machines.
GRINDING CYLINDRICAL WORK
In grinding any cylindrical piece of work, it will be found that its axis is constantly changing, and if heavier cuts are taken, it will appear to be, in fact is, out of truth to a greater or less extent, from the fact that at the grinding point the heat is greatest, and is constantly varying, and it will be found impossible to get a true job unless means are taken to equalize it. Hollow spindles and other tubes only aggravate the trouble, as there is less mass to absorb the heat generated. A good stream of water will always cure this, except in the case of tubes thin in section, when it is often found necessary to fill them and plug the ends. As an illustration of tube grinding the reader may imagine a tube with an oval hole, measuring 4 inches diameter outside, with a bore, say 3 1/2 and 3 3/4 inches. If ground without filling with water, it will probably measure .0005 oval on the outside, the smaller place being at right angles to the smaller diameter of the bore. Therefore we will venture to assert that it is impossible to get round and true work without water. Added to that, the production is as three or four to one against dry machine grinding of parts.
STRAIGHTENING HARDENED WORK BEFORE GRINDING
Straightening hardened work has generally been found a waste of time. By heating the work to a temperature that is not hot enough to soften it one may be able so to true the job that it will clean up to the finished dimensions, but it will almost certainly go back, although it may be weeks before this becomes evident. We have seen cases that would illustrate this in work from firms whose reputation is above question. It seems to be the best thing to soften, straighten, and then reharden. In soft work one has the same trouble, only it is in a reduced degree, though the distortion seems to depend much upon the previous machining. It may seem almost incredible, but it is a fact, that work that comes from the bar lathe frequently gives more trouble than work done on centers. It has been advanced that in the bar lathe - heavy reductions being the rule - there is not the same apparent necessity to true the stock before turning, and that on grinding away the hard skin left by the steadies, the previous distortion develops. If this is the reason it would seem to show that bars should be straight before commencing to turn. As we have mentioned before, we do not really know the reason, but think that it is a matter for discussion and experiment. A shaft that has sprung during turning and then been straightened will resume its bent form again more or less after a slight reduction has been made. It is a good plan to spring it over the opposite way first and then straighten it. It will be found that in the majority of cases it will remain straight if this has been done.
INDISPENSABLE CONDITION FOR GOOD GRINDING
It must not be imagined for a moment that grinding a job is a guarantee of its quality. As a rule, a sample of ground work looks very nice with its clean, sharp corners and uniformity of finish. It looks just as pretty when .001 below size. One can spoil work on a grinding machine as on any other machine, by want of thought, which is the usual reason for scrap, and the man at the wheel is sometimes a careless workman.
In this matter of good centers it may be added that very many shops need education, and probably there are far more of them than of those who do not. It ought to be obvious that it is useless to provide accuracy in the spindle bearings and movements of a grinder or lathe and then provide centers for the machine and for the work which do not fit each other at all, and which cannot possibly maintain the same axis of rotation from the beginning to the end of a job as centers should.
SURFACE GRINDING
In the following matter embodying the results of experience in surface grinding, we do not claim to point out the way to obtain absolute accuracy, but are confident that the hints here given will be of use to many in the effort to reduce the error limit. Best results are to be obtained only by the exercise of good judgment on the part of the operator, as a little common sense is one of the qualifications for the work.
It is believed that much of the trouble experienced with grinding machines is due to the use of unsuitable abrasive wheels and to a desire to force the wheel beyond its limit. It is also well to bear in mind that the size of the wheel bears an important relation to the successful removal of stock, and that heating is not necessarily harmful to work if it is distributed evenly.
In doing precision surface grinding every operator has doubtless run up against the following difficulties: In grinding wrought metal (especially machinery steel), difficulty is often experienced by the work showing a convex surface even after a very light cut has been taken. Sometimes when using the same wheel on the same work, the latter will show a concave surface. A chattery surface is a very common trouble experienced. In starting a light finish cut it sometimes happens that a cut .001 inch deep will run out after a few strokes.
Taking up, first, the case of the convex surface, the operator will be apt to jump at the conclusion that the trouble is due to an absence of water on the work or that a strain had been relieved in the work by the cut. If the emery wheel be carefully examined, it will be found, probably, that its surface is more or less filled up with particles which have in a measure transformed the wheel into a friction disk, the particles of metal rubbing down the surface of the work forming a crust with an effect like peening to stretch the surface and cause it to become convex.
Now, in the second case, where the reverse happens, there is a seeming paradox. The explanation is that the wheel has been forced to cut beyond its limit and that a good deal of heat has been generated, causing sudden expansion of the work immediately under the wheel where it is laboring the hardest. This, of course, causes the wheel to cut deeper at this point. As the wheel has gained added momentum at the starting end of the work, it starts on at each end without much 'heat. When it is well into the midst of its cut, there is considerable heat, the work undergoes a temporary expansion, and the wheel cuts deeper.
The remedy in the first case is to use a softer wheel, taking light cuts with coarse feeds. In the second case, do not try to force the grinding wheel beyond its limit; or if you must use the grinder as a roughing-out machine, you must employ the freest cutting wheel obtainable.
Chattery work is due to several causes, any one of which will cause trouble. First, a poor cutting wheel; second, an over worked wheel, and third, a machine lacking rigidity. Also slack in the spindle will tend to encourage vibration. An entirely smooth surface is difficult to obtain with grinding machines or indeed with any machine, but a close approximation can be obtained by observing the following rules.
RULES FOR ACCURATE SURFACE GRINDING
Take up all possible slack in the spindle. True the wheel frequently and run light cuts. The wheel must be given time to remove the metal, and the smaller the wheel the more time required.
Improved results are obtained generally by reducing the width of the wheel face. It is the best practice to bevel both sides about 30 degrees, leaving about J inch more or less for the cutting face. The more pressure required to hold the wheel to its work, the more trouble with chatter; hence, use wheels that will cut freely. Never let the wheel wear much tapering on the face. To prevent this, feed the plates or wheel backward as well as forward. The result of this will be that the face of the wheel will assume gradually a rounded contour. This is better than to have it wear tapering or rounding on one side only and wedge on to the cut.
A special truing machine should be added to the equipment of a surface grinder and should be arranged to be held on the platen directly under the wheel, and fed under so that the wheel face may be made parallel to the work face. It is a good plan to true the wheel just before taking the finish cut on very fine work.
We will suppose that the operator has mastered all the above details, has his wheel trued off, and wishes to grind off a finish cut of a fraction of a thousandth of an inch in depth. He sets the machine in motion and everything starts off well for a half dozen strokes, when the cut suddenly runs out. We wonder if it ever occurred to this operator that oil must necessarily occupy some space and that a spindle must necessarily have oil between it and its box; also, if a spindle be stopped, that this film of oil must gush out somewhere and the spindle settle down somewhat on account of its own weight? This is the explanation of the mystery. The moment the spindle is stopped it commences to settle and in its lowest position the wheel should not be adjusted to the work. When the spindle starts up, it gradually rises on the film of oil again. The remedy for the above trouble is simply to let the machine run for a minute before adjusting for the finish cut.
Hints for Surface Grinder Operators
The result of the foregoing is embodied in the following hints for surface grinder operators:
First, make sure that the machine is lubricated and that it runs freely in every part, especially in the emery wheel adjustment.
Don't expect to adjust the wheel to fractions of thousandths of an inch without rapping on the index handle.
Select an emery wheel of as large a diameter as possible and one that is coarse and free cutting.
On tough, tenacious metals like wrought iron, machinery steel or brass, the best results in respect to finish are obtained by the use of fine soft wheels taking very light cuts with coarse feeds. The wheel must wear away somewhat to insure good results.
A small wheel must not be expected to do the work of a large wheel in the same time. Finer feeds and slower platen speeds should be employed for small wheels.
A grain of emery has the capacity for performing a certain definite amount of cutting before disintegration, hence two grains of emery in a wheel will perform double the work of one, and the latter will change its diameter twice as fast and produce work of less accuracy.
Speeding up an emery wheel helps to keep it from wearing away, but the advantage to be derived is limited by practical considerations.
A glazed or a filled wheel can sometimes be remedied by slowing it down and thus forcing it to wear away.
Avoid generation of heat as far as possible, although heat does not necessarily cause the work to spring. All grinding wheels heat more or less, and little trouble will be caused by this if the heat is distributed evenly throughout the work. It is intense heat at one point that causes the trouble.
Where much heat is likely to be generated, employ coarse feeds and very light cuts and thus distribute the heat quickly.
A cut .001 inch deep is a large cut for finishing.
A cut .0001 inch deep is appreciable and looks larger, judging by the sparks.
On precision work, always let the machine run idle for a minute before adjusting the wheel for the cut.
The down feed must work easily to obtain best results.
Keep all wear of spindle taken up.
Do not oil the grinding spindle in the midst of a cut. It will make a jog in the work.
Coarse wheels of proper texture cut smoothly.
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An idea of the development that has taken place to date may be gained when it is understood that the first grinding machine built by those pioneers in the field - Messrs. Brown & Sharpe - had nothing but a tin of water below the wheel to catch the dust. A suds can over the wheel was an improvement, then a very small pump and tank were adopted. The largest machine we know of holds a hogshead of water, and delivers 50 gallons of water per minute at the grinding surface or point. Some condemn the plan of using water continuously, arguing, with reason, that upon using the water over and over again the lubricant becomes greasy and dirty, so much so in fact as to interfere with the wheel's efficiency. They condemn the use of soda for similar reasons, and advise a continuous supply from the public mains. The best results have been gotten from pure, clean water, and soda would never be used in the best shops were it not for fear of rusting the machines.
GRINDING CYLINDRICAL WORK
In grinding any cylindrical piece of work, it will be found that its axis is constantly changing, and if heavier cuts are taken, it will appear to be, in fact is, out of truth to a greater or less extent, from the fact that at the grinding point the heat is greatest, and is constantly varying, and it will be found impossible to get a true job unless means are taken to equalize it. Hollow spindles and other tubes only aggravate the trouble, as there is less mass to absorb the heat generated. A good stream of water will always cure this, except in the case of tubes thin in section, when it is often found necessary to fill them and plug the ends. As an illustration of tube grinding the reader may imagine a tube with an oval hole, measuring 4 inches diameter outside, with a bore, say 3 1/2 and 3 3/4 inches. If ground without filling with water, it will probably measure .0005 oval on the outside, the smaller place being at right angles to the smaller diameter of the bore. Therefore we will venture to assert that it is impossible to get round and true work without water. Added to that, the production is as three or four to one against dry machine grinding of parts.
STRAIGHTENING HARDENED WORK BEFORE GRINDING
Straightening hardened work has generally been found a waste of time. By heating the work to a temperature that is not hot enough to soften it one may be able so to true the job that it will clean up to the finished dimensions, but it will almost certainly go back, although it may be weeks before this becomes evident. We have seen cases that would illustrate this in work from firms whose reputation is above question. It seems to be the best thing to soften, straighten, and then reharden. In soft work one has the same trouble, only it is in a reduced degree, though the distortion seems to depend much upon the previous machining. It may seem almost incredible, but it is a fact, that work that comes from the bar lathe frequently gives more trouble than work done on centers. It has been advanced that in the bar lathe - heavy reductions being the rule - there is not the same apparent necessity to true the stock before turning, and that on grinding away the hard skin left by the steadies, the previous distortion develops. If this is the reason it would seem to show that bars should be straight before commencing to turn. As we have mentioned before, we do not really know the reason, but think that it is a matter for discussion and experiment. A shaft that has sprung during turning and then been straightened will resume its bent form again more or less after a slight reduction has been made. It is a good plan to spring it over the opposite way first and then straighten it. It will be found that in the majority of cases it will remain straight if this has been done.
INDISPENSABLE CONDITION FOR GOOD GRINDING
It must not be imagined for a moment that grinding a job is a guarantee of its quality. As a rule, a sample of ground work looks very nice with its clean, sharp corners and uniformity of finish. It looks just as pretty when .001 below size. One can spoil work on a grinding machine as on any other machine, by want of thought, which is the usual reason for scrap, and the man at the wheel is sometimes a careless workman.
In this matter of good centers it may be added that very many shops need education, and probably there are far more of them than of those who do not. It ought to be obvious that it is useless to provide accuracy in the spindle bearings and movements of a grinder or lathe and then provide centers for the machine and for the work which do not fit each other at all, and which cannot possibly maintain the same axis of rotation from the beginning to the end of a job as centers should.
SURFACE GRINDING
In the following matter embodying the results of experience in surface grinding, we do not claim to point out the way to obtain absolute accuracy, but are confident that the hints here given will be of use to many in the effort to reduce the error limit. Best results are to be obtained only by the exercise of good judgment on the part of the operator, as a little common sense is one of the qualifications for the work.
It is believed that much of the trouble experienced with grinding machines is due to the use of unsuitable abrasive wheels and to a desire to force the wheel beyond its limit. It is also well to bear in mind that the size of the wheel bears an important relation to the successful removal of stock, and that heating is not necessarily harmful to work if it is distributed evenly.
In doing precision surface grinding every operator has doubtless run up against the following difficulties: In grinding wrought metal (especially machinery steel), difficulty is often experienced by the work showing a convex surface even after a very light cut has been taken. Sometimes when using the same wheel on the same work, the latter will show a concave surface. A chattery surface is a very common trouble experienced. In starting a light finish cut it sometimes happens that a cut .001 inch deep will run out after a few strokes.
Taking up, first, the case of the convex surface, the operator will be apt to jump at the conclusion that the trouble is due to an absence of water on the work or that a strain had been relieved in the work by the cut. If the emery wheel be carefully examined, it will be found, probably, that its surface is more or less filled up with particles which have in a measure transformed the wheel into a friction disk, the particles of metal rubbing down the surface of the work forming a crust with an effect like peening to stretch the surface and cause it to become convex.
Now, in the second case, where the reverse happens, there is a seeming paradox. The explanation is that the wheel has been forced to cut beyond its limit and that a good deal of heat has been generated, causing sudden expansion of the work immediately under the wheel where it is laboring the hardest. This, of course, causes the wheel to cut deeper at this point. As the wheel has gained added momentum at the starting end of the work, it starts on at each end without much 'heat. When it is well into the midst of its cut, there is considerable heat, the work undergoes a temporary expansion, and the wheel cuts deeper.
The remedy in the first case is to use a softer wheel, taking light cuts with coarse feeds. In the second case, do not try to force the grinding wheel beyond its limit; or if you must use the grinder as a roughing-out machine, you must employ the freest cutting wheel obtainable.
Chattery work is due to several causes, any one of which will cause trouble. First, a poor cutting wheel; second, an over worked wheel, and third, a machine lacking rigidity. Also slack in the spindle will tend to encourage vibration. An entirely smooth surface is difficult to obtain with grinding machines or indeed with any machine, but a close approximation can be obtained by observing the following rules.
RULES FOR ACCURATE SURFACE GRINDING
Take up all possible slack in the spindle. True the wheel frequently and run light cuts. The wheel must be given time to remove the metal, and the smaller the wheel the more time required.
Improved results are obtained generally by reducing the width of the wheel face. It is the best practice to bevel both sides about 30 degrees, leaving about J inch more or less for the cutting face. The more pressure required to hold the wheel to its work, the more trouble with chatter; hence, use wheels that will cut freely. Never let the wheel wear much tapering on the face. To prevent this, feed the plates or wheel backward as well as forward. The result of this will be that the face of the wheel will assume gradually a rounded contour. This is better than to have it wear tapering or rounding on one side only and wedge on to the cut.
A special truing machine should be added to the equipment of a surface grinder and should be arranged to be held on the platen directly under the wheel, and fed under so that the wheel face may be made parallel to the work face. It is a good plan to true the wheel just before taking the finish cut on very fine work.
We will suppose that the operator has mastered all the above details, has his wheel trued off, and wishes to grind off a finish cut of a fraction of a thousandth of an inch in depth. He sets the machine in motion and everything starts off well for a half dozen strokes, when the cut suddenly runs out. We wonder if it ever occurred to this operator that oil must necessarily occupy some space and that a spindle must necessarily have oil between it and its box; also, if a spindle be stopped, that this film of oil must gush out somewhere and the spindle settle down somewhat on account of its own weight? This is the explanation of the mystery. The moment the spindle is stopped it commences to settle and in its lowest position the wheel should not be adjusted to the work. When the spindle starts up, it gradually rises on the film of oil again. The remedy for the above trouble is simply to let the machine run for a minute before adjusting for the finish cut.
Hints for Surface Grinder Operators
The result of the foregoing is embodied in the following hints for surface grinder operators:
First, make sure that the machine is lubricated and that it runs freely in every part, especially in the emery wheel adjustment.
Don't expect to adjust the wheel to fractions of thousandths of an inch without rapping on the index handle.
Select an emery wheel of as large a diameter as possible and one that is coarse and free cutting.
On tough, tenacious metals like wrought iron, machinery steel or brass, the best results in respect to finish are obtained by the use of fine soft wheels taking very light cuts with coarse feeds. The wheel must wear away somewhat to insure good results.
A small wheel must not be expected to do the work of a large wheel in the same time. Finer feeds and slower platen speeds should be employed for small wheels.
A grain of emery has the capacity for performing a certain definite amount of cutting before disintegration, hence two grains of emery in a wheel will perform double the work of one, and the latter will change its diameter twice as fast and produce work of less accuracy.
Speeding up an emery wheel helps to keep it from wearing away, but the advantage to be derived is limited by practical considerations.
A glazed or a filled wheel can sometimes be remedied by slowing it down and thus forcing it to wear away.
Avoid generation of heat as far as possible, although heat does not necessarily cause the work to spring. All grinding wheels heat more or less, and little trouble will be caused by this if the heat is distributed evenly throughout the work. It is intense heat at one point that causes the trouble.
Where much heat is likely to be generated, employ coarse feeds and very light cuts and thus distribute the heat quickly.
A cut .001 inch deep is a large cut for finishing.
A cut .0001 inch deep is appreciable and looks larger, judging by the sparks.
On precision work, always let the machine run idle for a minute before adjusting the wheel for the cut.
The down feed must work easily to obtain best results.
Keep all wear of spindle taken up.
Do not oil the grinding spindle in the midst of a cut. It will make a jog in the work.
Coarse wheels of proper texture cut smoothly.
DOWNLOAD FREE BOOK: Grinding and lapping
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