Abrasive grinding wheels
ABRASIVE GRINDING WHEELSOLD CATALOGUE
Manufactured by Abrasive Company, Philadelphia, 1919
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Abrasive grinding wheels
Use and Care of Wheels
Users of wheels sometimes complain of their being unsatisfactory without investigating speed at which they are operated. A wheel will appear too hard and glaze if run at excessive speed, while at proper speed it may be satisfactory. Again, if run at a very low speed, it may appear too soft. Speed, therefore, is a very important factor. When above conditions arise, change the speed and it will often give satisfactory results. If a wheel is unsuited for the work, do not use it; allow us to exchange it for one that is adapted to the work. In such cases, give us full information why it is not satisfactory. Avoid heavy pressure against the wheel and be sure to keep it true. For this purpose have a dresser ready to use when needed. Do not try to do all kinds of grinding with the one wheel. One size of twist drill will not bore all size holes; neither will one kind of a grinding wheel do all classes of work satisfactorily. It is economy to change wheels and use proper grades that suit the work.
A wheel that thumps does not cut on its entire periphery, and it is possible to have a wheel so badly out of true that it will lose a very large percentage of its cutting power. It is wise to use a wheel for each class of work. The "general use" wheel may be handy, but it is like that man who is "Jack-of-all-trades and master of none." Increase the speed as a wheel decreases in diameter, otherwise; it may appear soft towards the center. Do not crowd the wheel. If too soft, it will wear away fast without doing any more work. Never use a wheel at a higher speed than the manufacturer recommends. A surface speed of 5000 feet per minute is recommended as a safe grinding speed for grinding in general. See that the speed does not vary. It is sometimes not the same at all hours. Don't blame the wheel for everything. Sometimes something else may be wrong. Don't tell the manufacturer a wheel is "no good." He can help you much more if you say why it is no good. Don't work on a new wheel until you are sure it runs true. Never "hack" wheels, as it is liable to break or crack them. Use a dresser for this purpose.
The user must realize that a grinding wheel which is required to cut fast, consequently to wear away, cannot possibly be made as strong as iron or steel. It, therefore, must be handled accordingly with care and precaution. The most common causes of accidents are catching the work between the wheel and rest; heating and expansion of arbor; using flanges too small; screwing them too tight and not having them properly recessed so that they bear on the outer edge; not using any flanges, but simply screwing a nut against the wheel, allowing the arbor to become loose in boxes from wear; and running wheels on shaky machines. Against all these conditions we particularly caution all users of wheels.
The stress on the wheel at a speed of 9000 surface feet per minute is about 250 pounds per square inch, and as the stress on a wheel running at 5000 surface feet per minute is about 80 pounds it will be seen that when wheels are tested at a speed of 9000 feet per minute, they are subjected to more than three times the strain they would receive at recommended running speed. Wheels should not be run in excess of recommended speeds. As the centrifugal force of a body moving with different velocities in the same circle is proportional to the square of the velocity, it will be seen that if the velocity is doubled, the centrifugal force would be four times as great, hence the importance of not running wheels at a faster speed than is recommended by the manufacturer. The same peripheral speed should be maintained as the wheel decreases in diameter. In other words, the speed of the spindle should be increased correspondingly as the diameter of the wheel is decreased. The increase of the peripheral speed as the wheel wears away can be accomplished by means of a variable speed countershaft or cone pulley on the grinder, or by transferring from a larger grinder to a smaller one as the wheels wear away.
The last system has decided advantage and is highly recommended whenever there is sufficient amount of grinding to warrant the use of more than one machine. These grinders should then have but one pulley on the spindle, which removes all possibility of starting a new wheel, when full diameter, at the higher speed. When the single pulley system is not employed, great care and precaution should be taken to always start a new wheel on the low speed.
Don't start the grinder until you know the speed is right—not "near enough," but right. Even a slight variation in speed may be the cause of success or failure of any wheel. Failure is sometimes turned into success by merely changing the speed of either the wheel or the work.
Do not use a grinding wheel like a piece of cast iron. It is meant for work, but not abuse. Do not use hard wheels because they last longer. A fast-cutting wheel is the most economical in the end, even if it does wear away more rapidly. Output determines economy.
General Remarks About Wheels
As compared with any other cutting tool, the successful grinding wheel possesses one interesting characteristic peculiar to itself—that of sharpening itself while it works. When properly made and selected, the grains on the surface of the wheel, as they become dulled, are either broken or pulled out under the stress of the work, thus continually presenting new, sharp cutting points. A wheel is, therefore, more efficient when soft enough to cut freely and yet not hard enough to glaze. The use of modern grinding wheels has been extended from grinding a comparatively few metals to practically all metals. They are also used to grind such materials as bone, horn, pearl, rubber, marble, bronze, stone, wood, etc.; in fact, almost any material.
Increasing the surface speed of a grinding wheel decreases its tendency to wear away, and conversely, decreasing the surface speed increases its tendency to wear away. Grinding wheel manufacturers occasionally hear the complaint that the wheel has "soft spots." If the user will mark the wheel where he thinks the "soft spot" is and then "true the wheel" and grind with it again, he will invariably find that the "soft spot " has moved along to another point on the wheel. Such complaints are most likely due to the wheel running out of true or out of balance.
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A wheel that thumps does not cut on its entire periphery, and it is possible to have a wheel so badly out of true that it will lose a very large percentage of its cutting power. It is wise to use a wheel for each class of work. The "general use" wheel may be handy, but it is like that man who is "Jack-of-all-trades and master of none." Increase the speed as a wheel decreases in diameter, otherwise; it may appear soft towards the center. Do not crowd the wheel. If too soft, it will wear away fast without doing any more work. Never use a wheel at a higher speed than the manufacturer recommends. A surface speed of 5000 feet per minute is recommended as a safe grinding speed for grinding in general. See that the speed does not vary. It is sometimes not the same at all hours. Don't blame the wheel for everything. Sometimes something else may be wrong. Don't tell the manufacturer a wheel is "no good." He can help you much more if you say why it is no good. Don't work on a new wheel until you are sure it runs true. Never "hack" wheels, as it is liable to break or crack them. Use a dresser for this purpose.
The user must realize that a grinding wheel which is required to cut fast, consequently to wear away, cannot possibly be made as strong as iron or steel. It, therefore, must be handled accordingly with care and precaution. The most common causes of accidents are catching the work between the wheel and rest; heating and expansion of arbor; using flanges too small; screwing them too tight and not having them properly recessed so that they bear on the outer edge; not using any flanges, but simply screwing a nut against the wheel, allowing the arbor to become loose in boxes from wear; and running wheels on shaky machines. Against all these conditions we particularly caution all users of wheels.
The stress on the wheel at a speed of 9000 surface feet per minute is about 250 pounds per square inch, and as the stress on a wheel running at 5000 surface feet per minute is about 80 pounds it will be seen that when wheels are tested at a speed of 9000 feet per minute, they are subjected to more than three times the strain they would receive at recommended running speed. Wheels should not be run in excess of recommended speeds. As the centrifugal force of a body moving with different velocities in the same circle is proportional to the square of the velocity, it will be seen that if the velocity is doubled, the centrifugal force would be four times as great, hence the importance of not running wheels at a faster speed than is recommended by the manufacturer. The same peripheral speed should be maintained as the wheel decreases in diameter. In other words, the speed of the spindle should be increased correspondingly as the diameter of the wheel is decreased. The increase of the peripheral speed as the wheel wears away can be accomplished by means of a variable speed countershaft or cone pulley on the grinder, or by transferring from a larger grinder to a smaller one as the wheels wear away.
The last system has decided advantage and is highly recommended whenever there is sufficient amount of grinding to warrant the use of more than one machine. These grinders should then have but one pulley on the spindle, which removes all possibility of starting a new wheel, when full diameter, at the higher speed. When the single pulley system is not employed, great care and precaution should be taken to always start a new wheel on the low speed.
Don't start the grinder until you know the speed is right—not "near enough," but right. Even a slight variation in speed may be the cause of success or failure of any wheel. Failure is sometimes turned into success by merely changing the speed of either the wheel or the work.
Do not use a grinding wheel like a piece of cast iron. It is meant for work, but not abuse. Do not use hard wheels because they last longer. A fast-cutting wheel is the most economical in the end, even if it does wear away more rapidly. Output determines economy.
General Remarks About Wheels
As compared with any other cutting tool, the successful grinding wheel possesses one interesting characteristic peculiar to itself—that of sharpening itself while it works. When properly made and selected, the grains on the surface of the wheel, as they become dulled, are either broken or pulled out under the stress of the work, thus continually presenting new, sharp cutting points. A wheel is, therefore, more efficient when soft enough to cut freely and yet not hard enough to glaze. The use of modern grinding wheels has been extended from grinding a comparatively few metals to practically all metals. They are also used to grind such materials as bone, horn, pearl, rubber, marble, bronze, stone, wood, etc.; in fact, almost any material.
Increasing the surface speed of a grinding wheel decreases its tendency to wear away, and conversely, decreasing the surface speed increases its tendency to wear away. Grinding wheel manufacturers occasionally hear the complaint that the wheel has "soft spots." If the user will mark the wheel where he thinks the "soft spot" is and then "true the wheel" and grind with it again, he will invariably find that the "soft spot " has moved along to another point on the wheel. Such complaints are most likely due to the wheel running out of true or out of balance.
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