By E. L. 0.
One of the particular things in operating wood-working machines, is Grinding Cutters. Many of us remember how formerly we had to improvise forms, and study up Schemes to accomplish this part of our work. Rabbetting into a block, of wood was one plan. Making a sweep, pivoted. in the middle, so the end would just swing over the center of the stone, the knife bolted to a board, the grinder sitting on the board, which was pivoted to the end of the sweep to hold it in place, was — another. There were many other ways, any of which made it a very dirty, undesirable job.
Bye and bye came the knife grinding machine, to be made fast to a grindstone. This was a long step ahead, and, although it was still a dirty task, it helped the matter a great deal. The machine was warranted to grind straight, but the proof of the warrant was in the man who used it; it needed considerable skill to make the warrant hold good. Nevertheless, it was the pioneer of something better. Not a long time elapsed before the emery grinder became a necessity, and with that necessity came the genius that has brought out the many kinds and styles of machines now in use.
Now, no woodworking plant is complete without from one to six emery grinders in the different parts of the shops. We consider them now, one of the positive necessities. To have simply an emery grinder was not enough, and the automatic machine soon came to be the thing needful. Now most woodworking plants have a machine that works automatically. It would be entirely out of place here to give preference to any of the different automatic machines. They are all good. The thing for the proprietor to consider is, to get or not to get an automatic grinder, as those not automatic are still made and used. One of the great advantages of the automatic is economy of time. Another point is the quality of the grinding. The automatic feed grinds steadily and evenly There is consequently no danger from heating.
The cheapest machines are those which do the best work in the most rapid manner, with least cost of maintenance. First cost is one thing, last cost another. Proprietors and managers should not cramp a mill in this matter of tools and appliances. It is better to have a fixture that you don't use but once in a year, than not to have it and be obliged to refuse a job because you have nothing to do it with. Don't hold a cent so near your eye that you can not see a dollar on the other side of it. I have known firms that would not get more than three sets of heads, and every time the work changed the heads would have to be. This is holding a cent pretty close. It hurts the proprietor more than it does the operator. When you want machine work to pay you must keep the machine at work, and not have more time spent setting up tools than in running the stuff.
Inventors of machines that are expected to revolutionize things generally, should post themselves before spending much money on their revolutionizers. It often costs them considerable to find out that their ideas were used and forgotten years ago.
THE DETROIT EMERY WHEEL CO.,
MANUFACTURERS OF THE CELEBRATED
HART EMERY WHEEL, AND EMERY GRINDING MACHINERY.
There Is a lamentable amount of ignorance displayed by a great many users of Emery Wheels. We positively assert that there is no tool used in a shop that pays so large a per cent of profit on investment as a well managed emery wheel. We print the following suggestions from the Detroit Emery Wheel Co's catalogue, and earnestly ask that they be carefully read and remembered:
"Although solid wheels have been in use for many years, and today are considered an absolute necessity as a tool in nearly all metal working shops, still we think that quite a proportion of the mechanics using them are not as well informed in their use as they should be, and feeling that the interests of the manufacturer and consumer are mutual, and that what benefits one must benefit the other, we trust the suggestions we offer will be kindly received.
No one emery wheel can be made that will be just right for working all the different kinds of metal, so where more than one kind is to be worked with the same wheel the proportion of each should be stated in sending orders for wheels.
The speed of emery wheels is a subject of so much importance, that it should receive the consideration of all who use them. As a rule, the durability of an emery wheel is in proportion to its speed; or, in other words, a wheel that would give entire satisfaction at its proper speed would be quite certain not to give satisfaction if run at one half or two thirds speed. Where all that is required is to grind away the most metal in the least time, we advise the regular speed of about 5,500 feet per minute; or the number of revolutions for each diameter as given in the accompanying price list.
The grinding of tools for either Iron or woodworking is of such a nature that it can only be well done with a wheel that is made especially for that work , but with such wheels the most delicate tools can be shaped and sharpened better than in any other way. Every shop should have a speed indicator, in order that the speed of its maehinery could be known, especlally its emery wheels.
In no case should wheels be run at a greater number of revolutions than the manufacturer of them advises. Probably very few of the mechanics of the age think, or perhaps, know, of the great increase of centrifugal strain that is given a wheel in proportion to an increase of the velocity. No sane manufacturer would, for an instant, think of subjecting his steam boiler to a pressure two or three times as great as the maker of it advises; and still emery wheels are run at a speed that increases the centrifugal strain upon them a number of times.
In this connection we feel it a duty to quote the following from a standard author upon this point "The centrifugal force of a body moving with different velocities in the same circle is proportional to the square of the velocity. Thus the centrifugal force of a body making ten revolutions a minute is four times as great as the centrifugal force of the same body making five revolutions in a minute. Hence in equal circles the forces are inversely as the squares of the tinges of revolution."
The last thing done before our wheels are boxed is to test them at twice the number of revolutions they should be run at. This, as will be seen by reference to the preceding paragraph, insures their soundness when they leave our hands.
Grinding machines of all kinds should be set upon a solid floor, and where it is practical we advise, for large machines especially, a foundation of masonry. A strong and substantial rest should be used where the nature of the work will admit of it. In the matter of rests much care should be used in keeping them properly adjusted in relation to the wheel. As a rule, the rest should be kept close to the wheel. It is not an uncommon thing to find a workman at a wheel with the rest so far from it, and the work of such a nature that should it be drawn from his hands it would certainly be drawn between the wheel and rest. This, we believe, is a very common cause for the breaking of emery wheels, and many a workman has paid the penalty with his own life for his carelessness in this respect alone.