Cutting speed

“ The cutting speed for very soft steel or cast iron can be three or four times faster than the speed for hard steel or hard castings, but whether the material is hard or soft, the kind and quality of the tool used must also be considered, as the speed for a tool made of ordinary carbon steel will have to be much slower than for a tool made of modern “high-speed” steel. ”

“ It does not follow from this that finishing cuts in all cases require to be taken at a slower rate of cutting speed, because, as a rule, the opposite is the case, because of the lightness of the cut; but in cases where the work is long, the rate of cutting speed for the finishing cut should be sufficiently slow to enable the tool to take a cut the whole work length without grinding, if this can be done without an undue loss of time, which is a matter in which the workman must exercise his judgment, according to the circumstances. ”

“ The speed at which milling cutters are run varies very widely in the practice in different workshops. Thus upon cast iron, cutting speeds of 15 circumferential feet per minute will be employed upon the same class of work that in another shop would be done at a cutting speed of as high as fifty feet per minute. ”

“ If work of small diameter be turned at too slow a rate of cutting speed, it is difficult to obtain a true and smooth surface; hence, as the tool approaches the centre, it is necessary to increase the speed of rotation. As lathes are at present constructed, it is necessary to pass the belt from one step to another of the driving cone, to increase the speed. ”

“ It has also been proved that high-speed cutting is economical from a mechanical standpoint, and that a given horse-power will remove a greater quantity of metal at a high speed than at a low speed, for although more power is naturally required to take off metal at a high than at a low speed (by reason of the increased work done) the increase of that power is by no means in proportion to the large extra amount of work done by the high-speed cutting, for the frictional and other losses do not increase in anything like the same ratio as a high-cutting speed is to a low-cutting speed. ”

“ Then comes the task of getting up the speed, with the ponderous gearing and the enormous strains. Slow motion also prevents the use of the belt, immeasurably the preferable means of communicating power from a prime mover.
“But how about the wear and tear? The question comes from friends and foes alike. The only difference is in the expression of countenance, sympathetic or triumphant. The thought of high speed brings before every eye visions of hot and torn bearings, cylinders and pistons cut up, thumps and breakdowns, and engines shaking themselves to pieces. ”

“ The fact is, high speed is the great searcher and revealer of everything that is bad in design and construction. The injurious effect of all unbalanced action, of all overhanging strains, of all weakness of parts, of all [158] untruth in form or construction, of all insufficiency of surface, increases as the square of the speed. Put an engine to speed and its faults bristle all over. ”

“ The fog was so thick that I could not tell by passing objects how fast we ran, but the dull, heavy and oppressive roar, as we shot through rock cuttings and tunnels, the rocking and straining of my engine, and the almost inconceivable velocity at which the driving-wheels revolved, told me that my speed was something absolutely awful. ”

“ Two drivers A, A′, equally speeded in opposite directions, will drive the bevil gear at same velocity without revolving the spur wheel C′ which is loose on the shaft; but any alteration in the relative speeds of A and A′, causes the bevil pinion to travel round, carrying the spur wheel C′ at a speed equal to half the difference of the two velocities. ”

“ If the hill is a very steep one, as soon as the engine begins to lose speed, release the clutch, remove pressure from accelerator and, without applying the brake, shift to a lower speed gear. Let clutch in quickly and at the same time open accelerator wide. ”

“ The governor was speeded to hold the engine at 500 turns per minute. As it might be difficult for some persons to count this speed, I put a little pinion on the end of the shaft, engaging with a larger wheel, one to ten. Fifty revolutions per minute could be accurately counted, and the speed was put beyond dispute. I was guilty of one oversight: I did not protect this gear. A French gentleman had the skirt of his frock-coat caught in it, and I thought it never would be got out. The engine had been running only two or three days, but the speed being then well established, I took off the gear. ”

“ To get the best results, the proportions of fuel vapor and air should be the same for all running speeds of the engine. The proportions of the mixture, however, depend on the violence of the suction, which changes as the engine speed changes, becoming greater as the speed increases. ”

“ Overrunning the Engine.—We will suppose that you are running down a steep hill with the speed lever set in the third speed—with the left pedal down and the motor consequently disconnected—and this third speed gives, say, a rate of twenty miles an hour. The car, however, from its own momentum and the force of gravity, may be running at twenty-five miles an hour, and to let the clutch in then throws a very unfair strain on the engine. ”

“ If, however, we push it rapidly forward, the resistance greatly increases, for the air-molecules must have time to change their position, and we encounter them in their passage. If, now, we increase the velocity of the motion to the highest speed ever attained by a locomotive—say, one and one-fifth mile per minute—we should encounter still more particles, and find a resistance which no human muscle could overcome. Increase that velocity ten times, to twelve miles a minute, the velocity of sound, and the air would oppose such a resistance that our wooden board would be shivered into splinters. ”

“ If engine is supplied with a friction clutch, by simply pressing the clutch lever gradually until the friction shoes take hold, the engine will start slowly upon the road. This can be done while engine proper is running at full speed. ”

“ The velocity necessary to just sustain the load at a given angle of inclination is called the critical or soaring velocity. For a given machine, there is an angle of inclination (about half a right angle) at which the minimum speed is necessary. This speed is called the “least soaring velocity.” If the velocity is now increased, the angle of inclination may be reduced and the planes will soar through the air almost edgewise, apparently with diminished resistance and power consumption. ”

“ Even if the resistance of a fluid were not increased, the effect of a horse's power, by the condition of his nature, would be materially reduced by every increase of speed; and, on the other hand, even were a horse capable of working with the same effect at an increased speed, the resistance of a fluid, increasing in a greater proportion than the square of the speed, would impair the total effect. ”

“ Under such circumstances the velocity with which every part of the machinery is moved would suffer corresponding changes, increasing its rapidity with every augmentation of the moving power or diminution of the resistance, or being retarded in its speed by the contrary circumstances. ”

“ The tractive power, therefore, increases rapidly to a value far exceeding the frictional resistances, but this surplus energy serves to increase the velocity, and disappears as soon as a uniform velocity is reached.
The average speed, both with one and three cars, was 30 kilometers per hour.--Zeitsch. f. Elektrotechnik. ”

“ A. The different speeds required to meet road conditions are obtained by opening or closing the throttle. Practically all the running speeds needed for ordinary travel are obtained on high gear, and it is seldom necessary to use the low gear except to give the car momentum in starting. The speed of the car may be temporarily slackened in driving through crowded traffic, turning corners, etc., by “slipping the clutch,” i. e., pressing the clutch pedal forward into neutral. ”

“ Fluid Friction.—When a solid moves through a fluid, as when a ship moves through the water or railroad trains through the air, the resistance encountered is not the same as with solids but increases with the square of the velocity for slow speeds and for high speeds at a higher rate. This is the reason why it costs so much to increase the speed of a fast train, since the resistance of the air becomes the prominent factor at high speeds. ”

“ The damping out of the oscillations of the flight path, discussed in the last lecture, increased with the fourth power of the natural velocity of flight, and rapid damping formed the easiest, and sometimes the only, defense against dangerous oscillations. A machine just stable at 35 miles per hour would have reasonably rapid damping if its speed were increased to 60 miles per hour. ”

“ The idea is that when this monster has all its tubes shooting out the burning, expanding gases and liquids from the nozzles, the high pressure exerted on the atmosphere makes the wheel revolve at enormous speed—speed probably greater than that attained by any other human machine! ”

“ Engineers understand very well that, theoretically, the prime mover should overrun the resistance. Motion should be not multiplied but reduced in transmission. This can seldom be attained in practice, but high speed gives the great advantage of an approximation to this theoretical excellence. On the other hand, slow-speed engines work against every disadvantage. Coupled engines and enormous fly-wheels have to be employed to give a tolerably uniform motion; often great irregularities are endured, or the abominable expedient is resorted to of placing the fly-wheel on the second-motion shaft. ”

“ To increase the speed of the engine the handle nut is turned the opposite direction, which shortens the stem and increases the opening in governor valve, allowing more steam to enter the cylinder and the speed is proportionately increased. ”

“ This growth of speed is even more remarkable than might appear from the mere comparison of figures. A body moving through water is so retarded by the inertia and friction of the fluid that to quicken its pace a force quite out of proportion to the increase of velocity must be exerted. The proportion cannot be reduced to an exact formula, but under certain conditions the speed and the power required advance in the ratio of their cubes; that is, to double a given rate of progress eight times the driving-power is needed ”

“ A very good formula to follow in regard to changing speeds is to continue on the speed on which you are running until the engine cuts out or shows signs of extra vibration or noise, which will at once indicate to you that it is running faster than it ought, and that it is desirable to change on to the next speed. This will ensure there being a good run on the car, and that the next higher speed will take up the run and increase the pace. ”

“ Do you think that the velocity with which a Coach goes, has any thing to do with the wear of the road, or is it not actually less injurious in proportion to its velocity?—In some instances where any blow takes place the speed does more injury to the road by crushing the materials. ”

“ In this comparison, the engine is taken at its most advantageous speed, while horse-power is taken at its least advantageous speed, if regard be only had to the total quantity of weight transported to a given distance. ”

“ For example, when travelling on a level road at top speed, if the driver wishes to slow down to pass a vehicle, he does not necessarily change his gear, but operates the accelerator, so as to alter the speed of the engine. The car will then slow until the pressure on sleeve c c is once more increased by means of the lever. ”

“ Now, when the speed decreases and the weighted balls rise above their true position, the valve opens, allows more steam to enter the cylinder and the speed of the engine increases until the engine is again running at its proper speed. ”

“ When the engine speeds up, the weights tend to swing outward toward the rim of the wheel, the amount of the movement being regulated by the tension of the springs C. As the arms move outward, the levers at the ends turn the eccentric disk on the shaft, the effect of which is to change the angle of advance and shorten the cut-off. When the speed falls below the normal, the weights move toward the center and the cut-off is lengthened. The effect of this form of governor on the diagram is shown in Fig. ”

“ You cannot, by any combination of mechanism, get increased force and increased speed at the same time, or increased force without diminished speed; and it is from the ignorance of this inexorable condition, that such myriads of schemes for the realization of perpetual motion, by combinations of levers, weights, wheels, quicksilver, cranks, and other mere pieces of inert matter, have been propounded. ”

“ Thus, if the calculated speed of the second gear is, say, eighteen miles per hour, the driver should wait until the work of surmounting the gradient has caused the engine to slow the pace down to that, and not try to make the change when the car is still doing twenty. Some little practice and intelligent observation is necessary before this can be nicely done, but that sort of thing is where much of the charm of driving a good car comes in. ”

“ The speed of 300 revolutions per minute had proved to be admirably suited for the machine. Familiarity with this speed in the running of the stone-dressing machine made me alive to the value of high rotative speeds in all cases to which they are adapted. ”