pressure to remove it. The weight of metal removed per hour would be 14 X 12 X .375 .26 × 60 = 1082.8 lbs. Our earlier form of 36" planer has removed with one tool on 34" cut on work 200 lbs. of metal per hour, and the 120" machine has more than five times its capacity. The total pulling power of the planer is 45,000 lbs. Horse-power Required to Run Lathes. (J. J. Flather, Am. Mach., April 23, 1891.) The power required to do useful work varies with the depth and breadth of chip, with the shape of tool, and with the nature and density of metal operated upon; and the power required to run a machine empty is often a variable quantity. For instance, when the machine is new, and the working parts have not become worn or fitted to each other as they will be after running a few months, the power required will be greater than will be the case after the running parts have become better fitted. Another cause of variation of the power absorbed is the driving-belt; a tight belt will increase the friction, hence to obtain the greatest efficiency of a machine we should use wide belts, and run them just tight enough to prevent slip. The belts should also be soft and pliable, otherwise power is consumed in bending them to the curvature of the pulleys. A third cause is the variation of journal-friction, due to slacking up or tightening the cap-screws, and also the end-thrust bearing screw. Hartig's investigations show that it requires less total power to turn off a given weight of metal in a given time than it does to plane off the same amount; and also that the power is less for large than for small diameters. The following table gives the actual horse-power required to drive a lathe empty at varying numbers of revolutions of main spindle. = If H.P.o horse-power necessary to drive lathe empty, and N= number of revolutions per minute, then the equation for average small lathes is H.P.0 0.095 +0.0012N. For the power necessary to drive the lathes empty when the back gears are in, an average equation for lathes under 20" swing is H.P.o= 0.10+ 0.006N. The larger lathes vary so much in construction and detail that no general rule can be obtained which will give, even approximately, the power required to run them, and although the average formula shows that at least 0.095 horse-power is needed to start the small lathes, there are many American lathes under 20" swing working on a consumption of less than 05 horse-power. The amount of power required to remove metal in a machine is determin. able within more accurate limits. CW, where C is a constant, = Referring to Dr. Hartig's researches, H.P.1 and W the weight of chips removed per hour. Average values of C are .030 for cast-iron, .032 for wrought-iron, .047 for steel. The size of lathe, and, therefore, the diameter of work, has no apparent effect on the cutting power. If the lathe be heavy, the cut can be increased, and consequently the weight of chips increased, but the value of C appears to be about the same for a given metal through several varying sizes of lathes. HORSE-POWER REQUIRED TO REMOVE CAST IRON IN A 20-INCH Lathe. The above table shows that an average of .26 horse-power is required to turn off 10 pounds of cast-iron per hour, from which we obtain the average value of the constant C = .024. Most of the cuts were taken so that the metal would be reduced 14" in diameter; with a broad surface cut and a coarse feed, as in No. 5, the power required per pound of chips removed in a given time was a maximum; the least power per unit of weight removed being required when the chip was square, as in No. 6. HORSE-POWER REQUIRED TO REMOVE METAL IN A 29-INCH LATHE. The small values of C, .017 and .019, obtained for cast iron are probably due to two reasons: the iron was soft and of fine quality, known as pulley metal, requiring less power to cut; and, as Prof. Smith remarks, a lower cutting-speed also takes less horse-power. Hardness of metals and forms of tools vary, otherwise the amount of chips turned out per hour per horse-power would be practically constant, the higher cutting-speeds decreasing but slightly the visible work done. Taking into account these variations, the weight of metal removed per hour, multiplied by a certain constant, is equal to the power necessary to do the work. This constant, according to the above tests, is as follows: The power necessary to run the lathe empty will vary from about .05 to .S H.P., which should be ascertained and added to the useful horse-power, to obtain the total power expended. Power used by Machine-tools. (R. E. Dinsmore, from the Electrical World.) 1. Shop shafting 2 3/16" X 180 ft. at 160 revs., carrying 26 pulleys 1.32 H.P. 0.78 H.P. 3. Morse twist-drill grinder No. 2, carrying 2" X 6" wheels at 3200 revs.. 0.29 H.P. 4. Pease planer 30" X 36", table 6 ft., planing cast iron, cut 1⁄4" 1.06 H.P. 0.37 H.P. 0.43 H.P. 8. Sturtevant No. 2, monogram blower at 1800 revs. per minute, no piping.. 7. Engine-lathe 21" swing, boring cast-iron hole 5" diam., cut 3/16 diam., feeding 0.3" per minute.. 0.23 H.P. 0.8 H.P. 9. Heavy planer 28" x 28" X 14 ft. bed, stroke 8", cutting steel, 22 reversals per minute. 3.2 H.P. The table on the next page compiled from various sources, principally from Hartig's researches, by Prof. J. J. Flather (Am. Mach., April 12, 1894), may be used as a guide in estimating the power required to run a given machine; but it must be understood that these values, although determined by dynamometric measurements for the individual machines designated, are not necessarily representative, as the power required to drive a machine itself is dependent largely on its particular design and construction. The character of the work to be done may also affect the power required to operate; thus a machine to be used exclusively for brass work may be speeded from 10% to 15% higher than if it were to be used for iron work of similar size, and the power required will be proportionately greater. Where power is to be transmitted to the machines by means of shafting and countershafts, an additional amount, varying from 30% to 50% of the total power absorbed by the machines, will be necessary to overcome the friction of the shafting. Horse-power required to drive Shafting.-Samuel Webber, in his Manual of Power" gives among numerous tables of power required to drive textile machinery, a table of results of tests of shafting. A line of 2" shafting, 342 ft. long, weighing 4098 lbs., with pulleys weighing 5331 lbs., or a total of 9429 lbs., supported on 47 bearings, 216 revolutions per minute, required 1.858 H.P. to drive it. This gives a coefficient of friction of 5.52%. In seventeen tests the coefficient ranged from 3.34% to 11.4%, averaging 5.73%. Slotter (15" stroke).. Universal milling mach (Brown & Sharpe No. 1).... Small head traversing milling machine (cutter-head 11" diameter, 16 cutters). 0.18 Gear cutter will cut 20" diameter. 0.28 Horizontal boring machine for iron, 221⁄2" swing. 0.93 0.10 0.11 0.12; 0.10-0.12*; 0.10 to 0.25+ Hydraulic shearing machine. Large plate shears-knives 28" long, 3" stroke.. stock can be punched.. Small punch and shear comb'd, 71⁄2" knives, 11⁄2" str. Wood-mortising and boring machine. 0.49 0.34 Hor'l wood-boring and mortising machine, drill 4" diam., mortise 8% deep x 11" long Grindstone for tools, 31" diam., 6" face. Velocity 680 ft. per minute. 1.55 0.32 Grindstone for stock, 42"X12". Vel. 1680 ft. per min. *With back gears. Without back gears. For surface cutters. With side cutters. B. G., back-geared. T. G.. triple-geared. Horse-power consumed in Machine-shops. -How much power is required to drive ordinary machine-tools? and how many men can be employed per horse-power? are questions which it is impossible to answer by any fixed rule. The power varies greatly according to the conditions in each shop. The following table given by J. J. Flather in his work on Dynamometers gives an idea of the variation in several large works. The percentage of the total power required to drive the shafting varies from 15 to 80, and the number of men employed per total H.P. varies from 0.62 to 6.04. Horse-power; Friction; Men Employed. Abbreviations: E., engine; W.W., wood-working machinery; M. M., mining machinery; M. E., marine engines; L., locomotives; H. M., heavy machinery; M. T., machine tools; C. & L., cranes and locks; P. & D., presses and dies; P. & S., pulleys and shafting; H. F., heavy forgings; S. M., sewing machines; M. S., machine-screws: F., files. J. T. Henthorn states (Trans. A. S. M. E., vi. 462) that in print-mills which he examined the friction of the shafting and engine was in 7 cases below 20% and in 35 cases between 20% and 30%, in 11 cases from 30% to 35% and in 2 cases above 35%, the average being 25.9%. Mr. Barrus in eight cotton-mills found the range to be between 18% and 25.7%, the average being 22%. Flather believes that for shops using heavy machinery the percentage of power required to drive the shafting will average from 40% to 50% of the total power expended. This presupposes that under the head of shafting are included elevators, fans, and blowers. ABRASIVE PROCESSES. Mr. Abrasive cutting is performed by means of stones, sand, emery, glass, corundum, carborundum, crocus, rouge, chilled globules of iron, and in some cases by soft, friable iron alone. (See paper by John Richards, read before the Technical Society of the Pacific Coast, Am. Mach., Aug. 20, 1891, and Eng. & M. Jour., July 25 and Aug. 15, 1891.) |