ron is 20 ft. per minute, whether for the lathe, planing, shaping, or slotting machine. (Proc. Inst. M. E., April, 1883, p. 248.) 76.4 11% 17.0 11/4 15.3 13 13 9 27.8 41.7 11 12.7 25.5 38.2 10.9 21.8 82.7 9.6 19.1 28.7 8.5 17.0 25.5 152.8 229.2 305.6 382.0 458.4 534.8 611.2 687.6 764.0 50.9 101.9 152.8 203.7 254.6 305.6 356.5 407.4 458.3 509.3 38.2 76.4 114.6 152.8 191.0 229.2 267.4 305.6 343.8 382.0 30.6 61.1 91.7 122.2 152.8 183.4 213.9, 244.5 275.0 305.6 25.5 50.9 76.4 101.8 127.3 152.8 178.2 203.7 229.1 254.6 21.8 43.7 65.5 87.3 109.1 130.9 152.8 174.6 196.4 218.3 19.1 38.2 57.3 76.4 95.5 114.6 133.7 152.8 171.9 191.0 34.0 50.9 67.9 84.9 101.8 118.8 135.8 152.8 169.7 30.6 45.8 61.1 76.4 91.7 106.9 122.2 137.5 152.8 55.6 69.5 83.3 97.2 111.1 125.0 138.9 50.9 63.6 76.4 89.1 101.8 114.5 127.2 43.7 54.6 65.5 76.4 87.3 98.2 109.2 38.2 47.8 57.3 66.9 76.4 86.0 95.5 34.0 42.5 50.9 59.4 67.9 76.4 84.9 30.6 38.2 45.8 53.5 34.7 41.7 48.6 25.5 31.8 38.2 44.6 21.8 27.3 19.1 23.9 17.0 21.2 25.5 19.1 3.5 6.9 10.4 13.9 17.4 20.8 24.3 27.8 31.2 34.7 8.2 6.4 9.5 12.7 15.9 19.1 13.6 16.4 22.3 25.5 28.6 31.8 2.4 4.8 .7 1.1 1.4 1.8 2.1 2.5 2.8 8.2 3.5 .6 1.0 1.3 1.6 1.9 2.2 2.5 2.9 3.2 Speed of Cutting with Turret Lathes.-Jones & Lamson Machine Co. give the following cutting-speeds for use with their flat turret lathe on diameters not exceeding two inches: Tool steel and taper on tubing.. Cut which reduces the stock to 1⁄2 of its original diam.. Cut which reduces the stock to 34 of its original diam.. Cut which reduces the stock to % of its original diam.. 30 to 35 Cut which reduces the stock to 15/16 of its original diam. 40 to 45 Turning very soft machinery steel, light cut and cool work....................... 50 to 60 Forms of Metal-cutting Tools.-“Hutte," the German Engi neers' Pocket-book, gives the following cutting-angles for using least power: Angle of Cutting-edge. Top Rake. The American Machinist comments on these figures as follows: We are not able to give the best nor even the generally used angles for tools, because these vary so much to suit different circumstances, such as degree of hardness of the metal being cut, quality of steel of which the tool is made, depth of cut, kind of finish desired, etc. The angles that cut with the least expenditure of power are easily determined by a few experiments, but the best angles must be determined by good judgment, guided by expe rience. In nearly all cases, however, we think the best practical angles are greater than those given. For illustrations and descriptions of various forms of cutting-tools, see articles on Lathe Tools in App. Cyc. App. Mech., vol. ii., and in Modern Mechanism. Cold Chisels.-Angle of cutting-faces (Joshua Rose): For cast steel, about 65 degrees; for gun-metal or brass, about 50 degrees; for copper and soft metals, about 30 to 35 degrees. Rule for Gearing Lathes for Screw-cutting. (Garvin Machine Co.)-Read from the lathe index the number of threads per inch cut by equal gears, and multiply it by any number that will give for a product a gear on the index; put this gear upon the stud, then multiply the number of threads per inch to be cut by the same number, and put the resulting gear upon the screw. EXAMPLE.-To cut 111⁄2 threads per inch. We find on the index that 48 into 48 cuts 6 threads per inch, then 6 x 4 = 24, gear on stud, and 11 X 4 = 46, gear on screw. Any multiplier may be used so long as the products include gears that belong with the lathe. For instance, instead of 4 as a multiplier we may use 6. Thus, 6 x 6 = 36, gear upon stud, and 11% × 6 = 69, gear upon screw. Rules for Calculating Simple and Compound Gearing where there is no Index. (Am Mach.)-If the lathe is simplegeared, and the stud runs at the same speed as the spindle, select some gear for the screw, and multiply its number of teeth by the number of threads per inch in the lead-screw, and divide this result by the number of threads per inch to be cut. This will give the number of teeth in the gear for the stud. If this result is a fractional number, or a number which is not among the gears on hand, then try some other gear for the screw. Or, select the gear for the stud first, then multiply its number of teeth by the number of threads per inch to be cut, and divide by the number of threads per inch on the lead-screw. This will give the number of teeth for the gear on the screw. If the lathe is compound, select at random all the driving-gears, multiply the numbers of their teeth together, and this product by the number of threads to be cut. Then select at random all the driven gears except one; multiply the numbers of their teeth together, and this product by the number of threads per inch in the lead-screw. Now divide the first result by the second, to obtain the number of teeth in the remaining driven gear. Or, select at random all the driven gears. Multiply the numbers of their teeth together, and this product by the number of threads per inch in the leadscrew. Then select at random all the driving-gears except one. Multiply the numbers of their teeth together, and this result by the number of threads per inch of the screw to be cut. Divide the first result by the last, to obtain the number of teeth in the remaining driver. When the gears on the compounding stud are fast together, and cannot be changed, then the driven one has usually twice as many teeth as the other, or driver, in which case in the calculations consider the lead-screw to have twice as many threads per inch as it actually has, and then ignore the compounding entirely. Some lathes are so constructed that the stud on which the first driver is placed revolves only half as fast as the spindle. This can be ignored in the calculations by doubling the number of threads of the lead-screw. If both the last conditions are present ignore them in the calculations by multiplying the number of threads per inch in the lead-screw by four. If the thread to be cut is a fractional one, or if the pitch of the lead-screw is fractional, or if both are fractional, then reduce the fractions to a common denominator, and use the numerators of these fractions as if thev equalled the pitch of the scre to be cut, and of the lead-screw, respectively. Then use that part of the rule given above which applies to the lathe in question. For instance, suppose It is desired to cut a thread of 25/32-inch pitch, and the lead-screw has 4 threads per inch. Then the pitch of the lead-screw will be 14 inch, which is equal to 8/32 inch. We now have two fraction, 25/32 and 8/32, and the two screws will be in the proportion of 25 to 8, and the gears can be figured by the above rule, assuming the number of threads to be cut to be 8 per inch, and those on the lead-screw to be 25 per inch. But this latter number may be further modified by conditions named above, such as a reduced speed of the stud, or fixed compound gears. In the instance given, if the lead-screw had been 22 threads per inch, then its pitch being 4/10 inch, we have the fractions 4/10 and 25/32, which, reduced to a common denominator, are 64/160 and 125/160, and the gears will be the same as if the lead-screw had 125 threads per inch, and the screw to be cut 64 threads per inch. On this subject consult also "Formulas in Gearing," published by Brown & Sharpe Mfg. Co., and Jamieson's Applied Mechanics. Change-gears for Screw-cutting Lathes.-There is a lack of uniformity among lathe-builders as to the change-gears provided for screwcutting. W. R. Macdonald, in Am. Mach., April 7, 1892, proposes the following series, by which 33 whole threads (not fractional) may be cut by changes of only nine gears: Ten gears are sufficient to cut all the usual threads, with the exception of perhaps 112, the standard pipe-thread; in ordinary practice any fractional thread between 11 and 12 will be near enough for the customary short pipethread; if not, the addition of a single gear will give it. In this table the pitch of the lead-screw is 12, and it may be objected to as too fine for the purpose. This may be rectified by making the real pitch 6 or any other desirable pitch, and establishing the proper ratio between the lathe spindle and the gear-stud. Metric Screw-threads may be cut on lathes with inch-divided leading-screws, by the use of change wheels with 50 and 127 teeth; or 127 centimetres 50 inches (127 X 0.3937=49.9999 in.). Rule for Setting the Taper in a Lathe. (Am. Mach.)-No rule can be given which will produce exact results, owing to the fact that the centres enter the work an indefinite distance. If it were not for this circumstance the following would be an exact rule, and it is an approximation as it is. To find the distance to set the centre over: Divide the difference in the diameters of the large and small end of the taper by 2, and multiply this quotient by the ratio which the total length of the shaft bears to the length of the tapered portion. Example: Suppose a shaft three feet long is to have a taper turned on the end one foot long, the large end of the taper being two 2-1 3 inches and the small end one inch diameter. 2 X= 11⁄2 inches. Electric Drilling-machines -Speed of Drilling Holes in Steel Plates. (Proc. Inst. M. E., Aug. 1887, p. 329)-In drilling holes in the shell of the S.S. "Albania," after a very small amount of practice the men working the machines drilled the %-inch holes in the shell with great rapidity, doing the work at the rate of one hole every 69 seconds, inclusive of the time occupied in altering the position of the machines by means of differ ential pulley-blocks, which were not conveniently arranged as slings for this purpose. Repeated trials of these drilling-machines have also shown that, when using electrical energy in both holding-on magnets and motor amounting to about 34 H.P., they have drilled holes of 1 inch diameter through 16 inch thickness of solid wrought iron, or through 15% inch of mild steel in two plates of 13/16 inch each, taking exactly 134 min. for each hole. Speed of Drills. (Morse Twist-drill and Machine Company.)-The following table gives the revolutions per minute for drills from 1/16 in. to 2 iu. diameter, as usually applied: One inch to be drilled in soft cast iron will usually require: for 44-n. drill, 160 revolutions; for 2-in. drill, 140 revolutions; for 34-in. drill, 100 revolutions; for 1-in. drill, 95 revolutions. These speeds should seldom be exceeded. Feed per revolution for 4-in. drill, .005 inch; for 4-in. drill, .007 inch; for 34-in. drill .010 inch. 1/16 1 116 The rates of feed for twist drills are thus given by the same company: Diameter of drill..... 14 3% 12 Revs. per inch depth of hole. 125 125 120 to 140 MILLING-CUTTERS. 34 1 inch feed per min. George Addy, (Proc. Inst. M. E., Oct. 1890, p. 537), gives the following: Analyses of Steel.-The following are analyses of milling cutter blanks, made from best quality crucible cast steel and from self-hardening "Ivanhoe "steel: The first analysis is of a cutter 14 in. diam., 1 in. wide, which gave very good service at a cutting-speed of 60 ft. per min. Large milling-cutters are sometimes built up, the cutting-edges only being of tool steel. A cutter 22 in. diam. by 51⁄2 in. wide has been made in this way, the teeth being clamped between two cast-iron flanges. Mr. Addy recommends for this form of tooth one with a cutting-angle of 70°, the face of the tooth being set 10° back of a radial line on the cutter, the clearance-angle being thus 10°. At the Clarence Iron-works, Leeds, the face of the tooth is set 10° back of the radial line for cutting wrought iron and 20° for steel. Pitch of Teeth.-For obtaining a suitable pitch of teeth for millingcutters of various diameters there exists no standard rule, the pitch being usually decided in an arbitrary manner according to individual taste. For estimating the pitch of teeth in a cutter of any diameter from 4 in. to 15 in., Mr. Addy has worked out the following rule, which he has found capable of giving good results in practice: Pitch in inches = (diam. in inches x 8) × 0.0625 = .177 diam. J. M. Gray gives a rule for pitch as follows: The number of teeth in a milling cutter ought to be 100 times the pitch in inches; that is, if there were 27 teeth, the pitch ought to be 0.27 in. The rules are practically the same, for if d diam., n = No. of teeth, p = pitch, c = circumference, c = 31.83p2; p = .0314d = .177 Va; No. of teeth, n, = pn; d= 3 14d p. pn π = 100p2 = Number of Teeth in Mills or Cutters. (Joshua Rose.)-The teeth of cutters must obviously be spaced wide enough apart to admit of the emerywheel grinding one tooth without touching the next one, and the front faces of the teeth are always made in the plane of a line radiating from the axis of the cutter. In cutters up to 3 in. in diam. it is good practice to provide 8 teeth per in. of diam., while in cutters above that diameter the spacing may be coarser, as follows: Diameter of cutter, 6 in.; number of teeth in cutter, 40 Speed of Cutters.-The cutting speed for milling was originally fixed very low; but experience has shown that with the improvements now in use it may with advantage be considerably increased, especially with cutters of large diameter. The following are recommended as safe speeds for cutters of 6 in. and upwards, provided there is not any great depth of material to cut away: Should it be desired to remove any large quantity of material, the same cutting-speeds are still recommended, but with a finer feed. A simple rule for cutting-speed is: Number of revolutions per minute which the cutter spindle should make when working on cast iron = 240, divided by the diameter of the cutter in inches. Speed of Milling-cutters. (Proc. Inst. M. E.. April, 1883, p. 248.)— The cutting-speed which can be employed in milling is much greater than that which can be used in any of the ordinary operations of turning in the lathe, or of planing, shaping, or slotting. A milling-cutter with a plentiful supply of oil, or soap and water, can be run at from 80 to 100 ft. per min., when cutting wrought iron. The same metal can only be turned in a lathe, with a tool-holder having a good cutter, at the rate of 30 ft. per min., or at about one third the speed of milling. A milling-cutter will cut cast steel at the rate of 25 to 30 ft. per min. The following extracts are taken from an article on speed and feed of milling-cutters in Eng'g, Oct. 22, 1891: Milling-cutters are successfully employed on cast iron at a speed of 250 ft. per min.; on wrought iron at from 80 ft. to 100 ft. per min. The latter materials need a copious supply of good lubricant, such as oil or soapy water. These rates of speed are not approached by other tools. The usual cutting-speeds on the lathe, planing. shaping, and slotting machines rarely exceed about one third of those given above, and frequently average about a fifth, the time lost in back strokes not being reckoned. The feed in the direction of cutting is said by one writer to vary, in ordinary work, from 40 to 70 revs, of a 4-in, cutter per in. of feed. It must always to an extent depend on the character of the work done, but the above gives shavings of extreme thinness. For example, the circumference of a 4-in. cutter being, say, 121⁄2 in., and having, say, 60 teeth, the advance corresponding to the passage of one cutting-tooth over the surface, in the coarser of the above-named feed-motions, is 1/40 1/60 = 1/2400 in.; the finer feed gives an advance for each tooth of only 1/70 × 1/60 = 1/4200 in. Such fine feeds as these are used only for light finishing cuts, and the same authority recommends, also for finishing, a cutter about 9 in. in circumference, or nearly 3 in. in diameter, which should be run at about 60 revs. per min. to cut tough wrought steel, 120 for ordinary cast iron, about 80 for wrought |