Section 84.—TOOTHED GEARING.

[1515]. Spur gearing. For construction of teeth see text books.

[1516]. Strongest form of spur teeth for motion in one direction only.

[1517]. Half shrouded spur teeth.

[1518]. Whole shrouded spur teeth.

[1519]. Double helical spur teeth, stronger by 15 per cent. than straight teeth; work without backlash or noise, and may be half or whole shrouded; section of tooth on plane of motion is the same as the ordinary spur teeth ([No. 1515]).

[1520]. Crown wheel and pinion.

[1521]. Long teeth spur wheels or “star” wheels. Used on roller mangles, &c., where the centres rise and fall.

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[1522]. Plain bevil gear; shafts at right angles.

[1523]. Plain bevil gear; shafts at acute angles.

[1524]. Plain bevil gear; shafts at obtuse angle.

[1525]. Plain bevil gear; four shafts at right angles.

[1526]. Skew bevils; shafts not in line with one another.

Note.—Where the pair are both of same diameter they are called “mitre wheels.”

[1527]. Spur wheel and pinion; to increase or decrease power and speed the diameters can be varied to almost any proportion.

[1528]. “Screw gear”; single helical gear.

[1529]. Skew spur wheels; shafts not parallel.

[1530]. Dr. Hooke’s gear. Three or more separate wheels of similar or dissimilar pitch fixed together so as to divide the pitch and reduce backlash.

[1531]. The same result obtained by two wheels, one fixed to shaft, the other loose and forced round by a spring so as to follow the pitch of the pinion and destroy all backlash.

[1532]. Mortise wheel teeth.

[1533]. Mortise wheel teeth; another method.

Note.—Wood teeth are usually one-third thicker than the iron teeth they gear into.

[1534]. Pin wheel and pinion gear.

[1535]. Lantern wheel.

[1536]. Screw gear, used in place of bevil gear. Shafts at right angles; teeth at an angle of 45°.

[1537]. Variable speed cone gear.

[1538]. Variable speed square gear.

[1539]. Variable speed oval or elliptical gear.

[1540]. Irregular gear.

[1541]. Internal or epicycloidal gear. See [Nos. 550] and [1545].

Used for differential blocks, &c. Note that both wheel and pinion run in the same direction, and that more teeth are in gear at one time than with external gear as [No. 1527].

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[1542] & [1543]. Varieties of “mangle” gear. The pinion being revolved continuously in one direction produces a reciprocating motion of the wheel; the pinion shaft travels from inside the wheel to outside, and vice versâ, by rising and falling in the slot in the frame. See also [No. 423].

[1544]. Differential gear. See [Section 31]. One wheel has one or more teeth more than the other; used for counters, &c.

[1545]. Moore’s patent differential epicycloidal gear. The pinion and wheel are loose on the shaft and eccentric. One wheel has one tooth more than the other.

[1546]. Multiplying bevil gear. A is a fixed wheel, the cross C is keyed to shaft, B loose on ditto, D and E loose on C; then B is driven at a speed greater than the shaft in proportion to the diameters of the gear. See Patent No. 12,696, 1884.

[1547]. Double worm gear, right and left hand threads. Neutralises the end thrust on shaft. A and B may be geared together.

[1548]. Pointed gear; used for light work and for minimum of friction.

[1549]. Curved worm gear, for heavy strains. Several teeth are in gear at once, but the thread, having a varying section and pitch, is difficult to cut.

[1550]. Antifriction worm gear (Hawkins’). The wheel has four rollers; when one pair is nearly out of gear with the worm, the next pair is coming into gear. This worm is also difficult to cut.

[1551]. Crown worm gear.

[1552]. Ball joint mitre gear.

[1553]. Multiplying rack gear. The upper moving rack is driven at twice the speed of the spur wheel rod. The lower rack is fixed; used on planing and printing machines.

[1554] to [1557]. Varieties of worm gear, with straight, hollowed, and curved teeth; the latter are strongest.

[1558]. Worm and rack gear.

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[1559]. Differential worm gear. The worm gears into two wheels, one having one tooth more than the other.