8. What is the length of box for 118 in. dia. shaft?

9. Find length of box for 218 in. dia. shafting.

10. Find length of hanger bearing for 3 in. dia. shaft.

11. What is the dia. of shafting, when bearing for boxes is 12 in. long?

12. What length of shaft bearing will be required for 5 in. dia. shaft?

13. Find length of box for 6 in. dia. shafting.

14. Find dia. of shaft for hanger box 16 in. long.

15. What dia. of shaft will be required for box 9 in. long?

16. When 40 lbs. is allowed per sq. in. on bearings, what is the length of box for 4 in. dia. shaft, that carries 9 pulleys, with 31⁄2 in. belts at 55 lbs. per in. strain, each pulley weighing 35 lbs.?

Note. Use approximate formula in finding weight of shaft. Page 172.

17. What length of bearing will be required for a 3% in. dia. shaft, carrying 6 pulleys for 3 in. belts at 55 lbs. per in. strain and weighing 35 lbs. each, allowable pressure 40 lbs. per sq. in.?

18. How many 12 in. dia. pulleys weighing 40 lbs. each for 4 in. belts at 55 lbs. per in. strain, can be put on 3 in. shaft with allowable pressure 40 lbs. per sq. in.?

19. A jack shaft has 3 pulleys each weighing 1,500 lbs. The pulleys carry 26 in. double belts at 82 lbs. strain. Find length of 3 boxes used, at 8 ft. on centers, when shaft is 5 in. dia. and projects 6 in. beyond centers of end boxes, with 75 lbs. per sq. in. pressure on bearing.

20. What is the length of crank shaft bearing for 71⁄2 in. dia. of journal when shaft is 8 ft. long, fly wheel weighs 8

tons, belt 26 in. wide with 82 lbs. per in. strain and 80 lbs. is allowable pressure per sq. in. on bearing?

21. Find number of 3 in. belt pulleys 55 lbs. strain, each pulley weighing 100 lbs., that can be placed on a 4 in. dia. line shaft, 8 ft. between the centers of hangers.

22. What lengths of boxes will be required for 4 in. dia. jack shaft, 8 ft. long, to carry 2 drive pulleys, weighing 1,000 lbs. each with 24 in. single belt at 55 lbs. strain per in., allowable pressure being 65 lbs.?

23. A jack shaft with 5 in. journals, with 75 lbs. pressure per sq. in. will require 2 boxes of what length, when the total weight and pull of belt is 15,000 lbs.?

24. What is the bearing surface required for a 31⁄2 in. dia. line shaft with 40 lbs. allowable pressure, when there is a weight including shaft of 2,000 lbs. on each bearing?

25. Find the dia. of race ring for 10 in. dia. balls when the clearance between the balls is

inch.

26. What is the clearance between 8 in. dia. balls when the race ring is 24 in. diameter?

27. Find the dia. of the ball to be used in a 15 ball race ring when the clearance is .114 in. and the circle at the center of the balls is 13 in. diameter.

28. How many in. dia. balls will be required for a race ring 1 in. dia. when the clearance between the balls is .1365 inch?

29. Find D when n=8, d= 3 in. and s= .250 in.

30.

Find n when D= 1 in., d= in. and s=.199 in. 31. Find Find s when din., n=20 and D=4 in. 32. Find d when D= 1.82 in., n = 6 and s = .41 in. 33. Find s when n=9, d= in. and D= 13 in. 34. Find s when D= 11⁄2 in., d= in. and n =

11.

MACHINE KEYS

Machine keys are short bars of metal, usually either square or rectangular in cross section, used to prevent wheels, pulleys, cranks, or other pieces from rotating on the shaft.

Feather keys are used so that a piece can slide along a shaft and yet have a positive rotation with the shaft. The key is usually fastened in the sliding piece, and is square in cross section outline

1. A 6 in. dia. shaft is to be coupled to a 5 in. shaft with flange couplings. What are the sizes of keys required for each flange?

2. What is the thickness of key required for fastening pulley to a 2 in. dia. shaft?

3. What size of key will be required to fasten a 24 in. crank to an 8 in. dia. shaft?

4. What size key should be used on feed worm of an engine lathe, when feed rod is 1 in. diameter?

LINEAR MEASURING INSTRUMENTS

The meter is the only unit for linear measure legalized by the United States government, but the bronze bar No. 11, given to the United States by the British government, has been generally accepted as the standard unit for length of

the yard at a temperature of 61.79° F. From this bar the makers of measuring instruments have compared their standards, and have fixed lengths of bars, from which their instruments are made with as fine a degree of accuracy as it is possible for a trained and skilled mechanic to attain.

When it is remembered that the bronze No. 11 changes in length over 1080 inch for each degree Fahrenheit, it will be seen that extreme accuracy and close measurements depend not only upon the accuracy with which the standard bar is made, but also upon the temperature of the bar at the time that measurements are taken or comparisons made. Usually each shop has some standard bar, which is referred to as a standard gauge, with which all other measuring instruments are compared.

The micrometer is the measuring instrument that is now generally used to record dimensions of any body in thousandths of an inch. The principle of construction and operation of the micrometer is comparatively simple. It consists of a screw C, Fig. 46, having forty threads per inch, that turns through a stationary nut B, which is part of a curved bar to which is attached a round pivot E called the anvil located in line with the screw C. F is a lock nut which sets the screw C firmly in any desired position for taking dimensions. The barrel or thimble A is a part of, or fast to the screw C, and is divided into twenty-five divisions on the beveled end at a, each five divisions being marked with figures 0—5—10—15–20. A cylindrical part of the nut B has a line parallel to the axis of the longitudinal motion of the screw, and at right angles to this line are short lines which represent the position of the end of thimble A for each

revolution of the screw C. The first one marked O shows the

F

A

5 0 20

543210

B

C

E

a

1000

position of screw when it just touches the end of anvil E, and at this position the O line on thimble A, should coincide with this O point at its intersection with line parallel to axis of screw C. As one turn of a forty pitch screw is equal to of 1 inch, or 18 inch, the motion of thimble A through the space of one of the twenty-five divisions on end of thimble will give a longitudinal movement of the screw C of onethousandth inch (rooo inch). Each four turns of the screw C will be 1850×4, or 10 inch, these points being marked 1, 2, 3, 4, etc., up to 9, indicating 100, 200, 300, etc., thousandths of an inch between end of screw C and anvil E, according to the position of the beveled end of thimble. Suppose a dimension of .5625 inch is to be taken, the screw C is opened by revolving A until 0 on thimble corresponds with the axial line at 500 thousandths. As each turn of C is equal to 25 thousandths two turns are made with A which gives 550 thousandths. Now turning A through 12 spaces on thimble will give 562 thousandths, and 5 tenths or the half thousandth will be obtained when the axial line is half way between the twelfth and thirteenth division lines on the thimble. In this way .5625 inch can be obtained. Other dimensions are obtained in like manner, getting the number of thousandths required between the hundredths by adding

Fig.46.