S44

THEORY AND PRACTICE OF ENGINEERING.

Rook II.

In the foregoing table, supposing it is required to find the radius of a wheel having 105teeth, look for 100 in the first column, and under 5 in the top, we find 16*713, and sup-posing the pitch to be more than one inch, we multiply this number found by the pitch ininches. For a greater number of teeth than is given in the table, take half the givennumber, and double the quantity in the columns, and for any less number, the general rulemay be applied.

The following table contains the pitch and dimensions of teeth of wheels already executed,and satisfactorily performing their work, with their power and velocity per second.

Pitch ofTeeth inInches.

Thicknessof Teeth inInches.

Breadth ofTeeth iuInches.

Length ofTeeth inInches.

Horse-powerat 2 1 27 Feetper Second.

Horse-powerat 3 Feet perSecond.

Horse-powerat C Feet perSecond.

Horse-powerat 11 Feet perSecond.

4-2

2-

8*

2*40

13*33

17*61

35-23

1

64-6

3*99

1*9

7*6

2*28

13 03

15-90

31*80

58-30

3-78

1*8

7*2

2*16

10-80

14*27

28-54

52-32

3-57

1-7

6-8

2 04

9-63

12*72

25 54

46-68

3-36

T6

6*4

1*92

8-53

11-27

22*54

41-32

3*15

1*5

6*

1*80

7 50

9-91

19-82

36-33

2*94

1*4

5-6

1-68

6*53

8*63

17-26

31-64 ,

2*73

1*3

5*2

1*56

5-63

7*44

14-88

27-28 |

2*52

1*2

4*8

1*44

4-80

6*34

12*68

23-22

2*31

1*1

4*4

1*32

4-03

5*32

10-64

19*54

210

1*

4*

1*20

3-33

4*40

8*81

16*15

1*89

*9

3*6

1*08

2-70

3*57

7-14

13-09

1*68

*8

3-2

•96

2-13

2*81

5-62

10-33

1*47

•7

2*8

•84

1-63

2*15

4*30

7-88

1-26

*6

2*4

*72

1 -20

1-59

3*18

5-83

1-05

■5

2*

■60

-83

1*10

2-20

4 03 |

The thickness of the teeth, as given in the second column, varies one-tenth of an inch ineach line ; and it must be fu’ther observed that the breadth of the teeth is always four timesas much as their thickness. The strength of the teeth is ascertained by multiplying thesquare of their thickness into their breadth taken in inches and tenths. 'The pitch is foundby multiplying the thickness of the teeth by 2*1. ^ UUU1 .

Construction of JVheels . — When of wood, they are usuallyformed of three thicknesses, and the joints broke over eachother; the middle thickness is made in six or eight pieces:a solid rim is formed by bolting them together; this ismortised for the cogs, the tenons of which have a pindriven through to hold them in their place. The arms aremortised sometimes through the shafts, but which weakensthem, and is not the best manner; they may be halved intoeach other, and form a frame with a square opening in thecentre; the arms may be secured to the middle thickness of therim by bolting them well together.

A wheel of this kind may be easily attached or removed tothe shaft by the adjustment of wedges, which are insertedaround the shaft, and which close up the square hole left inthe framing.

Face Wheels have stays and braces attached to the back ofthe rim, some distance along the shaft into which they aremortised, in order that greater strength may be obtained:this is necessary, as the face wheel, when acting with a trundle,has its teeth thrown off, and requires a stay to prevent it.

The trundles usually arc surrounded with iron, tc preventthem from splitting, and small pinions are made out of asolid block of wood, with the cogs fitted into it.

Iron wheels are more usually adopted, and have theirteeth cast with them, or mortices left for the insertion ofwooden cogs : it has been found that wheels work with lessnoise and friction when wooden and iron cogs are used together.

When this practice is adopted, the thickness to be given tothe wooden cogs must be a little more than the space betweenthem; and the space in the wheel corresponding to it must bemade a little more than its teeth. The iron teeth generallygiven to the smaller wheel are chipped with a cold chisel,

Fig.1293.

Fig. 1294.