The columns, " Gage of Plate" refer to the Birmingham sheet-iron gage: for the comparison of which with ordinary linear measure, see Appendix, page 1013.

The columns, " Form of Tooth," refer to the diagrams on page 684.

The columns, " Revolutions per Minute" and "Horses Power" required for the maximum of effect, are from the experience of Mr. Ovid Topham, Engineer.

(1.) Single Plates of equal Thickness throughout.

Generally called Bench Saws, and used either for thick or thin Wood.

Intermediate sizes used, and also thick Saws for cutting Grooves.

Diameter.

Gage of Plate.

Form of Tooth.

Space of Tooth.

Revolutions per Minute.

Horses' Power.

2

inch

23

to

28

644

to

646

1/30

to

1/10

in.

2000

3

-

21

-

27

-

-

1/24

-

1/8

-

1800

4

-

20

-

26

-

-

1/16

-

1/5

-

1600

6

-

19

-

24

-

-

1/12

-

1/3

-

1400

9

-

17

-

22

644

to

653

1/8

-

1/2

-

1200

12

-

15

-

21

-

-

1/6

-

5/8

-

1100

1

15

-

14

-

20

-

-

1/4

-

3/4

-

1000

1 1/2

18

-

13

-

18

-

-

1/3

-

1

-

900

2

24

-

12

-

16

-

-

5/8

-

1 1/2

-

750

2 1/2

36

-

10

-

14

-

-

1

-

2

-

500

3

48

-

8

-

12

-

-

1 1/2

-

3

-

390

3 1/2

60

-

6

-

9

-

-

2

-

4

-

330

4

(2.) Single Plates bevilled on the Edge.

Generally called Bevilled Saws, and used for Veneers.

The largest, medium, and smallest of the ordinary sizes alone are given.

Diameter.

Width of Bevils.

Gage of Plate.

Gage of Edge.

Form of Tooth.

Space of Tooth.

Revs. per

Minute.

Horses' Power.

8

inches

2

to

3

in.

12

to

15

22

to

28

644

or

645

1/8

to

1/4

in.

1300

22

-

3

-

5

-

10

-

13

20

-

25

-

-

1/4

-

1/2

-

800

1

36

-

4

-

6

-

8

-

11

18

-

22

-

-

1/3

-

3/4

-

550

2

(3.) Segments fixed to a Disk, and bevilled on the Edges.

Generally called Segment or Veneer Saws, and used for Veneers and thin Wood.

The largest, medium, and smallest of the ordinary sizes alone are given.

Diameter.

No. of Segments.

Width of Segments.

Width of Bevil.

Gage of Plate.

Gage of Edge.

Form of Tooth.

Space of Tooth.

Revs, per

Min.

Horses' Power.

5

ft.

10

to

15

5

to

8

in.

2

to

3 1/2

in.

11

to

12

24

to

28

644

or

645

1/5

to

1/4

in.

320

3

12

-

15

-

20

5 1/2

-

9

-

2 1/2

-

4 1/2

-

10

-

11

22

-

26

-

-

1/4

-

1/3

-

130

5

18

-

20

-

30

6

-

10

-

3

-

5

-

9

-

10

20

-

24

-

-

1/8

-

3/8

-

85

6

Bench saws, below about one foot diameter, are usually mounted on spindles running on conical steel centers, and driven by catgut bands; those above one foot on spindles running in cylindrical brass bearings, and driven by leather straps.

Compared with the diameter of the saw, and speaking generally, the hole or eye may be considered to measure from 1/8 to 1/16 part of the diameter; that of the flange of the spindle, from J to J part of the diameter; of the pulley for leather straps about |; and for the catgut, 1 the diameter of the saw.

The velocity of the edge of the saw varies from about 4500 feet to 5000 feet per minute; and the greatest thickness of work done can scarcely exceed 1/3 the diameter of the saw, and is generally below J the diameter.

with only eight sectional teeth (see fig. 791, p. 797). The teeth of circular saws are more inclined, because such teeth cut more keenly, and the additional power they require is readily applied, by the great velocity and momentum that may be given to circular saws. The teeth of circular saws are more set, to make a wider kerf, which is required, because the large circular plate can neither be made nor retained, so true as the narrow straight blade. The general proportions of circular saws are given in the annexed table.

It is generally politic, to use for any given work, a saw of as small diameter as circumstances will fairly allow, as the resistance, the surface-friction, and also the waste from the thickness, rapidly increase with the diameter of the saw. But on the other hand, if the saw is so small as to be nearly or quite buried in the work, the saw-plate becomes heated, the free escape of the dust is prevented, and the rapidity of the sawing is diminished.

Hassenfratz, Emy, and other French writers on carpentry, have described the mode of cutting thick logs of timber, as in fig. 782, by means of two comparatively small saws, each extending alone to the center of the log. The saws are in the same plane, but one above and the other below the log, and a little removed to avoid the contact of their teeth; but from the reasons above stated, and some others, the plan is but rarely if at all adopted.

Figs. 782.

Table Of The Dimensions Of Circular Saws 200199

783.

Table Of The Dimensions Of Circular Saws 200200

Under moat circumstances, it is best to employ that part of the saw which is nearest to the center, and it may be stated generally that, as in fig. 783, the diameter of saw s, should be about four times the average thickness of the wood w, and that the flange on the spindle, should be as nearly as practicable flush with the saw table or platform p p.

In addition to various other particulars in the table on circular saws, an attempt has been made to tabulate the velocities proper for different saws, and the amount of power severally required, but these numbers must be received with some latitude, because they are very much influenced by accidental circumstances. Amongst these are the particular quality of the wood or other materia], as to its hardness and grain, its greater or less freedom from moisture, or from gummy or resinous matters, also its magnitude, and the degree of smoothness desired in the surfaces left by the saw; all these circumstances demand certain variations in the porportions and conditions of the saws used. A few words will be therefore added respecting each of these conditions.

The harder the wood, the smaller and more upright should be the teeth, and the less the velocity of the saw; hence it follows that the rate of sawing is proportionally slow.

In cutting with the grain, or lengthways through the fibres, the teeth should be coarse and inclined, and the speed moderate, so as rather to cut the removed wood into shreds than to grind it into powder; as the more minute the sawdust, the greater the power that must be expended in its production.

In cutting across the grain, the teeth should be finer and more upright, and the velocity should be greater than in the last case; so that each fibre of the wood may be cut by the passage of some few of the consecutive teeth, rather than be torn asunder by one tooth only.

Wet wood is softer than dry, and is therefore more easily cut, but the saw is required to be keener and more coarsely set; the waste is consequently greater.

For gummy or resinous materials, and for ivory, the saw teeth are required to be very keen, and the velocity comparatively slow, to avoid the dust becoming softened and rendered adhesive, as it will then stick to the blade. This disposition is lessened by lubricating the saw either with a tallow candle, solid tallow, lard, or oil applied with a brush.

When the object is to get through as much work as possible, the rapidity with which the wood is then advanced, will prevent regularity in its progress, and consequently likewise in the saw marks on the wood. The saw is then liable to be overloaded; if so, it vibrates rapidly sideways with great noise, requires greater force, but nevertheless proceeds through the wood slowly and leaves it full of coarse ripple marks.

Smooth sawing requires the work to be regularly advanced towards the saw, and the latter must be keen and very uniformly set; as one tooth projecting beyond the general line, is sufficient to score or scratch the work. It is a proof that the saw was in most excellent order and well applied, when the portion cut in every revolution of the saw, cannot be detected by the corre-sponding marks left on the wood or other material.