and some form of tannic acid as their base. Tannic acid has a slight action on the iron of the boiler and is reasonably efficient in preventing scale from sticking.

To prevent scale, or at least to diminish the injury it does to boilers, the feed water should be heated by live steam under boiler pressure in a separate vessel before going to the boiler. By allowing the water to settle for some time, sediment, mud, and dirt will be got rid of. Oil from the engine cylinder is particularly injurious to boilers, and, when noticed in the condensed steam, should be carefully removed.

STEAM PUMPS.

If water can not be obtained under sufficient pressure to cause it to flow into the intake by gravity, some sort of pump is necessary. Usually the pump runs by steam. If the pump runs badly, make sure the water valves and water pipes are all right before examining the steam end. When the pump is not in use in cold weather open all the cocks and drain plugs to prevent freezing. Always see that the pump has a full and steady supply of water to work on. Do not take the pump apart to see what is inside as long as it does its work well. Set a pump on a level solid foundation so as to avoid undue strain on the pipes and resulting leaky joints. Long pipes should be larger than short ones, to allow for increased friction. All pipes should be as short and straight as possible. A foot valve and strainer should be attached to the suction pipe.

Use few elbows, tees, and valves, substituting full round bends for elbows, and wyes for tees; sharp bends greatly increase the friction. Care must be taken to guard against leaks in the suction pipe, as a very small leak will supply the pump with air to its full capacity, and little or no water will be obtained. A suction air chamber made of a short nipple, a T, a piece of pipe smaller in diameter than the suction pipe and from 2 to 3 feet long, and a cap, screwed upright into the suction pipe close to the pump are always useful, and when the suction pipe is long, in high lifts, or when the pump is running at high speed, it is a positive necessity. Its use insures a steady and uniform flow of water through this suction pipe and prevents "pounding" or "water hammering."

Use good cylinder oil, and oil the steam end just before stopping the pump. Keep the stuffing boxes full of good packing, well oiled, and just tight enough to prevent leakage without excessive friction.

WATER POWER.

As a general thing, water power is not practicable for a portable mill. It may be found in one location, but not in the next. It is cheaper than steam, but the source of power is neither uniform nor

continuous; it is not as capable of control as is steam, and in most cases it gives low speed and low capacity. Decriptions of various types of water wheels will be found in the Appendix.

BELTING.

Belts transmit power from the engine to the saw. The heavier the belt the more power it transmits. Belt tighteners are required when a belt itself is not heavy or long enough to cause sufficient sag. The sag should always be on top, in order to increase the arc of contact with the pulley. Belts are made either of leather, rubber, or fabric. Leather belts are sold either single or double. The transmitting power of a single belt is only 70 per cent of that of a double belt. Rubber belts stand moisture better than leather and are cut from to inch shorter per foot than the circuit on which they run. They are run with the seam side out, while leather belts are run with the grain side in. Rubber belting is sold as 2, 4, 6, and 8 ply, the 4 ply being equal to single leather belting, the 6 ply to light double leather belting, and the 8 ply to heavy double leather belting. Small mills are usually equipped with either fabric or rubber belting.

When ordering belting of any kind it is necessary to specify (1) diameter of driving pulley, (2) its revolutions per minute, (3) diameter of driven pulley, (4) distance of pulley centers, (5) horsepower to be transmitted, and (6) width of pulley face.

Leather belting is spiked or joined either by studs or by belt cement. Next best to the cemented joint in a leather belt is that made with a rawhide or other lace. But this joint in a leather or any kind of belt must be made properly. Large lacing holes and a big bunch of lace may be almost as harmful and cause as much "jump' in the belt as a double row of studs. Where leather belting is exposed to moisture and waterproof cement is not accessible, lacing may be resorted to; but, as a general rule, all leather belts should be cemented.

In lacing a fabric belt never use a hollow punch, because it cuts the stitches and weakens the belt. Use a pointed awl. Cut the ends of the belt perfectly true with a try-square and punch or bore two rows of holes in each end. The holes in the second row should be punched directly back of the holes in the front row. The holes in both 、 ends of the belt should also be directly opposite. No hole should be less than one-half inch from either edge or end of the belt. The holes. should be spaced three-fourths inch from center to center. When an odd number of holes are to be laced, begin with the center hole; and when an even number, start with either of the two center holes. The straight stitch and hinge are the two forms of lacing in most general use. Other methods of splicing fabric and rubber belting

are also used in emergencies. Special endless belts with a diagonal splice are supplied by some manufacturers.

A belt should be capable of transmitting from 5 to 25 per cent more power than is actually needed, the excess capacity being governed by the type of drive, the smaller excess for heavy main drives, and the greatest for machine belts. Never use belts the full width of the pulley face, as a slight lack of alingment may cause part of the belt to run beyond the edge of the pulley and perhaps against a shifting finger or pulley flange. This is sure to result in loss of power and perhaps in a badly damaged belt. On the other hand, a belt too narrow necessitates high tension to transmit the required power, thus causing excessive journal friction and the early destruction of the belt.

Generally speaking, single belts, if heavy enough to carry the load, should be used on small pulleys. A single belt should never be wider than 13 times the diameter of the smallest pulley. Where small diameter pulleys and the load would require an unusually wide single belt, it is advisable to substitute narrower pulleys and a narrow double belt. Thin wide belts give the best service; working vertically, a thick narrow vertical belt will not grip the pulley well. Double belts of medium or heavy weight should never be used on pulleys less than 12 inches in diameter, or, even better, on pulleys less than 20 inches in diameter.

Belts too heavy for the load weave back and forth on the pulleys. This is best illustrated by a belt working under intermittent loads, which runs straight while carrying the maximum or proper load but shows a tendency to weave when the load is reduced.

The tightness with which belts are adjusted to the pulleys is of prime importance. If they are put on too tightly, there is a large unnecessary loss of power from excessive friction at the bearings, to say nothing of the overstrain and injury to the belt itself. If, on the other hand, the belt is too loose, it is likely to flop around and jump from the pulleys, particularly when a load is suddenly thrown on or off. The slacker a belt can be run up to a certain point while doing its work satisfactorily, the greater the economy. In installing belting and taking it up, it should be remembered that certain kinds of belting are affected by weather conditions, lengthening and shortening according to the amount of moisture in the air. Instances have been known where the babbitt was melted out of the boxes and even shafting pulled out of alignment as a result of belting being put on too tight.

Be sure to note carefully whether your shafting is properly in line. More belting is ruined by improperly lined shafting and pulleys than in any other way. The belts under this condition are

either kept on the pulleys by guides or rub against hangers and tear or stretch on one edge. Belts so stretched will not run straight and may slip the pulleys at any time. Remember that because your shafting was once in line it does not follow that it will stay so indefinitely. It is a very simple matter to connect two pulleys by a band in such a way that when one pulley is turned the other will go round. It is not at all a simple matter properly to proportion a drive and select the size and quality of belting which will transmit power most effectively and economically.

Shafts should not be located too close together. There should be distance enough between them to allow the belt to recover somewhat from the strain applied on the tight or working side. This distance depends entirely upon the size of the belt and pulleys, but should be sufficient to allow some slight sag to the slack side of the belt. Neither should the shafts be too far apart, for in such cases the weight of the belts draws heavily on the shafting and increases the friction load in the bearings, at the same time causing the belt to swing from side to side and sometimes to run off the pulleys. This constant swing is sometimes the cause of crooked spots in the belt, which wear out rapidly.

It is the best and most economical practice to use pulleys of large diameters, thus obtaining a high belt speed, which means a saving both in the transmission of power and in the wear and tear on the equipment. The speed of the belt being the same, pulleys of large diameters effect a slightly greater transmission of power than do those of small diameter. The speed of the shafts being the same, the advantage in favor of large pulleys over small ones is in proportion to their diameters. Wooden or leather-covered pulleys have a greater transmitting power than iron. Cold-rolled shafting is said to have 30 per cent greater strength than hot rolled. The usual diameters for shafting are from 1 to 3 inches. The proper speed is from 300 to 400 revolutions per minute, and its transmitting power D3XR is given as =H. P. D is diameter of shafting in inches, R 80 revolutions per minute.

Shafts that are to be connected with each other by belts should be far enough apart to allow a gentle sag to the belt when in motion. When narrow belts are to be run over small pulleys, 15 feet is a good average, the belt having a sag of from 13 to 2 inches. For larger belts working on larger pulleys the distance should be from 20 to 25 feet, with a sag of from 2 to 4 inches. For main belts working on very large pulleys the distance should be from 25 to 30 feet, with a sag of 4 or 5 inches. If the distance between pullies is too great the belt will have an unsteady flapping motion which will tend to destroy

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both belt and machinery. Regardless of the width of belt or diameter of pulley, the adhesion of the belt to the pulley is the same in all cases, provided the arc of contact and aggregate tension or weight are the same. Thus, other things being equal, a belt will slip just as readily on a pulley 4 feet in diameter as it will on a pulley 2 feet in diameter. To obtain the greatest amount of power from belts the pulleys must be covered with leather. This will allow the belts to run slack and will increase their durability by 25 per cent.

CIRCULAR SAWS.

KINDS AND COSTS.

Circular saws are either of the solid-tooth or inserted-tooth type. The advantages of inserted-tooth saws over solid-tooth saws are: The bits are cheap and can be readily set in position with the special wrench; less experience is required in dressing the saw; there is less filing and gumming; there are fewer saw repairs, which is important in a backwoods locality; and the diameter of the saw remains unchanged during its use. The disadvantages are: The saw kerf is heavy; the teeth are larger and fewer than in a solid-tooth saw; feed is comparatively slow; and the cost is higher.

For big logs and high speed a double circular saw must be used. The two saws are hung to revolve in opposite directions, so that the sawdust from the top saw will not be thrown into the lower one. The advantages of a top saw (double mill) are: It will saw bigger logs than a single mill; it will make a truer cut and saw lumber more evenly; it takes faster feed, saws more lumber, and entails less. expense for saws and less repairs. The top saw may remain inactive when small logs are being cut, to avoid using up power. Inserted teeth are not used in a top-saw rig.

The approximate prices of solid-tooth and inserted-tooth saws f. o. b. Seattle, in 1916, were:

Approximate price of solid-tooth and inserted-tooth saws.

The amount of horsepower required for a circular saw is equal to approximately one-third of the saw's diameter in inches. In large mills each horsepower is supposed to manufacture 1,000 feet of lumber per day; in small mills only one-half that amount.

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