ry
satisfactory, either with the tool or on the work itself.

Some compositions of metal require a high speed, and some a hooked tool.
These are things which each must determine as the articles come to the
shop; but there are certain well-defined rules with respect to the
ordinary metals that should be observed.

THE HACK SAW.--Our first observation should be directed to the hand
tools. The hack saw is one of the most difficult tools for the machinist
to handle, for the following reasons:

First, of the desire to force the blade through the work. The blade is a
frail instrument, and when too great a pressure is exerted it bends, and
as a result a breakage follows. To enable it to do the work properly, it
must be made of the hardest steel. It is, in consequence, easily
fractured.

[Illustration: _Fig. 28.--Hack Saw Frame._]

[Illustration: _Fig. 29.--Hack Saw Blade._]

Second. The novice will make short hacking cuts. This causes the teeth
to stick, the saw bends, and a new blade is required. Take a long
sweeping cut, using the entire length of the blade. Do not oscillate the
blade as you push it through the work, but keep the tooth line
horizontal from one end of the stroke to the other. The moment it begins
to waver, the teeth will catch on the metal on the side nearest to you,
and it will snap.

Third. The handle is held too loosely. The handle must be firmly held
with the right hand, and the other held by the fingers lightly, but in
such a position that a steady downward pressure can be maintained. If
loosely held, the saw is bound to sag from side to side during the
stroke, and a short stroke accentuates the lateral movement. A long
stroke avoids this.

The hack saw is one of the tools which should be used with the utmost
deliberation, combined with a rigid grasp of the handle.

FILES.--For remarks on this tool see Chapter IV, which treats of the
subject specially.

GRINDSTONES, EMERY AND GRINDING WHEELS.--A good workman is always
reflected by his grinding apparatus. This is true whether it has
reference to a grindstone, emery, corundum wheel, or a plain oil stone.
Nothing is more destructive of good tools than a grooved, uneven, or
wabbly stone. It is only little less than a crime for a workman to hold
a tool on a revolving stone at one spot.

CARELESSNESS IN HOLDING TOOLS.--The boy must learn that such a habit
actually prevents the proper grinding, not only of the tool he has on
the stone, but also o