There is no job the worker in metal is called on to do that
requires the exercise of his brain and muscle in the proper
direction than the grinding and polishing of metal surfaces on
that class of work where machinery cannot aid him. The more he
exercises his brain, the more saving he will be of both his time
The practice generally employed by machinists in grinding and
polishing either new or old work was to mix the polishing
material with oil, usually refuse machinery oil; in most cases
this is a great mistake, and has caused the loss of time,
patience and money.
Take for instance the grinding, to a true bearing of a stop
cock, a valve, seat, or a slide valve. There are few machinists
but what have had more or less of that class of work to do,
particularly in jobbing shops, and we seldom find one who uses
the same method of accomplishing the job that is practiced in
shops where that class of work is made a specialty.
In fitting and grinding in the plug into the barrel of a cock a
little judgment and care will save a great deal of hard labor,
and in no case should oil be mixed with any of the grinding
material, for the following reasons: If fine emery, ground glass
or sand are used with oil, it requires but a few turns of the
plug in the barrel to break up the grains of the grinding
material into very fine particles; the metal surfaces also grind
off; the fine particles of metal mixing in with the grinding
material and oil making a thick paste of the mass.
At this stage it is impossible to grind or bring the metal
surfaces to a bearing, as the gluey paste keeps the metal apart;
if more grinding stuff is applied it will prevent the operator
from seeing what part of the barrel and plug bears the hardest.
Again, if the grinding material be distributed over the whole
surface, the parts that do not bear will grind off as fast as
the parts that touch hard, as the particles work freely between
the surfaces; should the barrel and plug bear equal all over
when fitted it requires more care than if it were a top or
bottom bearing, as that part of the barrel and plug across the
"waterway' grinds twice as fast as the other parts, therefore,
it should be kept the dryest.
Now this objection holds good in the grinding of valve seats or
slide valves, to wit: the separation of the surfaces of the
metal by a thick, pasty grinding material. In order to bring the
surfaces to a perfect bearing rapidly and with little labor the
following directions will be found worth a trial.
To grind a stop cock of any kind, first see that the plug fits
the barrel before it is taken from the lathe. Run a half-round
smooth file up and down the barrel to break any rings that may
be in it; a few rubs of a smooth file back and forth over the
plug will break any rings or tool marks on it. Wipe both parts
Use for grinding material fine molder's sand sifted through a
fine sieve. Mix with water in a cup, and apply a small quantity
to the parts that bear the hardest. Turn rapidly, pressing
gently every few turns; if the work is large and the lathe is
used run slow; press and pull back rapidly to prevent sticking
and ringing; apply grinding sand and water until a bearing shows
on another part, then use no more new sand, but spread the old
that has worked out over the whole surface. Turn rapidly,
pressing gently while turning; withdraw the plug and wipe part
of the dirt off and rub on the place a little brown soap;
moisten with water and press the surfaces together with all the
force at hand, turning at the same time.
Remove the plug and wipe both parts clean; next try the
condition of the bearing by pressing the dry surfaces together
with great force. If the parts have been kept together closely
while grinding, and the plug has not rubbed against the lower
part of the barrel, the surfaces will be found bright all over
and a perfect bearing obtained. If an iron barrel and brass plug
are used, or two kinds of brass, a hard and soft metal, soap
should be used freely when finishing up, as the tendency to form
rings is greater when two different metals are used.
In grinding slide valve which has been in use until hollow
places have worn in the surface, emery mixed with water, or sand
and water, will be found better than oil, unless light body oil
such as kerosene is used.
If water is used with the grinding material soap should be
rubbed on hollow places, and the grinding stuff should be
applied to the high parts in small quantities, keeping the low
parts clean and dry until an even surface is obtained all over;
then the worn out stuff should be used for finishing up.
In polishing metal, oil that will "gum up" should not be used
with the polishing material unless for a dead fine polish. In
polishing old brass work which has been scratched and tarnished
by wear, pumice stone or bath brick should be used with soap and
water for scouring off with, and rotten stone with kerosene oil
for the wet finish, and dry for the final polish
The same method should be used for new brass work.
New work should require when leaving the lathe and vice tools
but little polishing or grinding, and every good workman should
try to avoid using an emery stick or emery cloth, as with proper
care in the use of tools a great deal of grinding and polishing
can be dispensed with.
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