The Magnolia gazette. [volume] (Magnolia, Miss.) 1872-current, 1883-09-27
MAGNoLTA, MISSISSIPPI THURSDAY. SEPTEMBER 27 1888

and appurtenances are required. The
head-stock is furnished, like that of the
ordinary back-geared 1athe, with back
shaft, on which is the driving pulley, or
the cone of step pulleys, from which the
spindle is driven by means of a gear and
pinion, the surface speed of n column
under process of grinding and polishing
being from go to 240 feet per minute,
giving to a twelye-inch column about
seventy-seven turns per minute and to
a thirty-siX-inch column about twenty
five turns per minute
To center and swing n column in the
lathe the stone has a square recess cut
in each end, into which is fitted a block
of cast iron with round hole through its
center. The place of this block is found
by means of cross of wood with slid
ing arms on each of the four limbs OF
the cross, the arms projecting over the
surface of the column longitunalty, and
when equidistant from the center de-
noting the place OF the center block, so
that the true center of the column or
shaft is found, Just as il is on an iron
shaft, from the circumference. The iron
block is secured in place by q running
of Babbit metal, or similar unshrink-
ing compound, around it, The centers
of the lathe spindles fit the holes in the
blocks, and when swung to the lathe
the column is rotated by means of II lug
or dog on the face plate engaging with
one seated in the end of the column.
Back of the lathe is wall of plank
against which rest the ends of NUM-
ber of iron blocks, three or four inches
diameter, long enough TO project over
the column and to have their rear ends
resting against the lulkhead or wall.
Their under sides are concayed to en-
brace the column one-fourth of its diam
eter or less, and as the motion of the
column in grinding is reverse to that OF
the ordinary lathe, the blocks are held
against the wall by the rotation of tho
column. These blocks are. arranged
closely side by side, and when the col
umn Is first worked its irregularities Of
chiseling and unevenness of contour
make these blocks play up and down
like the movement of pianoforte keys
under the fingers Of performer. But
as the grinding progresses this irregular
movement becomes very slight undu
lation, pleasant to see.
A trough runs under the column its
entire length, and from it an attendant
SlOfclS DcdtH StlUAl anu MitltI Oll INT
revolving column, the blocks with their
concaye faces acting as grinders, Just
as the hinge clamps of the machinists
are used in polishing turned shaft.
And like the clamps, the series of
blocks are occasionally pushed along
one-half of their width to avoid rings
of roughness. This quartz sand used
until all the bruises, "stunts, and
! ehisel marks are taken out, and the
4 surface shows a uniform color. Then
the trough is cleaned and emery of the
numbers forty to sixty, according to the
| quality OF the stone, is weighed out in
| the proportion of about half a pound
to every superficial foot; thus a column
of ten feet in length by three feet diame-
ter--ninety superficial feet-7would re-
4 quire from forty-live to fifty pounds.
| This is all weighed out at one time,
and is never added TO during the entire
process Mixed with water, it is fed to
| the grinders by the shoyelful, over and
over, until the grinding is entirely
/ completed. The reason for this is
! evident from the fact that, in using,
the emery becomes ground up and
mixed with the det1ItMs of the granite
and the particles of the iron blocks or
| grinders, and after time is q paSty
mass, losing much of its original sharp
gritiness. If, now, fresh, unused
emery was added, the effect would be
to scratch the half-fnished surface.
When the grinding is finished the
common cast iron grinding blocks are
removed and others are substituted
having their embracing under sides
faced with felt. To these is fed the
ordinary marble polish of oxide of tin
and water until the surface of the
column shines like glass and reflects
like mirror. The entire time required
to polish granite columns--dependent
on the exactness of their chiseling-is
from forty to fifty hours, diameter and
length making but little change, as the
work is Simultaneous and the surface
speed constant. Scientific Ansericon.