The St. Charles herald. [volume] (Hahnville, La.) 1873-1993, 1883-11-03

utlu uppurteuduceS are required. Inc
head-stock is furnished, like that Of the
ordinary back-geared lathe, with q 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 column
under process of grinding and polishing
being from 230 TO 240 feet per minute,
giving to a twelve-inch column about
seventy-seyen turns per minute and to
q thirty -inch column about twenty
five turns per minute.
To center and swing u column in the
lathe the stone has a square recess cut
in each end, into which is fitted q block
of cast iron with round hole through its
center, The place of this block is found
by means of a 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 it is on an, iron
shaft, from the circumference, The iron
block is secured in place by running
of Babbit metal, or similar unshrink-
ing compound, around 1t. 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 n lug
or dog on the face plate engaging with
one seated in the end of the column.
Back of the lathe is a wall of plank
against which rest the ends of num-
Der 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 conceived 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 the
column. These blocks are arranged
closely side by side; and when the col
hmn 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
shovels beach sand and water on the
revolving column, the blocks with their
concaye faces acting as grinders, Just
us the hinge clamps of the machinists
are used in polishing u 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 is used
VfNatn MI AhC lassAt
chisel marks are taken out, and the
surface shows 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 pound
to every superficial foot; thus column
of ten feet in length by three feet Diane
ter ninety superficial would re-
quire from forty-five 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 shovelful, over and
over, until the grinding is entirely
completed The reason for this Ia
evident from the fact that, in using,
the emery becomes ground up and
mixed with the detrttUs of the granite
and the particles of the iron blocks or
grinders, and after time is n pasty
mass, losing much of its original sharp
gritiness. If, now, fresh, unused
emery was added, the effect would be
to scratch the half-finished surface.
h When the grinding is finished the
c,s,9lnon cast iron grinding blocks are
Lteau;Sed and others are substituted
ndFin es-theit. srn hr.a ,,inor midas a;,laa
faced wiz felt n these H. fod 9i th',
ordinary mssble nolisb Of OXIDE Of tin lin
' an,',n "' sl,;noN the surface of the
i;Ilo s,,;,s.or ' RE glass and reflects
to polish granite c6o co., s'in Sa ,eau,rea
on the exactness Of en-. ch;SdP; unpeiis
from forty to fifty hours, = n,'s,a1 m,S
length making but little cliso o. 1 tho
work is simultaneous and tEe, "s tno
speed a constant. Scientific 4tsur r..
. hsS'eses