The Saint Paul globe., 1897-09-06

with a vertical bar as to admit Of three
separate rotary motions in three planes
at right angles to each other, with
other motions, all movements exact and
readily controllable. By these contri-
vances, the desired plane of section,
previously marked around the specl-
men. can quickly be brought into paral-
1elisn with the plane Of reference. This
adjustment is made by the assistance of
a 'Starret's surface gauge, as it stands
upon the table with its index-point
set at the exact height above the table,
at which the edge of the cutting-disk
should be.
ga cutting-disk-gu guide is rendered
necessary by the fact that the thin
metal disks charged with diamond pow
der at the edge, which are used IN
the cutting. cannot of themselves hold
to a true level, at least If more than
three or four inches in diameter. The
cutters guide is solid movable frame,
carrying two swinging adjustable horl-
zontal arms, one beneath, and the other
above the cutting disk; each arm car
ries three or more adjustable steel
wheels properly adjusted to the correct
height above the plane of reference by
the Starret's gauge, which hold the cut
ting-edge to it's true level as they re-
treat before the advancing specimen
during the cutting.
mo novel features have been applied
as yet to the cutting-disk in this ma
chine, though the latest, most pefnla-
nent. and best form of it is used.
"By these contrivances any ordinary
specimen may be very smoothly cut
In any desired plane, very exactly for
planes of ten and twelve square 1nches
surface. Since all these thin cutting
disks of large size Gen to twelve inches
diameter) are warped by use, and since
the cutter guide can only correct
thoroughly that portion of the warped
disk which is outside of the specimen,
larger surfaces can be cut with only
approximate and tolerable accuracy sun-
til the cutting-disk can be improved,
as it is hoped that it can be. How
ever, sections of from thirty to sixty
square inches of surface have been
cut with tolerable accuracy.
For cutting these sections, the pro
cedure is as follows: First, cut is
made across the specimen in the re-
quired plane by the method above de-
scribed. One of the faces thus obtained
is polished and cemented to a slip OF
glass of suitable dimensions, and
larger than the section. This glass
slip is set into a specially constructed
wooden clamping block which is then
locked firmly in the jaws of the OBJ
ject-holder.
"The upper surface of the glass slip
is now brought into exact parallelism
with the upper surface Of the table.
This may be done by the use of Star
ret's gauge, or preferably and more
rapidly, by a spirit-level which is sup
ported by a specially contrived level
ing-tripod' which stands upon the sur
face of the glass slip. This adjust
ment having been made, the object
holder must be raised until the glass
slip is brought to a slight distance be-
low the cutting-disk. This distance is
exactly determined by the insertion of
a gauge called a thickness-g -guage.
''1vhe requisite pressure is then ap-
piled to the object-holder and water
of fabrication is turned on. AS the
cutter makes its way through the
specimen, it leaves a thin film or
section of the latter on the surface
of the glass. This section may be
from 1-5O to 1-100 of an inch in thin
ness as cut, and may be transparent,
but there is no advantage in cutting 1t
so thin. 1t is generally preferable TO
cut the section somewhat thicker, and
then grind it down to the exact de-
gree of thinness which under the
microscope will best show it's struc-
+ure, since in any case this final grind
ing must always be done.
s'There are a number Of accessory
nieces of apparatus for extending the
capacity of the machine and facllltat-
ing it's work. One of the most impor-
tant' is an. arrangement by which the
pressure of the specimen against the
cutter can be increased at will, as the
cutter penetrates the larger specimens
and the friction increases. Another
accessory, of industrial rather than
scientific value, can be attached to the
cutter-guide, and would enable it to
guide several cutting-disks arranged
in gang one over another, and all
cutting strictly parallel kerfs. By this
arrangement several slips or tablets,
from one-eighth to one-sixteenth of an
inch thick, could be cut in one opera
ton from a piece of ornamental stone
as onyx, lapis 1azuli, etc. Moreover
a pile of such slips or tablets, tempo