Among the newer devices for ornamental turning, must be mentioned the
rose cutter frame of Holtzapffel and Co., an ingenious adaptation
of the principle of the rose engine, without the drawback of
cumbersomeness and costliness. It works like the ordinary eccentric
and other cutters by a cord from overhead motion. The apparatus is
represented in Fig. 290, and its various parts in Fig. 291, &c.
[Illustration: FIG. 290.]
[Illustration: FIG. 294.]
[Illustration: FIG. 291.]
[Illustration: FIG. 293A.]
[Illustration: FIG. 293B.]
In the first of these figures, A is the shank, fitting the receptacle
of the slide rest, and drilled to receive a hardened spindle, at one
end of which is a worm wheel, turned by tangent screw B C, and shown
again at A, B, C, Fig. 292. By this are turned the parts beyond K,
namely, the frame D, carrying the tool, as in the eccentric cutter,
adjacent parts S, representing chamfered bar, P, back plate, and
O, which is a round piece in one casting, with the back plate, and
having a hole through it for the coiled spring seen between O and N.
All these are secured to the spindle, and turn together as one piece
with it. Fig. 291 is a front view of these parts. H is the back plate
of brass, with steel chamfered bars on its face, E, E, as in the
eccentric chuck. Between these slides the plate, D, D, to the face
of which is attached the long steel frame, carrying the tool holder.
Close to the letter H, it will be noticed that a slot is cut in the
back plate, through which projects a hard steel pin, screwed into
the back of the sliding plate. This is seen at O, Fig. 290, and is
attached to one end of a coiled spring, the opposite end of which is
secured to a pin fixed in the back plate of this part. The pin O, is
thus kept in contact with the edge of the rosette or pattern plate,
K, and, as the whole turns with the spindle while the rosette is
fixed, the pin, or rubber, is compelled to follow the undulations of
the pattern, the motion being, of course, communicated to the tool.
An inspection of Fig. 294 will show the arrangement of the parts on
which the rosettes are fixed, and which is capable of turning, but
does not, unless the tangent screw and wheel, H, are brought into
requisition, as will be presently explained. The end of the main shank
of the instrument is round, as seen at C, the worm wheel B being
screwed fast, by four small screws, to the end of the square part of
the shank. Upon this rounded end fits what may be called the sleeve
E, to which is fixed the tangent screw, and on which also are placed
the rosettes. The latter have a large central hole, Fig. 293, A and B,
and fitting closely beyond the screw F, F, of the sleeve, and, being
prohibited from turning upon it by a small key or feather, are secured
by a screwed ring or ferrule seen at L, Fig. 296, the edge of which is
milled. At F, Fig. 291, is seen a short stop, or set screw, the head
of which is divided into ten degrees. By this, the rubber is prevented
from penetrating to the bottom of the undulations on the edge of the
rosette, and, if it is allowed only just to touch the summits of them,
the tool will cut a circle. Thus, as the screw stop can be accurately
set, one rosette will produce at pleasure graduated waved lines, the
waves growing less and less undulated as the centre (or circumference)
of the work is approached, giving a most delicate and chaste pattern,
and _chased_ it certainly is.
Another variation of the pattern producible from any rosette results
from the frame of the tool holder being extended beyond the axis
of the spindle in both directions. When the tool is on that side
of the axis nearest to the rubber pin, the undulations of the
rosettes will be so followed as to produce their exact counterpart
on the work. When the tool-holder is on the other side of the axis,
the undulations become reversed, the raised parts of the rosettes
producing hollows and _vice versa_. It may here be mentioned that in
the case of the rose cutter, eccentric, and universal cutter, and
similar apparatus, the screw heads carry ten chief divisions and ten
smaller divisions. The screws are cut with ten threads to the inch,
so that one turn advances the slide, or the tool, or wheel as the
case may be, one-tenth of an inch. One large division, therefore,
produces a movement equal to one-hundredth, and one small division one
two-hundredth of an inch. If the screw is small it is generally cut
with a double thread equal to one-twentieth of an inch. It is evident
that in addition to the movements of the various parts of the rose
cutter, the turner also has in his power those of the slide rest, and
of the division plate on the lathe pulley, by one or both of which
further complications become possible. Six modifications of pattern
produced from one rosette alone are shown in Holtzapffel and Co.'s
catalogue, and these may be further multiplied according to the taste
and skill of the operator.
It is not possible to apply rapid movement to this rose cutter, else
the rubber would probably miss touching the rosette in places; hence
the tangent or worm wheel is used to give motion to the central
spindle. An end view of this is given in Fig. 292. The object of the
other tangent screw is, to move the sleeve and therewith the rosette
at pleasure, so that the higher parts of the undulations in the second
cut may, if desired, be arranged to meet the lower parts of the same
in the first cut or to fall intermediately. The effect of the gradual
shifting of the rosettes in this way is perfectly marvellous, and the
writer much regrets that he is unable to supply specimen plates, as he
is not in possession of the rose cutter. In the end of Holtzapffel's
latest edition of his catalogue are several such specimens, but
without any drawing or description of the instrument, the cost of
which is moreover omitted.
[Illustration: FIG. 292.]
The centres of circles cut by this eccentric tool will be always
regulated in regard to position by the slide rest, because these
centres are, as explained, always in a line with the centre of the
spindle. Hence, to place a circle in any desired position, it is only
necessary to determine its centre, and, after drawing back the tool by
means of the screw till its centre runs truly as a mere drill, turn
the screw of the slide rest until the point touches the required spot.