Safety Feed Apparatus for Rotary Drills and similar Rotary Working Machines.
Year: 1893

page_text: Date of Application, 14th Dec., 1893
Complete Specification Left, 31st Aug.. 1894-Accepted, 6th Oct., 1894
[Communicated from abroad by Messrs. SIEMENS & HALSKE, of Berlin, in the
German Empire, Electrical Engineers.]
Safety Feed Apparatus for Rotary Drills and similar Rotary
Working Machines.
We, SIEMENS BROTHERS & Co. LIMITED, of 12 Queen Anne's Gate, West-
minster, in the County of Middlesex, Electrical Engineers, do hereby declare the
nature of this invention to be as follows:-
The automatic advance of the operative mechanisin in rotating working machines
such as rock drills and the like, can under certain circunstances be liable to
produce dangerous or detrimental action, as for instance in the case of rock drills,
when the drill suddenly meets with a portion of the rock which is harder than that
through which it has passed, whereby the continuance of the automatic forward
feed at the same rate as before may produce a detrimental pressure in the direction
of the longitudinal axis. It is therefore necessary with such automatic feed
apparatus to provide means whereby the feed may be automatically diminished to a
corresponding extent under the above named circumstances.
The present invention relates to an improved automatic feed mechanism whereby
the feed is capable of automatic regulation in so perfect, simple and reliable a
manner as to render the effectiveness of the drilling operation entirely independent
of the attention or skill of the operator.
For this purpose, according to an arrangement suitable for drilling soft stone or
mineral, the drill spindle of the machine receives rotary motion from a motor
engine through a transmission shaft and a pair of bevil wheels, of which the driven
one is fixed on a cylindrical sleeve through which the drill spindle passes the
sleeve having a feather entering a longitudinal groove in the spindle so as to carry
the same round with it, while at the same time the spindle is free to slide longi-
tudinally through the sleeve. On the rear end of the sleeve is fixed a spur wheel
which imparts motion through suitably proportioned intermediate gearing to a spur
wheel fixed on a nut through which the threaded rear end of the drill spindle
screws, so that by the rotation of such nut, which is held in the framing so as to be
prevented from longitudinal motion, the advance of the drill spindle at a definite
rate is effected, such rate depending upon the pitch of the screw thread and the
difference between the speed of rotation of the drill spindle and that of the nut.
In such advancing motion the longitudinal pressure to which the drill spindle is
subjected is transmitted by suitable ball bearings to the framing of the machine.
The said intermediate toothed gearing for transmitting the rotation of the sleeve
to the nut consists by preference of two spur wheels of different diameters on
one and the same spindle, of which wheels the larger one gears with the spur
wheel on the sleeve while the smaller one gears with a larger wheel on the nut.
These two transmission wheels are not both fixed on their spindle the one gearing
with the nut being loose, but pressed with a frictional surface against a corre-
sponding surface of the other wheel by a strong spring, so that the last named
wheel carries the first named one round by frictional contact, which is capable of
accurate regulation by the regulation of the compression of the spring.
Thus when the resistance offered to the advance of the drill spindle exceeds a
certain limit determined by the degree of frictional contact between the two
transmission wheels these will slide to a greater or less extent upon each other and
consequently the rotation of the nut and the advance of the drill spindle will be

page_text: retarded. Should the resistance to the advance of the drill spindle be such that
its advance is entirely stopped then the slip between the two transmission wheels
will be increased to such an extent as to cause the nut to rotate with exactly the
same speed as the drill spindle so that the screw action ceases.
By suitably proportioning the pitch of the screw thread of the drill spindle and
its nut to the ratio of the transmission gear the frictional work and consequently
the wear of the parts can be kept within moderate limits.
It will be seen that by suitably adjusting the pressure of the spring the above
described safety device may be made to enter into action on a definite longitudinal
pressure to which the drill spindle is subjected being exceeded, so that by effecting
such adjustment at the commencement of a drilling operation no subsequent
adjustment during the working will be necessary.
In the above described safety device the helical pressing spring is mounted upon
the spindle of the two wheels and is made to rotate with the loose wheel, being
made to press with its one end upon a sliding sleeve on the shaft which sleeve bears
on such wheel while the other end of the spring bears against a disc mounted loose
on a spindle and bearing against an adjusting screw nut screwed on the threaded
end of the shaft and consequently revolving therewith.
Should it be desired to be able to adjust the device while the drill is at work,
this can be effected by rendering the spring and its adjusting screw nut stationary,
for which purpose the spindle on which the one wheel is fixed is made separate
from the threaded spindle or stem on which the screw nut and spring are mounted,
this stem being fixed and having a socket end into which the end of the revolving
spindle takes. The sliding sleeve on which the inner end of the spring bears is in
this case also stationary and is made to bear on the loose wheel through an
intermediate ball bearing. The thrust to which the other wheel is subjected by
the spring may also be taken by ball bearings.
Dated this 14th day of December 1893.
ABEL & IMRAY,
Agents for the Applicants.
COMPLETE SPECIFICATION.
Safety Feed Apparatus for Rotary Drills and similar Rotary
Working Machines.
We, SIEMENS BROTHERS & Co. LIMITED, of 12 Queen Anne's Gate,
Westminster, in the County of Middlesex, Electrical Engineers, do hereby declare
the nature of this invention and in what manner the same is to be performed to
be particularly described and ascertained in and by the following statement :-
The automatic advance of the operative mechanism in rotating working machines
such as rock drills and the like, can under certain circumstances be liable to
produce dangerous or detrimental action, as for instance in the case of rock drills,
when the drill suddenly meets with a portion of the rock which is harder than
that through which it has passed, whereby the continuance of the automatic forward
feed at the same rate as before may produce a detrimental pressure in the direction
of the longitudinal axis. It is therefore necessary with such automatic_feed
apparatus to provide means whereby the feed may be automatically diminished to a
corresponding extent under the above named circumstances.
The present invention relates to an improved automatic feed mechanism whereby
the feed is capable of automatic regulation in such a manner as to render the
effectiveness of the drilling operation entirely independent of the attention or skill
of the operator.
The said invention as applied to a rotary drill suitable for working in soft stone,
is shewn on the accompanying drawing in which
Figure 1 shews a longitudinal section, Figure 2 shows a cross section at X X and
Figure 3 shews a modification.
.

page_text: In this arrangement a rotary motion is imparted from a separate motor, such as
an electromotor through a flexible or other shaft to the shaft of the bevil or
wheel R', which gears with the bevil wheel R' on a tubular shaft W that imparts
its rotation to the drill spindle S through a groove and feather, in the known
manner. On the front end of shaft W is fixed a spur wheel R³, which gears with
a wheel R fixed on the shaft a, loose on which is another spur wheel R'; this
wheel in its turn gears with a wheel R that is fixed to the screw nut M which
effects the advance of the threaded drill spindle S, the differential motion between
the nut M and spindle S for effecting such advance being produced by the relative
proportions of the wheels R³, R*, R, R, while the speed of advance is dependent
upon the pitch of the screw threads.
The pressure on the nut M in the axial direction due to the feed is taken by ball
bearings as shewn.
The wheel R is not fixed to the shaft a of wheel R*, but is carried round thereby
by the frictional contact between the annular surfaces r, R' being pressed against R*
by a helical spring F, the pressure of which is rendered adjustable for regulating
the degree of frictional resistance by a screw nut f. The pressure of F is trans-
mitted to R through a disc s, sliding with a groove and feather a¹.
The action of the apparatus is as follows:-
upon
The above metioned relative motion between M and S is opposed by the axial
pressure and the friction produced thereby between the threads of S and M.
When the sum of such pressure and friction exceeds a certain amount, a decrease
of the relative motion between S and M and a relative motion between R and R³
corresponding to such decrease will take place so that an equilibrium will be
established between the sum of the moments of the axial pressure and friction
between S and M on the one hand and the moment of friction between R* and R³,
on the other hand.
Any further increase of the axial pressure in S will cause a further decrease in
the relative motion between S and M and an increase in the relative motion
between R and R. In the event of such a resistance being opposed to the drill
that this ceases altogether to advance, then the relative motion between S and M
must cease altogether, so that they revolve at the same speed, and in consequence a
differential motion must take place between R and R equal to that due to the
proportions between their respective diameters and those of the wheels R' and R*
which then revolve at the same angular speed.
By suitably proportioning the pitch of the screw threads, and the relative
diameters of the toothed wheels, the friction between the wheels R' K' resulting
from such relative motion, and the consequent heating and wear of the contact
surfaces, can be kept within allowable limits.
By a correct adjustment of the spring F the above described action may be so
regulated that the safety feed mechanism will begin to act as above described when
a certain highest allowable degree of axial pressure is attained.
The adjustment can be made once for all for certain conditions of working, and
does not therefore require to be varied during the working. It can be effected
by a superintendent before the commencement of drilling, so that the workman
attending to the machine can work safely without requiring to attend to the
adjustment.
Should however it be found desirable to allow of the adjustment of the safety feed
apparatus during the drilling operation, the modification shewn at Figure 3 may be
employed in which the spring F is not carried by and rotate with the shaft a (as at
Figure 1) but is carried by a fixed bolt b which forms a bearing for the end of the
shaft a the spring F and nut f being thus kept stationary. In this case the front
end of the spring does not bear directly upon the disc s, which as in Figure 1
rotates with shaft a, but upon an intermediate disc z which can slide on b with
groove and feather, and which bears on s with ball bearings. In this case also ball
bearings are shewn provided between the wheel R' and the casing for taking the
thrust of the spring F with a minimum friction.

page_text: Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed we declare that what we
claim is :-
1. A safety feed apparatus for rotary drills and similar rotary machines wherein
a tubular shaft such as W receiving motion from a motor, and imparting the same
through a groove and feather to a threaded drill spindle such as S, is made to
impart a differential motion to the advancing nut M of the drill spindle through
toothed gearing with adjustable frictional coupling so arranged as to automatically
allow of a reduction of the relative motion between the screw spindle and the nut
on the occurrence of excessive axial pressure, substantially as described.
2. In safety feed apparatus such as is referred to in the first claim, imparting
rotation to the advancing nut M from the tubular sleeve W through toothed
gearing R R R R*, of which R' is kept in frictional contact with R by an
adjustable spring F which is either made to rotate with the shaft a of wheel R, as
at Figure 1, or is kept stationary as at Figure 3, so as to be capable of adjustment
during working, substantially as described.
Dated this 31st day of August 1894
ABEL & IMRAY,
Agents for the Applicants.