IMPROVEMENTS IN DIFFERENTIAL SCREW APPARATUS
Year: 1866

page_text: PROVISIONAL SPECIFICATION left by Richard Archibald Brooman at the
Office of the Commissioners of Patents, with his Petition, on the 27th
January 1866. A communication from abroad by François Durand
and Paul Baudet, both of Paris, France.
I, RICHARD ARCHIBALD BROOMAN, of 166, Fleet Street, in the City of
London, Patent Agent, do hereby declare the nature of the said Invention
for "IMPROVEMENTS IN DIFFERENTIAL SCREW APPARATUS," to be as follows:-
The object of this Invention is the combination of a double, screw
forming a differential mechanism applicable to presses, punches, breaks, and
other purposes.
The characteristic feature of the Invention is the combination of two
concentric screws of different pitch. The outer screw acts both as a nut to
the inner screw and as a screw working in an outer nut which supports.the
combined screws. One of the screws has a single thread, the other has a very
quick thread, that is to say, three, four, or more threads. The result. of this
arrangement is that under the impulse given by a hand wheel or other appliance
centred on the common axis of the screws the two screws, having at first little
power to exert, commence to descend rapidly according to their combined
actions; when the resistance increases the screw with several threads ceases to
act, and the action is therefore slow, but is capable of overcoming a much
greater resistance.

page_text: It
I proceed to describe the application of this Invention to a press.
consists of a central or inner screw threaded its whole length, and of a hollow
outer screw acting as a nut to the inner screw, and formed externally with a
quick thread which works in a nut in the frame of the press. A lever arm
for working the apparatus is fitted to the top of the inner screw, and the lower
end of this screw carries a plate or pressing appliance free to slide between
the side uprights of the press. Ratchet teeth are formed on the top of the
outer screw, and a paul is pivoted to the press frame. This paul is at a
certain time thrown out of gear by a rod forming part of a collar fixed to the
inner screw by a pressure screw.
The
action is as follows:-Suppose, for
example, the mechanism raised by the action of the lever arm. Owing to the
obliquity of the thread of the outer screw a rapid descent takes place until
this screw is stopped by the ratchet teeth meeting the paul; a shock is there-
fore produced near the object to be pressed, but the force acquired is utilized
by the continuation of the descent of the inner screw with the ordinary thread,
the result of which is to produce a progressive pressure regulated as required
upon the object under the pressing plate. To raise the mechanism the lever
arm is turned in the contrary direction, and the movements take place in the
reverse order. The inner screw alone rises at first slowly, but as soon as a
nut fitted on the inner screw a little below the outer screw meets the
latter the two screws rise together rapidly. During this action the rod
on the collar before mentioned has disengaged the paul from the ratchet
teeth.
In another arrangement instead of the ratchet teeth and paul I employ
an engaging apparatus consisting of a collar on the top of the outer screw
formed on its upper side with teeth, and of a collar fitted loosely on a
shoulder on the inner screw, and formed with corresponding teeth j the
last-named collar is pressed upon by a spring, so that its teeth engage
into those of the other collar. When the inner screw is rising the shoulder
lifts the collar fitted thereon clear of the other collar, so that the outer screw
is free to rise.
Another arrangement, chiefly applicable for working breaks, is composed of
a long inner rod threaded in two different ways. The upper part is formed
with three quick threads, and the lower part with a single slow thread. The
first produces the locking or tightening when the rod is turned from left to
right, and the second when it is turned from right to left. The left-handed
or upper thread works in an outer screw, which is formed with a single thread
and works in a fixed nut or female screw in the frame of the apparatus.
This outer screw acts when the rod is turned from right to left, and it carries
1.

page_text: a shoulder or collar at its upper end. The lower thread of the inner screw
carries a nut or collar threaded internally, on which it acts to tighten the
break blocks, the nut being connected with the rod of the break blocks.
When the inner threaded rod is turned from right to left it meets with no
resistance and rises quickly in the outer screw, drawing the nut or collar with
it, which rises at the same time with a relative movement. This nut is
therefore removed from its original position an absolute distance, which is the
sum of the displacement of the screw and of its own relative displacement
with regard to the screw. But as soon as a great resistance is to be overcome
the inner screw draws the outer screw into its movement, which in turning
descends a short distance; the nut or collar on the inner screw continues to
rise, but in reality it is only raised to an extent equal to the difference of its
own upward displacement on the screw and of the downward displacement of
this screw with the outer screw. This nut being thus displaced slowly is able
to overcome great resistance. When it is required to release the break blocks
the inner threaded rod is turned in the opposite direction; the outer screw
remains in place, the inner rod descending quickly; the nut on the inner rod
during this time is lowered rapidly. The shoulder or collar on the outer screw
limits the movement of this screw, and a shoulder on the upper part of the
inner rod meets a fixed bar or stop, and prevents at the proper time the rod
descending.