Improvements in Friction Catches.
Year: 1890

page_text: Date of Application, 29th Apr., 1890-Accepted, 31st May, 1890.
COMPLETE SPECIFICATION.
Improvements in Friction Catches.
I, JAMES YATE JOHNSON of 47 Lincolns Inn Fields in the County of Middlesex,
Gentleman do hereby declare the nature of this Invention (which has been communi-
cated to me from abroad by Wilfred Lewis, of Philadelphia, Pennsylvania United
States of America) and in what manner the same is to be performed to be
particularly described and ascertained in and by the following statement : —
This Invention relates to that class of machinery in which one part of a mechanism
is driven intermittently in a given direction by another part having a reciprocating
motion, and for which purpose a ratchet is commonly employed. In such devices,
the driving and "driven members are automatically connected by an engaging‘pawl
when motion takes place in one direction and disconnected when the motion of the
driving member is reversed.
The engaging pawl may be thrown into action by gravity or a spring, and it is
frequently so devised as to operate in either direction or remain in-operative at
pleasure, according to the position in which it is set. There is no novelty therefore.
in a reversible ratchet, but the ratchet has certain limitations and defects which
render it unsuitable in many cases where ratchets are used. The amount of movement
for the driven member is limited by the number of teeth in the ratchet wheel, but the
smaller the teeth, the weaker they become, so that it is practically impossible to obtain
a very small movement except at the sacrifice of strength and durability. Further-
more, the engaging pawl may not take a full bearing when in action, and the corners
may in consequence, become broken or rounded, ultimately causing failure in the
action of the ratchet. Another inconvenience in the use of this form of ratchet arises
from the difficulty of disengaging or reversing while in the act of driving.
It is an object of this invention to obtain a reversable catch feed of unlimited fine-
ness from a reciprocating part. It is a further object of this invention to be able to
set the catch at any time during a stroke, to cease feeding at the end of that stroke, or
to feed in the opposite direction on the return stroke, and to these ends this invention
consists in the combination of right and left hand helical cam faces on the engaging
member of the catch and corresponding faces of its mate.
It further consists in the
combination of a controlling switch with elastic stops between the engaging member
of the catch and its cam faced mate, whereby either right or left hand cam faces may
be brought into or thrown out of action.
Figure 1 is a plan of a reversible friction catch constructed according to this inven-
tion with one half of the engaging member removed to show more clearly the right
and left hand helical cam faces of its driver.
Figure 2 is an élévation of Figure 1 with one half of the driver and its abutment
collar removed.
Figure 3 is a section on the line "A B, Figure 1, shewing the elastic connection
between the engaging member and its driver, set to make the catch inoperative.
Figure 4 is a partial section on the same line showing the elastic connection set to
feed in the direction indicated by the arrow.
Figure 5 is an end view of the coned sleeve or driven member shown in Figures 1
and 2.
a is the cam faced driver having a reciprocating motion upon its axis. b is the
driven member, having a'coned surface at one end and the abutment collar c at the
other: d is the engaging member between a and b, having right and left hand cam
faces' o o¹ and nn' fitting against corresponding surfaces in a, and a coned friction
surface fitting against b. e is the switch turning in a and forming an abutment
against which the plungers 'f and g in d may act. hand i are springs in d actuating
the plungers and g respectively. k and I are stops on ƒ and g respectively, by which

page_text: their movement under the action of the springs is limited. m is a collar on the rod
to which the catch is required to impart motion.
The driving member a and the engaging member d fit loosely on the sleeve of the
driven member b, and when the right and left hand cam-faces of a and d are in contact,
there is a slight amount of clearance for these pieces between the collar c and the cone
face of b. Now, if the driving member a be rotated in either direction relative to the
engaging member b,it is evident that this clearance will be taken up, and. if the
motion of the driving member be continued, the driven member b; will be forced to
turn with a and d. This is necessary consequence, because the parts must be so
proportioned that the moment of friction between the conical faces of d and bis
greater than the driving moment between the helical faces of a and d.
If therefore the engaging member be free to engage with either of the cam faces o
and n on the drawing member a, the driven member 6 will follow the reciprocating
motion of the driver. On the other hand, if the engaging member is held in a central
position relatively to the driving member, no movement of the driven member can
result, and this relation is established by means of the switch e when set as shown in
Figure 3.
By tightening the nuts and Figure 3, the plungers and g can be drawn away
from the switch e so as to leave clearance sufficient to allow the engaging member to
connect the driving and driven members by the contact of either right or left hand
cam faces and thus cause the driven member to follow the reciprocating motion of
the driver.
By the adjustment of the plungers and g, therefore the catch may become inopera-
tive when set as shown in Figure 3 or it may become operative in both directions.
The purpose to which the catch is applied will in any case determine the adjustment
to be preferred. Ordinarily as a feeding catch the adjustment shown in Figure 3, is
preferable, but as applied to a carpenter's brace it is obvious that the ability to act in
both directions would at times be desirable
When the switch e is set as shown in Figure 4 the plunger fis forced back by the
end of the switch compressing the spring and forcing the left hand cam faces n n¹
on a and d together. At the same time the switch is disconnected from the plunger g,
and the force of the spring i is expended on the stop l. The left hand cam faces n ni
being thus brought together by the action of the spring hit is evident that when the
driving member moves in the direction indicated by the arrow, Figure 4, the engaging
member d and the driven member b will move with it. When the motion of the driving
member is reversed, however, the engaging member is driven only by the spring,
and the pressure exerted therefrom on the conical surfaces of d and being insufficient
to drive the latter, the engaging member simply slips around without effect as desired.
It is evidently possible to turn the,switch e at any time whether the catch is working
or not, as the work of moving it is only that required to compress the spring h or i.
When the switch e is turned in the opposite direction from that shewn in Figure 4,
compressing the spring i, the right hand cam faces, o o' will be brought in contact and
the catch will feed in the opposite direction. It is evident that the essential features
of this reversible friction catch are not limited to the form as shewn, and it will readily
be seen that the functions of the parts designated as driving and driven members can
be reversed. For, example, if.the-feed rod m be driven back and forth, a may be fed
in either direction. The controlling switch,e-might be pivoted in d and the plunger
springs be situated in a without affecting the essential features of this Invention, nor
is it necessary for an elastic connection between a and d to be made in precisely the
manner. shewn.
A great variety of such arrangements might be represented, the essential, features of
which are a controlling switch on one of the members acting against a spring abutment
on the other, to start or stop the motion of the rod.m in either direction. It will also
be observed that the driven member b may be a part of the feed rod m when there is
no occasion to remove the catch from the rod. As already pointed out the successful
operation of-the catch depends upon the moment of friction between band d being
greater than the driving inoment between a and d, and as the co-efficients of friction

page_text: vary with the lubrication and condition of surface, it may sometimes happen that the
friction on the cam faces becomes so great by the adhesion of gritty material as to
seriously interfere with good results. This surface is therefore generally protected by
a covering which is omitted from the drawings for the sake of clearness.
I am aware that singlo acting friction catches designed to drive or feed in one
direction only are known, but the reversible feature under control of a switch as
described is I believe novel.
Having now particularly described and ascertained the nature of my said Invention
and in what manner the same is to be performed I declare that what I claim is :-
1. In a friction catch, a driving member and a driven member in combination with
an engaging member provided with right and left hand helical or cam faces, substan-
tially as hereinbefore described.
2. In a friction catch, the combination of a driving member, a driven member, an
engaging member provided with right and left hand helical or cam faces, and a con-
trolling switch, substantially as hereinbefore described.
J. H. JOHNSON & Co.,
Agents.