Belt guard lock

A belt guard lock for a belt guard pivotable on a pivot shaft affixed thereto and supported in a pivot frame attached to the sewing machine table, which guard lock effectively prevents pivoting of the belt guard by a sewing machine operator but may be readily defeated by a suitably authorized maintenance man. The guard lock fits about the pivot shaft affixed to the belt guard and remains therewith, so as to be available for use in any machine to which it is attached. The guard lock is implemented by a collar slidable on the pivot shaft and having a flange thereof which extends between the lower edge of the belt guard and the sewing machine table to prevent rotation of the belt guard. The belt guard lock may be rendered ineffective by loosening a special set screw inpinging on the pivot shaft and sliding along the pivot shaft to a position where the flange thereof is aligned with a slot in the belt guard to accommodate the flange during pivoting motion of the guard.

BACKGROUND OF THE INVENTION 
This invention is in the field of sewing machines; more particularly, it is 
concerned with a device which prevents removal of a belt guard without 
some initial deliberate act designed to alert a person to the potential 
for bodily harm and deter removal by unauthorized persons. 
Belt guards have been used with sewing machines for many years for the 
purpose of protecting a sewing machine operator and other persons from 
injury due to entrainment of clothing or physical entanglement with moving 
parts of the sewing machine. An early form of sewing machine belt guard is 
shown in the U.S. Pat. No. 947,651 issued on Jan. 25, 1910 to Schreiber 
and discloses a belt guard which covers the handwheel end of a sewing 
machine in such a fashion as to permit limited access to the handwheel for 
rotation thereof, but cover a belt and pulley portion thereof to protect 
an operator against the dangers recited above. The belt guard disclosed in 
the above patent is fastened to the sewing machine bed with a hook which 
could be removed to swing the belt guard away for access to the belt, but 
the belt guard is available for protection during operation of the sewing 
machine when the operator's attention was diverted elsewhere. 
A more recent belt guard is disclosed in the U.S. Pat. No. 2,790,407, 
issued on Apr. 30, 1957 to Andres, which discloses a belt guard pivotably 
carried by a fixture attached to a sewing machine table, which belt guard 
was suitable for use with a variety of sewing machines which might be 
installed in that specific table. In a most recent prior art belt guard, 
predecessor to this invention, the belt guard itself is provided with a 
pivot rod extending between ears thereof, the pivot rod being slabbed on 
opposite sides thereof on the extremities adjacent the ears of the guard. 
A pivot frame was provided with lugs upstanding adjacent the ears of the 
belt guard, the lugs having slots therein extending to apertures which fit 
about the pivot rod. In operation the belt guard could be rotated until 
the slabbed portions of the pivot rod align with the slots in the pivot 
frame permitting access of the pivot rod to the apertures in the 
upstanding lugs. Thus, the belt guard could be removed rather readily for 
service by swinging back the belt guard until the slabbed surfaces were 
aligned with the slots in the pivot frame and removed therefrom. 
Unfortunately, the ease of removal of the belt guard contributed to 
frequent operation of the sewing machine without the belt guard due to 
removal thereof by the sewing machine operator. 
What is required is some means for preventing ready removal of the belt 
guard from the sewing machine by a sewing machine operator, but retain 
this ease of removal feature for a maintenance or repair person. 
SUMMARY OF THE INVENTION 
The above desired end is achieved by the addition of a collar encircling 
the pivot rod of the above-mentioned most recent prior art belt guard, the 
collar having a flange extending between the belt guard and the table top 
so as to prevent rotation of the belt guard on the pivot rod. The position 
of the collar may be locked by a special socket screw since a special 
wrench is required for manipulation of the screw, which special wrench is 
not generally available to a sewing machine operator. A slot is provided 
on the end of the belt guard adjacent the upstanding lug of the pivot 
frame, the slot being of a sufficient width to accommodate the flange 
attached to the collar. By loosening of the special socket screw and 
positioning of the collar and flange adjacent the upstanding lug of the 
pivot frame, the belt guard may be rotated to where the slabbed sides of 
the pivot rod align with the slots in the pivot frame to permit removal 
therefrom. Removal of the belt guard from the pivot frame brings with it 
the collar and flange thereby ensuring that a belt guard reinserted on the 
sewing machine would be provided with its locking device. Retrofitting of 
sewing machines having a belt guard without a locking device is 
accomplished rather readily by installing a belt guard lock on the pivot 
rod thereof.

Referring now to FIG. 1 there is shown a rear perspective view of a sewing 
machine 10 one end of which is covered by a belt guard 12 for safety of a 
sewing machine operator from the belt 17 extending about the handwheel 
pulley 15 of the sewing machine down to the sewing machine motor 11 
supported below a sewing table 14. The belt guard 12 is formed with ears 
16 on both sides of the rear extremity thereof, which ears support a pivot 
rod 18 extending therebetween (see also FIG. 2). The pivot rod 18 is 
fashioned with slotted end 19 to permit rotation of the pivot rod to a 
selected position which may be locked by means of a set screw 20 extending 
through one ear (see FIG. 3). The pivot rod 18 is further fashioned with 
slabbed sides 21 180.degree. apart on the rod and spaced close to the ends 
thereof for a purpose which will be described below. 
The sewing table 14 supports thereon a pivot frame 24, which pivot frame 
may be fashioned of sheet metal. The pivot frame 24 includes two 
upstanding lugs 25 on the ends thereof, which upstanding lugs include 
aligned apertures 26 extending therethrough. Slots 27 in the upstanding 
lugs 25 provide access to the apertures 26, the slots being of such a 
width as to accommodate the slabbed sides 21 of the pivot rod 18 which are 
spaced apart so as to be aligned with the upstanding lugs. Thus, the pivot 
rod 18 is rotated in the ears 16 of the belt guard 12 by means of the 
slotted end 19 so that the slabbed sides 21 of the pivot rod are not 
aligned with the slots 27 in the upstanding lugs 25 when the belt guard 12 
is positioned in a first position as shown in FIG. 1. However, if the belt 
guard 12 were to be rotated in the pivot frame 24 on the pivot rod 18, the 
slabbed sides 21 of the pivot rod would be aligned with the slots 27 so 
that the belt guard could be withdrawn from the pivot frame. 
However, in order to ensure that a sewing machine operator will not remove 
the belt guard 12 and possibly defeat its purpose by operating the sewing 
machine 10 without the belt guard in position, a means was necessary to 
make it impossible for a sewing machine operator to remove the belt guard 
but not appreciably increase the difficulty of removal thereof from the 
sewing machine 10 by maintenance personnel. In order to accomplish this 
objective a lock 30 is provided as is shown in FIG. 2, which lock includes 
a collar 31 encircling the pivot rod 18. A set screw 32 is threadedly 
carried by the collar 31, the set screw bearing against the pivot rod so 
as to lock the collar in a selected position. Ideally, a type of socket 
set screw is selected since a special tool is required for removal 
thereof, a tool not commonplace or normally available to a sewing machine 
operator. Alternatively, special heads may be provided for the set screw 
32 which would permit loosening of the set screw only by specially 
provided tools. On one end of the collar 31 there is situated a flange 33 
which extends out from the collar between the sewing table 14 and the 
lower edge 13 of the belt guard which is spaced from the sewing table when 
the belt guard 12 is in the first position. Thus, the lock 30 by 
interposing the flange 33 between the belt guard 12 and the upward facing 
surface of the sewing table 14 prevents rotation of the belt guard. 
Adjacent one ear 16 of the belt guard 12 an extra wide slot 36 may be 
provided to accommodate not only the upstanding lug 25 of the pivot frame 
24, but also the flange 33 of the lock 30. Thus by loosening the set screw 
32 fixing the position of the lock 30 in the central portion of the pivot 
rod 18, the lock 30 may be moved so that the flange 33 is accommodated in 
the space as (see FIG. 3) provided by the extra wide slot 36. With the 
lock 30 thus positioned, the belt guard 12 may be rotated to a second 
position where the lower edge 13 is adjacent the sewing table 14 and the 
slabbed sides 21 of the pivot rod 18 are aligned with the slots 27 in the 
pivot frame, so as to permit removal of the belt guard from the sewing 
machine 10. The belt guard 12 may be as readily reinserted in position on 
the sewing machine 10 and the lock 30 may be positioned as shown in FIG. 3 
and retained in this position by tightening of the set screw 32 to prevent 
further removal of the belt guard 12 by any unauthorized person.