Miniature belt grinder

A portable belt grinder having a casing, a drive pulley supported in the casing, a contact pulley mounted on an arm extending from the casing, an endless belt trained about the pulleys and a belt tensioning assembly having a roller eccentrically mounted on a manually rotatable rod, a camming surfaced plunger coacting with the roller and a spring interposed between the arm and the plunger. A cover is pivotally mounted on the casing having an aperture which coacts with a latching button rotatably fixed to the casing and having a vertical axis slightly spaced from the vertical axis of the aperture.

SUMMARY OF THE INVENTION 
The present invention relates to portable belt grinders for use within 
small cavities or restricted openings in sheet metal, castings, forgings 
and the like for deburring and finishing operations wherein an endless 
belt having an outer abrasive surface is extended between a drive pulley 
and contact pulley and, more particularly, to an improved arrangement for 
adjusting the tension of the belt between the two pulleys. 
The present invention also relates to an improved safety cover latching 
arrangement for collective use in combination with such grinders, and for 
use, generally, with other types of grinders as well. As a safety 
precaution, the casing opening of the grinder adjacent the hand held motor 
portion or other operational components thereof contains a protective 
cover to protect the operator from flying debris and the like from the 
abrasive belt as portions thereof move from the contact pulley adjacent 
the work to the drive pulley within the casing. It is important that the 
means for latching the cover to the housing have a relatively long useful 
life in view of the frequent openings and closings of the cover for 
changing the belt or the like. It is, therefore, a feature of the present 
invention to provide an improved latching structure which will permit 
frequent openings and closings of the cover without the necessity of 
replacing the same because of wear. 
Essentially, the latching structure of the present invention comprises a 
button fabricated of a suitable resilient material, removably secured to 
the casing of the hand grinder and cooperates with an opening or aperture 
in the cover for securing the cover in its closed position by snap action 
of the aperture about the resilient button. According to the present 
invention, the button is substantially symmetrical about the vertical axis 
thereof and has a peripherally enlarged lip, only a portion of which 
engages the aperture in the cover at any one time. The axis of the 
aperture is spaced from the axis of the button such that the peripheral 
lip thereof is eccentric to the aperture. In this manner, as the portion 
of the peripheral surface of the button wears due to frequent openings and 
closings of the cover, a new, unworn portion thereof may be brought into 
contact with the aperture by simply rotating the button about its axis. 
Further, the resilient peripheral lip may be enlarged radially to extend 
the useful life thereof and to also accommodate enlargements in the cover 
opening due to wear. 
With belt grinders of the type indicated above it is important to have an 
effective, quick and efficient way of replacing the belt and of adjusting 
the tension thereof for proper operation. To this end, it is an additional 
feature of the present invention to provide, in combination with a belt 
driven portable grinder, means for efficient, simple and rapid adjustment 
of the belt tension, either for belt removal or for optimum operating 
conditions. 
More specifically, the combination of the present invention comprises in a 
grinder having a casing, a drive pulley rotationally supported within the 
casing, a contact pulley spaced from the drive pulley and supported for 
rotation by an arm assembly slidably extending from the casing, a belt 
trained about the pulleys and an improved belt tensioning mechanism 
including spring means for normally biasing the arm to a position of 
maximum extension from the casing and manually actuated means for reducing 
the biasing force of the spring means whereby the arm can be easily 
retracted from its position of maximum extension, wherein both the spring 
means and manually actuated means are supported by a common post 
upstanding within the casing. 
According to a second aspect of the present invention there is provided in 
the combination of a portable grinder having a casing, an opening in the 
casing, a cover, for closing the casing opening, pivotally supported by 
the casing, an aperture in the cover, the improvement comprising; 
substantially symmetrical latching means removably supported by the casing 
and rotatable about an axis that is parallel to and spaced from the axis 
of the cover opening whereby only a portion of the periphery thereof 
contacts the opening as the cover is closed. 
It is to be understood that the latching means may be a component of the 
grinder in combination with the belt tensioning mechanism or, 
alternatively, a component of other types of grinders having covers 
enclosing portions of the interiors thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings in detail, a tool modified in accordance with 
the present invention is generally depicted at 10 and is shown as having a 
casing 12 and an associated power source, such as a pneumatically operated 
motor 14, which may be gripped by the hand of an operator for manipulation 
of the tool. Motor 14 may have any suitable shutoff or speed control, such 
as that afforded by pivotally supported lever 16, which is adapted to be 
squeezed by the hand of an operator during use. However, it will be 
understood that the invention to be described hereinbelow is not limited 
to the use of a pneumatically operated motor or the specifically 
illustrated design of casing 12. Thus, as by way of example, the operating 
motor may be electric and housed within a casing having a pistol-like hand 
grip. 
A drive pulley 18 is located in casing 12 and driven by motor 14 for 
rotation about a substantially vertical axis, as viewed in FIG. 3; pulley 
18 functions to frictionally drive a flexible, endless belt 20 having an 
outer abrasive surface for contacting a workpiece. 
Casing 12 has a forward projecting, generally channel-shaped open end 22 
bounded by a pair of sidewalls 24, defining an upper opening 25, and a 
bottom platform or wall 26 containing a centrally located slot 28 
extending from end 22 to a point short of a central post 30 vertically 
projecting from platform 26, as viewed in FIG. 3. A compound arm assembly, 
generally depicted at 32, slidingly projects outwardly from housing 12 and 
supports a contact pulley 34 for rotation thereof about an axis 
substantially parallel to the rotational axis of drive pulley 18. The 
endless belt 20 is thus supported between pulleys 18 and 34 for 
translational movement thereabout in a well known manner. 
The arm assembly 32 is formed of two sections; a longitudinally extending 
forward section 32a supporting the pulley 34 and a rearward section 32b 
fitted into the casing and projecting slightly therefrom. Section 32a is 
fitted within bifurcated ends 32c of section 32b and adjustably secured 
thereto by means of a fastening device 36 spanning the surfaces of the two 
sections. A spring 38 is located between sections 32a and a ledge 32d of 
section 32b for normally biasing them away from each other. This 
arrangement is generally similar to that disclosed in prior U.S. Pat. No. 
3,823,513 for the purpose of adjusting the effective relative tilting of 
the contact pulley supporting section for controlling tracking of 
non-uniformly worn belts. 
Turning now to a description of the belt tensioning mechanism of the 
present invention and with specific reference to FIGS. 3 and 4, it can be 
seen that rearward arm section 32b has a guide member 40 depending 
therefrom for coaction with slot 28 for limiting translational movement of 
the arm between the limits imposed by the casing end of the slot and a pin 
42 located at the other end thereof; and for constraining rotational 
movement of the arm. Between these limits the arm can slide about a 
generally tubular support or guide rod 44 fitted at one end into a coaxial 
blind bore 46 in the arm section 32b; the other end of which being fixedly 
secured within casing post 30 by fastening means 48. A tension plunger 50 
is slidably received in bore 46 and is of generally cylindrical 
construction having one end in engagement with a compression spring 52 
that is interposed between this end and a spring plug 54 in abutting 
contact with the bore 46. The other end of plunger 50 terminates in a 
substantially V-shaped transverse camming surface 56. Coacting with 
camming surface in contacting relation therewith is a roller 58, supported 
by a pin 60 projecting eccentrically from the central axis of a rod 62 
which passes through, and is supported for rotation by, a bushing 64 that 
is fixedly secured within a throughbore 66 in casing 12 adjacent the drive 
pulley 18. A tension lever 68 is suitably affixed to, and perpendicularly 
disposed in relation to, an end of rod 62 that projects from the bottom 
surface of the casing, to facilitate rotation of the rod by the hand of an 
operator. A resilient material dust seal 69 or the like may surround the 
outer surface of bore 46 and support rod 44. 
The operation of the belt tensioning mechanism should be readily apparent 
from the foregoing description thereof. More specifically, in the solid 
line position of the roller 58 it can be seen that the plunger 50 exerts 
maximum force on the spring 52 which, through spring plug 54, causes 
maximum extension of arm assembly 32 and contact pulley 34 for applying 
maximum tension to the belt 20. As the roller 58 is moved to the dotted 
line position in FIG. 3 by counterclockwise rotation of actuating lever 68 
and rod 62, the roller rides out of contact with the longitudinal center 
of the V-shaped depression of surface 56 to thereby permit the same to 
move closer to the casing 12 under the biasing pressure of spring 52, 
which causes the tension on belt 20 to be relieved by reducing the bias of 
the spring. After substantially 180 degrees of movement of the roller 58, 
it again assumes a rest position in the center of V-shaped surface 56; 
this being the position of minimum bias on spring 52 and, accordingly, the 
minimum belt tension position whereby the arm can be easily retracted 
towards the casing and the belt 20 can be quickly and easily removed and 
replaced. 
Referring now to the second aspect of the present invention wherein an 
improved latching means is provided for the miniature tool grinder and 
referring, more particularly, to FIGS. 1, 3 and 5 the casing 12 is 
provided with a pivotally mounted cover or safety shield 70 which, in the 
closed position thereof, rests on side walls 24 of the casing and closes 
upper opening 25, to prevent flying debris, grit or the like from injuring 
the operator. Cover 70 has an aperture 72 therein which in its closed 
position coacts with a latch means 74 removably secured to the casing post 
30 adjacent the fastening means 48 thereon. Latch means 70 may 
conveniently take the form of a resilient material button having an 
enlarged diameter central section 76 defining an annular lip or the like 
which is symmetrical about a vertical axis thereof, as viewed in FIG. 3. 
As depicted in FIG. 5, it is important to note that this axis of the 
button is parallel to, but slightly spaced from, the central axis of 
aperture 72 which thereby provides an eccentric relationship between the 
aperture and the lip. Because of this relationship, only a portion of the 
lip contacts the cover opening as the cover is snapped thereover into its 
closed position. As illustrated in FIG. 3 the button is secured to the 
post 30 by means of a screw 78 and is rotatable about the shank portion 
thereof. Thus, it should be readily apparent that as the portion of the 
lip which contacts the cover opening wears to the point where it can no 
longer function to securely latch the cover in place, it is a relatively 
simple matter for the operator to rotate the lip about the shank of the 
screw to provide a new unworn peripheral surface thereof for contacting 
the aperture of opening. Further, since the button is fabricated of a 
resilient material the lip can be enlarged in diameter by tightening screw 
78 to thereby cause a bulging out of the lip. In either case, the life of 
the button is significantly extended. Moreover, in the event that opening 
72 enlarges due to wear, the enlarged lip can still coact therewith. The 
cover 72 may be fabricated of any suitable material such as metal or 
plastic that is less resilient than the button. 
Although a preferred embodiment of the present invention has been disclosed 
and described changes will obviously occur to those skilled in the art. 
For example, the belt tensioning mechanism and the latching means could 
obviously be applied to a grinder wherein a single pulley supporting arm 
is employed instead of the specific compound arm described. Further, the 
latching means can be applied to other types of grinders. It is therefore 
intended that the present invention is to be limited only by the scope of 
the appended claims.