Abstract:
A holder for flexible abrasive sheets. An abrasive sheet is gripped by a gripper actuated by a rotationally mounted cam pin that reciprocates a cam plate which pulls an edge of the sheet tightly against a backing surface so it can respond to oscillation of a sander to which the holder is mounted.

Description:
FIELD OF THE INVENTION 
   Mounting of abrasive sheets such as sandpaper and emery paper to a holder which can be manually or mechanically moved to abrade or smooth a surface. 
   BACKGROUND OF THE INVENTION 
   While abrasive sheets such as sandpaper and emery paper are stiffly flexible and are often directly pressed against a surface to be smoothed or suitably abraded, it is more common practice to mount the paper to a holder which can more readily be manipulated, or which can be attached to an appliance that vibrates or orbits it on the surface. 
   This is far from a new concept and the art is replete with examples of useful holders for this purpose. One is entitled to be surprised to learn that there is still room for improvement. 
   It is clear that the prior art provides holders to which abrasive sheets can be attached. Any one of them, once the sheet is applied, can usefully be employed for the same purpose. The problem that remains is getting the sheet on the holder with least effort, least exposure to injury to the hand, and with sufficient retention to resist wrinkling of the sheet and relative in-plane movement between the sheet and the holder during vigorous operation. 
   It is an object of this invention to enable user to take a loose sheet of abrasive material, readily insert it into an opening at one end, and equally readily to insert the other end into an opposite-facing opening and lock both ends in place with the sheet brought tightly against the holder, stressed and ready for use. 
   BRIEF DESCRIPTION OF THE INVENTION 
   A sheet holder according to this invention, while useful with a manual “block”, is principally intended for use as an accessory for a powered sander, which may be vibratory or orbital. 
   It includes a base plate with a flat backing surface having a pair of spaced apart parallel edges. It is intended that a strip or sheet of abrasive material such as sandpaper be wrapped around both edges and drawn tightly so there is no slack in the sheet and it bears tightly against the backing surface. 
   According to this invention, at each edge, supported on and movable on the back side of the holder is a gripper with an engagement lip directed toward the back side of the base plate and adapted to hold and draw the strip. The gripper is movable parallel to the back side of the base plate for this purpose. 
   A rotary actuator mounted to the holder includes a cam system reactive with the gripper, whereby rotation os a handle on the actuator causes the edges of the sheet to be drawn toward each other, tightening the sheet and thereby holding the sheet tightly against the backing surface. 
   The holder can optionally be attached to a block to be held by the hand, or mounted to a powered vibratory or orbital mechanism, often replacing the holder that already may be provided on the mechanism. 
   The above and other features of this invention will be fully understood from the following detailed description and the accompanying drawings, in which: 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exploded view of the holder and sander assembly; 
       FIG. 2  is a side view of the assembly with the sheet loosely engaged; 
       FIG. 3  is a side view similar to  FIG. 2  with the sheet tightly engaged; 
       FIG. 4  is a top view of the holder in the condition of  FIG. 2  with the sheet loosely engaged; 
       FIG. 5  is a top view of the holder in the condition of  FIG. 3 , with the sheet tightly engaged; 
       FIG. 6  is a fragmentary end view of the tensioner; and 
       FIG. 7  is a fragmentary end view showing an alternative embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A holder  10  shown in  FIGS. 2 and 3  mounted to the base  11  of a powered sander  12 . The sander may be of any desired type, for example vibratory or orbital in plane normal to the drawing. 
   Its purpose is to hold a sheet  15  of abrasive material, for example sandpaper or emery paper, to the holder so the sheet will move with the holder in response to forces exerted by the sander. In  FIG. 1 , a hand  16  is shown gripping the sander. If desired, the holder may be used separately from the sander, and directly held. Alternately a block (not shown) may be substituted for the sander to provide a good grip. 
   In  FIG. 2 , the sheet is shown loosely on the holder. In  FIG. 3  the holder has been actuated to draw the sheet tightly to the holder. 
   The holder includes a rigid base plate  18  having a flat backing surface  19  on its lower side. On its upper side there are two parallel strips  21 , 22 . Strips  21  and  22  provide gripping surfaces  23 , 24  adjacent to parallel edge  25 , 26  of the base plate. The edges may be somewhat rounded if desired. 
   Also if desired, a metal shroud  27  ( FIGS. 2 and 6 ) can be wrapped around the bottom of base plate  18  with a central portion  28  bearing against surface  19 . The central portion may be considered part of the backing surface when it is used. 
   Shroud  27  includes springy flanges  29  that overhang gripping surfaces  23  and  24  when the shroud is used, these act as gripping surfaces against which the sheet will bear. 
   A gripper  30 , 31 , comprises a cam plate  32 , 33  axially reciprocable between the upper surface of the base plate and a respective cover plate  34 , 35  ( FIG. 1 ). The cover plates are fixed to the base plate by screws  66  and have an upwardly-turned flange  37  to stiffen the cover plate. 
   Both grippers are identical, so only gripper  30  will be described in detail. Each cam plate has a central portion  40  ( FIGS. 4 and 5 ) with a cam slot  41  through it. The central portion  40  is bounded on two opposite parallel sides by guide surfaces  40   a  and  40   b , that are normal to the gripper edge where the sheet is to be attached. Guide surfaces  40   c  and  40   d  are formed on inner edges of a depression  40   e  ( FIG. 1 ) in the top of the base plate. Guide surfaces  40   c  and  40   d  are parallel to, and closely adjacent to, guide surfaces  40   a  and  40   b , respectively. Guide surfaces  40   c  and  40   d  are preferably part of the cover plate. These cooperating guide surfaces restrain the cam plate to its motion normal to the gripping edge. The cam plate includes a downwardly-directed lip  50 . 
   The cover plate has a lateral slot that permits motion of a cam pin to be described. Stop pins  43 , 44  fixed to the base plate fit in slots  45 , 46  (also normal to the gripping edges) assure that the cam plate will be normal to the edge at the end of its travel, both inwardly and outwardly. Thus, the cam plate is free to move normally to the edge, and is assured to be aligned when opened and closed. 
   An actuator is a centrally mounted ring shaped rotor  51  fitted onto a circular wall  5  for rotation in it. It includes a pair of cam pins  54 , 55 , and a pair of handles  56 , 57 . The handles extend far enough out to be pushed or pulled but not so far as to impede the use of the device. 
   The cam pins extend outwardly from the ring and upwardly into a respective cam slot, and also into the shot in the cover plate. 
   The cam slot includes cam surfaces  60 , 61 , which are engaged by the pin so as to move the cam plate when the actuator ring is turned. 
   The backing surface  19  or the central portion  28  of the shroud will, of course, be rigid for strength and support and the sheet could be brought directly against them. Frequently a stiffly flexible pad  65  ( FIG. 6 ) will be placed directly against the metal surface, and the sheet drawn against the pad. In such event, pad  65  will be regarded as the backing surface, performing the same functions as that of backing the sheet. 
   Mounting screws  66  secure the holder to the sander. They extend through holes  76  in the plate. 
   As best shown in  FIG. 6 , the lower edge of lip  50  is the gripping edge that engages the sheet and draws it over a strip such as strip  23 . The metal strip is quite rigid. Unless some flexibility of the cover plate at the lip is allowed as shown in  FIG. 3 , there must be some dimensional allowance. 
   The shroud can provide for this by its flanges  29 . These flanges are stiffly flexible, and the lip and cam plate can be rigid, because as the lip draws the sheet toward the center, it springly deflects the flange, resulting in a tight grip on the sheet. This is the preferred embodiment. Both arrangements are shown in the drawings. 
   The operation of this device will now be described. In  FIG. 2 , sheet  15  has its edges loosely inserted between the lip on this cam plate and the edge of the base plate. The ring has been turned to move the cam plate outwardly to create a sufficient opening for the edges of the sheet to be inserted. 
   As shown in  FIG. 3 , the rotor is then turned by pushing on the handles, and the cam pins force the cam plates inwardly. The lip on the cam plate (which may be a serrated edge), grips the sheet and draws it toward the center. The sheet is thereby strongly held flat against the backing surface. 
   The sheet is released by turning the ring in the reverse direction. The cam pin will then push the cam plate out, which will take the sheet edge with it and release it. 
   The embodiment as shown and described is preferred because the cam action draws both edges of the sheet at the same time. Included in this invention is to provide a separate clamp at one edge, and the described gripper only at the other edge. The same cam action, but only at one side, is provided, but will tighten and hold the sheet. For example,  FIG. 7  shows an alternate embodiment gripper  31   a  in place of gripper  31  as shown in  FIG. 1   
   In  FIG. 7 , gripper  30  functions as it does in  FIG. 1 . Arrow  30   a  shows that its movement is lateral to the central axis. In contrast to  FIG. 1 , in which cam plate  32  slides laterally, plate  33   b  ( FIG. 7 ) is fixed by a schematically illustrated restraint  33   d  which in the illustration is a bolt so the free edge  33   e  of cam plate  33   b  can be raised and lowered as shown by arcuate arrow  33   f , but not moved laterally. 
   Thus, while gripper  30  operates as shown in  FIG. 1 , the free end  33   e  of gripper  31   a , acting as a fixed clamp can be raised or lowered to admit or to grip the respective edge of the sheet. 
   This is an elegantly simple device, made of rugged parts that can resist the vigorous forces of sanders. The sheet can readily be removed and replaced, with only minimal contact with them. 
   This invention is not to be limited by the embodiment shown in the drawings and described in the description, which is given by way of example and not of limitation, but only in accordance with the scope of the appended claims.