Patent Publication Number: US-2013244543-A1

Title: Shim-mask stencil

Description:
The present invention relates to a stencil to protect the surface surrounding an area being abraded, for example in the vehicle refinishing trade. 
     When a technician is performing a repair for example abrading excess material after filling a stone chip or scratch with paint or needs to remove a run as a result of incorrect lacquer application, the area surrounding the area to be abraded must be protected if damage is to be avoided. This is commonly done by applying adhesive masking tape, the disadvantages of which are that the tape is easily abraded by the abrasive material employed and is too thick to be near flush with the surface so that when the abrasive is passed over the tape, the area under repair is still considerably higher than the remaining surface, meaning that the repair must be finished without masking tape if a flush repair is to be achieved, increasing the risk of damage to the surrounding area. 
     By using a protective stencil having the properties of being very thin whilst being resistant to abrasive materials, a high spot as previously mentioned may be removed by selecting a stencil with a suitable size and shape of hole, placing this hole over the high spot (the stencil maybe taped into position or hand-held against the surface to be worked on), so that the high spot is exposed and then slicing the excess material with a very sharp blade eg a one sided razor blade over the stencil held at near to horizontal to the stencil, before abrading either by hand with an abrasive wrapped around a suitable sanding block, or by means of a sanding machine. The result will be that the material within the selected hole in the stencil will stand as high as the thickness of the stencil, if a hard block or backing plate is employed, which may then be finished with a fine abrasive once the stencil has been removed, so minimising risk of damage to the surrounding surface. 
     If a softer block or backing pad is employed the area inside the stencil shape will be abraded and can be feathered by placing successively larger sized shapes over the repair spot and abrading with successively finer abrasives. 
     Masking stencils U.S. Pat. No. 6,099,388 and U.S. Pat. No. 5,399,421 are cited as they perform the function of protecting the surrounding area while an abrasive process is carried out. 
     The key difference is that the current application is designed for protection of a surface on which undesired high spots need to be eliminated by abrasion and to a precision that is as close as possible to the surface surrounding the high spot, including the exposed area inside the stencil hole, without causing damage to it. 
     The current application is not intended to eliminate low spots. Although application U.S. Pat. No. 6,099,388 cites a mask  20 , this mask is not designed to be used in conjunction with a sanding block being used across its surface, but rather to limit the repair area, the abrasion being carried out inside the stencil shape to eliminate a scratch which is lower than the surrounding surface. 
     There is no evidence that mask  20  would resist an abrasive being passed across its surface nor is it designed to be as thin as practically possible and so would not permit the abrasion of a high spot to near flush with the surface. 
     U.S. Pat. No. 6,099,388 shows a protective mask whose characteristics are: “Preferably the mask is of a plastics material” Column 4 line 40; “The material of the mask has electrostatic cling” Column 4, line 41. 
     Neither of the above features suggests that the mask would withstand a mechanical sander being passed over the top whilst still protecting the area underneath, in fact quite the contrary is suggested. This is because the mask is not intended to be sanded across, but rather to limit the repair area, the mild abrasion process being carried out within the limits of the exposed area. Abrasion is carried out “with radial strokes relative to the compact disc” column 7, line 30 “the radial strokes extending from side to side IN the localised area” column 7, lines 31 and 32. Also if the hole to localise the “area is cut in the mask” column 7 line 3, this suggests that the material is not sufficiently resistant to withstand sanding with a mechanical sander. If the hole were cut by a mechanical method eg scissors or a sharp knife, this would lead to burring or at least an inexact edge which would result in the stencil not lying perfectly flat on the surface, if the mask were made of a sufficiently resistant material. If the mask did lie flat after manually cutting a hole, this would suggest that the material would not be resistant enough to serve the purpose of the current invention. 
     The reason that the current invention lies perfectly flat is that stencil holes in a very abrasion resistant material are chemically etched so no burring of edges occurs. 
     Neither is patent U.S. Pat. No. 5,399,421 designed to abrade undesired high spots to a level near flush with the surface, but rather to protect the surrounding area only outside the stencil hole while the abrasive process removes material from the surface to a level lower than the remaining surface. There is no evidence that the vinyl material proposed would allow an abrasive sheet with block to be passed over it with little resistance nor that the surface is as flat and regular as the stainless steel proposed in the current application to allow the precision of sanding required, nor indeed that the stencil is thin enough to allow slicing and sanding to near flush as is the objective of the current application. 
    
    
     A preferred embodiment of the stencil will be given referring to  FIG. 1  which shows a top view of the stencil ( 1 ), manufactured from 0.05 mm to 0.03 mm hard quality stainless steel shim in a sheet measuring 12 cm by 12 cm, with holes ( 2 ) designed to expose typical spot repairs, namely lacquer runs, imperfections and paint-filled chips or scratches, and created by a process to ensure that edges are flush with stencil body, for example an etching process. The etched holes are calculated to be of a dimension that will not allow the abrasive block, sanding machine pad or blade, when held horizontal to the surface, to make contact with the surface to be protected at any point, ie the dimensions of the holes are too small to allow the sanding block, machine pad or blade to fit completely inside. The stainless steel employed to make the stencil offers high durability to the abrasion process so that the surface to be protected is so, prevents the stencil from oxidation, which would affect its uniform positioning on the surface, and allows the stencil to be re-used.