Abstract:
A rotatable turntable tool is used in trimming wheel-thrown pottery. The turntable tool includes a base portion, a bearing member, and a cap portion which is rotatably attached to the base portion. A method of trimming an unfired clay workpiece includes steps of inverting the workpiece and placing it at a central portion of a wheel head on a potter&#39;s wheel; placing the turntable tool on top of a central portion of the inverted workpiece; pressing downwardly on the cap portion of the turntable tool while rotating said wheel head to stabilize the workpiece, whereby the base portion of the turntable tool rotates with the workpiece, while the cap portion is substantially restrained from rotating; and applying a trimming tool to an edge of the workpiece to remove unwanted clay therefrom.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present invention is a divisional of U.S. patent application Ser. No. 11/824,377, filed on 29 Jun. 2007. The present application claims priority under 35 USC 119(e) based on U.S. provisional patent application No. 60/831,758 filed on Jul. 19, 2006. The subject matter of each of the referenced priority documents, including claims, specification and drawings, is incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the invention 
     The present invention relates to a method of trimming unfired pottery, using a turntable tool. The tool includes a base which spins with a pottery workpiece, and a cap member operatively attached to the base and adapted to rotate relative to the base. 
     2. Description of the Background Art 
     It has been a common practice in trimming pottery for an artisan to invert a wheel-thrown workpiece on a rotatable wheel head of a potter&#39;s wheel, when the workpiece has partially dried to a stage referred to in the art as “leather hard”; to center the workpiece on the wheel head; and to press downwardly on the inverted base of the workpiece during trimming. It has also been known to place an inverted metal lid in the center of the base of the workpiece during a trimming operation on unfired pottery. This lid may be, for example, a lid from a baby food jar. Then, the artisan places a finger in the center of the lid and applies a light downward pressure to the workpiece, through the lid, while the wheel spins at an appropriate trimming speed, and this stabilizes the workpiece on the wheel head and distributes the finger pressure, while the artisan trims away unwanted superfluous clay from the exterior and base of the workpiece. 
     Using this type of inverted lid, however, does not entirely avoid the occurrence of friction between the spinning lid and the user&#39;s fingertip. Such friction may generate heat and be uncomfortable for the user. 
     Many different designs for turntables have been patented, for a number of different applications. Examples of some of the known turntables include U.S. Pat. No. 1,409,257 (Staley), U.S. Pat. No. 1,732,113 (Van Der Meer), U.S. Pat. No. 4,117,627 (Slingerland, Jr.), U.S. Pat. No. 4,549,714 (Busch), U. S. Pat. No. 5,479,867 (Blevins et al.), U.S. Pat. No. 5,779,309 (Lu), and U.S. Pat. No. 5,783,123 (Edwards et al.) 
     Although the known turntables have some utility for their intended purposes, a need still exists in the art for an improved tool for use in trimming unfired clay pots, and to an improved method of trimming unfired clay pots using such a turntable tool. In particular, there is a need for an improved trimming tool which will overcome the difficulties encountered with the known art, and which will speed up the trimming process. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide an improved method and turntable tool for use in stabilizing an unfired clay workpiece during a trimming operation thereon, in an intermediate stage of manufacture. 
     A turntable apparatus according to an illustrative embodiment includes a base member, a bearing member which fits into an opening in the base member, and a cap member including a dependent central post which fits into a hole in the center of the bearing. 
     The base member may be textured on a bottom surface thereof, to better grip the clay surface of a workpiece during use. The base member may further have a plurality of open cutouts formed in the lower surface thereof, and may also have a plurality of radial ribs on the underside thereof extending between the cutouts. 
     The bearing member may be a bearing, such as a sealed bearing, or alternatively, may be an annular bushing. Where a bushing is used, it may be formed from sintered plastic or metal, impregnated with a lubricant. 
     The cap member includes a relatively thin upper disc, which may have a shallow recess formed centrally therein to receive a fingertip of a user. The cap member also includes a post attached to and extending downwardly from the upper disc, where the post is dimensioned and configured to fit into the central hole of the bearing member. 
     The diameter of the upper disc may be in a range between 3 cm and 7 cm. 
     For a more complete understanding of the present invention, the reader is referred to the following detailed description section, which should be read in conjunction with the accompanying drawings. Throughout the following detailed description and in the drawings, like numbers refer to like parts. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view of a turntable tool according to a first illustrative embodiment of the present invention; 
         FIG. 2A  is a top plan view of the turntable tool of  FIG. 1 ; 
         FIG. 2B  is a partial side plan view and a partial sectional view of the turntable tool of  FIG. 1 ; 
         FIG. 2C  is a bottom plan view of the turntable tool of  FIG. 1 ; 
         FIG. 3A  is an environmental perspective view of a first step in a trimming process according to the present invention, showing an inverted clay workpiece centered on a wheel head; 
         FIG. 3B  is an environmental perspective view of a second step in the trimming process according to the present invention, showing a turntable tool according to the invention centered on an inverted workpiece; 
         FIG. 3C  is an an environmental perspective view of a third step in the trimming process according to the present invention, showing finger pressure being applied downwardly on the turntable tool while a user removes unwanted clay from the base of the workpiece using a conventional metal trimming tool; 
         FIG. 4  is a schematic diagram showing a sequence of steps in an illustrative method according to the present invention; 
         FIG. 5  is a perspective view of a turntable tool according to a second illustrative embodiment of the present invention; 
         FIG. 6  is a cross-sectional view of the turntable tool of  FIG. 5 , taken along the line  6 - 6 ; and 
         FIG. 7  is an exploded lower perspective view of the turntable tool of  FIGS. 5-6 . 
     
    
    
     DETAILED DESCRIPTION 
     The present invention provides an improved turntable tool, and method of using the disclosed tool to stabilize an unfired clay workpiece during a trimming operation thereon, in an intermediate stage of manufacturing the workpiece. 
     Referring now to the drawings, a turntable apparatus according to a first illustrative embodiment of the invention is shown generally at  10  in  FIG. 1 , in exploded perspective view. The turntable apparatus  10  includes a base member  12 , a bearing member  16 , and a cap member  20 . Each of these components will be discussed in further detail below. 
     In the first embodiment of the turntable apparatus  10 , the base member  12  is formed generally in the shape of a flattened cylinder with a hollow cylindrical recess  14  formed centrally therein, to receive the bearing member  16 . The base member  12  includes a substantially smooth and unbroken side wall  15  extending therearound. Also in the first depicted embodiment, the base member  12  includes a closed floor portion  35  extending across a lower surface  30  thereof at the bottom of the recess  14 , sealing the recess  14  from contact by water or other environmental elements below the tool. The base member  12  may be formed of a slightly resilient plastic material, so as to be non-brittle. 
     The base member  12  may be knurled, or otherwise may be textured, on a lower surface  30  thereof. The lower surface  30  of the base member  12  may have a plurality of open cutouts  32  ( FIG. 2B ,  2 C) formed therein to create such a textured surface. The lower surface  30  may also have a plurality of radial ribs  34  thereon extending between the cutouts  32 , as shown in  FIG. 2C . 
     The bearing member  16  is generally annular in shape, with a hollow central hole  18  formed centrally therein to receive a post  22  of the cap member  20 . The bearing member  16  is configured and dimensioned to fit snugly inside of the recess  14  of the base member  12 , with a slight interference fit to retain the bearing member therein. The bearing member  16  may be a multi-component bearing assembly, such as a sealed ball bearing or roller bearing. Alternatively, the bearing member  16  may be an annular bushing. Where a bushing is used, it may be formed from sintered plastic or metal, and optionally, may be impregnated with a wax or with another lubricant. However, the relatively low speed at which the cap member  20  is expected to rotate, in relation to the base  12 , makes the use of a lubricant optional. 
     The cap member  20  includes a relatively thin upper disc  21 , which may have a shallow recess  25  formed centrally therein to receive a fingertip of a user. The diameter of the upper disc  21  may be in a range between 3 cm and 7 cm. The cap member  20  also includes a cylindrical post  22 , integrally attached to and extending downwardly from the upper disc. The post  22  is dimensioned and configured to fit into the central hole  14  of the bearing member, and to suspend the upper disc  21  slightly above, and spaced away from the base member  12 , so as to avoid direct contact therebetween. This spacing provides a narrow gap between the upper disc  21  and the base member. 
     Referring now to  FIGS. 5-7 , a turntable apparatus according to a second illustrative embodiment of the invention is shown generally at  110  in  FIG. 5 , and this same apparatus is shown in cross-section in  FIG. 6 , and in exploded perspective view in  FIG. 7 . The turntable apparatus  110  in this second embodiment includes a base member  112 , a bearing subassembly  116 , and a cap member  120 . Each of these components will be discussed in further detail below. 
     In the turntable apparatus  110  according to the second embodiment, the base member  112  is formed generally in the shape of a flattened cylinder with a hollow cylindrical open space  114  formed therein, to receive the bearing subassembly  116 . The base member  112  includes a substantially smooth and unbroken side wall  115  extending therearound, with an upper lip flange  113  extending substantially horizontally outwardly at the top of the side wall  115 , as shown. The upper lip flange  113  is provided for cooperating with a lower lip flange  121  of the cap member  120 , to retain the cap member on the base member through an interference fit between the upper lip flange  113  and the lower lip flange  121 . 
     Also in the second embodiment, the base member  112  includes a closed floor portion  135  extending across a lower surface  130  thereof at the bottom of the recess  114 , sealing the recess from contact by water or other environmental elements below the turntable tool. The base member  112  may be formed of a slightly resilient plastic material such as polyethylene or another suitable polymer, so as to be non-brittle. 
     The base member  112  may be knurled, or otherwise may be textured, on the lower surface  130  thereof, as shown in  FIG. 7 . 
     The bearing subassembly  116  includes a perforated ring member  125  which is generally annular in shape, and which may have a hollow central hole  118  formed centrally therein. The perforated ring member  125  has a number of evenly-spaced collars  126  formed therein, including hollow apertures in each of the collars to retentively receive ball bearings  127 . The bearing subassembly  116  is configured and dimensioned to fit loosely inside of the recess  114  of the base member  112 . The bearing subassembly  116  may be a multi-component bearing assembly, as shown. Alternatively, the bearing subassembly  116  may be replaced with a sealed bearing assembly or by an annular bushing. Where a bushing is used, it may be formed from sintered plastic or metal, and optionally, may be impregnated with a wax or with another lubricant. However, the relatively low speed at which the cap member  120  is expected to rotate, in relation to the base  112 , makes the use of a lubricant optional. 
     The cap member  120  includes a relatively thin upper disc  123 , which may have a shallow recess  124  formed centrally therein to receive a fingertip of a user. The width, or diameter of the upper disc  123  may be in a range between 3 cm and 7 cm. 
     The cap member  120  also includes an integral side wall  122 , integrally attached to and extending downwardly from an outer edge portion of the upper disc  123 . The side wall  122  of the cap member  120  is dimensioned and configured to fit outside of side wall  115  of the base member  112 , and the bearing subassembly  116  suspends the upper disc  123  slightly above, and spaced away from the base member  112 , so as to avoid direct contact therebetween. This spacing provides a narrow gap between the upper disc  123  and the base member  112 . 
     Referring now to  FIGS. 3A-3C  and  4 , an illustrative method of trimming an unfired clay workpiece, using the turntable tool  10  or  110 , will now be described. 
     Those in the relevant art will understand that immediately after a clay workpiece has been hand-formed on a potter&#39;s wheel  36  ( FIG. 3A ), the workpiece is quite soft and malleable, and is generally too soft to undergo an immediate trimming operation. Therefore, the workpiece is air-dried for a period of time, until it is partially dried to an intermediate state known in the art as “leather hard”, whereupon it can withstand the forces exerted thereon in a trimming operation. This drying operation can take place overnight in a “wet box”, or the workpiece may be allowed to sit out uncovered to dry immediately after it is formed, where the user is available to wait for the partial drying process to take place. 
     Once the workpiece  38  has attained a leather-hard condition, it is inverted and placed at the center of a rotatable wheel head  37  of a potter&#39;s wheel  36 , with the base  40  of the workpiece oriented facing upwardly. The base  40  includes a rough, uneven outer edge portion  42  in need of trimming. This step of the method is depicted in  FIG. 3A , and is also shown at  50  in the method flowchart of  FIG. 4 . 
     Once the workpiece  38  has been centered on the wheel head  37 , the turntable tool  10  or  110  is then placed on a central portion of the inverted workpiece base  40 , with the cap portion of the tool facing upwardly. This step of the method is depicted in  FIG. 3B , and is shown at  52  in the method flowchart of  FIG. 4 . 
     After the turntable tool  10  or  110  has been centered on the base  40  of the workpiece  38 , the user then presses downwardly on the turntable tool to stabilize the workpiece, while rotating the wheel head at an appropriate trimming speed. A selected fingertip of the user fits engagingly into the recess  25  in the top of the cap portion  20  during this step. The base portion  12  of the turntable tool rotates with the workpiece  38  and spins about the stationary post  22  of the cap portion  20 , while the cap portion  20  remains substantially still. This step of the method is depicted in  FIG. 3C , and is shown at  54  in the method flowchart of  FIG. 4 . 
     In the next step of the method hereof, a trimming tool  44  is applied to the rough edge  42  of the workpiece  38 , to remove unwanted clay  45  therefrom. This step of the method is also depicted in  FIG. 3C , and is shown at  56  in the method flowchart of  FIG. 4 . 
     Optionally, the trimming tool may then be removed, and additional clay may be removed from a central portion of the base. 
     After the trimming operation has been completed, the workpiece is allowed to dry completely over a period of days until it reaches a “bone-dry” condition, after which it is vitrified in a conventional firing process in a kiln. This may be a two-stage process in which a glaze is applied to the finished workpiece after an initial bisque firing, and the glaze is then melted in a final, high-temperature firing. 
     Although the present invention has been described herein with respect to a number of specific illustrative embodiments, the foregoing description is intended to illustrate, rather than to limit the invention. Those skilled in the art will realize that many modifications of the preferred embodiment could be made which would be operable. All such modifications, which are within the scope of the claims, are intended to be within the scope and spirit of the present invention.