The present invention generally relates to an automatic part processing machine for fully automatically processing a part or workpiece by methods such as shot peening and the like, having a novelly constructed part hold down apparatus.  The invention more specifically relates to a novel construction of a part hold down apparatus for use in fully automatic processing of a part or workpiece. 
Today, many machined or fabricated parts or workpieces must be processed before they are included in or assembled into a larger, final product or machine.  An example of such a part is a gear utilized in automobile transmissions.  Once these gears are formed, they should be processed by shot peening machines, and the like, to insure that the gears meet government and manufacturer specifications, as well as to insure that the gears are suitable for performing their intended functions.  The methods of shot peening or processing of such parts can be quite complex, difficult, and time consuming. 
Utilizing the machines, apparatuses and methods of the prior art, such parts are processed or shot peened in the following manner.  The parts are manually mounted on a part hold down apparatus of a shot peening machine in a predetermined disposition such that the relevant surfaces of the part are subjected to the peening process Because it is desirable to subject all such surfaces to peening equally to achieve uniform processing of the part, the apparatus is rotated, usually on the order of thirty to forty revolutions per minute (rpm's), while a high velocity peening fluid, usually bearing a shot of sorts, is forcibly directed at the part. 
When the high velocity shot interacts with the part, the part may begin to rotate with respect to the apparatus under the influence of forces applied to the part by the shot.  Accordingly, the part does not rotate conjointly with the apparatus, thereby resulting in uneven peening of the part as well as possible damage to the part and the apparatus.  Furthermore, the part may become operatively dislodged from the apparatus such that the part does not rotate at all, again resulting in uneven peening.  Parts unevenly peened or damaged during processing often do not meet the relevant government or manufacturer standards.  Thus, these parts may have to be discarded, resulting in lost revenues to the manufacturer. 
In an effort to prevent rotation of the part with respect to the apparatus during peening, or other processing for that matter, a forced fit is formed, such as by pressing the part onto the apparatus by means of repeated strikes with a hammer.  This forced fit provides the part with sufficient resistance to the forces generated by the interaction with the high velocity shot so that the part does not rotate with respect to the apparatus during peening. 
This forced fit, however, has certain drawbacks.  While the forced fit may be sufficient for preventing rotation of the part independent of the apparatus, the application of the forced fit makes processing of the part tedious and time consuming.  Specifically, because of the nature of the forced fit, each individual part must be manually applied to the apparatus.  This manual application results in increased labor costs to the processor or part manufacturer.  Also, the forced fit must be carefully manually applied so as to prevent damage of the part. 
This is particularly important upon consideration of variances inherent in many manufactured parts. 
Additionally, after processing, the part may be difficult to remove from the apparatus, due to the necessary strength of the forced fit.  Thus, each part must be individually manually removed from the apparatus after processing.  This removal must also be done with care to avoid damage of the part.  Accordingly, utilization of a forced fit between the part and the apparatus adds significantly to the cost of the part. 
A part hold down apparatus, constructed according to the teachings of the present invention, is intended to solve some, if not all, of the problems inherent in the prior art hold down apparatus discussed hereinabove.  The part hold down apparatus of the invention eliminates the need for a forced fit and allows for fully automatic part processing, thereby reducing manufacturing costs.