Tension disc assembly
BACKGROUND OF THE INVENTION 
     At present, there are numerous methods for insuring proper insertion of thread into thread tension devices. Many of these methods employ guides separate from the tension device itself for urging threads between various sets of tension discs. While these devices perform their function with reasonable success, the mere fact that they are separate from the tension discs leaves room for possible failure. Another prior art approach to solution of these problems is disclosed for instance in the U.S. Pat. No. 3,841,248 of Adams et al., which teaches that by enlarging one of the tension discs, the same function as that performed by the separate guides may be achieved, i.e., guiding thread between the tension discs. Enlarging one of the tension discs, however, is expensive because a tension disc requires costly hardening and polishing. Moreover, this patented approach entails the costly manufacture of at least two sizes of tension discs. 
     SUMMARY OF THE INVENTION 
     The object of this invention is to provide a tension disc assembly which performs the same functions as the enlarged tension discs without the need for manufacturing two different sizes of tension discs. This object is achieved by forming a relatively large supporting structure out of an inexpensive material and then securing in said structure a standard-sized tension disc. 
     With the above and additional objects and advantages in view as will hereinafter appear, this invention will be described with reference to the accompanying drawings of the preferred embodiment. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front elevation of the sewing head of a sewing machine incorporating the invention. 
     FIG. 2 is a front elevation of the tension disc assembly. 
     FIG. 3 is an enlarged cross-sectional view of a portion of a tension device taken along the line 3--3 of FIG. 1 showing the tension disc assembly of this invention in relation to the other tension discs within the tension device. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention is disclosed as embodied in the needle thread tension of a sewing machine. Referring to FIG. 1 of the drawing, a sewing machine head is generally referred to by the reference number 10. The sewing machine head 10 includes a reciprocatory needle bar 12 having a needle 14 attached thereto, and a presser foot assembly 16 along with a presser foot lifter mechanism 18. The sewing machine head 10 also includes a tension device 20. 
     The tension device 20 has a central shaft 22, on which tension discs, along with the tension disc assembly 24 of this invention, are mounted, a locking nut 26 mounted on the end of the shaft 22 and means (not shown) for providing a compressive force to the tension discs. 
     The tension disc assembly 24 is formed of a plate 28 having an aperture 30 therein for receiving a standard-sized tension disc 32. The over-all size and shape of the plate 28 is arbitruary and may be tailored to suit any particular application. In the subject embodiment, the plate 28 is also formed with a hole 33 so positioned as to fit over a locating pin 34 mounted in the tension device frame 36 thereby preventing the tension disc assembly 24 from rotating while in use. 
     The tension disc 32 may be mounted in the aperture 30 of the plate 28 by any suitable means. FIGS. 2 and 3 show the tension disc 32 mounted to the plate 28 by staking the plate 28 substantially around the periphery of the aperture 30; the staking line being identified by the number 38. 
     The tension disc 32 is circular and has a centrally located aperture 40 for receiving the shaft 22. The size of the tension disc 32 is the same as that of the other tension discs used in the tension device 20 thereby allowing all the discs to be manufactured to the same specification. 
     For ease in threading the tension device 20, the plate 28 should have a thickness somewhat less than that of the tension disc 32.