UnionSpecial 39500AB Instructions For Adjusting And Operating

NEEDLE THREAD CONTROL (Continued)The eyelet i s adjusted correctly i n its front to back position when the desired st i tch isobtained with the least amount of needle thread tension when sewing over the completespeed range.FOR 39500 AB AND 39500 AEUsually, all needle thread is drawn on needle down stroke. At top of needle stroke,thread should be just tight enough to feed chain off stitch tongue. Needle threads tend to pulldown slightly if excessive thread is pulled on the up stroke. With needles at bottom of stroke,positionneedlethreadpull-offeyelet (H, Fig. 2) sothattheneedlethreadpull-off (G) drawsthe proper amount of needle thread to satisfy the above conditions.UPPER LOOPER THREAD CONTROLDuring needle down stroke, forward stroke oflooperthreadpull-off(F, Fi g. 1 or Fi g. 2)will draw upper looper thread through the tension. When normal amount of looper thread isdrawn, upper looper thread will have almost all slack taken up as looper thread pull-offreaches its most rearward position.FOR 39500 ACIf upperlooperthread has alooseappearancein the seam, move looper thread pull-offeyelet (D, Fig. 1) forward and ra i se slightly. If, however, the eyelet is raised too high andmoved too far forward, the looper thread will tend to break excessively--even with aminimum amount of loope r thread tension applied.FOR 39 500 AB AND 39 500 AEIf upper looper thread has loose appearance in the seam, move looper thread pull-offeyelet (D, Fig. 2) forward slightly. If, however, the eyelet i s too far forward, the looperthread will tend to break excessively--even with a minimum amount of looper thread tensionapplied.CAUTION! Do nottry to obta in a tight looper thread appearance on the seam by carryinghigh tensions.POSITIONING THE PURL TO OBTAIN A F LAT SEAMIf the purl i s at the top edge of the garment, the seam can be opened into a near buttedappe a rance. If, however, the purl is under the edge, a l ess fl at and tighter s eam re s ultswhen opened.FOR 39500 ACRais i ng and br i nging the looper thread pull-off eyelet (D , Fi g. 1) forward cau ses lessthread to be pulled from the cones as the looper travels to th e t op of its stroke and cau se sthe purl to form more onthe top of the edge. If the eyelet is raised and brou ght too farforward, however, the thread becomes too tight, resultin g in looper thread breakage.With a reasonable amount of looper thread tension to insu r e a flexible cha i n, the l ooperthread pull-off ey e let should be adjusted to position the purl as desired.FOR 39500 AB AND 39500 AEMoving th e needle thread pull-off eyelet (H, Fig. 2) back causes less thread to be pulledfrom the cones a s the needles travel to the top of th ei r stroke and causes the purl to f ormmore on the top of t he edge. If the eyelet is moved back too far, how e ver, the threadsbecome slack at the top of the stroke and the chain will not feed off the throat plate tongue.With a reasonabl e minimum needle thread ten si on to insure uni f orm i ty, the needle threadpull-off eyelet should be adjusted to position the purl as desired.THREAD TENSIONS WITH R ESPECT TO STITCHFOR 39500 ACThe needle th r ead tension required is a funct i on of needle thread and the material bein gs ewn. In g eneral, uppe r looper thread tens i on should be s et as high as poss i bl e withoutcausingthe needle threads to be pulled too f ar ove r th e top of the seam and l ow enough toprevent looper thre a d breaka g e.FOR 39500 AB AND 39500 AEThe needle th r eads and looper thread tens i ons should be s et at a minimum to ins ur euniformity of st i tch. NOTE: Tension applied to the threads at the thread s tand te ns i onpads (X, F ig. 2) s hould only be enough to preven t the th re ads f rom becoming s lac k betweenthese ten s ion pad s and the ten s ion disc s mounted on the machine. All cont r oll i ng ten si onsett i ng s to insur e uni f orm i ty of st i tch should be obt ai ned by vary i ng the t e ns ion s at th etension disc s , which are mounted on the machine.13From the library of: Superior Sewing Machine & Supply LLC