US2516861A - Machine for and method of sewing heavy materials - Google Patents

Description

MACHINE FOR AND METHOD OF SEWING HEAVY MATERIALS- Filed April 6, 1946 Aug. 1, 1950 J. 1 FREDERICKSEN 3 Sheets-Sheet 1 @7623 r V I I r l 1 Aug. 1, 1950 J. P. FREDERICKSEN MACHINE FOR AND METHOD OF SEWING HEAVY MATERIALS 3 Sheets-Sheet 2 Filed April 6, 1946 152299721???" Jmesme derob/ifsen 35y 726's Q6607?! g 1950 J. P. FREDERICKSEN 2,516,861

MACHINE FOR .AND METHOD OF SEWING HEAVY MATERIALS Filed April 6, 1946 3 Sheets-Sheet 5 Patented Aug. 1, 1 950 UNITED STATES OFFICE.

MACHINEF'OR AND METHOD. OF SEWING.

HEAVY MATERIAL S 1 James P. Fredericksen, Braintree, Mass'.,- assign'o'r' to United Shoe Machinery Corporation, Fleme ington, N. J., a corporation of New Jersey 5" Claims.

bility and a. peculiar property of delayed recovery characterized by a substantial. amount of residual. contractility which persists for a. considerable lengthi of time after any stretching force which has been exerted upon, the thread is reduced.

Because of these characteristics, Whi'ChL differ greatly from those of cotton or linen thread, these new threads cannot be used satisfactorily in. for example, the conventional inseam and outsole sewing. machines. as employed in. commengialr shoe manufacture with cotton or linen thread, but it has been discovered that,.by establishing a new relation between certain of. the thread handling parts of. such machines, and changing their action in certain. respects, the synthetic fiber thread not only canibe USBdxSllC- oessiully but seams can be made. having new and unexpected characteristics which render the sewed article definitely superior to; similar articles as heretofore made.

x .The invention consists in the novel features hereinafter fully disclosed and described in their usurious aspects in connection with the accompanying drawings, which Fig. 1 is a sectional view, illustratingthe. principal parts of a shoe sewing machine constructed for use in carrying out the present invention, together with a portion of a shoe being; operated upon, the parts of the machine being indicated in positions taken after the needle has been retracted during the formation of a stitch;

Fig. 2 is a detail plan. view of a portion of a shoe being presented to the machine, with the machine parts in the positions of Fig. 1;

. Fig. 3 is a view similar to Fig.1., with portions orthe frame omitted and with partsin positions assumed directly after a stitch is set;

Fig. 4 is a detail plan view of a portion of a shoe presented to the machine with the parts. in the positions shown in Fig. 3;

Fig. 5- is a sectional view of a portion of a shoe, illustrating the relations between the parts immediately after a seamihas been. inserted;

Fig. 6 is a similar view of a portion of. a sewn r 2 shoe; illustrating theconditionof the seam after an extended period oftimehas elapsed;

' Figi '1 is a detail diagrammatic view of a tem sion' wheel, illustrating the action whenrelatively inextensible sewing thread is employed in the" machine of Fig. 1

Fig: 8 is atime'ch'art, illustrating thei-mproved manner of operation of the machine, with a com; parison' between the action occurring when linen thread under normaP operating conditions is employedand wheira speciallyprepared thread, such as nylon, is employed;

Fig; 9'- isacharacterisfic stress-strain diagram; comparing linen, cotton and nylon threads? and Fig. 10 is a sectional view taken along the-line X- X" of Fig. 1, showing? a portion of the tension brake actuating mechanism:

The" machine and method of the present invention are illustrated as employed inthe manufacture of a Goodyear-welt shoe in which a sole member is permanently attached to an upper by an inseam the stitches of" which are under heavy tension approaching the breaking strength oithe thread employed, to bring the partsinto close conformity with a last on. which they are mounted. The inseam sewing operation supplements thelasting operation in stretching the upper overthe last and in giving it its final tension to bring it" into close-fitting relationship with the surfaces of the" last; Because of the heavy tension required'in the thread to bring'the partstogether, a heavy thread is: customarily empioyed; having a" diameter sometimes a proxi; mating one-sixteenth of an-inch in its largest In some instances, for lighter weight shoe manufacture, smaller sizes of thread are employedbut; in any case, a tension is exerted which heavy for thread of the size being used.

Referring to'Fi'gs. 5 and 6E ofthe drawings, a Goodyear welt inseam. is ill ustratedi by a section .tahen-throughla shoe, The shoe is ready for intions, the upper ordinarily is held under such tension that it bridges the angle between the rib and the feather on the insole.

During the inseaming operation, a grooved welt strip Ill is directed against the outer surface of the upper and a chain-stitch inseam I2 is formed with the stitches entering the groove of the welt and passing through the upper, the exposed threads appearing on the welt and in the angular channel between the insole rib and the upper surface of the insole inside the rib. It is the practice to insert the inseam as close to the upper surface of the insole as is practicable so that the stitches act to draw the bridged upper securely into the angle between the rib and the feather of the insole.

With extremely heavy work, such as that found in military footwear, it is difficult if not impossible to bring the upper, bridged from the staples in the rib to the feather on the insole, closely into conformity with the angle between the two parts of the insole. Thisdifficulty is increased by the resistance of the welt to bending along the line of the groove therein, such resistance adding to the tension in the thread necessary to break the materials down into the angle of the insole. When the materials are insufficiently broken down, there is a void space, indicated at M, between the upper and the angle of the insole. In

many instances, the thread is ruptured before conformity is obtained or, where the substance of the rib, upper or welt is weak, the thread will cut through the parts before closing the void space. Y

The next operations on the shoe are the inseam trimming, during which the upper portion of the sewing rib, including the staples 8, is cut off close to the inseam, and the welt beating operation for flattening the remaining portions of the rib, upper and welt more closely together against the bottom of the last. The welt beating operation assists in some degree in filling up the void space I4 but, at best, it is only an expedient. After the shoe is completed by attachment of an outsole to the welt If! and the last is removed from the shoe, the forces exerted upon the inseam during wear of the shoe will cause the inseam, when linen or cotton thread is used, to open up between the welt and upper, exposing the inseam thread to entry of moisture and other destructive agents and constituting a weakness in the construction of the shoe which reduces its eifective life, besides giving it an unattractive appearance.

Even under the best conditionswith' extreme tension in the thread, the shoe parts are compressed somewhat by the thread but, because of a peculiar characteristic of delayed compressibility found in all leather, full compression is not obtained in the parts until an appreciable length of time has elapsed after each stitch is inserted. Thus, even though a tension be applied to the thread of an intensity close to its breaking strength in setting each stitch, the tension thereafter becomes gradually reduced as the leather yields comparatively slowly to the pressure of the thread. In some instances, with inextensible thread, after the work yields, the tension may be reduced to a small fraction of that employed to set the stitch within afew minutes after the seam has been sewn. If the thread itself does not have suflicient contractility to take up the compression or the parts operated upon, there will be no possibility of closing up void spaces, such as thatindicated at 14.

Cotton and linen threads now in general use, and having elongation and contraction of only from three to ten per cent, do not follow up the compression of heavy leather or similar stiff substances, of a thickness substantially greater than the diameter of the thread, sufficiently to hold the materials together securely and tightly.

In the shoe produced by the machine and method of the present invention, even if the seam after being inserted has insufficient tension to draw the parts together without void spaces such as indicated at M, the thread employed is so composed and treated, as will be explained, that it will have sufiicient elasticity or contractility to close up such spaces while the shoe is retained on the last and will maintain the parts securely in contact after the void spaces are closed up, with a firm seating throughout the area of contact. The tightening action due to contraction of the thread takes place Within a few hours of the time the seam is inserted and is of an extent greater than the yielding action of the substances held under compression by the thread. With a proper balance of forces, the upper will be brought into conformity with the shape of the last and the parts will be maintained securely and firmly together, without danger of separation under the stress of wear, for a time far in excess of that required to wear out the leather in the shoe, with the result that no opportunity is provided for entry of deteriorating agents into vital points of the shoe structure.

Examples of materials which can be utilized successfully as sewing threads in the manner outlined above are synthetic, fiber-forming ma.- terials such as nylon (polyamide resin of proteinlike structure), rayon (cellulose base materials), vinylidene or Vinyon (polymerized vinyl compound), or the like, given the proper mechanical working and heat treatment after either formation of the basic fiber or of the completely spun thread.

To assist in orientation of the molecules and to reduce as smuch as possible the tendency of sewing threads to stretch while in use, substantially all such fiber-forming materials from which they are composed are ordinarily at some time during their manufacture subjected to heat and mechanical stretching treatment, frequently accompanied by the application of chemicals. Stretching treatment also strengthens the threads composed of such fibers until eventually they display characteristics of strength and durability in the maximum possible degree.

Instead of carrying out the stretching treatmentin such threads to an ultimate maximum as usual, the stretching is terminated substantially before that maximum is reached and a thread is produced having sufficient strength for shoe inseam sewing and other similar operations while at the same time retaining a marked degree of elastic and other qualities which assist in later contraction. Such thread has a character which may be termed high contractility and which enables the fibers to become elongated somewhere within the range of from twenty to fifty per cent before breakage. Thus, if such a thread is employed for shoe inseam sewing operations, sufficient strength is retained in the thread to retain the shoe parts in assembled relation, while at the same time the ability to contract after a stitch setting tension has been released is sufficient to close up any void spaces left between the parts during the sewing operation, as well amper as to offset the compressibility of the parts after the seam has been inserted. I

In order to insert an inseam connecting the welt, upper and insole of a Goodyear-weltshoe, using specially treated highly contractile thread: of the typeemployed in the shoe construction herein described, it has been found unnecessary to exert such heavy tensions during sewing as arewused in the formation of the usual i nseam in which commercial linen or cotton threads are employed It is only essential to apply to such specially treated thread while each stitch is being" set sufiicient initial tensiontotstretch the thread to such a degree that its subsequent con traction will draw the parts securely and ii-rmly together while thesnoe is on the last and" the delayed compression of the parts will be wholly offset, so as to prevent substantial release of tension in the thread after the seam is formed and the" last is removed from the shoe; Thus; it becomes possible to reduce the initiaf stitch setting-tension in the thread substantiallybelow the intensity which will draw the shoeparts' securely and firmly together immediately at the time the stitch is set. Furthermore, after setting each stitch, the initial tension is retainedJin' the stitch. without permitting slippage ofthe thread through the substance of the shoe parts or such release as will cause substantial loosening of that stitch after being set or while the succeeding stitchis being formed.

With a reduced initial stitch setting tension, also, the tension may more readily be controlled uniformly from one stitch to another than with higher initial tensions, the only requirement being, a retention of sufilcient residual contractility' in the thread to draw and maintain the parts. into firm. contact with each other after the seam. is inserted. Moreover, it is no longer necessary to apply a lubricant or hot wax to the. thread to insure uniform tightening action of the stitches during sewing operations.

The improved machine illustrated herein is of; atype similar in some respects to. that of? the inseam shoe. sewing machine disclosed. in United: States Letters Patent No. 1.,b30f743, granted, June 25,. 1912, upon application. of William. C. Meyer, and No..1,108,560, granted August 25,1914,.upon an application of Andrew Eppler. The stitch forming. devices comprise a curved hook needle. k8, azlooper I8; a thread finger, 28, a main take-up 22,-. an auxiliary take-up i l, and a; frictionally retarded rotary thread tension wheel 28; The needle 16 oscillates about a stud 28- toward and from the work, entering the groove in the welt, passing through the portion of the upper which. is bridged across between the sewing. rib and the feather on the insole, and finally. penetrat ing the base of the sewing rib to receive the thread within its hook from the looper. The thread finger thereafter acts to hold. aside a portionof thread, as indicated in Fig. 3, between thelast-formed stitch and the looper before the; needle is looped. The main take-up 22 is. actuated by at earn 3!] on a main. sewing shaft 32 of the machine at thevproper times to give up thread. during. the retracting stroke; of. the needle (Figs; 1 and 2) and to take up thread asztheneedle: enters the work. until. a final stitch setting tension is applied by upward movement of the takeup. just before the thread is engaged by the thread finger. The auxiliary take-up is: pressed downwardly continuously by:a plunger 34abetween the. upper" ends. of which. and. an adjustable:

air

threaded plug 36- there is disposed anaux-illary take-up compression spring 38 i The tensionw-heel 26 is secured to a shaft 40 rotatable in the machine frame and having keyed thereto a brake drum 42 acteduponlby a brake shoe M. The brake shoe is pivotally mounted on a lever 46 fulcrumed at 48 on the m'achineframe and actedupon along its straight-1 upper surface We pair of adjustable abutments Wand 52*. i i i The abutments wand 52 are slidingl ymounted on a pair'of individually spring-pressed actuating levers- 54 and 553, respectively. To adjust the tension on the thread, the abutments have; threaded openings to receive adjusting screws 5'8-provided with suitable knurled heads rotatablein the levers; The actuating levers 54 and 56 for the brake shoe M are pivotally mounted at? their rearward ends on a stud Ed in the frame ofthe machine and, at their forward ends, the levers are forced downwardly by a vertical tension' rod 62 slidingly mounted in a perforated fixed lug 64 at its lower end and. arranged w bear against a short arm t6 serving as a balancing member to distribute the downward pressure at'the lower end'of the rod 52 equally againstthet actuating levers Hand 56. The upper end of the tension rod carries atension wheel brake spring 68; compressed between an adjustable collar W clamped to therod t2 and a perforated arm of a"- governor-actuated lever l2; throughthe perfora- The manner of operation of the conventional .1 machine of this type using a substantiallyin extensible thread composed of either linen or: cotton willnow be described. Referring to Fig. 8 of the drawings, it is pp that the -1 D stroke of the take-up occurs between 70 and 1-25" of rotation of the main sewing shaft while the-needle engages the work, or during less than one sixth of the time in each complete sewing cycle. Assuming that the machine is operating at a-speed of 600 cycles-per minute or 10 cycles per second, the take-up stroke of the take-up occurs within onesixtieth of a second. The major portion of the active stroke of the take-up is utilized in taking up the slack in the threadso that only a small portion (approximatelyfid main shaft rotation) of the take-up stroke, indi'cated at 13, actually can cause thread to, be pulledpa'st the tension wheel, the brake i 'iresisting rotation of the tension wheel at other times; It can be assumed, therefore, that the velocity of inextensible linen thread as it is being pulled past the tension wheel ranges upwardly to an amount of inches. per second maximum. At this velocity, the tension wheel is rotated so rap idlyjthat there is provided asubstantial surplus of thread between the tension Wheel andthe' work as a result of overthrow caused by failure of the brake 42 to bring the tension wheel to rest the exact instant at which the tension on the"- thread is released. On account of variations in 65 mechanical adjustments and conditions -of the work, the surplus in the amount of thread drawn past the'tension wheeldurihg-each stitch varies substantially from one sewing cycle to another. 'lf'o reduce this variation of surplus thread in the machine of the Eppler patent, the pressure-on the tension wheel brake is increased in each sew ing' cyclein a" manner set forth in United States Letters Patent No. 2342243991 granted on august fir 1947, upon an application of Henry A, Landroche by" actuating the spring pressed lever 56 to p theabutment 52 into engagement with the brake supporting lever 46. During the take-up stroke of the take-up, the tension on the thread thus is increased, as indicated by the line labeled Frictionlncrease in Fig. 8, and the auxiliary takeup is moved against the stop screw 14. Assoon as a stitch is set andthe take-up completes its stroke,.the friction is again decreased to enable easy withdrawal of thread if necessary for the succeeding stitch formation. Decrease in friction is obtained by raising the abutment 52 from the lever 46 to a position indicated in Figs. 1 and 10. During the time the friction is decreased, the needle is looped and is retracted to the position of Fig. 1, with the loop of thread carried in its hook. At this time, the take-up is giving up thread to the needle so as to provide little or no tension in the thread which will resist the retracting movement of the needle. If any substantial degree of tension exists at this time, the auxiliary take-up 24 yields a. short length of thread, being raised slightly against the force of the plunger 34 before causing any rotation of the tension wheel.

Except during the needle looping and retracting operations and the stitch setting action, with the use of inextensible cotton or linen thread, the auxiliary take-up is arranged to maintain an intermediate position between a pair of motion-limiting stops, comprising a set screw 14 a threaded into the machine frame and a block 16 screwed to the machine frame, which block may be engaged by a set screw 18 passing through the auxiliary take-up. With proper adjustments of the auxiliary take-up for relatively inextensible thread, the reduced frictional force on the tension wheel usually is sufficient after setting each stitch to prevent slippage or other movement of thread in the substance of the work during formation of the succeeding stitch, into the set stitch, as will effect a substantial release of tension in that stitch. However, in some instances, the thread may slip through the substance of the work sufficiently to cause excessive looseness in spite of the high degree of tension applied to the thread by the increase of pressure on the tension wheel brake while setting each stitch. In the latter instance, the resulting seam will be faulty from looseness.

.[The mechanism for engaging and disengaging the abutment 52 from the brake supporting lever 46 is more fully described in the said Landroche patent. Briefly, this mechanism includes a pin 8,0 engaging the underside of the forward end of the actuating lever 56 and projecting laterally from a pivotally mounted block 82 having a recess within which a tooth-shaped projection 84 is mounted upon a lever 86 fulcrumed on a shaft 88. fixed in the machine frame and, at its forward end, the lever carries a roll 9t engaging a cam 92 on the sewing shaft 32.

As thus far described, the machine is substantially the same as in the patents above referred to. The elongation or extensibility of linen and cotton threads now in common use is illustrated in Fig. 9, in which the comparable characteristic stress-strain curves, correspondingly labeled, are indicated. Linen has an elongation before breakage of not substantially more than three per cent, whereas cotton may become elongated three times this amount before breakage. Cotton, however, is not as strong as linen and, consequently, the actual tension is less in the stitches formed of cotton thread since the adjustments required for-cotton thread in the machine are such that a lower braking pressure is applied to the tension wheel brake drum 42. In any event,- the amount of linen or cotton thread taken up bythe take-up is suificient to cause the major portion of each thread length required per stitch to be pulled suddenly past the tension wheel against the relatively heavy tension directly after each stitch is set.

The rotation of the tension wheel with inextensible linen or cotton thread is indicated in Fig.

8 by the line designated Linen. During the time the threaded needle is retracting from the work with a loop of thread to be employed in the formation of the succeeding stitch, a small further amount of thread may be pulled off the supply and drawn past the tension wheel if insufficient thread is provided by the auxiliary take-up. In some in;

stances, this small further amount of thread is drawn past the tension wheel at some portion of the sewing cycle other than during the needle retracting stroke, depending upon adjustments.

An illustration of the relative proportions of tension wheel rotation while the machine is being ings being one third actual size. During that por tion'of tension wheel rotation between the'lines 94 and 98, the frictional braking pressure applied to the tension wheel is increased, for instance, to an amount requiring a steady pull of fifteen pounds on the thread during the take-up stroke of the take-up. Thus, the major, portion of the total thread is drawn past the tension wheel during the take-up action in substantially less than a sixth of the complete rotation Of the sewing shaft, as explained above. The major portion of linen or cotton thread for each stitch, accordingly, may be drawn past the tension wheel in less than 25 of the sewing shaft rotation, necessitating sudden, jerky and irregular rotation of the wheel with consequent non-uniform lengths of thread being measured for successive stitches. During the remaining 335 of sewing shaft rotation, including the time of the needle retracting stroke, a small portion of the thread required in a succeeding stitch is drawn past the tension wheel under a decreased frictional braking pressure, as indicated by the angular distance between the lines 98 and 96.

An important feature of the present invention,- more particularly relating to the machine and method of sewing, consists in substituting, in place of linen or cotton thread, the specially treated synthetic, fiber-forming plastic thread of the type hereinbefore referred to, and in improving the machine to avoid the necessity of drawingpast the tension wheel the major portion of total thread required in forming a stitch during a small As above explainedpart of the take-up stroke. in connection with Fig. 7 in the drawings, the amount of thread drawn past the tension Wheel of the present machine during the take-up stroke is drawn past the tension wheel graduallythroughout the rest of each sewing cycle after the take-up stroke has been completed or through ap'-.

.justments than heretofore.

on the tension wheel. Accordingly,the forceof the spring 38 causes the auxiliary take-upto overcome the action of the tension wheelbrake when the brake pressure is relieved. Furthermore, the major portion of the thread tension in setting each stitch is no longer caused by the inertia effect of the tension wheel and brake drum, as with the use of inextensible thread, and accordingly a tension wheel brake spring of a greater strength is required to make up for the difierence resulting from loss of inertia effect. Thus, the spring 68 employed with the improved thread has several times the strength of the spring employed with inextensiblethread, inasmuch as the inertia of the tension wheel and brake drum affects the stitch setting tension in the thread in a comparativel small degree, the tension wheel rotation being smooth, without inertia effects.

With the adjustments thus made, the auxiliary take-up 24 acts as a stitch setting tensionlimiting device (see Fig. 3). Also, the action of the auxiliary take-up is such as to reduce still further the rotation required of the tension wheel during the stitch setting operation by giving up a short length only of thread during the stitch setting stroke of the take-up. It also prevents sudden,

excessive strains in the nature of impacts on the thread under stitch setting tension and distributes the time of tension wheel rotation over a longer period so that a slower continuous rotation of intensity of suddenly applied strains on the thread and correspondingly in the machine itself, a

smoother sewing operation is produced with greater uniformity both in formation and in setting of successive sitches in a seam. Also, the

moving parts of the machine and the bearing surfaces are less subject to damage from excessive impacts ,so. that less attention is needed on the part of the operator in maintaining proper operation of the machine. .A sewing machine operated .in this manner, consequently, is able to operate over a longer period of time and with fewer ad- Furthermore, the seam inserted actually is of a superior nature in that the threads continue to contract as the substance sewn yields and to draw the parts more tightly together for a substantial period of time after seam insertion. Thus, in the case of the i inseam in a shoe, the difficulties formerly encountered are overcome in the manner hereinbefore .set forth. In some instances where the upper of a shoe has been already tightened roughly about a last, it is possible by the, use of the presentmachine to tighten the upper sufficiently by means of the contracting thread to eliminate the necessity of a separatelasting operation.

The improved action of the thread to produce after. a lapse of time, the parts are drawn much closer together.

Also, an advantage of the present invention is apparent when the use of a liquid lubricant or hot wax on the thread is found unnecessary to eifective insertion of atight scam in sole leather, the ability of the thread to stretch and contract being far beyond the range of. similar qualities in threads previously employed for such purposes.

" The ability of the thread to contract the manner outlined is due in part to treatment and elongation of the thread prior to its use; In certain instances, the contractility is enhanced after a seam has been inserted by the presence of moisture in the sole leather or the action ofv tannin or the presence of other common astringent chemicals brought into contact with the thread.

Certain features of invention relating to a shoe and the method of making it herein disclosed are claimed in a divisional application for United States Letters Patent Ser. No. 790,111, filed December 6, 1947.

The nature and scope of the invention having been indicated and a particular manner of carrying out the invention having been described, what is claimed is:

1. That improvement in methods of inserting in a Work piece a seam composed of elastic thread of a size normally employed for attaching shoe soles, which comprises forming each stitch and applying to the thread a stitch setting tension and maintaining the major portion of said tension in the thread throughout the formation of each succeeding stitch to prevent retrograde slippage of the thread through the substance of the Work being sewn after each preceding stitch is set.

2. A shoe sewing machine for inserting thread seam, the thread of which has a size normally employed for attaching shoe soles and is composed of a fiber-forming material with a substantial elasticity, having a hook needle, a tension wheel located a sufiicient distance from the point of needle operation to enablethe thread to stretch substantially more than the length employed in a stitch, a tension wheel brake, and a spring for actuating said brake of sufficient strength to resist rotation of the tension wheel until the thread has stretched substantially more than the length employed in a stitch, in combination with, a main take-up acting during its stitch setting stroke to take up a length of thread approximately equal .to that employed in a stitch and to draw thread past the tension wheel while the thread is under a stitch setting strain, an auxiliary take-up, and a spring for actuating the auxiliary take-up constructed to limit the tension applied to the thread by the main take-u during its stitch setting stroke. w

3. A shoe sewing machine for inserting a thread seam, the thread of which has a size normally.

to that employed in a stitch and to draw. thread past the tension wheel while the thread is under a stitch setting strain, an auxiliary take-up, a spring for actuating the auxiliary take-up constructed to limit the tension applied to the thread by the main take-up, during its stitchsetting stroke, a brake acting frictionally to retard rotation of the tension wheel, a spring for actuating said brake with sufficient pressure to resist rotation of the tension wheel until the thread has stretched substantially more than the length em ployed in a stitch, and mechanism for applying the brake with two degrees of pressure, one of which causes the tension wheel to resist rotation under a stitch setting strain onthe thread,\and

proximately 335 of the complete-sewing shaft rtation without releasing the tension .on the previously formed stitch. in this way, jerky, irregu lar rotation of the tension wheel with overthrow .is avoided and uniform lengths of thread for suc 'oessive stitches of a seam are obtained.

The elongation characteristic of specially treated thread. is indicated in Fig. 9 by the curve labeled Nylon. For a comparable size the specially treated thread has greater strength and is capable of greater elongation before its elastic limit is reached than either linen or cotton thread. Furthermore, even beyond the elastic limit, to a considerable extent, elongation of the specially treated thread is reversible, particularly after a lapse of time. With the improved machine, advantage is taken of this and other characteristics of the speciall treated thread and full benefit is obtained from its contractility after the setting tension on each stitch is released. While thread thread is used is illustrated in Fig. 3 of the drawings, in which the angular distance between the lines H10 and I02 represents the amount of rotation of the tension wheel required to supply thread for each stitch. The tension wheel is located a substantial distance from the point of sewing op erations, the length of thread extending between the tension wheel and the sewing point being approximately eighteen inches. With this length of thread, an elongation occurs when a stitch setting tension is applied equal to several times the amount of thread used in each stitch. Thus, if the take-up acts to take up an amount of thread substantially equal to that used in a stitch, in- .sumcient tension will be applied to set the stitch during the first sewing cycle of a seam. A full stitch settin tension will not be set up in the thread until the third or fourth sewing cycle is completed, the thread between the tension wheel and the work being stretched during this time to supply the required thread without rotating the tension wheel.

After a full stitch setting tension has finally been set up after the be inning of a seam, the take-up gives up thread only in an amount equal.

to that taken up in setting the stitch. In giving up thread, the thread itself contracts so that no substantial release of tension occurs, a limited amount of residual contractility remaining in the thread, depending upon its preliminary elongation. On account of the continuous elongation in the thread thus held over from one stitch to another, less thread actually is used in sewing than with relatively inextensible linen or cotton threads. Accordingly, the angular distance between the lines it and :02 is indicated as being somewhat less than the corresponding distance between the lines 94 and st in Fig. 7, representing rotation of the tension wheel with inexten-- sible thread.

Since, by reason of the ability of the thread to stretch, it is elongated during the take-up stroke of the take-up, only'a small amount of thread is drawn past the tension wheel at this time suffi- -cient in length to maintain a uniform stitch setting tension in the thread, as indicated throughout the short angular distance [00, I04. This takes place :at the time both abutments '50 and 52 engage the bra-kc supporting lever 46 and a .heavy frictional pressure is applied to the tension wheel brake. Because of the comparatively short length of thread drawn past the tension wheel at this time, a less jerky, more nearl uniform, movement takes place in the tension wheel from one cycle .to another, with no opportunity for overthrow. After the stroke of the take-up has been completed, the braking pressure on the tension wheel brake is decreased by disengaging the abutment 52 from the brake lever '46. As soon as the braking pressure is relieved in this way, the elasticity in the thread causes the tension wheel to start rotating until the total amount of thread used in a stitch is drawn past the wheel. If the shorter portion of thread is drawn past the tension wheel between the lines I00 and HM within25 rotation of the sewing shaft 32., the remaining major portion of the thread is drawn past the tension wheel during 335 rotation of the sewing shaft, which obviously enables the tension wheel to rotate relatively slowly for the major portion of each sewing cycle. Also, the amount of thread drawn past the tension wheel while the heavy braking pressure is applied, being much less than that drawn past with a light pressure, a comparatively smooth uninterrupted rotation is produced in the tension wheel. The rotation of the tension wheel throughout a complet sewing cycle with the improved thread and corresponding changes in the machine is illustrated b the line designated Nylon in Fig. 8. The smoothness of this line in comparison with the Linen line is obvious.

In giving up thread the take-up relaxes a portion of the tension in the thread but the elasticity of the thread prevents the major portion of the tension from being relaxed. In other words, the length of the take-up stroke is insufficient to prevent the major portion of the tension in the thread from being maintained. The major portion of the tension, therefore, is maintained throughout the formation of each succeeding stitch and is of advantage in preventing retrograde slippage of the thread through the substance of the work being sewn after the preceding stitch has been set.

To limit the tension on the thread during each stitch setting operation when highly extensible or elastic thread of the improved type is employed, the auxiliary take-up 24 is yieldingly actuated downwardly against the thread with a pressure of such stitch setting intensity that the auxiliary take-up is held. from movement against the lower stop block 16 while relieved frictional pressure isapp'lied to the tension wheel brake during stitch formation. Thus, instead of employing a spring 38 designed to actuate the auxiliary take-up against the force of the thread during the needle looping and retracting operations only, as when inextensible thread is employed, the spring is replaced with one having approximately four times the strength to hold the auxiliary take-up set screw 18 against the stop block 76 substantially throughout the sewing cycle except while a stitch is set, the elasticity of the sewing thread taking up and giving out thread as required during the formation of a stitch, without causing excessively rapid or jerky rotation the other of which enables the auxiliary takeup to draw thread past the tension wheel.

4. A sewing machine for inserting a thread seam, the thread of which has a size normally employed for attaching shoe soles and is composed of a fiber-forming material with a substantial residual contractility after a stitch setting strain has been applied, having a hook needle, a frictionally retarded thread tensioning device, a main take-up acting to take up a length of thread substantially equal to that employed in a stitch and to set each stitch, and other stitch forming devices including mechanism for increasing the frictional action of the tensioning device to retard movement of thread drawn past the tensioning device during the stitch setting stroke of the take-up and to relieve the frictional action of the tensioning device to cause a substantially greater length of thread to be drawn past the tensioning device throughout the remainder of each sewing cycle without releasing the tension on the previously set stitch, in combination with a yielding auxiliary take-up, and a fixed stop for the auxiliary take-up, the force of the auxiliary take-up being insufficient to prevent its movement during the stitch setting stroke of the main take-up but the force being sufficient to cause it to move toward its stop during withdrawal of thread during relieved frictional action.

5. A sewing machine for inserting a thread 14 seam having a hook needle, a tension wheel, a main take-up for setting each stitch, and an auxiliary take-up, a stop for the auxiliary takeup, and mechanism for applying a heavy frictional force to the tension wheel while setting each stitch and a relatively light frictional force during stitch formation, in combination with an auxiliary take-up spring constructed with sufficient strength to cause the auxiliary take-up to give up a short length of thread for limiting the tension applied to the thread only while each stitch is being set and to overcome the tension in the thread and hold the auxiliary take-up in a position against the stop while the light frictional force is applied to the tension wheel.

JAMES P. FREDERICKSEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,030,743 Meyer June 25, 1912 1,108,560 Eppler Aug. 25, 1914 1,370,797 Egerton Mar. 8, 1921 2,045,644 Haas June 30, 1936 2,339,525 Stritter Jan, 18, 1944 2,340,632 Wheaton Feb. 1, 1944 2,355,107 Quinn et al. Aug. 8, 1944 2,388,333 La Chapelle Nov. 6, 1945

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