US1656264A - Typewriting machine - Google Patents

Description

Jan. 17, 1928.

' W. G. BOSWORTH TYPEWRITING MACHINE Filed Dec. 24. 1923 Patented J an. 17, 1928.

UNITED" STATES PATENT OFFICE.

WILLIAM G. BOSWORTH, OF NEW YORK, N. Y., ASSIGNOR T UNDERWOOD TYPE- WRITER COMPANY, 0F NEW YORK, N. Y., A CORPORATION OF DELAWARE.

` TYPEWRITING- MACHINE.

Application led December 24, 1923. Serial No. 682,398.

This invention relates to releasable connections between the line-space wheel and the platen in a typewriting machine, arranged to enable the platen to be rotated any desired amount greater or less than a linespace movement without disturbing the line-space wheel.

Devices of-this character usually comprise friction clutch-members arranged to be op-v erated by a finoer-piece or handle through pressure-multiplying means to move under high pressure into firm Lgrippingengagement with theline-space wheel. It is desirn able that the clutch-actuating` handle have only ashort movement, and, as a result of the shortness of this movement and `of the pressure-multiplying connections, the range of movement of the clutch-members is very short. indeed. The clutch mechanism is required, therefore, to be made with extreme precision in order to function` properly, that is, in order to cause the clutchmembers to grip the line-space wheel firmly and with substantially equal force when moved to effective position, and to completely release the line-space Wheel when. moved only a short distance to` ineffective position. The members. moreover, `are subject to Wear, and are therefore apt to operate defectively after they have been in use for awhile. l

In accordance with one feature `of the present invention.. the need for this extreme precision in the manufacture of the clutch mechanism is eliminated. The clutchasse1nbly is so constructed and arranged that the clutchanembers, when fully assembled, may be adjusted quickly and easily to theproper i i operating relation in the assembly from the exterior thereof, and this bythe operation of a single, very simple, adjustingr device. To this end. the clutch-members may consist of outwardly-extending arms forming, in effect, a topje-le. The inner ends of the arms abut against aplung'er, or abut each other within a slot in the plunger. which may be moved in a directionpartially to straighten the toggle and thereby to force the outer ends of the arms into powerful gripping en- `agement with the line-space Wheel. The plunger is arranged to be operated by a cam forming one arm of an operating lever, which is pivoted in a support that may be adjusted froml the exterior of the assembly to adjust the cam toward and from the plunger, so that the adjusted cam, when swung about its pivot, may be caused to produce the desired gripping co-action between the clutch-members and the linespace wheel, regardless of the exact size of the clutch-arms, the plunger, the cam, the line-space wheel, etc. The adjustable camsupport preferably consists of aplug or bushing threaded into alsocket in an enlarged end of the platen-axle. It willbe seen that the cam, and therefore the operating range of the clutchanembers, may be veryV finely adjusted by the turning of the plug.. and that there will be no tendency for the force exerted by the cam to displace the plug.

The cam v`is arranged to be moved to or slightly beyond a deadcenter position to `lock the plunger and the clutch-arms positively in effective position. The locking of the clutch-arms in effect-ive condition does not, therefore, depend upon a straightening of the toggle formed by them. The arms are made. in fact, of such length that they liccoine effective when the toggle has been only partially straightened. The clutch may, therefore, be adjusted again and again as the ends of the clutch-arms wear away without its being necessary to replace said arms with new ones, as would be the case each time a little wear occurred if the arms were required to be straightened.

The pressure multiplication effected by this arrangement of the plunger and togglearms is considerably less than that which would result from a full straightening; .of the toggle. This deficiency is more than compensated for, however, by arranging the cam-lever to transmit the force applied to its handle, with multiplied effect. The cam and plunger, therefore` in addition to locking the toggle-arms effective in their partially straightened condition, form also auxiliary pressure-multiplyingr means. The combined `effect of the cam and the toggle enablesa high. pressure to be exerted bythe cluteh-arms upon theV application ofla very moderate force to the clutch-operating handle. A j

Heretofore j alatenwclutches employingV the principle of straightening out a toggle-linkage have depended upon large coacting surface areas to create a rictional resistance under the pressure troni the toggle. Surface contacts oi this character provide a self-locking clutch when the toggle is at a deadcenter position, and require considerable manual torce to hreal: the toe'g'le in releasing the clutch. Furthermore, a lirictional engagement or contact is not recognized as a positiv-e means to transmit power.

Another Jfeature ot the present invention provides a non-selt--locking toggle by conditioning diametrically-disposed clutcharms to become eliieetivc t a point in advance of a deadenter position, and which point will lie-predetermined by the angula coaction between the clutch-arms and the ratchet-wheel, and troni which point the clutchearms will automatically` release themselves. The outer end ot each clutch-arm is beveled or backed ott so that there will he no iiat surface on the arms te engage with the ratchet-wheel, but the hutte-cd a, which is formed with an angle ot' less than 90", may be forced into biting engagement' with an internal square corner et 900 termed at the juncture of the clutch-drum to the 'tace of the ratchet-wheel. 's knife-edge tormation not only7 provides tor a positive driving clutch connection between the linaspacc wheel and the platen-shaft, but also pcrmits the instant release ot the clutch due to the absence of surface friction between the arms and the wheel. when the pressure against the arms is manually removed. The inner ends of the clutch-arms may be similarly backed oit, and the knife-edges so formed may be slightl;7 rounded to facilitate a rocking` non-cutting movement of the arms at the points et engagement with the plunger, to reduce trictional Contact to a minimum.

It may be that the clutch-arms will be et slightly diifercnt lengths. or that some other part of the clutch will be unsvmmetrically made, which would cause thc arms to tend to grip the line-space wheel unequallv. In accordance with a feature disclosed in one form of the invention. imperfect operation due to such irregularity ot construction is obviated. The ifilung'cr is slotted througi'h to rece`ve the inner ends ot the clutch-arms and to permit them to abut against each other. The clutch-arn'is, liou'ever.y are unconnected to the plunger or to each other. By this construction the pressure exerted by each of the arms depends upon resistance.

be moved transversely of the platen and hence in a direction not tending to disturb the letter-space position of the carriage.

By arranging the clutch-operating mechanism within the platen-axle, a very simple and etiicient construction is obtained. The number and the sizes of the operating parts are reduced. The direct and re-acting forces involved in operating the clutch are fully taken care of in the platen-axle itself, without any tendency to strain or displace other parts held insecurely to the platenaxle.

Other features and advantages will hereinafter appear.

In the accompanying drawings,

Figure 1 is a front elevation, partly in section, of a part of a typewriting machine having the present improvements applied thereto; the clutch being shown in its effective condition.

Figure 2 is a vertical section on the line 2-2 of Figure 1, looking in the direction et the arrows.

Figure 3 is a view similar to Figure 1, but showing the clutch ineffective.

Figure 4 is a side elevation of the platentrame and the clutch-assembly, the cover plate of the platen-rame being removed.

Figure 5 is a detail perspective showing parts of the clutch-assembly separated from cach other.

Figure 6 is a detail perspective showing the clutch-arms, plunger and p1ungerspring separated from each other.

Figure 7 is a vertical section similar to the sectioned portion of Figure 53. showing a form of the invention different from that disclosed in Figures 1 to G; the clutch being ineiiective.

Figure 8 is a vertical section on the line 8-8 of Figure 7, looking in the direction of the arrows.

The machine, which may be of the Underwood type, comprises a platen 1() made fast to its axle 11 by screws 12' and journaled bv means of said axle in a platen-frame 13, mounted in a traveling carriage (not shown). The line-space lever (not shown) is arranged for operation to engage and thrust 4to theV rear a line-space slide 14, which carries a pawl 15 to engage the ratchet-teeth 16 of a line-space Wheel 17. normalli7 tast to the platen-axle 11, for imparting line-space movements of definite extentto the platen 10. A detent 18al is pressed by a spring 19a against the ratchetteeth 1G to engage between successive teeth to assist in controlling the exact line-space position of the platen 10,

It is sometimes desirable to rotate the platen 10 more or less than a whole number ot line-spaces, and this without disturbingl the position ot the line-space wheel 17, so that the regular line-feeding of the platen may be resumed immediately after such irregular feedingV movement. There is accordingly provided a clutch operable to "effect a firm driving connection between the linespace Wheel 17 and the platen 1() or to completely disconnect them at the will of the operator.

The line-space wheel 17 includes a hub portion 1S and a drum 19 which comprises an annular tlange 20 forming 'a clutch element fast to the line-space wheel.- The platen-axle 11 is enlarged at its left end by stages, the first enlargement 21 being larger than the axle proper, the secon-d enlargement 22 being largerthan the iirst enlargement 21, and the third or outermost enlargement 23 being the largest of all. The line-space Wheel 17 is journaled by its hub portion 18 upon the first enlargement 21, and has a vertical Wall 24 engaged by the shoulder 25 formed at the inner end of the second enlargement 22. A retaining nut 26 is threaded onto the axle 11 to prevent longitudinal movement of the line-space wheel 17 thereon. Clutch-arms or dogs 27 extend through radial slots 28 in the second enlargement 22 into recesses 29 formed in a plunger 30 and having shoulders 31 and 32 at their outer and inner ends. lThe plunger 30 is` slidable in a bore 33 in the center of theenlargements 21 and 22 of the platen-axle 11.

The clutch-arms 27 are conditioned to effect a clutching engagement `Within the drum 19 by a toggle action which becomes effective at `a point in advance of a straightcned-out or dead-center position. Contrary to prior forms of toggle-actuated platenclutches, frictional surface contact between the clutching elements is avoided. The ends of both arms 27 are beveled or backed off to provide for knife-edge formations at each end thereof` the outer knife-edge of each arm diametrically engaging the drum 19, and the. inner ends engaging the end face 31 of the recess 29 and the plunger' 30. When the arms 27are in clutching relation with the linespace Wheel as shown in Figure 1, a line drawn diagonally through an arm to bisect both knife-edges gives an angle of approximately 30O removed from a dead-center position`- The outer knife-edge of each arm is forced to bite into the square corner of the drum 19 2O and has the same curvature as the inner face of the drum. The inner ends of the arms are fulcrumed at the plunger 30, and these ends may be slightly rounded.` As both endsof the arms 27 have only knifeedge contacts, one edge with the drum and the other edge with thel plunger', there are no frictional face contacts to retard the Withdrawal of the arms the instant `pressure is manually removed from the plunger;

The outermost enlargement 23 has a large threaded socket 3G within it, into which isV threaded a plug or bushing 37 bearing a clutch-operating cam-lever 38; The cam-lever 38 consists ofa cam 39 mounted on a pivot-pin 40 in the plug 37, the pivot-pin y extending at right angles to the platen-axle 11, and an operatinghandle or finger-piece 41 for the cam 39. The finger-piece 41 is op-` erable in a 'slot 42 in the plug 37, being limited in its ineffective position by engagement with the endwall 43 of the slot 42, and in its effective position by engagementwith the end Wall 44`of the slot 42. In thislatter position, the cam 39 is slightly beyond the deadcenter position, and hence serves to lock the clutch in effective condition. In this position, ythe finger-piece 41 is substantially in alignment with the` axis of the platen 10, and doesnot, therefore, have any substantial movement at the rotation ofthe platen, so that it can be readily found by the operator in any rotated position of the platen. The finger-piece 41 extends slightly beyond the left platen-turning knob 45, and hence will necessarily be engaged by the operators hand when the platen-knob is seized to rotatethe platen. In order to avoid injury to the hand of the operator, the linger-piece is substantially spherical at its outer end 46, but, in order to assist the operator in determining the direction in which the fingerpiece should be moved to render the clutch ineffective, smooth and rough flats 47 and 43 are provided on the spherical portion, one of which Will 4always be in the view of the operator. These flats also enable the ope-rator to grip the end 46 Without slipping.

Naturally the heavy end 47 will vibrate by gravity at each revolution of the pla-ten Vwhen the clutch-elements are in' a released state as shown in Figure 3. To prevent suoli vibration and to remove anyi'ubbing contact between the arms 27 and the drum 19, a light coil-spring 34 may be seated Within the end of the bore 33 to press against the end of the plunger 30 to prevent idle vibration of the lever 41 from the position in Figure"3 when the platen is rotated independently of the ratchet-Wheel.

In assembling the device, the plungerspring 34 and the plunger 30 are placed in the bore 33 and the clutch-arms 27 are inserted through the `slots 28. The line-space Wheel 17 is then put in'place on the platen-axle 11, and is secured against end-Wise movement thereon by the retaining nut 26. The plug or bushing 37 is then threaded into the socket 36. In performing this last step, the correct adjustment of the plug 37 may be quickly determined by placing the iinger-piece`41 in position to hold the clutch effective, that is, in the position shown in Figure 1, and by using it as a handle to turn the plug. When `the ,p'lug 37 has been turned just as far as possible in this manner, it will befound that the `clutch is securely locked and that the movement of the finger-piece 41 about the pivot 40zto render the clutch ineffective, as seen in Figure 3, Will permit the clutch-arms 27 to be completely disengaged from the drum 19, so that the platen-axle may rotate freely with respectthereto. A retaining screw 4-9, threaded through the platen-turning Yknob and the enlargement 3, to bear against the plug 37, may now be tightened to prevent accidental rotation of the plug. The platen-axle 11 is then passed through the platen-frame 13 and the platen 10, and is secured to the latter b y the screws 12. A platen-turning knob is then secured upon the platen-axle 11 by screws 51. It Will be seen that, in order to again adjust the clutch when the arms 2T or the drum 19 has become worn, it is only necessary to loosen the retaining screw l19 and turn the plug 37 in the manner just described.

In Figures 7 and 8 a form of the invention is disclosed which is different in an important respect from the form shown in Figures 1 to 6, and heretofore described. This form is the same as that already described in every respect, except that the plunger 30 has a slot 52 extending through it to receive the clutch-arms 27 and permit them to be arranged with their inner ends in abutting and supporting relation to each other. These clutch-arms 27 are unconnected to the plunger 30. or to each other, and hence `the plunger and arms form pressure distributing and equalizing means for transmitting the pressure of the cam 39 equally to the outer ends of the arms 27 so that they will be caused to grip the drum 19 with equal force, even though they may be of slightly different lengths, or other parts of the clutch may he arranged in an unsymmetrical manner.

Variations may be restorted to Within the scope of the invention, and portions of the improvements may be used Without others.v

Having thus described my. invention, I claim:

1. In a typewriting machine, the combination of a platen and a platen-shaft, a linespace Wheel loose on the shaft and formed with a clutch-drum, a detent for the linespace Wheel, a pair of rigid, co-operative, loose. separately-mounted, nipping, radial clutch-arms having knife edges. said arms being over-length to serve as self-opening tog gle-elements and opposed to each other, and self-locking manual means operable upon both arms to force them radially into nipA ping engagement with the drum.

2. In a. typervriting machine, the combina.- tion With a revoluble platen and a line-space Wheel, of a bearing member for the line-space Wheel, said member being fast to the platen and having an axially-extending bore and radial slots extending outward from the bore, a plunger slidable in said bore, clutch-arms extending through the slots and engaging thc plunger, said arms beingV arranged to be forced outward into clutching engagement With the 1ine-space Wheel by movement of the plunger in one direction, and to be released by movement of the plunger in the reverse direction, a plug threaded into the outer end of said bearim.r member, and a plunger-operating nger-piece pivoted in the plug, the arrangement being such that the plug can be turned to adjust the position of the finger-piece, and so to adjust the range of movement of the clutch-arms, to assure perfect gripping of the clutch in effective position and complete disengagement of the clutch in ineffective position.

3. In a typewriting machine, the combination of a platen and a platen-shaft, a linelspace wheel loose on the shaft and formed with a clutch-drum, a detent for the linespace wheel, a pair of rigid, co-operative, loose, separately-mounted, nipping, radial clutch-arms having knife edges, said arms being over-length to serve as self-opening toggle-elements and opposed to each other', a plunger to guide and push both of the clutch-arms into nipping engagement with the line-space Wheel. and manual means operable to apply pressure to the plunger.

al. In a typeivriting machine, the combination Vof a platen and a platen-shaft, a` finger-Wheel for the platen, a line-space Wheel loose on the shaft and formed with a clutchdrum, a detent for the line-space wheel, a pair of rigid, co-operative, loose, separatelymounted, nipping, radial clutch-arms having knife edges, said arms being over-length to serve as self-opening toggle-elements and opposed to each other, a central, slidable element provided with means to force the arms radially into nipping diagonal engagement with the line-space Wheel, and means rotatable With the finger-Wheel and operative independently thereof to actuate the sliding element. Y

5. In a typewriting machine, the combination of a platen and a platen-shaft, a linespace Wheel'loose on the shaft and formed with a clutch-drum, a detent for the linespace Wheel, a pair of rigid, co-operative, loose, separately-mounted, nipping, radial clutch-arms having knife edges, said arms being over-length to serve as self-opening toggle-elements and opposed to each other, and self-locking manual means operable upon both arms to force them radially into nipping engagement with the drum, said arms mounted at their inner ends .to form a self-equalizing toggle Within the drum.

6. In a typewriting machine, the combination with a revoluble platen and a linespace Wheel therefor, of a line-space Wheel support fast to the platen, a platen-turning knob fast to the support, and means for clutching the linespace wheel to its support, comprising a pivoted linger-piece extending from the support beyond the platen-turning v toggle-elements and opposed to each other,`

knob, the finger-piece being round to prevent the operators injuring `his hand upon it when rotating the platen-tui'ning knob, and having rough and smooth flats at o osite sides to indicate to the operator t e irection in which the finger-piece should be moved to operate the clutch.

7. In a "typewriting machine, the combination ofy a platen and a platen-shaft, a linespace wheelloose on the shaft and formed with a clutch-drum, a detent for the linespace wheel, a. pair` of rigid, co-operative, loose, separately-mounted, ',nipping, radial clutch-armshaving knife edges, said arms being over-length to serve as self-opening a central plunger to guide the clutch-arms and support their inner ends to effect the toggle movement, and manual means operable to engage the plunger.

V8. In a typewriting machine, the combination of a platen and a platen-shaft,a lincspace Wheel, a detent therefor, a finger-knob forrotating theplaten independently of said line-space Wheel, a non-sclf-locking clutch including a pair of loose, diametrically-expansible, rigid, sharpened, nipping, opposite, toggle-acting clutch-arms, a slidable`,'central element provided with means to expand the clutch-arms radially into nipping engagements with the line-s ace wheel,

and meansrotatable Withl the nger-knob and operable independently thereof to actuate the sliding element.

9. In a typewritin machine, the combination with a revolu le platen and a lnespace Wheel therefor, of means for effecting driving connection between the line-space Wheel and the platen, comprising clutching members, a common operating means for said members, a cam movable in engagement with said operating means to make the' clutching members effective to grip the linespace Wheel, and means for adjusting the position ofthe cam for varying `the effect on the clutching members produced by its operation. i

10. In a typewriting machine, the combination with a revoluble platen and a linespace Wheel therefor, of aline-space Wheel su port fast to the platen and having an axially-extending bore and radial slot-s extending out from the bore, a slotted plunger slidable` in said bore, diametrically-arranged clutch-arms extending through said slots `in the support-member and into abutting engagement with each other Within the slot in the plunger, and means for moving .the plunger to force the arms outward into clutching engagement With the line-space wheel, the arms, by reason of'their abutting relation to each other, acting with equal pressure against the line-space Wheel.` 11. In a typeWriting machine, the combination of a platen and a line-space wheel spacewheel and its support includin therefor, a support for the line-space wheel fast to the platen, means for efectln a ositive driving connection between t e inefr a pair of diametrically-disposed knife-edgeda clutcharms;` supported and operable to diagonally engage the line-space Wheel under a clutchprcducing pressure, and an adjusting device to predetcrn'iiiie the pressure to be applied to the clutch-arms. 4

l2. In a typenfriting machine, the combination with ayrevoluble platen and a linespace Wheel therefor, of a lline-space Wheel support fast to the platen, a finger-piece mounted on the support,and a clutch operated by the finger-piece for making the linespace Wheel fast to its support, said clutch comprising a plurality of sharpened, loose, opposed toggle-members movable into nipping enfragement with the line-space Wheel, means 'eing `provided for automatically equalizing the nipping pressure exerted by said members, manual means to operate the toggle, and a single adjusting device operable t0 change the nipping force exerted by said members.

13. In a-'typeivriting machine, the combination withv a platen and aline-space ratchet- Wheel for the platen co-axial therewith, ofia platen-axle fast to the platen, and means for effecting a driving connection between the line-space ratchet-Wheel andthe platen-axle,

comprising -a` drum fast to the line-space ratchet-Wheel, a pair of toggle arms positively driven by the platen-axle but unconnected thereto, a slide movable in the direction ofthe axis of the platen to press against the inner ends, of the toggle arms and thereby force` their outer ends outward into gripping engagement with the drum, and "a spring for flexing the toggleV to make the arms inedective, the toggle arms being unconnected to the slide and being therefore free to rock about their outer ends in moving to ineffective position, and the outer ends of the arms being rounded to prevent binding and to facilitate such rocking movement.`

14. In a typeivriting machine, the combination With a platen and a line-space ratchet- Wheel for the platen co-axial therewith,` of a platen-axle fast to the platen, and means for effecting a driving connection between the line-space ratchet-Wheel and the platen-axle, comprising a drum fast to the line-space ratchet-wheel, a pair of toggle arms positively `driven by the platen-axle but unconnected thereto, a slide movable in the direction of the axis of the platen to press against the inner ends of the toggle arms to artially straighten the toggle and thereby orce the outer ends of the arms outward into gripping engagement with the drum, means for positively locking the arms in effective gripping position, and a spring for flexing the toggle when the arms are released by the locking means, the arrangement being such that the arms can be easily moved from effective position by the spring, due to the fact that the toggle formed by them is only partially straightened when eective. g

15. In a typewriting machine, the combination with a platen and a line-space ratchet- Awheel for the platen eo-aXial therewith, oft a platen-axle fast to the platen, and means for effecting a driving connection between the line-space ratchet-wheel and the platenaXle, comprising a drum tast to the ratchetwheel, a pair of toggle arms positively driven by the platen-axle, a toggle-operating member movable in a direction to straighten the toggle to torce the toggle arms outward into gripping engagement with the drum, the arms heilig of such length that they grip the drum and are arrested by it when the toggle is only partially straightened, the toggle arrangement serving to multiply thc force exerted by the vtoggle-operating member, and a cam lever for actuating the toggle-operating member, the cam lever comprising a handle arm and a cam arm and being arranged to transmit to the toggleoperating member with multiplied effect the force applied to the handle arm.

16. In a typewriting machine, the combination with a platen and a line-space ratchetwheel for the platen co-axial therewithA` ot a platen-axle fast to the platen, and means for effecting a driving connection between the line-space ratchet-wheel and the platenaxle, comprising a. drum fast to the ratchetwheel, a pair of toggle arms positively driven by the platen-axle, a toggle-operating member movable in a direction to straighten the toggle to 'torce the toggle arms outward into gripping engagement with the drum, the arms being of such length that they grip the drum and are arrested by it when the toggle is only partially straightened, the toggle arrangement serving to multiply the force exerted by the toggle-operating member, and a cam lever for actuating the toggleoperating member,'the cam lever comprising a handle arm and a cam arm and being arranged to lock the toggle-operating member positively in position to maintain the toggle arms in effective gripping relation to the drum,

17. In al typewriting machine, the combination with a platen and a line-space wheel for the platen coaxial therewith, of a linespaee-wheel support fast to the platen, means for effecting a positive driving connection between the line-space wheel and the platen, including a pair of diametricallydisposed clutch-arms arranged to become efeotive when the toggle formed by them engages with the line-space wheel, a lever pivoted within said support and operative to force both arms into angular clutching engage-1 ments with the line-space wheel, and operating connections between the lever and the clutch-arms, including adjustable pressuremultiplying means and positive locking means for retaining the clutch-arms in positive clutching engagement with the linespace wheel.

18. In a typewriting machine, the combination oi' av platen and a platen-shaft, a linespace wheel loosely mounted upon the shaft and including a drum having an annular interior corner formed therein, a pair of slidahle clutch-arms, each arm having knifeedged end-formations and movable to diagonally engage the knife-edge thereof with said corner ot the drum, a plunger supporting the inner end of each clutch-arm to expand both arms, and manually-operable camming means to apply pressure to the plunger to force the clutch-firms into positive locking engagement with the corner of the drum only. i

19. In a typewriting machine, the combination of a, platen and a platen-shaft, alinespace wheel loosely mounted upon the shaft and including a drum having an annular interior corner ilormed therein, a clutch including a pair of clutch-dogs rotatable with the shaft and diagonally disposed towards the annular corner, the ends of both dogs being backed of to provide a knife-edgeengaging forn'lation, a plunger operatively connected to the inner ends of both dogs to force the outer sharpened ends into engagement with the corner of the drum and positively lock the drum and line-space wheel to ,the platen-shaft, and manual'means operable to actuatc and finally lock the plunger.

20. In a typewriting machine, the combination of a platen and a platen-shaft, a linespace ratchet-wheel including a clutch-drum mounted for a free movement on said shaft,

a detent for the ratchet-wheel, a finger-wheel permanently secured to the platen-shaft to rotate the platen, a clutchincluding a pair of clutch-arms diametrically related to each other to effect a toggle-clutching engagement within said drum `under pressure and be automatically sel-opening'when the pressure is removed, a plunger operable to diagonally expand the clutch-arms, and a manually-operable pivoted cam to operate the plunger to expand the clutch-arms and positively hold the expanded arms under pressure.

WILLIAM G. BOSWORTH.

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