US2135650A

US2135650A - Adjustable compensator for nail driving mechanism

Info

Publication number: US2135650A
Application number: US97788A
Authority: US
Inventors: Herbert E Twomley
Original assignee: FMC Corp
Current assignee: FMC Corp
Priority date: 1936-08-25
Filing date: 1936-08-25
Publication date: 1938-11-08
Anticipated expiration: 1955-11-08

Description

NOV. 8, 1938. E TWOMLEY 2,135,650

ADJUSTABLE COMPENSATOR FOR NAIL DRIVING MECHANISM Filed Aug. 25, 1936 2 Sheets-Sheet l INVENTOR.

' ATTORN EYS NOV. 8, 1938. H, E. TWQMLEY 2,135,650

ADJUSTABLE COMPENSATOR FOR NAIL DRIVING MECHANISM Filed Aug. 25, 1936 2 Sheets-Sheet 2 ATTORNEYS INVENTOR.

Patented Nov. 8, 1938 PATENT OFFICE ADJUSTABLE COMPENSATOR FOR NAIL DRIVING MECHANISM Herbert E. Twomley, Riverside, Califl, assignor,

by mesne assignments, to Food Machinery Corporation,,San Jose, Calif., a corporation of Delaware Application August 25,

9 Claims.

My invention relates to nail driving mechanism and has particular reference to nail driving apparatus employedin connection with box and crate manufacturing machines.

' In the art of manufacturing boxes or applying lids or covers to boxes made of wood, it

is the common practice to provide a machine including a suitable nailing table or'support upon which the box parts may rest and above which 1 is mounted a reciprocating nail driving mechanism, usually consisting of one or more nail driving drivers telescopically mounted in nail chucks or nail guides into which nails may be fed so that upon the downward movement ofthe nail drivers 1 through the nail chucks the lower ends of the nail drivers will engage the nails and drive them through nail chucks and into and through the boards of the boxes which are to be operated upon.

Typical examples of box making and lidding machines are represented in United States Letters Patent granted to George D. Parker, on J anuary 3, 1911, No. 980,431, and No. 1,576,213, granted March 9, 1926, each of which illustrates nail driving mechanism including the nail drivers and chucks as stated above.

In the manufacture of different types of boxes, or in the manufacture of a series of boxes from different kinds of boards, it frequently happens 30 that the lumber from which the boards are made varies considerably .in hardness so that the amount of force required to drive a given sized nail through the same thickness of board will vary between considerably wide limits, depending upon the density or hardness of the particular boards used. It has been discovered that when the machines are adjusted to drive a nail through the hardest board expected to be encountered,

such machines will overdrive the nails when softer wood is used, or the amount of force required to drive the nail being less than the force for which the machine is adjusted, an objectionable hammering or pounding in the machine will occur.

In order to prevent the overdriving of nails, I have devised a nail compensating mechanism by which the nail drivers are connected to a reciprocating nail driving head in such manner that when a predetermined resistance is encountered, the connection between the nail drivers and the nail driving head will relieve the strain. This device is illustrated and described in my copending application Serial No. '750,289, filed October 27, 1934, and provides a 55 nail driving mechanism which will automatically 1936, Serial No. 97,788 (oi. 1-10) compensate for different thickness of board and prevent crushing of the wood or overdriving of the nails,that is, will insure the nail heads being just driven flush .with the upper surface of the boards and no further.

It is an object of the present invention, however, to add to such nail driving mechanism as is described in my said copending application adjustable means for predetermining the maximum force exerted by the nail driver upon a nail and thus to compensate for variations of hardness in the boards.

Another object of the invention is to provide a nail driving mechanism for nailing machines wherein the nail drivers are connected to a reciprocating nail driving head in such manner as will permit the nail driving head to be moved through the same distance for all nail driving operations but which will permit the nail driver to exert only a predetermined force upon a nail, which predetermined force may be suitably varied by a simple adjustment.

Another object of the invention is to provide a nail driving mechanism which will drive the nails through boards of varying hardness and in which the force exerted upon the nail may be adjusted in accordance with the hardness of the board to prevent the exertion of more force than is actually required to drive the nail flush with the surface of the board.

Another object of the invention is to provide a machine of the character set forth in the preceding paragraph wherein the force exerted by the nail drivers is adjustable to require the consumption of only that amount of energy necessary to drive the nails flush with the boards, and in which the nail drivers can be readily adjusted to suit boards of varying hardness.

Other objects and advantages will be apparent from a study of the accompanying drawings, read in connection with the following specifications, wherein Figure 1 is a vertical sectional view of a nail driver, nail chuck, and nail driving headconstructed in accordance with my invention, and provided with my adjusting means;

Fig. 2 is a vertical elevational view of the nail driving mechanism illustrated in Fig. 1, looking in the direction of the arrows IIII shown in Fig. 1;

Figs. 3, 4 and 5 are diagrammatic views, illustrating the relative positions of the nail driving head, the nail drivers, and the linkage connecting the nail drivers and the nail driving head in their three positions assumed by these parts dur- 55 ing the operation of driving a nail with one setting of my adjusting mechanism, Fig. 3 illustrating the start of the cycle of operations; Fig. 4 illustrating the position assumed as the nail is being driven and just prior to encountering the maximum resistance to the driving of the nail; and Fig. 5 illustrating the position assumed at the end of the nail driving operation when the nail has been driven flush with the surface of the board; and

Figs. 6, '7 and 8 are diagrammatic views similar; respectively, to Figs. 3, 4 and 5 but illustrating the positions assumed by the nail driving mechanism parts when my adjusting means is set to exert a lesser driving force upon the nails.

Referring to the drawings, I have illustrated in Figs. 1 and 2 a portion of a box making or lidding machine of a type familiar to those skilled in this art, the only features of improvement in the general construction of such machine with respect to the present invention being that such machine is provided with a vertical frame memher I at each end of the machine, connected together at their upper ends by a pair of cross rods 2 and 3 which may be secured to the frame member I by means of a clamp 4. The-vertical upright frame member I may be of any desired size though I have illustrated the same herein as being circular in cross section to constitute a cylindrical guide upon which a nail driving head assembly may be reciprocally guided. The nail driving head assembly is preferably constructed as a cross head indicated generally by the reference character 5' and including a suitable end casting 6 surrounding the upright frame member I (it being understood that there is one of these castings surrounding the vertical frame member at the opposite end of the machine), the casting 6 constituting an end support for apair of cross bars or rods I and 8 which extend across the machine. The rods I and 8 with their bearing castings 6, constitute a vertical reciprocating cross head from which may be suspended a plurality of nail drivers and nail chucks distributed in any desired spaced relation between the ends of the machine, as will be more fully described hereinafter.

The cross head or nail driving head 5 may be vertically reciprocated by any suitable power means, and I have illustrated awell known form of driving mechanism therefor'including a connecting rod 9, the lower end of which may be connected to a crankpin not shown but which corresponds in all respects to the crankpins on the driving wheels or shafts of nail driving machines such as those illustrated in the Parker patents hereinbefore referred to), and the upper end of which is pivotally connected, as indicated at II], to a pin II extending from and preferably integral with the bearing casting 6.

The nail drivers I2 are suspended from the cross rods 1 and 8 of the nail driving head 5 by toggle link connections illustrated in my co-' pending application, Serial No. 750,289, hereinloefore referred to, which include'a pair of toggle link'assemblies, one including a link I3, the upper mentary lower links I 6 and IT. The lower ends. of the links I 6 and I! are coupled together by means of a pin I8, which pin also passes through one side of a cross head I9.

The other toggle link assembly includes an upper link 29 similar in all respects to the link I3,

the upper end of which is connected at H ,to the cross rod 8 and the lower end of which is coupled by means of a pivot pin 22 to the upper end of a pair of complementary

lower links

23 and 24, while a'pin 25, similar to the pin I8, connects the lower ends of the links 23-24 and also passes through the opposite endfof the cross head I9.

The cross head I9 constitutesan attachment for the nail driver I2 and is illustrated herein as comprising a substantially rectangular block having a central bore 26 extending therethrough to receive a threaded stem 21 attached to or formed integrally with an enlarged upper portion 23 of the nailpunch I2, the junction between the stem 21 and the enlarged upper portion 28 of the nail driver constituting a shoulder against which the lower faceof the cross head I 9 bears, the nail plunger I2 being secured to the cross head I9 by means of a suitable nut 29 threaded upon the stem 21. The lower portion of the nail driver I2 is illustrated as a relatively small rod, preferably havinga diameter slightly in excess of the diameter of the head of the nail to be driven thereby. A nail chuck assembly 30 is mounted upon the nail driver I2 and is illustrated herein as comprising a substantially cylindrical body member '3l having a bore 32 extending from its upper end of a diameter to just fit the enlarged portion 28 of the nail driver I2. The nail chuck may be supported relative to the nail driverin any suitable manner, though I prefer to support the same'directly upon thenail driver I2 as by providing an elongated longitudinal slot 33 extending into the side of the enlarged portion 28 of the nail driver and intowhich projects the end of a set'screw 3 1. The nail chuck assembly is therefore suspended from the nail driver I2 so' that as the naildriver is elevated the set screw 34" will engage the lower end of the slot 33 and thereafter any further upward movement of the nail driver I2 will lift the nail chuck assembly 30 while when the nail driver I2 is moved downwardly the nail chuck assembly will also move downwardly therewith until the lower end of the nail chuck assembly 30 engages the board to be operated upon and thereafter further downward movement of the nail driver will cause the nail driver I2 to move'down through the nail chuck to engage the nail and drive the same out through the lower end of the nail chuck assembly and into and through the board to be operated upon.

v A nail entrance opening '35 is formed in the lower side portion of the nail chuck body 3I through which nails may enter the chuck. In the normal or elevated position of the nail driver I2, (that is when the nail driving head is in its elevated position), the lower end of the nail driver I2 will be in the position shown in Figs. 1 and 2, the extreme lower end of the nail driver I2 being spaced upwardly from the lower end of the chuck body 3I, permitting a free passage for the nail through the chuck body 3I so that the nail may fall into a position immediately below the nail driver I2. Upon the lower end of the chuck body 3| is mounted a pair of

chuck jaws

36 and 31 which are formed as complementary members,

each having a nail-guiding groove fil formed,

therein to guide a nail 38 into position immediate- 1y below the nail driver I2. The nail chuck jaws 3'5 and 31 are each mounted respectively upon the lower end of a

spring support

39 and 40 attachedas by means of screws on opposite sides of the chuck body 3| so that as the nail driver I2 is moved downwardly through the nail chuckland engages the nail 38, the jaws 35 and 3I'may spring outwardly to permit the passage of the nail driver 12 therethrough in the nail drivingoperatiom A nail guide 42, including a tunnel 43, is attached to one side of the nail chuck body 3!, preferably by forming the inner side of the nail guide 42 to just fit the cutaway section of the nail chuck body 3| and is held in place thereon by means of a pair of spring fingers 4% (only onerof which is shown in Fig. 1) which e11- gage flanges 45 on the guide 42 and hold the same in the position illustrated in Fig. 1.

With the construction thus far described it will be apparent that whenever the nail driving operation is to take place the connecting rod 3 will be moved downwardly to move the nail driving head 5 downwardly. This movement will cause the nail driver [2 to move downwardly toward a workpiece supported in any suitable manner in the machine. In Fig. 1 a workpiece is shown consisting of a box end 62 having a bottom board 63 secured to the lower edge thereof, the box being supported upon rollers 64 forming a part of the nailing machine for rigidly supporting the box during the nail driving operation. A board 50 is shown in position on the upper end of the head 62 ready to be nailed. At the same time that the connecting rod 9 is moved downwardly to move the nail driving head 5 downwardly, the nail chuck assembly 33 will also be 1 movement will be arrested, while the continued downward movement of the nail driving head 5 v will cause the nail driver E2 to move down through the nail chuck assembly 38 to engage the head of the nail 39, and as the nail driving head 5 continues its downward movement the nail driver i 2 will press the nail out through the jaws 3B and 3? and into and through the board or other workpiece until the nail has been driven just flush with the surface of the board.

When the nail is driven just flush with the surface of the board, the nail driver I2 should be just flush with the lower surface of the chuck jaws 36 and 31 (though it is the common practice to arrange thenail driver l2 to project a slight distance below the jaws to insure the full driving of the nail) and at this time the shoulder 45 formed between the enlarged portion 28 of the nail driver l2 and the nail driving head portion thereof will engage the shoulder 57 formed by the reduction in the diameter between the bore 32 through which the enlarged portion 28 operates and the smaller bore 59 in the nail chuck body 3! through which the reduced nail driving head operates and any further effort to drive the nail driver 82 downwardly will transfer the driving force to the nail chuck assembly 30 tending to press the nail chuck assembly down into the surface of the board which is operated upon.

As is explained in detail in my copending application hereinabove referred to, the arrangement of the toggle links l3-l6l1 and 2G--2 2a is such that when the increased resistance to the downward movement of the nail driving head 5 is encountered when the nail has been driven flush with the board, the toggle links will break, that is, will swing about their pivots 'il5-i3 and 8--2225, respectively, and any further downward movement of the nail driving head 5 will be accomplished without forcing the nail 75'? driver l2 and its chuck assembly to a further The nail chuck assembly 39.

downward position. It will be noted that this breaking of the toggle links occurs by reason of the fact that the pivot I 8 is spaced out of vertical alignment with the pivots l5 and I for the toggle links I3l? and the pivot 25 is disposed out of vertical alignment with the pivots B-22 of the links 29-24.

It will also be observed that the links l6ll and 2324 are each provided with outwardly extending ears 50 through which pins 5| and 52 extend, the pin 5| extending through the ears on the links is and l! to receive upon its outer end a pair of

clevis

53 and 54. The clevis 54 constitutes a connection between the pin 5! and a tension spring 55, the opposite end of which is secured to a clevis 56 secured upon the pin 52 which extends through the ears 50 on the

links

23 and 24 while a similar spring, not shown, extends between the clevis 53 on the opposite end of the pin 5! and a similar clevis (not shown) on the opposite end of the pin 52.

By properly selecting the tension of the spring 55 and its component spring the amount of effort or resistance required before the toggle links will break may be selected to insure any desired driving force to be exerted by the nail driver [2 and it will be noted that when the toggle link assembly breaks the vertical component of the downward force exerted by further movement of the nail driving head 5 will be reduced in direct ratio with the motion or angle through which the links l6-l'l are moved relative to the associated link I 3, and similarly the angle through which the links 23-24 are moved relative to the link 20. Thus if the springs are selected to achieve a predetermined driving force prior to the breaking of the links, then upon the breaking of the links the increased tension of the springs 55 will be compensated for by the angular position of the toggle links relative to each other and a substantially downward force will be thereafter exerted upon the nail driver l2 equal to or slightly less than the force which was exerted prior to the breaking of the toggle links.

The construction hereinbefore described provides for a definite limitation of the driving force transmitted between-the nail driving head 5 and the nail driver l2 which will insure that the nail will be driven with a definite force and that if the board to be operated upon its atahigherlevel, or is thicker than another board, the toggle link assembly will break to avoid overdriving the nail or crushing of the board, and it frequently occurs that the boards will vary considerably in hardness, and while a suitable adjustment for boards of one hardness may be made by the selection of the springs and the angular disposition of the links of the toggle assembly, such selection would permit of the driving of the nail with more force than is necessary if the wood to be operated upon is not quite so hard and a considerable Waste of energy will occur when theboards aresoft. Furthermore, with the initial selection of the spring and toggle link angles for the driving of nails in extremely hard wood, the driving of nails in relatively soft wood would cause the nail driving mechanism to unnecessarily pound the softer wood, crushing the same and making the machine unnecessarily noisy.

I have provided a ready means for adjusting the force to be exerted by the nail driving mechanism tolimit the energy required to just that necessary to drive the nails in wood of any selected hardness, which adjusting mechanism inobserved that the nail driving head 5 has: been face of the board 66 and in this figure it will be cludes a tapered abutment for the toggle links which may take the form of a nut 51 of substantially truncated rectangular pyramid shape threaded upon the stem 21 upon opposed side surfaces which bear inwardly extending ears. 58, formed upon the links lB-H and 23-24 respectively. By moving the nut 51 upwardly, the tapered surface of the nut will cause the links Iii-Ii and 23-25 to be swung outwardly, thereby reducing the vertical component of the force transmitted from the nail driving head 5 to the nail driver I2 and moving the nut 51 downwardly while allowing the links l5-l6 and 23-24 to assume a more nearly vertical position and will increase the vertical component of the force exerted between the nail driving head 5 and th nail driver l2.

It will thus be observed that by merely adjusting the nut 51 upwardly or downwardly the vertical component of the driving force transmitted to the nail driver l2 may be adjusted Within relatively great limits and may be selected to fit the hardness of the boards which are to be nailed in the machine.

By referring particularly to Figs. 3, 4 and 5 it will be observed that the nut 51 is in one of its lower positions selected for driving nails through boards of relatively great hardness. In Fig. 3 I have illustrated the relative position of all of the boards in this adjustment prior to the start of the nailing operation, and it will be observed that the toggle links I3-l6 and 20-23 are almost straight, that is, in a position wherein the vertical component of the force to be exerted is almost the full force exerted by the downward movement of the nail driving head 5.

In Fig. 4 I have illustrated the relative position of the parts with the same adjustment when the nail has been driven almost fiush with the surface of the board 60. In this position it will be moved through the distance indicated at c and that the nail driver l2 has similarly been moved through the same distance only. The total distance through which the nail driver l2 must move is indicated by the arrow a. Fig. 4 illustrates the parts immediately prior to the breaking of the toggle links. In. Fig. 5 I have illustrated the relative position of the parts when the nail 38 has been driven just flush with the surobserved that the nail driving head 5 has been moved through a total distance T, this distance representing the distance through which the nail driving head will always be moved upon a single downward movement of the connecting rods 9. However, it will be observed that the nail driving head 5 has moved through a distance in excess of that required to drive the nail 38 flush with the board 60, this excess distance or overdrive being indicated. by the arrow m and unless the toggle links are used or a similar arrangement is made, the nail driver I2 would drive the nail below the surface of the board 60. However, due to the fact that the nail chuck assembly 30 stops at the surface of the board 60 and the nail driver l2 can move down through the chuck only to a position substantially flush with the lower ends of the chuck jaws, the resistance which has been built up against the further downward movement of the nail driver l2 has reached a value in excess of the tension of the spring 55 and the toggle links have broken permitting this overdrive of the nail driving head 5 without requiring further downward movement of the nail driver I2, and in this manner the nail is driven just flush with the surface of the board.

By referring to Figures. 6, '7 and 8, it will be observed that I have illustrated the relative position of the parts in the same form of the nail driving operation with the nut 5! adjusted to an upper position for use in driving nails in and through boards which are considerably softer than indicated in Figs. 3, 4 and 5. In Fig. 6 it will be observed that initially, before any downward movement of the nail driving head 5, the toggle links lit-l6 and 20-23 are disposed at a greater angle than that illustrated in Fig. 3 so that while the nail driving head 5 still moves downwardly through the total distance T, but due to the disposition of the'toggle links at a; greater angle, the nail driver [2 has been elevated slightly above its normal position as shown in Fig. 3, and hence this nail driver must move through the distance indicated by the arrow'b in order to drive the nail flush with the board 6|. By referring to Fig. '7, it will be observed that when the nail driver 12 has been moved down to a position wherein the nail is almost flush with the surface of the board 5 i, the nail driving head 5 still has a distance, indicated by the arrow to travel, but it will also be observed that the distance o is less than the distance m indicated in Fig. 4. In other words withthe adjustment of the nut 51 as indicated in Figs. 6, 7 and 8, the amount of o-v-ertravel of the nail driving head 5, in order to drive the nail just flush with the surface of the board, is considerably lessened.

As indicated in Fig. 8, the final position of the parts when the nail is driven completely flush with the board is substantially the same as that indicated in Fig. 5, wherein the resistance to further downward movement of the nail driver H has built up to the value necessary to swing the toggle links outwardly, as indicated in this figure.

It will therefore be observed that the machine may be constructed and assembled in the same manner whether the boards to be nailed are hard or soft and the nail driving head may be constructed to have the same stroke or total downward movement irrespective of the hardness of the boards for which the machine is to be used and by the mere adjustment of the nut 51 the effective length of the stroke of the nail driver l2 before the toggle links yield, may be varied to fit the hardness of the boards which are to be nailed. In other words, the machine is essen tially constructed independently of the hardness of the boards with which it is to be operated and after it is in service the operator of the machine may, by the simple adjustment of the nut 51, adapt the machine to boards of various hardness as he observes the effect of driving the nails through any selection of boards.

By employing the adjustment as disclosed herein, the total amount of energy which is required to be exerted by the nail driving head 5 and the nail driver I 2 is just that amount which is required for the driving of the nails flush with the surface of the boards and objectionable pounding or hammering by the machine, due to the exertion of an excess force, is eliminated.

While I have shown and described the preferred embodiment of my invention, I do not wish to be limited to any of the details: of construction shown herein, except as defined in the appended head movable through a predetermined distance relative to a workpiece upon each of its operations, a nail driver, means coupling said nail driver to said driving head for movement there with including toggle links yieldable upon the exertion of a predetermined resistance to movement of said nail driver, and means for adjusting the relative angle of said toggle links to vary the resistance required to cause them to yield.

2. In a nail driving mechanism, a nail driving head movable through a predetermined distance relative to a workpiece upon each of its operations, a nail driver, toggle link means connecting the nail driver to said driving head, the midpoint of said toggle link means being dis-aligned with the ends of the toggle link means, means yieldably restraining further dis-aligning movement of said midpoint but permitting it to yield upon the exertion of a predetermined resistance whereby said nail driver may travel a lesser distance than said driving head, and means for varying the extent of said dis-alignment to vary the resistance required before said links will yield.

3. In a nail driving mechanism, a nail driving head movable through a predetermined distance relative to a workpiece upon each of its operations, a nail driver, coupling means connecting said nail driver with said driving head adapted to yield upon the exertion of a predetermined resistance to the movement of said nail driver, and means for adjusting said coupling means to lengthen or shorten the distance traveled by said nail driver prior to engaging said workpiece.

4. In a nail driving mechanism, a nail driving head movable through a predetermined distance relative to a workpiece upon each of its operations, a nail driver, coupling means for connecting said nail driver to said nail driving head for movement therewith including a toggle link, one end of which is connected to said driving head and the other to said nail driver, and an abutment engaging said toggle link to limit movement of the midpoint of said toggle link in one direction toward but short of the position of alignment with the ends thereof, said abutment being adjustable to vary the degree of disalignment of said toggle link, and means for yieldably restraining movement of said toggle link away from said abutment.

5. In a nail driving mechanism, a nail driving head movable through a predetermined distance relative to a workpiece upon each of its operations, a nail driver, coupling means for connecting said nail driver to said nail driving head for movement therewith including a toggle link, one end of which is connected to said driving head and the other to said nail driver, a tapered abutment engaging one of said toggle links to normally dispose the midpoint of said toggle links out of alignment with the ends thereof, means for variably positioning said abutment relative to said links to vary the said disalignment, and means for yieldably resisting further movement of said midpoint of said toggle link out of alignment with the ends thereof.

6. In a nail driving mechanism, a nail driving head movable through a predetermined distance relative to a workpiece upon each of its operations, a nail driver, coupling means for connecting said nail driver to said driving head, including a pair of sets of toggle links disposed upon opposite sides of the longitudinal axis of said nail driver, one end of each of said sets of toggle links being connected to said nail driver and the other end being connected to said driving head, a stem disposed between the midpoints of said toggle links, an abutment adapted to be moved along said stem to engage links of both of said toggle links to variably dispose the midpoints of said toggle links out of alignment with the ends thereof, and means for yieldably resisting movement of said midpoints of said toggle links out of alignment with the ends thereof.

7. In a nail driving mechanism, a nail driving head movable through a predetermined distance relative to a workpiece upon each of its operations, a nail driver, coupling means for connecting said nail driver to said driving head, including a pair of sets of toggle links disposed upon opposite side" of the longitudinal axis of said nail driver, one end of each of said sets of toggle links being connected to said nail driver and the other end being connected to said driving head, a stem disposed between the midpoints of said toggle links, a tapered abutment adapted to be moved along said stem to engage links of both of said toggle links to variably dispose the midpoints of said toggle links out of alignment with the ends thereof, and means for yieldably resisting movement of said midpoints of said toggle links out of alignment with the ends thereof.

8. In a nail driving mechanism, a nail driving head movable through a predetermined distance relative to a workpiece upon each of its operations, a nail driver, coupling means for connecting said nail driver to said driving head, including a pair of sets of toggle links disposed upon opposite sides of the longitudinal axis of said nail driver, one end of each of said sets of toggle links being connected to said nail driver and the other end being connected to said driving head, a stem disposed between the midpoints of said toggle links, a tapered abutment threaded upon said stem and adapted to be moved therealong to engage links of both of said toggle links to variably dispose the midpoints of said toggle links out of alignment with the ends thereof, and means for yieldably resisting movement of said midpoints of said toggle links out of alignment with the ends thereof.

9. In a nail driving mechanism, a nail driving head movable through a predetermined distance relative to a workpiece upon each of its operations, a nail driver, means coupling said nail driver to said driving head comprising a toggle link, and means for variably positioning the elements of said toggle link at various angles to each other to vary the normal spacing between said driving head and said nail driver.

HERBERT E. TWOMLEY.