US2613963A - Wood clamp - Google Patents

Description

A. A. HOCHER Get. 14, 1952 WOOD CLAMP Filed March ll Patented Oct. 14, 1952 WOOD CLAMP Andrewy A. Hocher, Glenshaw, Pa., assignor to Hubbard & Company, Pittsburgh, Pa., a corporation of Pennsylvania Application `March 11, 1949, Serial No. 81,005

21 Claims.

My invention relates to gripsor clamps lfor gripping or clamping a bar or link of wood for the purpose of transmitting stress longitudinally to or from the said bar or link of wood.

The specific embodiment herein illustrated and described is utilized in a wood strain insulator for transmitting tension from a guy wire to a wood insulating bar or link. The clamp of my invention may be utilized for the transmission of stress in compression as well as in tension between the clamp and the Wood link.

, The problem to which the present invention is addressed is to provide a simple and inexpensive clamp which will be capable of developing a grip on the wood link substantially as strong as the link itself in tension or in compression. I have observed that the least expensive form in which wood for links of this character may be obtained is straight sticks of rectangular cross section,

such as may be produced easily and inexpensively by standard mill operations, that is, lengthwise sawing with or without planing of the surface. I conceived therefore that a specicaspect of the present problem lay in the'provision of a clamp which would be capable of developing substantially the full strength of a wood link or timber of rectangular cross section without the need for special formation of the end or ends to ie clamped.

I am aware that it is old to use the principle of the wedge to construct a self-tightening attachment or grip for a wood bar or shaft, and I do not claim the broad application of that principle as my invention. But, so far as I am aware, the self-energizing or servo principle of increasing the grip by the force of the load has never been applied to a straight sided piece of wood without special preparation or shaping of the part to be gripped. That is to say, heretofore the wedge has been essentially a part of the wood, whereas, according to my invention, it is a part of the clamp.

My present invention introduces the servo principle into the metallic parts of the clamp, so that the wood bar requires no special shaping or preparation. .This application of the self-energizing or servo principle involves allowing a certain degree of motion of the clamping members under the heads of the clamping bolts in order to increase or multiply the clamping pressure of the clamping members upon the bar.

A simple form of clamp which illustrates this principle as applied to` gripping the end of a bar or stick of timber comprises a pair of clamp `members applied to opposite sides of the bar.

The members have clamping faces preferably of non-lacerating character for engaging vthe wood surface to be clamped. The members have registering openings through which a clamping bolt may extend. These openings are such as to permit longitudinal motion of the clamp members under the bolt heads. In the preferred form herein shown, the openings are in the form of longitudinally extending slots. I employ `the term slotted to designate an Vopening which will permit the required longitudinal motion of the clamp member relative to the bolt. The clamping bolt, of which several may be utilized, is snugly seated in a transverse hole in the bar ofwood, and the opposite ends of the bolt pass out through openings in the clamp members. The bolt has a head and nut or a nut at each end, both of which may be termed heads 'The bolt isput under initial tension by drawing up the nut. This puts pressure upon the plates or clamp members vand forces them Y against the wood. The vbolt is adapted to remain stationary by virtue ofits seating in the transverse hole in the wood, yand the plates or clamp members are able to slide along the surface of the wood when the force of the load is applied to them.l A wedge which presents initially at least a relatively low angle is carried either on the plate or clamp members for movement under the bolt, or is carried onr the bolt for movement thereunderby thecooperating surface of thel plate or clamp member. Both the bolt and the plate or clamp member may carry wedging surfaces. The necessary relation Vis that as the load causes relative motion of the plate or clamp member under the bolt head, the wedge is driven in further between theplate or clamp member and the bolt head, increasing 4the tension of the bolt and increasing the clamping action of the clamp member. When the lwedge is to be moved with the plate or clamp member, it may be formed as a `Separate part carriedpby the clamp member. When the wedge is carried by the bolt, it may be formed as apart of the bolt head, or may be formed as a separatepart carried under the head. 1 y

Upon applying a pull (or push, as the case may be) upon the clamping members, they will move along the surface of the wood and the incline? or wedge Vparts will move relative to each other under the bolt heads. The reaction of the inclined surfaces against the bolt heads forces the` clamp members towards each other4 upon the surface of the stick thereby greatly increasing the frictional grip. The stress imposedon the bolt in tension to secure the desired compression 3 of the members upon the wood is a definite function of the effective angle of the engaging wedge surfaces. The shearing stress imposed on the bolt tending either to shear it off or to shear out the wood in front of the bolt towards the end of the stick is also dependent upon the angle of the wedge surfaces. The pull upon the clamp members slides the clamp members on the wood and slides the wedge of the clamp plates under the heads of the bolt, or slides the clamp plates under the wedge of the bolt heads. The pull is thereby resisted by two forces. The major part of the pull is taken by the friction of the clamp members gripping the bar and tending to pull it apart, and the minor part of the pull comes sidewise upon the bolt tending to shear off the bolt, and this being transmitted to the wood tends to shear out the grain ahead of the bolt or to split the end of the bar or stick.

vThus the Ywedge between the bolt and the clamp provides a servo or self-energizing effect in increasing the pressure upon the clamp members, and increasing the friction of the members on the Wood surface. The faces of the members which engage the wood surface are preferably relatively smooth, that is, they should not be so rough as to break the grain of an appreciable part of the section of the bar.

`The best application of this principle requires that the wood of the bar be prevented from escaping' sidewise under the pressure of the clamping members. When the two clamping members apply pressure to opposite sides of the stick only, there is a tendency for the wood, if not restrained, to escape sidewise, particularly under varying conditions of moisture, absorption and drying out. This aggravates the tendency of the wood to shear out ahead of the bolt, or to be split by the bolt.

My invention contributes a second principle, namely, to apply, at the same time that the clamp members are pressed towards each other on opposite sides of the wood, a similar selfenergizing pressure upon the wood laterally relative to the length of the bolt. This accomplishes two things: First, it prevents escape of the wood sidewise away from the grip of the clamp members, and, second, it compresses the wood sidewise against the tendency of the bolt to split the wood ahead of it, or to shear out the wood endwlse of the grain ahead of the bolt.

In the preferred form of the invention herein described and illustrated, these two actions are performed by two separate pairs of clamping members, one pair clamping front and back, and one pair clamping on the flanks. But the two actions may be attained in large part by a single pair of concave or channel shaped members which apply pressure upon the anks at the same time that they apply pressure front and back.

The lateral pressure may be developed sufficiently for some purposes by the provision of restraining walls along the flanks of the clamp members. Such walls may be continuations cf the margins of the front and back clamp members to extend over the flanks of the bar to be clamped. Such flank walls may, if desired, be interdigitated so as to cover the entire extent of the flank walls, but yet to allow movement of the fiank wall members towards each other.

The channel shape of the face of the clamp members may be round, that is, an arc of a circle, or an oval or polygon, or it may be a V, like the cross section of an angle bar, or it may be like the cross section of a channel bar. The cross 4 section of the wood bar under the clamp will in each case be such as to t the clamp.

While self-energization, as herein developed, depends upon a certain degree of travel of the clamp face upon the wood surface in order to bring the wedge into action, and to compress the grain of the woodl this is generally not objectionable. If desired, the clamp may be subject to pre-stress in the course of manufacture, so as to take up the amount of travel required for developing the desired clamping effect. The wedge is preferably of so low an angle, for example 10 to 20, as to fall within the critical angle of friction, so that the clamp once set or tightened up will remain tight, even if the endwise stress which sets up the clamping action is released. It' may even be reversed to the extent that it will not produce backward slip of the wedge surfaces under the bolt heads.

When the clamp is to be used to resist a stress in either of two directions, the wedge surfaces may lie to the back as well as to the front of the bolt head, the slot allowing the appropriate wedge surface to be pulledY under the head of the bolt in case the clamp is to resist tension or to be pushed under the bolt head when the clamp is to resist compression on the stick.

It is desirable to load the clamp members substantially equally since uneven loading tends to produce a lateral bending stress upon the bar at the region where the clamping stress is applied. Strictly equal loading is not essential so long as the disposition is such as to bring the stress substantially in line with the axis of the bar whereby the above requirement is observed of not producing excessive bending stress upon the bar.

Now in order to acquaint those skilled in the art with the manner'of constructing and operating the preferred form of my invention, I shall describe the same in connection wtih the accompanying drawings in which said form is illustrated.

While the preferred form of the invention herein specifically illustrated and described embodies the novel principles above referred to, it is only an illustrative exemplification of the invention, the true scope of which is to be ascertained from the appended claims.

In the drawings:

Figure 1 is a side elevational view of a wood strain insulator utilizing the clamp of my invention;

Figure 2 is a vside elevational View. on an enlarged scale of the clamp shown at the right hand end of Figure 1;

Figure 3 is a top plan view of the device of Figure 2 on the same scale;

Figure 4 is a cross sectional view taken on the line 4-4 of Figure 2; and

Figure 5 is a cross sectional view of a modified form of my invention.

The wood strain insulator shown in Figure l comprises a central wood shaft I rectangular in section and parallel sided and straight throughout. It may be produced by the inexpensive operation of sawing and planing. It is a bar or link, sometimes referred to as the wood section of the device. For the purposes of the specification the term wood is intended to cover not only the natural product as sawn from the tree, but also any similar product having the same general characteristics, among which are compressibility and the ability to absorb and to give off moisture. A self-energizing clamp is attached at each end of the wood section. These clamps are of the saine construction, and they vprovide yokelike portions 3, 3 which include a grooved metal sheave 4 mounted on a bolt 5 which extends through the offset ends of a pair of straps 6, 6 to form a suitable hitch or bearing for connection with the eye of the guy strand 1. This attachment is generally made by looping the strand over the sheave 4 and clamping the loose end against the main run of the guy as by U-bolts and clamps of known construction, as indicated at 8.

Each self-energizing clamp 2 includes a pair of clamp members G, each of which comprises a main body portion 9 adapted to iit flat against the corresponding side of the rectangular wood section I. Beyond the end f the wood section I the strap has a portion II bent diagonally inwardly and then a terminal portion I2 which is bent back into parallelism with the main body portion 9. In other words, the parts 9 and I2 are in parallel planes. A grooved sheave 4 is clamped between the terminal portions I2, I2 of opposed straps G by means of a bolt 5, which completes the yoke portions 3 of the clamp. The guy strand is laid around the grooved sheave 4 in the form of an eye, as previously described, and the object of this con-struction is to distribute the stress of the pull of the guy as evenly as possible upon the strands of the guy and upon the two straps 6, 6. The hitch is in any case intended to bring the stress of the load into line with the axis of the wood section. The straps each have slots I3, I3, in this case two in number, for receiving clamping bolts 23, 23. The bolts are preferably galvanized machine bolts. I may employ washers under the head and under the nut of each bolt. From a point near the front of the slot towards the rear of the slot the metal of the strap is embossed upwardly to form a wedge-shaped projection I5, I5, partly surrounding the rear of the slot I3 in each case, and having its feather edge disposed immediately behind the head of the bolt, so that upon initial movement of the strap 6, with respect to the bolt head (or nut), the inclined wedge-shaped boss I5 will be forced under the bolt head (or nut) and pressed against the flat side face of the wood section. These inclined wedges may be constructed in any desired manner so long as they travel with the plate or clamp members under the heads of the bolts.

It will be noted that the initial position of the strap relative to the bolt is such that the bolt is disposed in a part of the slot ahead of the wedges I5-I5 and the heads of the bolts with or without washers thereunder lie flat against the adjacent surfaces of the straps with the wedges immediately behind them. If desired, the bolt head may bear against a part of the wedge. In that case a suitably wedge shaped washer may be employed. Both the clamp member and the bolt washer have coacting surfaces which include a wedge driven between the bolt head and the clamp member as the clamp member is moved relatively to the bolt.

In one embodiment of my invention given by way of example, and constructed as shown in Figures l to 4, the cross section of the wooden bar, or wood section I, is two and three-quarter inches in the dimensionl shown in Figure 2, and three inches in the dimension shown in Figure 3. The strap G is made of one-quarter inch bar Steel. The bolts 23, 23 are one-half inch diameter machine bolts, and the yoke bolt 5 is a three-quarter inch diameter machine bolt. The strap B is three and one-quarter inches wide, so that the edges of this strap overhang the edges of the wood section I for the purpose of cooperating by interdigitation with the side plates I1, I8 on each side of the wood section I. In this specic example the angle of the wedges I5, I5 is about 18. While I have shown two side plates Il, I8 on each side of the wood section, it isv to be understood that there will be no departure from my invention in connecting these side plates together into a single side plate, or in having a greater number of side plates than there are shown in this specific embodiment. The straps 6, 6 vhave rectangular notches I9, I9 and 20, 20 cut in the edges thereof, these notches being, for example, one-half inch in depth and one inch long to receive tongues or projections 2I, 22 on each side of the side plates providing suitable interdigitation. The side plates I1, I8, are, in this example, of a width of two and one-half inches, which allows the plates to lie at against the corresponding side of the wood section without interfering with the movement of the straps 6, E towards each other in shrinking their grip upon the wood section I. These plates I7, I8 are of a total width, includingA the tongues 2l, 22, ofthree and one-half inches, so that when the clamp is first applied, the tongues 2 I, 22 lie in the notches I9, 20, respectively, with the tongues 2l, 22 registering with the adjacent edges of the clamping portions 9, 9 of the straps. The side plates are clamped upon opposite sides of the wood section I by means of bolts I4, I4, which are of the same diameter and character as the bolts 23, 23. These bolts pass through slots I3, I3 which are identical with the slots I3, I3 in the straps '5, 6, and there are similar inclined embossed wedge shape portions I5, I5 with their feather edges just at the bolt heads, so that any forward movement of the side plate clamp member 2I or 22, as the case may be with respect to its bolt, will immediately force the corresponding plate or clamp member inwardly by reaction of the inclined wedge I5 with the bolt head. The side plates I'I, I8 are preferably made of the same weight of stock as the straps.

For quantity manufacture, the embodiment illustrated is simple and inexpensive. The straps E, 5 are alike, and hence only one set of dies or die operation is required for both lefts and rights. Similarly, the side plates II, I8 are all alike, and may be formed as a single piece, four being required for each complete clamp. The ends of the wood section I are drilled to receive the bolts I4, I4 and 23, 23. lThe bolt holes in this specific embodiment are tangent, soA that the bolts, when inserted, will be tangent in the relation shown in Figures 2 and 3. Since the stress initially comes upon the straps 6, 5, it is desirable to `have maximum resistance of the bolts I4, le, to

endwise pulling out of the wood. Hence, the center of each bolt I4, I4, rests against the center of each bolt 23, 23, as isvshown in dotted lines in Figures 2 and 3, so that, instead of requiring merely the pulling out of the wood in front of the bolts I4, I4, it becomes necessary at the same time to pull out the wood in front of the bolts 23, 23 as well, if the clamp is to be pulled ofi' of the wood section. This feature of having the crossing bolts tangent is a refinement which is optional.

Upon pulling on the sheave 4, as in tightening up the guy strand, the pull comes upon the straps E, 5 substantially'y equally. It tends to slide the strap members along the surface of the wood section I, thereby bringing the wedges I5, I5 under the heads of the bolts I4, I4 and creating an inward pressure upon the surface of the wood.

The resistance of the wedges to movement under the bolt heads ltends to pull the bolts I4, I4 through the wood vof the Wood section. This is resisted by the wood section in front of the bolts.

Any movement of the straps 6, 6 on the surface of the wood section I requires the side plates I', i8 on each side of the wood section I likewise to move along the surface of the wood by virtue of the interengaging shoulders or interdigitation provided by the notches and tongues I9, 2I and 2S, 22, respectively. Consequently, the movement of the plates I'I and I8 to bring the wedges I5, I5 under the bolt heads of the bolts 23, 23 will produce a substantially comparable pressure on the opposite sides or flanks at right angles to the straps 6, 6. In other words, this is a rectangular self-energizing gripping mechanism which boxes in the four sides of the wood section I with a fairly even distribution of pressure at all points. the clamp upon the end of the Wood section I is surprisingly effective. In testing the strength of such an attachment upon a piece of fir wood for the wood section, and of the dimensions above given, the load and movement resulting therefrom are given in the following table:

Under this test, the metal of the yoke portion failed in front of the bolt 5, but there was prior thereto no failure, or any appearance of incipient failure ol the clamp or the wood.

The dimensions and proportions and the test data above given are by way of example, and are not intended to be limiting.

When the clamp is thus stressed, the endwise motion of the clamp members has a tendency to drag the outer ends of the bolts along with them, since there is considerable resistance of the bolt heads to riding up on the wedges. This causes the ends of the bolts to swing forward slightly and to compress the grain of the wood ahead of them. This action assists in tightening the grip of the members upon the bar.

l'f desired, the clamp may be given an initial stressing or prestressing to set up the clamping ei'ect at the factory. This will take up the strain or creep which imposition of the load otherwise tends to produce.

It will be observed that the side plates are separated instead of employed in a single side plate. I prefer this in order to make these side plates selfadjusting, each to accept its own load and to make its own engagement with the straps 6, 6. The simplicity, ruggedness and ease of manufacture are apparent.

In the event that it should be desired to reverse the direction of stress upon the clamps it is obvious that wedge portions, such as I5, would then be provided on the opposite end of the slots through which the bolts pass. Such inclined wedge shaped portions might be disposed at both ends if so desired. This will generally not be necesary, since in strain insulators the stress is uniformly in one direction. It is to be understood that washers, or thin plates may obviously be put under the bolt heads and nuts if so desired.

In consequence, the grip of In Figure 5 I have illustrated in connection with a round bar of wood how the self-energizing action may be applied from opposite directions along the longitudinal axis of the bolt, with confinement of the Wood sidewise of the bolt. In this case, a, round wood bar Ia is gripped between two concave clamping members 25 of sul;- stantially semi-cylindrical form. A through bolt 26 extends diametrically through the clamp members 25, 25 and the wood bar Ia. Slots 2l, 2l arranged as in the former embodiment permit the clamp members 21 to be slid along the surface oi the wood bar I a to bring into elect the inclined wedge portions 28, 28 lying on each side of each slot 27, 27. The bolt 26 has a head 2S at one end and a nut 30 at the other bearing either directly or through a washer upon the inclined portions 23, 2B, so that as the clamp pieni bers 25, 25 are slid along the surface of the wood bar Ia, the inclined portions 23, reacting against the bolt head and nut, will tighten the clamps to increase the grip of the clamping members 25, 25 upon the surface of the wood bar Ia.

The margins of the clamp members each side may be interdigitated by tongues and notches as indicated at 39, 3G, but this feature is optional. As the clamp inem ers 55, 25 are forced toui'ards each other to increase the pressure upon the wood bar Ia, the wood is compressed, 'out cannot escape sidewise with respect to the bolt even under the variations of wetting and drying to which an exposed device of this character is generally subjected. It will be ap parent that the clamp members 25, 25, instead of being cylindrical, might be V-shapecl in section and applied to a square bar with the same advantage. rIhe clamp members 25, 2a have at their forward end extensions by which a hitch may be effected, as in the embodiment shown in Figures l to Il, inclusive, or as otherwise desired Where interdigitation is provided, the load may be applied to an extension of one member only, and because of the interdigitation the two members will move as a unit. For certain purposes, it is not essential that the entire cross section of the wood bar be boxed in. However, for exlposure to the weather, as in the service to which a strain insulator as shown in Figure l may be subjected, the confinement of the wood about the entire pcri'oheral surface is advantageous, for the -wood becomes compressed and is less likely to 'absorb moisture and escape out of the grip o'f the clamp by what might be termed plastic dcformation.

I do not intend to be limited to lthe details shown or described, save only as they are made essential by the terms of the claims hereto appended.

I claim:

l. A self-energizing clamp for clamping a bar of wood comprising a pair of clamp members for engaging the bar between them and having hitch portions for connection of the load thereto, the clamp members having registering bolt openings and being adapted to have limited longitudinal motion endwise of the bar, a bolt adapted to be seated ixedly in the bar, and to extend through the bolt openings in the clamp members, said bolt having a pair of head members, said clamp members and said head members having engaging surfaces, said bolt openings in the clamp members extending longitudinally of the bar a distance substantially in excess of the diameter of the bolt to permit movement of the clamp members relative to the bolt longitudinally of the bar.

the engaging surfaces on one of said pair of members being inclined inwardly in the direction in which the clamp is adapted to be moved by application of the load whereby longitudinal movement of the clamp members relative to the bolt by application of the load forces the clamp members towards each other.

2. A self-energizing clamp for clamping a bar of wood comprising a pair of clamp members having faces for engaging opposite sides of the bar, said members having registering slots, a through bolt adapted to be seated xedly'in the bar, said vbolt having its ends extending through said slots and terminating in heads, the members being provided with inclined wedges tapering outwardly of the members in the direction opposite the direction in which the clamp members are adapted to be moved, said wedges being adapted to be forced under the heads upon relative endwise motion of the members with respectrto the bolts and thereby to move the membersv toward each other to increase their clamping grip upon the bar.

3. A self-energizing clamp for a wood bar comprising a pair of .opposed clamp members having terminal portions for attachment to a load, said members having inside clamping facesadapted to grip a wood bar between them and having reg-- istering slotted openings for receiving a through bolt, a bolt adapted to be disposedin and held against movement by said bar and toextend out through said openings and having heads for clamping the clamp members uponI the wood bar, and Isaid plates being provided with wedge surfaces tapering outwardly of the members in the direction opposite the direction in which the clamp members are adapted to be moved, said wedge surfaces being adapted to slide under said heads to increase the pressure of the clamp members upon the bar when the force vof the load slides the clamp members along the surface of the bar.

4. An element of a `self-energizing clamp for a wood bar comprising a clamp member having on its inside a bar engaging face, and having on its outside a longitudinally extending inclined wedge member, there being a slot extending lengthwise of said wedge member for receiving a clamping bolt and a terminal hitch portion oiset in the direction of said bar engaging face and extending forwardly of said wedge member, said wedge member being inclined outwardly in the longitudinal direction away from said terminal hitch portion. Y

5. A clamp for clamping a wood bar comprising a pair of clamp members having faces for engaging the surface of the bar to be clamped' and having hitch extensions oifset toward each other, a connection between said hitch extensions for applying a load substantially equally tosaid members, said members having registering vslotted openings and a through bolt adapted to be seated in the bar to be clamped and have its ends extend through said openings, heads on the ends of the bolt, said plate having wedge surfaces tapering outwardly cf the members in the direction opposite the direction in which the clamp members are adapted to be moved, said wedge surfaces being adapted upon motion of the plates longitudinally of the openings to be drawn under said heads, and thereby to force the plates toward each other to increase their grip upon the bar.

6. The clamp of claim wherein the members are formed with the inclined wedge surfaces, em-

10 bossed outwardlyalongl the sides of the slotted openings.

'7. Means for applying endwise stress to a wood bar which comprises a first pair of opposed clamp members having means to apply endwise stress upon both of them, a second pair o-f opposed clamp members adapted to be disposed laterally of the members of the rst pair, interengaging shoulders between the members of one pair with the members of the other pair, whereby endwse stress imposed upon the rst pair of members imparts endwise stress to the members of the second pair, at least one boltl extending through and connecting the members of each pair, said bolts having heads, said members having slotted openings through which said bolts extend, and having wedge surfaces adjacent said slots and in line with said heads, said wedge surfaces being inclined outwardly from the clamping surfaces of the clamp members in a direction opposite to the direction in which the membersare forced to move by the application of the load, the motion of the members relative to the bolts being adapted to cause the wedge surfaces to move under the bolt heads and to press the members of the corresponding pair toward each other.-

8. A clamp member comprising a substantially oblong body portion adapted to be pressed against the lateral surface of a wood bar, a hitch portion extending from the end of the body portion, said body portion having a longitudinally slotted opening for receiving a bolt and having the metal adjacent the sides of the opening pushed up to forma wedge shaped projection at the side of the slot, the surface of the wedge shaped portion being inclined outwardly relative to the body portion in a direction longitudinally of the clamp member away from the hitch portion.

9. A clamp member formed of heavy plate stock comprising a flat substantially oblong body portion adapted to be pressed against one side of a wood tension bar, a diagonal portion Yat one end of the body' portion and a hitch portion extending from the end of the diagonal portion, said hitch portion having an eye for attachment of a tension connection, said body portion having a longitudinally extending slot for receiving a bolt and having the metal adjacent the sides of the slot pushed up to form a wedge shaped projection at the side of the slot, said wedge shaped projection being inclined outwardly rela` tive to the body portion in a direction away from the end which has the hitch portion.

10. The clamp member of claim 9 having a shoulder at each lateral edge of the body portion for engaging a shoulder on a cooperating side clamping plate.

11. A wood bar clamping plate of slightly'less width than the side of the wood bar to be engaged, said plate having a longitudinally extending slot with the metal on the side of the slot raised in the form of an incline to provide a wedge shaped projection at each side of the slot and a projection at each edge of the plate providing a shoulder for forcing the plate longitudinally of the slot.

l2. Means for applying tension to a rectangular wood bar comprising four platelike clamping members adapted to engage the four sides of the bar, each member having a longitudinally extending slot for receiving the end of a'bolt, and having the metal at the sides of each slot shaped into an incline to wedge under thehead ofthe bolt, said incline extending outwardly relative to the plate in a direction opposite to that in which the plate is moved under load, a bolt extending through the slots of each pair of opposed members, said bolts having heads drawn against the members at the edges of the slots, and hitch means for simultaneously applying tension to one pair of said opposed members, the other pair of said members having interdigital connection along their edges with the edges of the said one pair of members.

13. A device of the class described comprising a straight sided wood bar rectangular in cross section, a rst pair of opposed plates lying on opposite sides of the end of the bar, a second pair of opposed plates lying on the other two sides of the end of the bar, said pairs of plates having interengaging shoulders, a bolt extending through each pair of plates and through the bar and having heads, said bar having bolts holes of substantially the same size as the cross section of said bolts, said plates having slotted openings for receiving said bolts and said plates having wedge surfaces adapted to be drawn under the bolt heads and pressed inwardly by motion of said plates relative to said bolts, and hitch means for applying endwise stress to said rst pair of plates, said wedge surfaces tapering outwardly from the plates in the direction opposite the direction of motion of said plates.

14. In combination, a wood section of substantially uniform cross section with straight sides, a pair of clamp members on opposite sides of said Wood section, coupling means for connecting a load to said members, bolts extending through the members and the wood section, and being seated in the wood section against motion longitudinally of said wood section, longitudinally extending slots in said members for receiving said bolts, there being inclined projections carried on the members to react against the bolt heads and to press the members toward each other when the members move forward on the surface of the wood section, said inclined projections tapering outwardly from the clamp members in the longitudinal direction opposite the direction in which the clamp members move under load.

15. In combination, a wood section of substantially uniform rectangular cross section with parallel sides, a pair of straps on one pair of opposite sides of said wood section, coupling means for connecting a load imposing member with said straps, a pair of plates on the other pair of opposite sides of the wood section, bolts extending through the straps and the wood section, slots in said straps for receiving said bolts, bolts extending through the plates and the wood section, said bolts being seated in the wood section against motion longitudinally of the wood section, said plates having slots for receiving said bolts, there being wedge surfaces carried on the straps and on the plates and disposed under the bolt heads to react against the bolt heads when the members move forward on the surface of the wood section under stress, said wedge surfaces being inclined outwardly relative to the straps and plates respectively in the direction opposite the direction in which the straps and plates are adapted to be moved under load, and interengaging shoulders on the straps and plates for compelling motion of the plates when the straps move, said shoulders permitting the straps to move toward each other and likewise permitting the plates to move toward each other to grip the wood section on all four sides simultaneously when load is imposed upon the straps.

16. The combination of claim 15 wherein the 12 bolts for the plates are tangent to the bolts for the straps and disposed at right angles to them, whereby the stress on the bolts that connect the straps are partially supported by the bolts that connect the plates.

17, A self-energizing clamp for clampingthe end of a Wood section, comprising pairs of opposed clamping plates covering the sides, a through bolt for each pair, self-actuating wedge means carried on each pair of plates reacting with the related through bolt, the plates or each pair having shoulders interengaging with plates of the other pair for common endwise motion on the wood section and for separate inward motion of each plate independently.

18. In combination, a pair of clamp members adapted to clamp a straight sided bar of wood between them, a through bolt seated in the wood bar and having its ends extending through slotted openings in said members, said bolts having heads pressing upon said clamp members to grip the bar, the members having engaging surfaces adapted to be wedged under the bolt heads when the members are moved longitudinally relative to the bolt, said heads having engaging surfaces cooperating with the engaging surfaces of said members on an incline which extends outwardly away from the members in the longitudinal direction opposite the direction in which the clamped members are moved by the applied load.

19. A self-energizing clamp for clampingf a wood bar of rectangular cross section, comprising a pair of clamp members for engaging a bar of Wood between them, said members having ex tensions connected together to form a hitch, said members being Wider than the faces of the bar to be engaged, whereby the members will everhang the edges of the said bar, said members having notches formed in said overhanging edges, a pair of clamp plates of less width than the faces of the bar to be engaged thereby, said plates having at their sides extending ears which project into the notches on said clamp members to provide interengaging shoulders between the members and the plates, the plates and the members lying substantially in planes at right angles to each other, at least one bolt extending between the clamp members to press them against the engaged faces of the bar, and at least one bolt extending between the plates to press them against the engaged faces of the bar.

20. The clamp of claim 19 further charactcrized by the provision of registering slotted bolt receiving openings in the members and registering slotted bolt receiving openings in the plates for receiving the corresponding bolts, said bolts having heads for pressing the corresponding plates and clamp members against the sides of the bar, and said plates and clamp members hav ing Wedging surfaces under said bolt heads inclined inwardly in the direction of the hitch connection for forcing the plates toward each other and the clamp members toward each other simultaneously by movement of said plates and clamp members relative to said bolts in the direction of the hitch.

21. In combination, a bar of wood the end of which is adapted to be gripped for the applica tion of a tension load thereto longitudinally of the bar, a clamp member having a clamping face adapted to engage a lateral surface of the bar adjacent its end, said member having a hitch portion extending beyond the end of the bar, bolt disposed transversely in the bar and held substantially against motion longitudinally of 13 the bar, said clamp member having an opening to receive said bolt, said opening being slotted longitudinally of the bar to allow motion of the clamp member relative to the bolt in a direction longitudinally of the bar, said bolt having a head for pressing the member against the side of the bar, and said clamp member having a wedge portion inclined inwardly in the direction of said end of the bar, said Wedge portion lying under the bolt head.

ANDREW A. HOCHER.

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

Number UNITED STATES PATENTS Name Date Schimmel July 16, 1900l Barney v Oct. '164, 1917 Fields June 7, 1921 Austin Dec. 15, 1931 Austin Sept. 13, 1932 Austin Sept. 4, 1934 Warren Dec. 7, 1943 Manke May 18, 1948

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