US3774875A

US3774875A - Retractable concrete form

Info

Publication number: US3774875A
Application number: US00106035A
Authority: US
Inventors: F Ecker
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-01-13
Filing date: 1971-01-13
Publication date: 1973-11-27
Anticipated expiration: 1990-11-27

Abstract

A retractable form for casting material, such as concrete, thereabout, has an elongate, substantially unitary structure including a pair of oppositely facing side legs connected together by an upper portion with the legs being movable relative to each other. The structure further includes first means coupled between the legs for setting them in a first position when the first means is in a first state, and for moving them out of the first position and toward each other, thereby retracting the form, when the first means is moved into a second state so that the form may be disengaged from material cast thereabout. The structure also includes second means coupled between the legs and cooperating with the first means for preventing movement of the legs relative to the upper portion when the first means is in the first state, the second means permitting movement of the legs out of the first position and toward each other when the first means is moved from the first state into the second state.

Description

United States Patent [1 1 App]. No.: 106,035

Related .U.S. Application Data Continuation-impart of Ser. No. 777,941, Oct. 3, 1968, abandoned, which is a continuation-in-part of Ser. No. 696,536, Jan. 9, 1968, abandoned.

[52] US. Cl..... 249/178, 249/180, 249/185 [51] Int. CL... B28b 7/30 1 [58] Field of Search 249/29, 50, 176, 249/182, 184, 185; 25/128 K; 52/695 [56] References Cited UNITED STATES PATENTS 3,148,434 9/1964 Gage 25/131.5 1,363,391 12/1920 Carpenter.. 249/29 975,242 11/1910 Higgins 249/29 2,628,403 2/1953. Garrison 25/128 K X 975,083 11/1910 Shepard 249/180 875,551 12/1907 McDonald... 249/185 X 2,892,237 6/1959 Nelson et a1... 249/176 X 1,285,295 11/1918 Marqua 249/185 1,016,284 2/1912 Meek 2 49/180 2,914,816 12/1959 Lundgren 52/695 X FOREIGN PATENTS OR APPLICATIONS Italy 249/185 Ecker Nov. 27, 1973 1 RETRACTABLE CONCRETE FORM [76] Inventor: Fred 'L. Ecker, 1905 Liliano PL, Z f'f g w g f g M d C Ssls an xammer- 0 Or lerra a re a l 9 Attorney-Christie, Parker & Hale 22 Filed: Jan. 13,1971

[5 7] ABSTRACT A retractable form for casting material, such as'con- Crete, thereabout, has an elongate, substantially unitary structure including a pair of oppositely facing side legs connected together by an upper portion with the legs being movable relative to each other. The structure further includes first means coupled between the legs for setting them in a first position when the first means is in a first state, and for moving them out of 1 the first position and toward each other, thereby re- 1 tracting the form, when the first means is moved into a second state so that the form may be disengaged from material cast thereabout. The structure also includessecond means coupled between the legs and i 13 Claims, 14 Drawing Figures WENTEUnuvzT I973 SHEET OMUF 11 I N VEN TOR. Q50 A AZ 5F PAIENTEUnnvm r975 SHEET UBUF 11 PAIENIEDunvm ms SHEET 08 0F 11 INVENTOR. Ffm A. 644 52 M%ZM/J% PATENTEUNHVZY ma SHEET OSUF 11 PATENTEVUNQYU 1975 saw 110F11 v lllllllllllllllll RETRACTABLE CONCRETE FORM CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of patent application Ser. No. 777,941, now abandoned, filed on Oct. 3, 1968 as acontinuation-in-part of patent application Ser. No. 696,536, now abandoned, filed on Jan.

BACKGROUND OF THE INVENTION This invention relates to apparatus for casting material. More specifically, the invention relates to a form for casting concrete beams.

Concrete beams are cast in many different shapes and sizes. Normally, they are cast at a manufacturing facility and then transported to the construction site where the, beam is actually to be used. Certain known pan forms for making concrete beams make it impractical to cast the beams at the construction site, the reason being that it is generally impossible to remove the concrete form from the beam without lifting the beam off of the form. This requires a large rig capable of lifting the heavy concrete. beam. The cost of cranes and other rigs capable of lifting the heavy concrete beams is very high. Accordingly, where a large number of beams are being cast, the cost would be prohibitive to have such a rig stand by merely to lift the concrete beams off of the'forms after the beams are cast so that the forms can be used over again. Also it would be entirely too costly to have enough forms on the job site to allow all beams to be cast at once.

a form which can be removed from concrete cast thereabout once the latter has hardened. To this end, he provides a pair of pivotally joined bracing rods having opposing ends coupled to a respective pair of form legs, the legs being connected together by a form top. When the bracing rods are locked in horizontal alignment, they fix therelative position of the legs so that concrete may be poured around the form without the legs collapsing. In this state, the bracing rods act in compression to prevent such collapse. When the concrete has hardened, the bracing rods are lifted upwardly at their joined ends thereby pivoting the legs inwardly toward each other to retract the form which may then be removed from about the concrete.

This type of device suffers from a serious disadvantage in that there is no means for preventing relative movement between the legs and top when concrete is being poured. For instance, if concrete were poured initially on one side of the form only, the resultant forces would tend to shift the position of the legs relative to the top. This is undesirable and leads to imperfectly casted beams.

McAbees form arguably cures the defects of Shepard by using a pair of bracing rods each coupled between the top and an adjacent leg. These rods act in compression to prevent collapse of the legs during the pouring of concrete and, additionally, to prevent relative movement between the legs and top during concrete pouring. Notwithstanding these advantages, the

form of McAbee is not of unitary construction and i must be assembled before casting and disassembled by a time consuming procedure aft-er hardening for removal of the form. In todays need to conserve labor,

expenses, therefore, McAbees form would not be very satisfactory.

SUMMARY OF THE INVENTION The present invention provides a retractable concrete form which is substantially unitary in structure and which enables beam casting at the construction site by means of the ready retractability and removability thereof. Thus, the labor time involved in casting concrete beams is substantially reduced over many of the prior art fonns discussed above. In addition, the form is extemely stable during the pouring of concrete in preventing both the collapse of "the legs and relative movement between the legs and the top. The latter is done without in any way detracting from the unit structure of the form or the ready removability thereof.

Generally speaking, a form according to thisinvention is of the retractable type having a substantially unitary structure including a pair of oppositely facing side legs connected together by an upper portion with the legs being movable relative to each other. The structure further includes first means coupled between the legs for setting them in a first position when the first means is in a first state, and for moving them out of the first position and toward each other, thereby retracting the form, when the first means is moved into a second state so that the form may be disengaged from material cast thereabout. The structure also includes second means coupled between the legs and cooperating with the first means for preventing movement of the legs relative to the upper portion when the first means is in the first state, while permitting movement of the legs out of the first position and toward each other when the first means is moved from the first state into the second state. It is not first necessary to remove the second means prior to form retraction, as in the McAbee patent, above discussed.

In another aspect of this invention, the first means includes a first bracing structure which acts in compression to prevent collapse of the side legs when in its first state.

In a further aspect of this invention, the second means includes a second bracing structure which acts in tension to prevent relative movement between the 1 relationship is such that when the legs are collapsed by movement of the first means into its second state, not only are the legs retracted from the sides of the casted beam to which they abut, but, additionally, segments of the upper boundary of the form are also retracted. The result is that a substantial spacing exists between the inner sides of the casted beam and the adjacent ends of the top, thereby making withdrawal of the form a simple matter without causing any scraping or damage of the beam.

1 Stated another way, the preferred embodiment comprises a form of the type above described wherein the legs extend in substantially a first direction from the upper portion of the form. The form has anupper peripheral surface facing in substantially the opposite direction from that in which the legs extend, the upper peripheral surface having a segment on the upper portion of the form and a separable segment on each of the legs so that movement of the legs correspondingly moves the segments thereon away from the segment on the upper portion of the form.

BRIEF DESCRIPTION OF THE DRAWING These and other aspects and advantages of the present invention are more clearly defined and described with reference to the accompanying drawing wherein:

FIG. 1 is a pictorial view of a double T concrete beam cast using the concrete form and using the method in accordance with the present invention;

FIG. 2 is a pictorial sketch illustrating the concrete form and other forms used therewith and embodying the present invention. Details of the withdrawing apparatus are only shown in one of the forms and indicated by dashed lines in the others. The bulk head forms are shown in dotted lines so as not to cover up the concrete form;

FIG. 3 is a view of the concrete form taken along the line 33 of FIG. 4;

FIG. 4 is a side elevation view of the concrete form shown in FIG. 2 with portions of the form broken away to reveal parts of the withdrawing apparatus therein;

FIG. 5 is a view of the concrete form taken along the line 5--5 of FIG. 4 and showing the withdrawing apparatus;

FIG. 6 is a plan view of the joist plate assembly on which the concrete forms are placed;

FIG. 7 is a pictorial view of a preferred embodiment of the present invention in which the form has hinged sides;

FIG. 8 is a bottom view of the top which has been removed from the form of FIG. 7;

FIG. 9 is a section view of the top shown in FIG. 8 taken along the lines 99;

FIG. 10 is a front elevation view of the preferred embodiment of the present invention shown in FIG. 7;

FIG. 1 1 shows a front elevation view of the preferred embodiment of the present invention shown in FIG. 7 with the retracting unit forced in a vertical direction to pull the sides toward each other; FIG. 11 has portions of the form broken away for a clearer understanding of the invention;

FIG. 12 shows a front elevation view of the preferred embodiment of the present invention shown in FIG. 7 with the retracting unit rotated 90 in order to allow longitudinal movement of the retracting unit to pull the sides together. Portions of the form are broken away I for a clearer understanding of the present invention;

FIG. 13 is a partial elevation view of the embodiment of FIG. 7, but with an alternative side retracting member substituted for the one shown most clearly in FIG. 10 and FIG. 14 is a front elevation view of a further preferred embodiment of the present invention showing an alternate form of the cross-bracing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Refer now to the concrete T beam cast using the method and apparatus of the present invention and shown in FIG. 1. The concrete beam shown in FIG. 1

is known as a double T concrete'beam. The double T concrete beam has two legs 10 and a top 12.

FIG. 2 is a sketch illustrating the apparatus for making the double T concrete beam shown in FIG. 1. The apparatus for FIG. 2 includes three concrete forms The concrete forms 100 rest on a joist assembly 200. The joist assembly 200 includes four soffits 202.

The joist plate assembly 200 is shown in more detail in FIG. 6. As shown, the joist plate assembly also includes metal straps 204. Although it is not essential, the metal straps are preferably placed parallel to each other and are spaced apart from each other. The soffits 202 are long planks which, for example, may be boards 2 X 6 inches which are laid on top of the metal straps. The sofiits 202 are laid out parallel to each other and spaced apart the same distance as the legs are to be on the T beams. The soffits 202 are attached to the metal straps 204. The soffits 202 may be attached to the metal straps in any one of a number of different ways. However, the straps are shown herein as having shoulders (not shown) which extend up into grooves 206 formed on the bottom of the soffits. The grooves are shown in dashed lines on the left-hand soffit shown in FIG. 6.

Thus, it can be seen that the metal straps and soffits form a grid of intersecting members substantially at right angles to each other.

Refer now to the form 100. The details of the concrete form 100 are best seen in FIGS. 3, 4 and 5. The concrete forms 100 include a pan form 102 and a withdrawal apparatus 104. The pan form 102 is elongated and has a pair of opposing sides 102a connected by a top 102b. The pan form 102, including the sides 102a and the top 102b are of a unitary construction, preferably cast out of a fiberglass material which is deformable when pressure is applied thereto. It should be under stood that fiberglass is a tough material yet it is light in weight and, therefore, is a preferred material for the pan form 102. However, the pan form can be made of other materials as well within the scope of the invention, for example, lightweight metal or plywood.

The sides 102a have a lower portion which extend up at a very slight angle in towards each other as one moves towards the top of the form. The upper portion of the sides 102a extend inwardly at more of an angle as one moves towards the top of the form. The top of the pan form 102 tapers downwardly from the center of the form towards each side. The top and sides of the form are interconnected by a semi-circular comer. It will be evident to those skilled in the art that the shape of the pan form is such that, when the sides are pulled in towards each other, the form can easily be moved downwardly and outwardly from the concrete which has been poured around the form.

The pan form 102 also includes a chamfer 1020 near the bottom of each side 102a. The chamfer 1020 has a bottom edge extending in a substantially horizontal direction outwardly from the form and at right angles to the lower portion of the sides 102a. It should also be noted that the sides 102a extend downwardly below the bottom surface of the chamfer l02c providing a notch 102f which can be seated against the comer of the soffits 202 as shown in FIG. 2.

The chamfer 1020, and the thus formed notch, is an important feature to the pan form 102 as it actually rests on the top of the soffits and when the sides 102a are pulled in towards each other, the chamfer slips off of the soffits allowing the form to be easily removed out from the interior of a newly cast beam.

Anotherimportant aspect of the pan form 102 is the withdrawal apparatus 104. The withdrawal apparatus 104 has a center bar 1040. The center bar 104a is a member which extends the length of the pan form 102 and has ends 104) and 104g. Extending at right angles from the center bar 104a are a number of side bars or arms 104b. The side bars extend in pairs from the center bar in opposite directions to each of the sides 102a of the pan form. The side bars are distributed alongthe form so that connections are made to the sides 102a at a number of different points along the length thereof. The side bars l04b are pivotally mounted on the center bar and to the sides 102a by means of hinges 1040. The hinges 104ceachhave a pin which extends up through the side bars to secure the side bars to the center bar 104a and the sides 102a. Other suitable hinges will be evident to those skilled in the art within the scope of i the invention.

Normally, when the form is in use, the center bar 104a is in a nonretracted position and the side bars l04b are perpendicular to both the center. bar and the sides 102a. The sides 102a are then forced out to the position shown in the solid lines in FIG. 5. When it is desired to retract the withdrawal apparatus and pull the cement form out of a cement beam, the center bar is retracted or pulled towards the left (in FIG. 5), causing theside bars 104b to rotate and, as the side bars rotate,

. 5, the stop 104d stops movement when the side bars are straight as shown in FIG. 5. A second stop 1042 is rigidly attached to the center bar and has two surfaces, each extending at approximately a 60 angle to the center bar 104a. When the center bar 104a is retracted or pulled tothe left, these surfaces of the stop l04e come into contact with the side bars which are adjacent thereto, thereby stopping movement of the withdrawal apparatus in the form. Thus, the stops 104d and 104e provide a limit on the amount of travel that the withdrawal device can undergo inside of the form. The position of one of the side bars 104b and one of the sides 102a when the center bar has been retracted to the stop 104e is indicated by dashed lines in FIG. 5.

The forms 100 can be stacked end to end in order to make a longer beam. In this manner fixed length forms can be manufactured but made to most any length by adding on more forms end to end. The fonns have an indentation 102d around the entire edge at the lefthand end as seen in FIG. 4. This allows the left-hand end of one form to be slipped inside of the right-hand I end of an adjacent fonn. When joining forms end to end it is also necessary to rigidly attach one form to the adjacent form, so that all of the forms can be withdrawn at once. To this end, the extensions 104f and 104g are constructed to form a connector. The lefthand extension 104f as seen in FIG. 5 has a pin 10412 I which extends in an upward direction. The left-hand extension 104f is also depressed near the end so that it drops down. The right-hand extension 104g has an opening therein through which the pin 10411 extends. For purposes of illustration, a right-hand extension 104g is shown attached to what would be a left-hand extension l04f in FIG. 4.

Thus, it should now be evident that one or more forms are connected together end to end by slipping one form inside the other and attaching the left-hand I top of the pan forms 102. The divider forms 14 are bevelled so that the edge against which the concrete is poured slopes inwardly of the beam. The divider form 14 is attached by means of bolts 14a to the pan form 102. The pan form 102 has a'threaded insert l02e and the bolts 14a. extend through the divider form 14into the threaded insert 102e, thereby attaching the divider forms 14 to the top of the form 102.

Bulk head forms 16 determine the length of the beams being cast. The bulk head forms can be posi tioned at opposite ends of the pan forms 102 or as indicated by dotted lines in FIG. 2 they can be cut to fit the shape of the pan forms and thereby positioned any where along the length of the forms as desired.

Consider now the steps in the method for casting the T beams:

First, a flat surface is cleaned and prepared to receive the joist plate assembly.

Second, the joist plate assembly is laid out. In accordance with this step the straps 204 are first laid out es- I sentially parallel to each other and spaced apart the desired distance from each other and subsequently the soffits 202 are laid on top and at right angles to the I straps. The sofiits 202 are laid out parallel to each other and are spaced apart corresponding to the desired distance between the legs on the beam being cast.

Also the soffits are attached to the metal straps so that they will not move around. The number of soffits required depend on the number of legs in the beam to be cast and the number of beams to be cast side by side.

Third, the concrete forms are then placed so that they extend from one of the adjacent soffits to the next with the notch l02f resting on'the top of the corre-.

sponding soffit. The withdrawal apparatus 104 is positioned so that the side arms l04b are perpendicularto the sides of the form and to the center bar. The number of forms which are laid side by side as indicated in FIG. 2 is detennined by the number of legs desired on the concrete beam and the number of beams to be cast at once. For example, if one double T beam isto be cast, then only three forms are required. If on the other hand one triple T beam is to be cast, four forms are required. Also, if a beamis required which is longer than one of the forms 100, then forms are added end to end as described hereinabove.

Fourth, the bulk head forms 16 are positioned. The

forms 14 are then placed on the top of the forms 100 I and are bolted in place as described above.

Fifth, tension cables and other reinforcing are then placed into the forms as required in a conventional manner known in the art. I

Sixth, concrete is then poured into the forms and vibrated to insure that it is firmly packed into the form. The step of pouring the concrete into the forms and vibrating to provide proper compaction is also well known in the art.

Seventh, the concrete is allowed to set up and harden.

Eighth, the bulk head and divider forms are then removed.

Ninth, the concrete forms 100 are then withdrawn from the inside of the concrete beam by pulling on the center bar 104a of the left most form, causing the perpendicular arms to pivot pulling the sides of the pan forms into each other causing the chamfer strips 102c todrop off of the soffits 202 releasing the forms from the concrete. The forms 100 are then pulled out from the beam.

If forms have been connected end to end then the sections are disconnected. The forms are then wiped off with a light oil or other substance to keep the concrete from adhering to them.

Beams may be cast one on top'of another. Such a process would include the additional steps of casting one or more beams and then placing soffits and one or more forms of the type described herein on top of such beams and casting other beams using the processes described hereinabove. This process may be repeated over and over as desired. After the beams have been cast in this manner, they may be raised into place in a building as desired.

Refer now to FIG. 7, which shows a preferred embodiment of the form of the present invention. More specifically, a form 300 is shown in FIG. 7 which is defined by an elongate, essentially unitary structure including a right side leg 302 and a left side leg 303 interconnected by an upper portion 304. The upper portion 304 includes a plurality of upper rib members 308 and a top 306. As shown in the Figure, both legs are hinged at opposite surfaces of upper n'b members 308. This is to be distinguished from the embodiment of FIG. 2 wherein the legs were of unitary construction.

The top 306 is shown removed, but is indicated by dashed lines, in FIG. 7, to expose the interior of the removable form. A bottom view of the top 306 and a section view thereof taken along the lines 9-9 are shown in FIGS. 8 and 9. The removable top 306 has an outer covering 306a. A plurality of ribs 306b are rigidly attached to the lower surface of the outer skin 306a for providing rigidity to the top to prevent deformation during casting of a beam and to connect the top to the rest of the form. It will be noted that there is one rib 306b corresponding to each of the ribs 308 of the upper structure 304. Each of the ribs 306b has an opening 3060 therein into which a pin 308a of the corresponding rib 308 extends. The outer covering 306a rests on a shoulder 309 above the ribs 308 when in position on the form 300.

To attach the top 306 to the form 300, the top is laid with each of the ribs 306b extending down adjacent to the corresponding rib 308. The top 306 is then moved longitudinally towards the rear of the form as shown in FIG. 7 causing each pin 308a to be inserted into the opening 3060 in the corresponding rib 306b. In this manner, the pins 308a lock the top in place preventing movement during casting of a beam.

Corresponding to each of the ribs 308 are a right side rib 310 and a left side rib 312 within hinged

legs

302 and 303, respectively. The

legs

302 and 303 include

outer skins

302a and 303a. The

outer skins

302a and 3030, similar to the skin 306a of the top, are rigidly connected to the

ribs

310 and 312. [n this manner, the

ribs

310 and 312 provide a rigid structural support for the

skins

302a and 303a preventing deformation thereof during casting of a beam.

The

outer skin inluding

302a, 303a and 306a may be formed of many different materials but is preferably formed of a laminated plywood.

A pin 314 pivotally connects each hinged

side rib

310 and 312 to the corresponding top rib 308. The pins 314 provide the hinge connection between upper portion 304 and

legs

302 and 303. Consider the point at which the legs are pivoted by the pin 314. The positioning of pivot pin 314 with respect to the legs is important and should be noted. Pivot pin 314 should be positioned in a manner such that when the legs are rotated toward each other at the bottom, the outer extremities of

legs

302 and 303 will, at all times, move away from any beam cast thereabout. Thus, in FIG. 10, pins 314 are located adjacent the upper and inner extents of

legs

302 and 303. If, for example, the point 302C or the point 302b (see FIG. 10) were to move even slightly outwardly into a beam cast thereabout, the legs would bind and not be capable of movement. Accordingly, the pivot pin 314 is positioned with respect to

legs

302 and 303 so that it is above the broken line A passing through the break point 302b and to the left of the broken line B going through the break point 3026' as seen in FIG. 10. If the pivot point 314 were to the right of the line B or below the line A, the sides would bind up as described hereinabove.

With regard to the above, it should be noted that each of

legs

302 and 303 has an upper portion which forms a segment of the upper peripheral boundary of the form. These segments are adjacent opposite ends of top 306 and extend thereto from

side shins

302a and 303a. The fact that the legs, as defined in part by such segments, extend more in a transverse direction than does the top of the form, facilitates removal of the form when the legs are retracted toward each other. More specifically, no portion of the top can scrape against the casted concrete during removal of the form since it is spaced therefrom on either side by the transverse extent of the segments and since the form is moved away from the concrete in a direction normal to the top. The legs are prevented from scraping against the concrete because of the pivotal relationship between themselves and the top as described above, i.e., all portions of the legs move away from the concrete during retraction.

The above phenomena may also be recognized by noting that the form comprises an upper peripheral surface running between

side shins

302a and 303a and including a stationary segment defined by the upper portion of the form and a pair of separable segments defined by the upper portions of the legs extending from the associated side shin to adjacent top 306. During leg retraction, the leg segments of the peripheral surface are separated therefrom thereby moving away from the surrounding casted concrete beam.

Refer now to the withdrawing device shown generally at 316. Withdrawing device 316 includes a leg bracing and retracting mechanism shown generally at 318. Apparatus 318 includes a left transverse bracing rod or arm 318a and a right transverse bracing rod or arm 318b for each pair of

ribs

310 and 312. The transverse arms 318a and 318b are aligned in a straight line (in the unretracted position) between the

corresponding side ribs

310 and 312. The transverse arms 318a and 318b are connected to the

sides

310 and 312 by hinged units which allow the arms 318a and 3l8b to be rotated in an upward position as shown in FIG. 1 1. The

arms

318a and 318k areL-shaped angle iron. The hinged units for the left arm 318a include a U-shaped member 318d and a pin 318f which pivotally interconnects the arm 318a and the U-shaped member 318d. Similarly, the right transverse arm 318b has a U-shaped member 318e and a pin 318 which pivotally interconnects the arm 318b and the U-shaped member 3182. A pair of pivot points are thereby defined at pins 3l8f and 318g.

The leg retracting apparatus 318 also includes a member 3181', having a U-shaped cross section, which extends on three sides around the ends of the arms 318d and 318b at the center where they join together.

. The right arm 318b is welded to the U-shaped member 318i and forms an integral structure therewith. The U- shaped member 318i has an opening 318h therethrough and the left transverse arm 318a has an opening 318C coaxial with the opening 318h. The openings 318c and 31811 in all retracting units 316 are aligned and a longitudinal retracting rod 321 extends through the openings 318C and 318k in each of the retracting units 317, as indicated in FIG. 1.

A third pivot point is thus defined at opening 318h. This point is disposed below an imaginary line (not shown) connecting the pivot points at

pins

318f and 318g when mechanism 318 is in the position shown in FIGS. 7 and 10. More specifically,.mechanism 318 is designed to operate in compression when in the position shown in FIGS. 7 and 10 to prevent collapse of

legs

302 and 303 during hardening of material poured about the fonn. It thus becomes necessary to maintain the pivot point at opening 318k lower than the pivot points at pins 3l8f and 318g. I

In operation, an operator may actuate retracting apparatus 318 causing

legs

310 and 312 to be moved together and thus collapsed for removal from a beam by taking hold of the rod 321 and moving it in an upward direction as shown in FIGS. 10 and 11. The arm 318a and the U-shaped member 318i rotate about the rod 321, and as movement takes place in the vertical direction, the lower ends of the

sides

310 and 312 are forced toward each other in a similar manner to that described in regard to FIG. 2. FIG. 11 shows the rod 21 actuated vertically and

legs

302 and 303 retracted toward each other. By pulling the rod 321 back down to the position shown in FIG. 10 the transverse arms 318a and 318b move the legs apart and lock them in place so they do not move together as cement is poured about the form.

Side retracting apparatus 318 also has I a transverse guide structure which prevents deformation of the sides of the form and causes both legs to be retracted by the same amount for a given movement of the rod 321. The

transverse guide structure includes rods 3l8j and 318k.

The rod 318j is a hollow tube into which the rod 318k extends. The rods 318j and 318k are welded to the U shaped members 3182 and 318d, respectively.

Retracting apparatus 318 is actually connected to the

side ribs

310 and 312 by means of left and right rotational supports 322a 322b. The rotational supports permit retracting apparatus 318 to be rotated about 360. Retracting apparatus 318 may be rotated by removing the rod 321. Retracting apparatus 318 can then be rotated 180 from that shown in FIG. 10 to permit a downward vertical movement to retract the legs rather than a vertical movement as indicated in FIG. 11. The advantage of using vertical movement to retract the legs becomes important when beams are cast up off the ground. Under these conditions, it may be much more convenient to force the rod vertically up or down than in a horizontal direction.

Retracting apparatus 318 can also be rotated through a rotational movement from that shown in FIG. 10

so that the openings 318C and 318th extend vertically to that shown in FIG. 10 and as is shown in FIG. 12, a longitudinal member 324 can be used extending along the length of the form, similar to that shown in FIG. 5. A bolt 325 extends through the member 324 at each side retracting apparatus 318 and extends up through the corresponding openings 318k and 3180 (which now extend in a vertical direction). Only the first bolt 325 is shown in FIG. 12. By moving the member 324 in a longitudinal direction of the form, the arms 318a and 318b in each of the side retracting apparatus 318 are rotated similar to that described hereinabove in connection with FIG. 12 but in a horizontal direction causing the sides 302a and 302b of the form to be retracted.

Consider now the details of the

rotatable connecting units

322a and 322b which permit rotation of the retracting apparatus 318 to its various angular positions. The

rotational units

322a and 322b have rods 322cand 322d (FIG. 10) which are welded or rigidly connected by other well known means to the

U-shaped members

318d and 318e. The opposite ends of the

rods

322a and 322d are rotatably connected by means of

U-shaped members

322e and 322f to the

corresponding side ribs

312 and 310, respectively. The

U-shaped members

322e and 322f have two legs (only one being shown) extending on opposite sides of the:

ribs

310 and 312. to which they are rigidly connected. The

U-shaped members

322e and 322f each have an opening therein (not shown) in which the

rods

322e and 322d are rotatably mounted. The

rods

322C and 322d may be threaded to permit bolts 322g and 322k or other means to be used to hold the rods in place and yet permit rotational movement about the axis thereof.

Referring to FIG. 10, cross-connected brace structures 330 are provided for acting in tension to prevent deformation of the form under the weight of a beam which is being cast thereabout. More specifically, the structures 330 represent a means cooperating with compression action of the retracting mechanism 318 for acting in tension to prevent movement of

legs

302 and 303 relative to the upper portion of the form (top 306 and ribs 308), while allowing collapse of the legs during the retracting operation of mechanism 318.

A cross-connected brace structure 330 is provided for each pair of

ribs

310 and 312. Each crossconnected brace structure 330 includes a pair of diagonal structures, one extending from the lower end of the rib 312 to the top rib 308 and the upper end of the rib 310 and the other extending from the top rib 308 and the upper end of rib 312 to the lower end of rib 310. The diagonal structures include a rod 332 and a rod 334. The rods 332 are pivotally connected to the

ribs

308, 310 and 312 by means of pins 336 and the rods 334 are pivotally connected to the

ribs

308, 310 and 312 by means of the hinge pins 314. However, it will be evident'that the

rods

332 and 334 may be connected by separate pins and need not share the common pivot pins 336 and 314.

Each of the diagonal structures includes a flat rectangular plate 338 having a sleeve 340 welded thereto. The opposite ends of the rods 332 from that connected to the side ribs are also welded to the plate 338. The rod 334 fits inside of and slides in the sleeve 340; The end of the rod 334 is threaded and nuts 342 are threaded thereon to provide a stop or limit of movement of the rods in a direction along their axes.

In operation, the legs may be moved toward each other in a manner described hereinabove causing the rods 334 to slide inside of the sleeves 340 in a direction along their axes, and the

rods

332 and 334 to pivot on the side ribs. When the

sides

310 and 312 are moved outwardly away from each other, the rods 334 again s lide inside of the sleeves 340 until the nuts 342 engage the sleeves 340 and provide a limit stop to prevent further outward movement. Due to the tension of the cross connection between top and bottom of the

side ribs

310 and 312, a rigid structure is provided to prevent deformation of the form due to outward movement of the legs during the pouring of concrete about the form.

With this arrangement, the

rods

332 and 334 along each diagonal form a brace. For each brace, the pivot pin 336 forms means for connecting a first end of the corresponding brace to a different one of the pair of

sides

302 and 303 from a first end of the other brace. For each brace,means including rod 334, sleeve 340, nuts 342, and pivot pin 341 forms means for connecting a second end of the corresponding brace to one of the other sides from the side to which the first end thereof is connected. The means for connecting for each brace comprises the pivot pins 314 and 336 which are affixed to a side and are rotatably connected to the brace. Each brace comprises at least one elongated brace (i.e. 332). The end 340 of sleeve 340 forms a stop affixed to the at least one elongated member and the facing side 342 of the nuts 342 forms another stop affixed through rod 334 and pivot pin 364 to one of the sides. The sleeve 340 and rod 334 form means slidably connecting the stops relative to each other, guiding the stops into engagement during actuation of the withdrawing device 318 into the aligned condition. As a result, the withdrawing device 318 acts in compression and the braces cooperate with the stops to act in tension, thereby preventing movement apart by the pair of

opposite sides

302 and 303 when material is cast thereabout. Significantly, the braces are released and the form sides are retracted by actuation of the withdrawing device 318 out of the aligned condition.

It should also be noted in connection with the embodiment of the invention shown in FIGS. 7 and 10 that the

lower edges

302d and 303d of the

sides

302 and 303 extend at an angle with respect to the horizontal plane as oppposed to being perfectly horizontal. The purpose of this arrangement is to permit the legs to easily slip off of the soffits and allow the form to drop down out from inside of a beam cast therearound. Additionally, as can be seen in FIG. 10, outer surfaces of the

sides

310 and 312 diverge so that the outer edge of the

inclined surfaces

302d and 303d extend out beyond any other point along the outer extremity of the

sides

302 and 303. This cooperates with the segments of the form upper periphery defined by

legs

302 and 303 to facilitate removal of the form from the inside of a beam poured around the form.

It should be noted that the word T-beam is used in a very general sense herein as the beams need not be in the shape of a T but could be in many other shapes and configurations and have one or many legs within the spirit and scope of the present invention. By way of example, the interior cross section of the beam may be virtually an inverted V and under these circumstances the pan form would need very little, if any, top surfaces. Instead, the legs would essentially meet at the top and diverge toward the lower edge.

The preferred form of the invention contains a withdrawing device or retracting apparatus which permits the side legs to be locked in place for receiving concrete and actuated together merely by actuating the withdrawing device in the described manner. However, within the broader concepts of the invention the withdrawing device might be replaced by one or more removable spreader members. The spreader members would be positioned or wedged in between the opposing side legs to lock them in place to receive concrete and then repositioned or removed to unlock the sides and allow the sides to be moved together and removed from the beam.

Similarly, the preferred method in accordance with the present invention includes the step of actuating the withdrawing apparatus to move the sides together and allow removal of the form. However, within the broader concepts of the invention a spreader member is positioned in between the sides of the form to spread them apart and lock them in place to receive concrete. The spreader member is then repositioned or removed, unlocking the sides and permitting the sides to be moved togetherfor removal from the beam being cast.

It should also be noted that the preferred embodiment of the invention has the common longitudinal member interconnecting each of the transverse arms to permit all arms to be actuated by movement of the single longitudinal member. However, within the broader concepts of the invention, the common longitudinal member may be eliminated. This is shown in FIG. 13 wherein a form 400, very similar to the form of FIGS. 7-10, has a leg bracing and retracting mechanism 318' with rods 3l8j and 318k removed. The rods, which form the common longitudinal member, are not required in order for mechanism 318 to perform its leg bracing and retracting function since arms 318a and 318b may be actuated individually. It should be noted that, as with the form of FIGS. 7-10, the pivot points defined at pins 3l8f and 318g are disposed above a pivot point for mechanism 318 defined at opening 318k. Thus, when mechanism is in the position shown in FIG. 13, and concrete is poured about the form, it will properly act in compression to prevent collapse of the legs.

It should be understood that the above mentioned apparatus and method has been described by way of example and that there are other variations of the apparatus and method described above within the scope of the invention defined in the claims herein. For example, the forms may be made of other materials. Additionally, the forms may take on different shapes although the shape shown herein is preferred because it is readily released from the concrete beam. Additionally, other means can be devised for connectingthe side arms to the center bar and to the side legs of the form and other means can be designed for interconnecting the ends of the side arms. Also the soffits can be formed in many different ways. For example, they could be raised up out of the floor or by other means within the scope of the invention.

Bracing structure 330, although preferred, may be replaced by an alternative structure, as depicted in FIG. 14. FIG. 14 is a similar view to FIG. 10 with the cross-bracing from lower right to upper left shown partially broken away, it being the same as the other brace. More specifically, and with reference to FIG. 14, it is not essential for there to be two

rods

332 and 334 slidablymounted relative to each other with rod 332 fixed inposition and rod 334 slidably housed within a sleeve 340. For example, FIG. 14 shows a

single rod

1002 and 1004 for each diagonal portion of the bracing structure. The single rod 1002 has one end coupled to a lower portion of left side leg 303 and another end coupled to an upper portion of right side leg 302. Similarly, the single rod 1004 replaces

rod pair

332 and 334 and i is coupled between the lower portion of right side leg i I 1004 adjacent the form top slidable in a direction along its axis between predefined limits, such end continuing to be pivotal as before- This may beaccomplished by means well known in the art. For instance, FIG. 14

scribed, are within the contemplation of this invention; i

The embodiment of FIGS. 7-10 could be further modified within this invention by forming the soffits in diiferenat ways. For example, they could be raised up out of the floor or by other means. Additionally they could be placed at the point in a structure where the a beam is finally to be placed. The concrete forms would shows the end of the rod could be defined with an elongate aperture 1006therein in which a pivot pin 1008 attached to the form is designed to ride between limits defined by the ends of the aperture and connect the rod to side 320.

The opposite end of

braces

1002 and 1004 are pivotedabout pivot pins 1010, which pins are affixed to the

sides

303 and 302.

. Thus the

bracingrods

1002 and 1004 each form a brace and pivot pins 1008 and 1010 form pivots or means for connecting the ends of each brace to different sides. An end 1014 of aperture 1006 in each of the bracesforms a stop. The side 1016 of pivot pin 1008 which faces the end 1014 forms a second stop. The

elongated aperture 1006 and the opposite sides of the pin 1008 form means for slidably connecting the stops relative to each other, guiding them into engagement during actuation of the withdrawing device 318 into an aligned condition. As a result, the withdrawing device 318 acts in compression and the braces cooperate with the stops to act in tension, thereby preventing movement apart by the pair of sides when material is cast thereabout- Significantly, the braces are released and the form sides retracted easily and automatically by actuation of the withdrawing device 318.

In the above regard, it is not essential for the pivot points for each rod to be positioned at the location of

pins

314 and 336 in FIG. 10 and 1008, 1010 in FIG. 14. For instance, the upper end of each rod could be pivoted at a pointdefined in form upper portion 304 adja cent a side leg; whereas the lower end of each rod could be pivoted at a point separate and apart from pivot then be placed on the soffits and the other forms put in place as described hereinabove. This application would call for the retracting apparatus 318 to be rotated to the position shown in FIGS. 7, l0 and 1 l (or therefrom) to permit vertical movement to actuate the retracting apparatus anddraw the side legs together. The retracting apparatus will generally be rotated to the position shown in FIG. 12 when pouring a concrete beam on the floor of a construction site to permit horizontal movement for actuation. The concrete beam would then be poured right in place in the structure and the form removed in accordance with the novel method described herein.

Although each associated set of

ribs

310, 312 and 308 is shown connected to the skins on the sides of the form, it should be understood that a separate similar set of hinged ribs may be provided (without the side skins) with the corresponding cross members 330 and the connected transverse arms of the retracting apparatus. This unit may have many different uses. For example, a flat sheet of material or skin having the same cross sectional shape as the form may be affixed to the ribs to cover over the end of a form. In this manner the, separate rib structure with the skin could be slipped into the end of the form and the retracting apparatus actuated to expand the ribs so that they engage the side skins and hold the separate rib structure and skin in place at the end of the form. Such a structure can be used to form a flat end on a beam or to form a stiffener tional size along its full length and butted end to end with another form. The forms then may be connected together by inserting one of the separate rib structures a at the joint with the outer surface of the separaterib structure overlapping the two forms. The ribs may then be forced apart as in the manner described hereinabove so they frictionally engage the inside of the two abutting forms and hold the forms together.

Another modification within the contemplation of this invention would be toclamp the lower ends of the side legs to the soffit. This would further stabilize the form during the pouring and hardening of the concrete.

It will also be evident that there are variations on the apparatus for holding the top in place within the scope of the invention. For example, the pins 308a may be replaced by a rod that is slidably mounted to the top so that it can be moved and engage the rib 308 and form a lock to hold the top in place. Also, the number of ribs and number of transverse actuating devices in the retracting or withdrawing apparatus shown herein are given by way of example and the invention is not limited thereto.

These and other variations of the basic invention will be evident to those skilled in the art within the scope of the following claims,

What is claimed is:

1. An easily retractable form for casting material, the combination comprising:

a three sided elongated structure comprised of a first side, a pair of opposing spaced apart further sides, each one of said pair of sides having a first edge pivoted on said first side and a second edge movable toward and away from the other second edge; bracing and withdrawing device having spaced apart ends pivotally mounted on said pair of sides adjacent said second edges and having a-further pivotal connection in between the pivotally mounted ends to permit pivoted de-actuation to a retracted non-aligned condition for drawing the pair of sides together to withdraw the form from material cast thereabout and pivoted actuation to a substantially longitudinally aligned condition for casting material; and 1 first and second cross braces each having first and second ends, the braces each comprising: first means for connecting the first end of the corresponding brace to a different one of said pair of sides from which the other first end is connected,

second means for connecting the second end of the corresponding brace to one of the other sides from the side to which the first end thereof is connected,

said first and second means each comprising a pivot affixed to one of the connected brace and side and rotatably connected to the other, at least one elongated member,

a first stop affixed to said at least one member, a

second stop affixed to the side to which the second end of the corresponding brace is connected,

and

means relatively slidably connecting the first and second stops so as to guide the stops into engagement during actuation of the withdrawing device into analigned condition acting in compression causing the cross braces to act in tension thereby preventing movement apart by said pair of sides when material is cast thereabout,

said means for relatively slidably connecting being adapted for guiding the stops apart to thereby self release the first and second stops during deactuation of the withdrawing device.

2. The form of claim 1 wherein the bracing and withdrawing device comprises:

a first rigid elongate member having opposing ends, one end being pivotally coupled to one of the pair of sides at a first pivot point; and

a second rigid, elongate member having opposing ends, one end being pivotally coupled to the other one of the pair of sides at a second pivot point and the other end being pivotally coupled to the other end of the first rigid member at a third pivot point, the third pivot point being disposed below the first and second pivot points when the bracing and with drawing device is in its aligned condition, thereby preventing movement out of such condition due to forces acting on the form.

3. The form of claim 1 comprising a hinge for pivotally mounting each of said pair of sides to said first side.

4. The form of claim 1 wherein the form has an upper peripheral planar surface facing in substantially the opposite direction from that in which the second edges of the pair of sides extend, said upper peripheral surface having a fixed segment on the upper portion of the form and a fixed segment on each pair of sides so that movement of the sides toward each other correspondingly moves the separable segments thereon away from the fixed segment on the upper portion of the form.

5. An easily retractable form for casting material, the combination comprising:

a three sided elongated structure comprised of a first side, a pair of opposing spaced apart further sides, each one of said pair of sides having a first edge pivoted on said first side and a second edge movable toward and away from each other;

bracing and withdrawing device having spaced apart ends pivotally mounted on said pair of sides adjacent said second edges and having a further pivotal connection in between the pivotally mounted ends to permit pivoted actuation between a retracted condition for drawing the pair of sides together to withdraw the form from material cast thereabout and a substantially longitudinally aligned condition for casting material; pair of cross-connected brace structures comprising a first elongate tension member having opposing ends, a first such end being pivotally coupled to a first one of said pair of sides adjacent said second edge and a second opposing end being pivotally coupled to a second one of said pair of sides adjacent said first edge, and a second elongate tension member having opposing ends, a first such end being pivotally coupled to the first one of said pair of sides adjacent said second edge and a second opposing end being pivotally coupled to the first one of said pair of sides adjacent said first edge, the first and second members each comprising a pair of relatively movable rigid members movable within predefined limits in a direction parallel with their axes for permitting retraction of the pair of sides, said pair of cross-connected brace structures being adapted in cooperation with said withdrawing device to permit pivoting movement of the pair 0F sides toward each other upon actuating said withdrawing device to a retracted condition, the withdrawing device when actuated into an aligned condition acting in compression so as to cause the cross-connected brace structure to act in tension and thereby provide a rigid form, preventing movement apart by said pair of sides when material is cast thereabout, thereby preventing deformation of the form during casting,

6. The form of claim 5 further comprising limiting means for each pair of members defining the limits of movement thereof along their axes.

7. The form of claim 6 wherein the limiting means comprises a stop connected between each pair of members for limiting the effective longitudinal length formed by each of said pair of members.

8. An easily retractable form for casting material, the combination comprising:

Claims

1. An easily retractable form for casting material, the combination comprising: a three sided elongated structure comprised of a first side, a pair of opposing spaced apart further sides, each one of said pair of sides having a first edge pivoted on said first side and a second edge movable toward and away from the other second edge; a bracing and withdrawing device having spaced apart ends pivotally mounted on said pair of sides adjacent said second edges and having a further pivotal connection in between the pivotally mounted ends to permit pivoted de-actuation to a retracted non-aligned condition for drawing the pair of sides together to withdraw the form from material cast thereabout and pivoted actuation to a Substantially longitudinally aligned condition for casting material; and first and second cross braces each having first and second ends, the braces each comprising: first means for connecting the first end of the corresponding brace to a different one of said pair of sides from which the other first end is connected, second means for connecting the second end of the corresponding brace to one of the other sides from the side to which the first end thereof is connected, said first and second means each comprising a pivot affixed to one of the connected brace and side and rotatably connected to the other, at least one elongated member, a first stop affixed to said at least one member, a second stop affixed to the side to which the second end of the corresponding brace is connected, and means relatively slidably connecting the first and second stops so as to guide the stops into engagement during actuation of the withdrawing device into an aligned condition acting in compression causing the cross braces to act in tension thereby preventing movement apart by said pair of sides when material is cast thereabout, said means for relatively slidably connecting being adapted for guiding the stops apart to thereby self release the first and second stops during deactuation of the withdrawing device.

2. The form of claim 1 wherein the bracing and withdrawing device comprises: a first rigid elongate member having opposing ends, one end being pivotally coupled to one of the pair of sides at a first pivot point; and a second rigid, elongate member having opposing ends, one end being pivotally coupled to the other one of the pair of sides at a second pivot point and the other end being pivotally coupled to the other end of the first rigid member at a third pivot point, the third pivot point being disposed below the first and second pivot points when the bracing and withdrawing device is in its aligned condition, thereby preventing movement out of such condition due to forces acting on the form.

5. An easily retractable form for casting material, the combination comprising: a three sided elongated structure comprised of a first side, a pair of opposing spaced apart further sides, each one of said pair of sides having a first edge pivoted on said first side and a second edge movable toward and away from each other; a bracing and withdrawing device having spaced apart ends pivotally mounted on said pair of sides adjacent said second edges and having a further pivotal connection in between the pivotally mounted ends to permit pivoted actuation between a retracted condition for drawing the pair of sides together to withdraw the form from material cast thereabout and a substantially longitudinally aligned condition for casting material; a pair of cross-connected brace structures comprising a first elongate tension member having opposing ends, a first such end being pivotally coupled to a first one of said pair of sides adjacent said second edge and a second opposing end being pivotally coupled to a second one of said pair of sides adjacent said first edge, and a second elongate tension member having opposing ends, a first such end being pivotally coupled to the first one of said pair of sides adjacent said second edge and a second opposing end being pivotally coupled to the first one of said pair of sides adjacent said first edge, the first anD second members each comprising a pair of relatively movable rigid members movable within predefined limits in a direction parallel with their axes for permitting retraction of the pair of sides, said pair of cross-connected brace structures being adapted in cooperation with said withdrawing device to permit pivoting movement of the pair oF sides toward each other upon actuating said withdrawing device to a retracted condition, the withdrawing device when actuated into an aligned condition acting in compression so as to cause the cross-connected brace structure to act in tension and thereby provide a rigid form, preventing movement apart by said pair of sides when material is cast thereabout, thereby preventing deformation of the form during casting.

8. An easily retractable form for casting material, the combination comprising: a three sided elongated structure comprised of a first side, a pair of opposing spaced apart further sides, each one of said pair of sides having a first edge pivoted on said first side and a second edge movable toward and away from each other; a bracing and withdrawing device having spaced apart ends pivotally mounted on said pair of sides adjacent said second edges and having a further pivotal connection in between the pivotally mounted ends to permit pivoted actuation between a retracted condition for drawing the pair of sides together to withdraw the form from material cast thereabout and a substantially longitudinally aligned condition for casting material, said bracing and withdrawing structure comprising means for rotating same about an axis thereof to change the movement required for retracting the pair of sides from a longitudinal movement to movement perpendicular to said first side; and a pair of cross-connected brace structures, each brace structure coupled in between said pair of sides, said pair of cross-connected brace structures comprising means cooperating with said withdrawing device to permit pivoting movement of the pair of sides toward each other upon actuating said withdrawing device to a retracted condition, the withdrawing device when actuated into an aligned condition acting in compression so as to cause the cross-connected brace structure to act in tension and thereby provide a rigid form, preventing movement apart by said pair of sides when material is cast thereabout, thereby preventing deformation of the form during casting.

9. A removable form for casting material, the combination comprising an elongated, essentially unitary structure including a pair of spaced apart sides interconnected by a top, the sides being movable toward and away from each other, and a withdrawing device comprising a plurality of side retracting units, each retracting unit being connected between said opposing sides and at least one member extending longitudinally in said elongated structure and interconnecting said retracting units so that movement of said longitudinal member causes all said retracting units to act together and pull said sides toward each other to remove the form from material cast thereabout, each retracting unit comprising a first pair of members positioned transverse to said elongated structure, said transverse members being slidably coupled together for longitudinal movement relative to each other and each having an end connected to a different one of said sides and a second pair of members rotatably connected together and extending in opposite directions and having their opposite ends pivotally connected to said opposing sides, said at least one longitudinal member being coupled to said second pair of members for causing pivoting movement thereof and thereby force said opposiNg sides to be pulled toward each other, said second members being pivotally connected to said sides and rotatably connected so that longitudinal movement of said longitudinal member causes the rotatable connection of said second members to be moved longitudinally with respect to said elongated structure and thereby retract said sides.

10. A removable form according to claim 9 wherein said second members are rotatably connected together and pivotally connected to said sides so that movement of said longitudinal member perpendicular to said top causes the rotatable connection of said second members to be perpendicular with respect to said top and thereby retract said sides.

11. A removable form according to claim 9 wherein said longitudinal member is rotatably coupled to each of said second pair of members at substantially the midway point between said sides and said second members are rotatable about an axis thereof to change the movement required for retracting the sides from a longitudinal movement to movement perpendicular to said top.

12. The form of claim 1 wherein said means for slidably guiding comprises an elongated aperture in the end of said at least one elongated member into which one of said pivots extends and said first stop comprises one end of said elongated aperture and said second stop comprises said pivot slidable in said elongated aperture.

13. The form of claim 1 wherein said second means for connecting comprises a further elongated member and said means for slidably connecting the first and second stops comprises means for guiding the elongated members relative to each in a direction parallel with the axes of the elongated members, one of said stops being connected to one elongated member and the other stop being affixed to the other elongated member.