US2220898A - Flexible plywood construction - Google Patents

Description

Nov.. 12, 1940. D, J, FRANKLIN FLEXIBLE PLYWOOD CONSTRUCTION Filed Jilly 30, 1958' Patented Nov. 12, 1940 UNITED STATES PATENT OFFICE FLEXIBLE PLYWOOD CONSTRUCTION This invention relates to a flexible plywood like it is common practice among architects to provide forone or more steps with curved ends, usually at the bottom' of the staircase. Stair risers are usually made of lumber andin some instances faced with a thin ply of suitable hardwood veneer. Heretofore in forming such curved ends it has been necessary for the builder to resort to well known expedients such as kerfing or otherwise cutting away part of the plywood and then forming the curved end by special treatment such as the application of pressure and heat, steaming, soaking, etc. Such operations entail considerable time and labor with consequentincreasedcost. Moreover, it is necessary to use materials capable of withstanding the heat and pressure, such as special glue for uniting/the plywood. :1

It is an object of the invention to provide a novel plywood structure which is inherently flexible so that it can be bent readily by hand and without special treatment to any desired curved r shape while possessing at the same time the requisite mechanical strength for the intended purpose. s

Another object is to provide a plywood construction which can be used in forming a curved surface of any desired shape without pressure or heat whereby operations such as soaking,

steaming, kerfing, etc., and the use of special ma-.

terials are eliminated.

A further object is to provide a novel stair riser having a portion at least that is suffloiently flex- 5 ible to be bent readily by handto any desired rcurvaturaAvhereby said stair riser constitutes an article of manufacture which is capable of substantially universal use for all'conventional shapes of steps,

'50 Other objects will appear more fully hereinafter as the description proceeds.

One embodiment of the invention has been illustrated in the accompanying drawing but it is tobe expressly understood that said drawing 55 is for purposes of illustration only and is not to construction adapted for theformation of curved In designing staircases for dwellings and the step,

David J. Franklin, York, Pa. Application July so, 1938, Serial No. 222,290

' 2 Claims. (01. 20-91 be construed as a definition of the limits of the invention, reference being had to the appended claims for this purpose.

In said drawing-- I Fig. 1 is aperspecticewiew, partly in section, showing the lower end of a staircase of which the bottom step has a curved end;

Fig. 2 is an enlarged plan view of a portion 'of the curved end showing the construction and t'arrangement of the plies; m Fig. 3 is a sectional view taken on the line 3 -3 of Fig. 1'; and

Figs. 4 and 5 illustrate diagrammatically and byway of example other curved shapes which can be formed with a stair riser embodying the m invention.- Referring tothe drawing, the lowest step of the staircase shown in Fig. 1 comprises the usual or any suitable treadl amLplywood riser 2. In this figure ,the right-hand end of the 20 tread has been broken away to show a suitable riser construction comprising any suitable num-- ber of plies 3, here shown as threein number, faced with a thin flexible ply 4 of suitable hardwood. As will be understood, this construction is substantially rigid and provides the necessary strength and stiffness to support the tread. At, the end of this rigid portion of the riser. is a flexible portion which has been bent to a desired curvature to, form the-curved endof the 30 said flexible portion as shown in Fig. 2 comprising the outer hardwood facing 4 referred to above and a flexible crossband or back.- ing ply 5, which is described more fully hereinafter. The flexible and rigid portions of the riser can be joined in any suitable manner and 35 as here shown the hardwood facing 4 is continuous and the outer ply 3 terminates at the point 6 (Fig. 1) and is replaced by the crossband or backing ply5. It will be understood that all of the plies are suitably secured together as by any suitable adhesive.

The inherent flexibility of the curved portion shown in Fig. 1 is attained by the use of a crossband or backing ply which, as shown in Fig.2, is-loose-cut on its outer-side, that is, the side away. from the facing 4. 'The grain of ,the crossband extends in a direction substantially parallel to the g eneratrix of the curved surface to be formed, or in other words, substantially vertically o as shown in Fig. 1, and the loose-cut outer surtance into the wood. Plywood of this type can be readily bent by hand and without special preparation or treatment toa desired curvature, the split grain of the loose-cut surface opening orclosing depending on the direction of curvature. For example, at the upper right-hand end of Fig. 2 the direction of curvature is such as to close the grain tightly together, whereas toward the left of this portion the direction of curvature is reversed and the grain tends, to open up.

The method of manufacturing veneer having.

the above described characteristics of the crossband 5 will be understood by those skilled in the art, of cutting veneer from a relatively soft wood, the log is rotated on its own axis against a knife which thus in effect pares a sheet of veneer from the log. The cutting conditions are controlled by the adjustment of a presser bar or similar device bearing on the outside of the wood adjacent the knife. By suitably loosening the presser bar, the loose-cut condition described above is obtained in a manner that will be apparent to-those skilled in the art.

. A stair riser such as shown in Fig. 1 can be manufactured and sold as a unit, and the flexible end portion can then be bent by hand and without any special treatment or preparation to the desired shape conforming to the designof the step which is to be made. Preferably, although not necessarily, the builder will form a template 8 having the desired curvature and then merely bend the flexible portion of the stair riser against the template and fasten it in place in any suitable manner as by gluing. The tread is then secured to the top of the riser in any suitable manner. If desired, means such as one or more blocks 9 can be used adjacent the curved end of the step to support the tread. It will therefore be seen that such a riser can be used to form any desired shape and also for curved ends at either the right or left-hand ends of steps as may be desired.

The thickness of the crossband may vary according to the use to be made of the construction;

When the construction is to be employed for interior trim or for curved corners of cabinets'and similar purposes Where strength is not important, the crossband may be relatively thin and the construction correspondingly more flexible. In

such cases it may not be necessary to provide arigid portion as described above, the whole construction being made flexible. In the case of a stair riser, however,-it is preferable in the interest For example, in the conventional method of providing strength to support the tread to provide the rigid portion and also to use a somewhat thicker crossband for the flexible portion. A crossband of the order of A in thickness has been found to provide adequate strength to support the tread and at the same time sufficient inherent flexibility to permit bending to conventional shapes such as shown in Figs. 1, 4 and 5.

While only one embodiment of the invention has been illustrated in the drawing, it is to be expressly understood that the invention is not ,limited to this embodiment and that changes may be made in th details of arrangement and construction without departing from the spirit of the invention. Thus for some purposes it will be unnecessary to provide a rigid portion such as described above in connection with a stair riser. It will also .be understood that the flexible portion need not necessarily be at one end of the rigid portion, the arrangement in this respect depending on the use to which the construction'is to be put. Reference should therefore be had to the appended claims for a definition of the limits of the invention.

What is claimed is:

1. A stair'riser adapted for the formation of a curved stair end and comprising a substantially rigid plywood construction having one or more plies faced with thin hardwood veneer and a tion of a curved stair end comprising a substantially rigid portion and a flexible portion integral therewith, said flexible portion comprising a-thin flexible face ply and a backing ply secured to said facing ply on one side and having an exposed loose-cut surface on the other side with its grain extending ina direction substantially,

parallel to the generatrix of the curved surface and at right angles to the grain of said facing ply, whereby said flexible portion can be bentto the desired curvature with the loose-cut grain opening or closing according to the direction of curva- DAVID J. FRANKLIN.

) ture;

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