US2674770A - Wood patch - Google Patents

Description

m E. v. BENNETT Erm. 2,674,770

woon PATCH Filed Aug 29I 1950 2 sheets-sheet 1 f A MMM April 13, 1954 E. v. BENNETT ETAL 2,674,770

WOOD BATCH Filed Aug. 29, 1950 2 Sheets-Sheet 2 MMM A ZTOQ/VEYJ Patented Apr. 13,V 1954 WOOD PATCH Elbert V. Bennett and Harrell Renn, Albany, Oreg., assignors to M and M Wood Working Company, Portland, Oreg., a corporation of Oregon Application August 29, 1950, Serial No. 181,982

2 Claims. l

This invention relates to a new and improved form of patch for repairing defects in plywood, veneer, lumber, and the like.

It has long been the custom to improve the grade of wood by routing out small knots, pitch pockets, checks and such defects, to form a shallow recess of some standard size and shape, and then fitting in a thin patch of clear grained wood veneer to cover the underlying defect. Various forms of patches have heretofore been devised for this purpose. For the most part, such patches have been circular, boat-shaped or elongated patches with rounded ends, all of which have a number of" disadvantages. They are wasteful of the high grade patch veneer, they are not well suited for rapid production in quantity, they are not conveniently adaptable to the patching of defects of different sizes, and they leave much to be desired in the quality of the bond obtained at the end grain edges of the patch.

Objects of the present invention are, therefore, to provide a better form of patch which overcomes the shortcomings and disadvantages of prior known patches, particularly with respect to reducing waste of the patching veneer, simplifying and accelerating the production of the patches, facilitating the application of patches of different sizes and improving the glued joint at the edges of the patch.

The present patch is referred to as a sled patch because it is rectangular in outline and has a bottom surface which slopes upwardly at the ends of the patch like the front of a sled or toboggan. 'I'.his form of repair enables Tlhe patches to be made in strip form for convenient handling, and utilizes the high grade patching veneer with very little waste. The patches may be machine made to different lengths Without involving more than simple adjustments in the patch cutting machine and the defect routing machine, using the same strip stock and the same heat and pressure applicator for setting patches of different size. Some of the most common defects in Wood, such as checks and pitch seams, are relatively narrow but may run a considerable distance with the grain, with the result that there is considerably more need for a long patch than there is for an abnormally wide patch. Heretofore, long defects have been repaired by applying a series of short patches in overlapping, end to end relation, involving duplication of elort, and making the patches quite conspicuous where they intersect each other. By the use of the present patch, a single long patch will usually repairsuch defects in one operation. The most noticeable parts of a patch repair are its ends, the side joints being relatively inconspicuous, and so a long defect can be repaired even more inconspicuously with the present type of patch than a short defect because the two ends of the patch are farther apart.

The present sled patch also effects a marked improvement in the bond at the end of the patch by substantially eliminating end grain in the joint. Glue bonds between Wood surfaces are the weakest in end grain joints, and the end grain joints reach their maximum peripheral extent in the circular and rounded end patches heretofore used. In such patches, the bonds at the end grain surfaces are relatively ineffective, and the principle edge bond is limited tov the short extent of edge grain surfaces, which are a minimum in circular patches. In the present patch, the sloping sled ends cut across the grain at a relatively flat angle so that a nat grain joint is obtained, in effect, to the very ends of the patch. This is particularly important in the patching of single sheets of veneer where the patch can be secured only at its edge surfaces.

In the repair of plywood, the sloping ends of the sled patch are bonded securely to the top or face veneer, in addition to the bond between the under surface of the patch and the core veneer of the panel. Circular and boat-shaped patches are decient in edge grain joint surfaces, but the present sled patch has edge grain bonds extending the full length of the patch. Thus, the present patch is not merely stuck in its prepared opening with suicient adhesion to hold it in place, but is bonded securely in the edge joint around its entire perimeter with the veneer from which the defect was removed, regardless of whether the patch is in a single sheet of veneer or the face veneer of a multi-ply panel.

Other objects and advantages will become apparent and the invention will be better understood with reference to the following description Figure 5 is a perspective lview, with partsin section, showing the present patch installed in a plywood panel;

Figure 6 is a perspective view, with parts shown in section, to illustrate the application of the present patch to a single sheet of veneer;

Figure 7 is a diagram illustrating the relatively nat angle of the sloping edge surfaces in the end joints;

Figure 8 illustrates the first step in a preferred method of making the present patch;

Figure 9 is a sectional view taken on the line 9--9 of Figure 8 and Figure l illustrates another step in the making of the patches.

In Figures l, 2 and 3 the patch P is rectangular in outline, having a top surface I6, a bottom surface II having longitudinal flat grain, sloping side grain edges I2, and curved, sled-shaped end joint edge surfaces I3 terminating at the lines I. 'I'he curvature of the sled ends I3 is such that near the bottom surface II the grain has flat grain characteristics, and near the top surface I0 it is still predominantly flat grain but has a relatively small component of end grain. No surface on the patch presents a major component of end grain.

The patches are preferably made in strips having a series of patches joined together at break lines Illa to present a continuous, flat, top surface. Figure fl shows the underside or" such a strip 20.

In patching plywood as shown in Figure 5, the patch veneer is usually made of the same thickness as the face veneer I of the panel. The

thickness of the core veneer I5 is ordinarily greater than that of the face veneer, but the relative dimensions of core and face veneers are mmaterial to the patching operation. The panel is prepared by routing out the defect in the face veneer down to the glue line II to leave a recess 0f substantially the same shape and dimensions as the patch P. Thus, the routed recess has longitudinally parallel, inwardly sloping sides substantially to t the edges I2 of the patch, and curved sloping ends tangent to the glue line Il. The patch P is glue coated on its bottom and end surfaces II and I3 with suiicient spread to cause glue to be squeezed up on the edge grain surfaces I2 when the patch is pressed into the prepared opening.

In practice, the recess is cut by a rotary routing tool on a horizontal axis parallel with the work surface, the tool having cutting blades with tae pered side edges corresponding to the inclination of side edges I2 of the patch, as illustrated in our copending application, Serial No. 182,285, filed August 30, 1950. Hence, the side edges of the recess on the top surface of the work piece are not parallel at the ends of the recess but converge slightly at the corners I8 of the recess, causing the very ends of the patch to be compressed to some extent in a lateral or transverse direction when the patch is pressed into the recess. This is advantageous as it insures a tight fit at the ends of the patch. The original square corners of the patch P are indicated by phantom lines in Figures 5 and 6.

This sled type of patch is particularly advantageous for plywood and lumber when the glue is cured and set by high frequency dielectric heating applied only to the top side of the work. A pressure member, not shown, having electrodes for dielectric heating is pressed down on the top surface of the patch and energized to produce a direct field across the top surface of the patch and stray iield heating in the continuous glue line on surfaces II, I2 and I3, without any electrode under the work. The long sweeping curves of the end surfaces I3 bend up to the plane of the direct electrostatic field at the ends of the patch whereby the entire glue line is brought substantially into the direct eld and the heating is much more effective than in the usual case of stray eld heating where the glue line is electrically isolatedY from the direct field. Strong edge grain bonds are effected along the edges I2, and a strong fiat grain bond is obtained on the bottom surface II. The sloping end surfaces I3 have predominantly flat grain characteristics and have large joint areas relative to the thickness of the patch. Thus, the ends I3, as well as the edges I2, are bonded securely to unite the perimeter of the patch in tegrally with the face veneer I5, in addition to the bottom bond at I I.

Figure 6 illustrates how the improved bond 0btained at the ends of a sled-shaped patch strengthens the repair of a single veneer where there can be no bond on the bottom face I I. With reference also to Figure 7, it will be seen that if the radius of curvature of the circular arc 30 is made large in relation to the thickness of the veneer, the grain on the surface I3 will be predominantly nat grain and the arcuate length of surface I3 will greatly exceed the thickness of the veneer to provide a large joint area. The arc 3E) has its center at 3l, and the point 32 is spaced 45 degrees from the point of tangency 33 with the bottom surface II. As long as point 32 lies above the surface of the patch, the flat grain component in all parts of surface I3 exceeds the end grain component, and so the grain characteristic in surface I3 is said to be predominantly fla-t grain.

A two-inch radius is appropriate for the arc 3i] in commercial thickness of veneer, but this dimension is not critical and the invention is not to be limited by the mention of a specic value. With a two-inch radius in 3315" thick veneer, for example, the arcuate length of surface I3 greatly exceds the veneer thickness and the maximum end grain component, at point I4, is quite small. By way of contrast, in conventional patches the width of the joint surface is only negligibly greater than the veneer thickness, and a large part of this small bonding surface comprises predominantly end grain. Figure 'I is drawn to scale to illustrate accurately the actual curve of surface I3 in 53g" veneer when the radius of arc 30 is two inches. It is apparent that there is wide latitude in the veneer thickness and arc radius without causing point I4 to approach closely to point 32.

It is preferred to make the present sled patch by rst cutting a piece of patch veneer V into a plurality of patch strips 20 having the desired width of the patches, as shown in Figure 8. This is done by cutting parallel tapered slots 2l to make the desired width of faces I0 and II and the desired inclination on the edge grain surfaces I2. The only waste in cutting these strips comprises the material removed from the slots 2i and the side trimmings 22.

The strips 2U are then grooved transversely at intervals to form the sled-shaped end surfaces I3. In forming these sled ends, the patches may be severed from the strips, if desired, but, preferably, a thin web of connecting material Ida is left on the face I0, sothat the completed patches may still be handled in strip form. In Figure. l0, three such shaping operations' have been pere formed on a patch strip, leaving the webs llar to orzn break lines by which the patches may be broken apart as they are needed. Additional shaping operations will convert the remainder of the strip into patches all connected together in end to end relation. The only waste in the shaping operation comprises the material removed in cutting the transverse grooves to form the surfaces I3, and the small end pieces 26. Obviously, the patches may be made in a variety of different lengths, as needed, to cover the lengths of the defects to be repaired, so that it will not be necessary to overlap the patches on a single defect, as has been the conventional practice.

By leaving the patches connected together at |411., a ragged feather edge is avoided at the ends I4, and the ends do not tend to split or splinter. The patches may be handled in strip form, if desired, until they are ready for use, piles of strips of different length patches being made available to the patcher. Upon breaking the patches apart at the lines Ida, clean-cut square ends I4 result. The web portions at Isa may be left very thin, so that after the patches are broken apart there will be no apparent thickness at the ends. In any event, the usual sanding operation makes the top of the patch smooth with the face veneer.

In setting a long patch, the pressure and heat applicator may be moved along the patch in repeated applications to set patches of any length. The patch becomes less conspicuous as the ends I4 become farther apart. Since the patches are of uniform width, the routing tool used for removing the defect, and the pressure and heat applicator, do not have to be changed for patches of different size. Long and short patches may be applied one after another without any interruption in the work.

Having now described our invention and in what manner the same may be used, what we claim as new and desire to protect by Letters Patent is:

1. A repaired veneer having an opening iitted with a rectangular sled-shaped patch, said opening and patch having at, downwardly converging, sloping side walls and cylindrical surface end walls tangent to the bottom surface of the veneer and patch, said end walls having uniform predetermined width and an arcuate length considerably less than the side edges of said opening in the top surface of the veneer converging at their ends to said predetermined width and holding the ends of the patch under transverse compression.

2. A plywood panel patched by a rectangular sled-shaped patch, said panel having a sledshaped recess in its face veneer and said patch and recess having iiat, downwardly converging, sloping side walls and cylindrical surface end walls, the bottom of the recess including said end walls being of uniform predetermined Width and the side edges of the recess on the surface of the wood converging at their ends to said predetermined width and holding the ends of the patch under transverse compression, said end walls being tangent to the bottom of the recess and having an arcuate length considerably less than 45.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 519,553 Rounds May 8, 1894 1,005,546 Hobart Oct. 10, 1911 2,263,536 Dike Nov. 18, 1941 2,583,396 Skoog Jan. 22, 1952

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