US2136730A - Method of treating lumber - Google Patents

Description

Nov. 15; .1938." E. J. SWEETLAND METHOD OF TREATING LUMBER Fiied Nov. 15. 1955 2 Sheets-Sheet 1 INVENTOR.

E. J. SWEETLAND 2,136,730 METHOD OF TREATING LUMBER Nov. 15, 1938.-

2 Sheets-Sheet 2 Filed Nov. 13, 1935 INVENTOR.

- jecting the boards sealing agent which Patented Nov. 1938 OFFICE METHOD or TREATING LUMBER 'Ernest J. Sweetland, Piedmont, cam. Application November 13, 1935, Serial No. 49,517

i 8 mains.

This invention relates to a specially surfaced and hardened lumber and method of preparing the same. I

An object of my invention is to harden lumber such as is used in building construction, cabinet wor furniture manufacture and the like.

Aiurther object is to harden lumber and simultaneously provide it with a smooth and irregular surface which has an artistic value for use as interior trim, paneling, cabinet work and the like, particularly where rustic effects are desired.

p A further object is to ,harden lumber and isimultaneously raise certain of the grains theren.

A further object is to provide lumber of substantially equal-hardness throughout as an improvement for certain purposes over lumber which is composed of alternate hard and soft layers.

[A further object is simultaneously straightening and hardening lumber.-

A further object is filling the pores of lumber, especially those adjacent the surface thereof, with a sealing agent such as linseed oil, varnish or shellaclthen'subto compression whereby the penetrates beneath the surface of the boards is permanently enclosed within the board structure.

A further object is to preserve lumber from attack by insects by compression which tends to destroy insects or larvae that may be confication isoutlined in full. form of the invention is shown, but it is to be cealed .within the structure of the board and also tends to prevent the'further invasion of the board by insects; the use of chemical agents such as creosote either prior or subsequent to compression may be employed if desired.

A further object is to hardenlu'mber by compression in a manner which makes it especially amenable to the action of liquids-fer raising the grain thereof and thus decorative purposes. f

The invention possesses other advantageous features, some of which with the foregoing, will be set forth at length in the follow'ng description where that form of the invention which has been selected for illustration inthe drawings accompanying and forming a part of the present speci-= In said drawings, one

understood that it is not limited to such form. since the invention as set forth in the claims may be embodied in a plurality of forms,

be pressed in a'single operation, but rather to the to provide. a method for.

toprovide a method for adapting it to certain The term lumber as used herein is a general term to define wood which has been sawn into boards, planks, timbers, etc-regardless of the nature of the wood from which the lumber is made. t

I am aware that the art of compressing wood in the form of small blocks for variouspurposes is old, and also that railroad ties have been sub- Jected to compression for purposes of hardening etc. The present application is not concerned with the compression of'blocks of wood that may completely enclosed in a mold and comtreatment of commercial lumber of various sizes and lengths by a method which is believed to be entirely novel and which accomplishes a new and useful purpose which cannot beachieved by the methods of the prior art.

All woods are irregular in hardness and density particularly the softer woods most commonly used for making commercial lumber such as pine, fir, spruce etc. The irregularity is 'due to 'the fact that the growth of the tree is more rapid in the spring than at any other time of the year. The spring growth is therefore an open cellular structure which is quite soft by comparison with the denser wood which grows later in the season. is built up of alternate hard andsoft annular layers. When the tree is cut into lumber the boards are composed of alternate hard and soft layers which lie in planes approximately parallel to the flat surface of the board in lumber known as "slash grain"; whereas the boards are known as vertical grain when the alternating hard and soft layers lie approximately at right angles to the flat surface of the board. Naturally the soft grain of the wood is not as durable as the harder grain as may be frequently observedin flooring, where the soft grain wears away leaving an uneven surface which eventually becomes splintered and has to be replaced. One of the objects of my invention is to increase the density and hardness of the softgr'ain without materially affecting the-hard grain, thereby producing a lumber of fine texturewhich is greatly increased in strength and will wear uniformly.

Boardsused in building construction frequently range from- '10 to feet in length and may be,12 inches or more in width. In carrying out my process of hardening lumber the pressure required may vary from one to five tons per square inch, and it is obvious that the cost of equipment would in most cases be prohibitive if.

' it'were necessary to provide a, press and dies or The result is that the tree hibitive.

method herein set forth a reciprocating press, such as an ordinary punch press, may be used, and very satisfactory, results produced where the maximum capacity of the press is'from 100 to 500 tons and automatic feeding methods may be tion is imparted to 38 which. drives the gear wheel 38 through the.

a powerful downward stroke to this graduated entrance to the die is used to reduce the cost of labor to a minimum. Furthermore, by my method dies of adjustable width and depth may be used. so that the cost of equipment to handle the entire range of commercial sizes of lumber represents but a com- I paratively small investment. The same press may be used on the entire range of sizes.

My invention will be understood by reference to the accompanying drawings wherein:

Figure 1 illustrates a toggle pressand feeding mechanism in side elevation.

Figure 2 represents a front elevation of a die that may be used in connection with the press shown in Figure 1. i Figure 3 is a side elevation which diagrammatically-represents a modification of the invention wherein a plurality of presses may be used in series to compress lumber in successive stages. Figure 4 represents a method of compressing two or more .boards simultaneously. Figure 5 represents means of boards against compressin a resilient surface, such as 'rubber, to accentuate the grain of the wood.

' Figure 6 shows a die for use in giving a decora-' tive design to boards being compressed.

Referring particularly to Figure 1 the numeral 3| indicates the base of the toggle press which supports the bolster plate 32 and the die 33. The upper portion of the press 34, which may be called the ram, carries the upper die 35. The ram I4 is mounted in guides (not shown) which inaintain the lower surface the horizontal tion to the die surface of die 35 'in parallel rela- 33. A vertical reciprocating mo- 34 and 35 by means of pulley pinion 31. 39 is a crank pin which is eccentricaliy mounted with I wheel I8 and is carried thereby, and 4| is a link journaledtopin 39 which transmits the motion of crank pin 39 to the toggles 42 and 43. The upperend of toggle 42 is journaled to the stationary shaft 44 which is supported in the housing of the press (not shown). Upon rotation of the gear wheel 34, the toggles 42 and 43 are straightened to a vertical position thus imparting theupper die 35.

Itwill be noted that the forward end of the upper die I! departs from a horizontal line as indicated at 40 to form a gradual sloping entrance between the dies,'thereby making. the distance between the lower die 31 and the upper die it somewhat wider at the entrance than it is throughout the body of-the die. The object of t'o avoid a sudden disturbance of the fibers of the board at the forward edge of the die. Generally speaking it inadvisable to have the amount of slope at the" forward end ofthe die equivalent to the amount of reduction in thickness it is desired to give the lumber as each piece of lumber passes exceedingly expensive On the other hand, by the step by step 1 .the press the cam feed rod of the ram 34 and relation to the center of the gearwith a cam surface 43 applies the necessary inch in one pass through thedie then the forward edge of the upper die 35 is made at least l inch higher than the horizontal face of the die and the slope continues for a distance of several inches. By this arrangement a sudden step in the thickness of the board which would tend to disrupt the fibers is avoided.

at its forward end as is represented in Figure 3, if desired.

'To provide automatic feed of lumber through 45 is keyed to the central shaft 50. The follower 46 which is integral with the 41 imparts a reciprocating motion to the rod 41 which is slidably mounted in the .guides 48 and 49 and the follower is kept in contact with the surface pression spring 5i. 4

represents a table which is supplied with a plurality of rollers 54 which serve as a support for the boards 52 which are fed through the press in a step by step motion by the dogs. 53 which are carried by the rod 41.. The length of stroke'bf the rod 41 and consequently the amount of feed imparted to the boards may be adjusted by pins inserted in the holes 8| which regulate the length of the return stroke of the rod 41. The dogs 53 are pivotally mounted and are sharpened at the point. The weight of the dogs keeps their sharp points in contact with the board 52 and the angle at which they rest on the board permits them to slide freely over the board during the return stroke of rod 41. y Thus the dogs bite" into the board surface to feed it into the press while cam 45 is acting upon follower 46 and rod 41 during the forward stroke, and the dogs slide over the surface of the board with a ratchet-like action during the return stroke.

Figure 2 represents a front vertical section of a die which may be used in the press illustrated in Figure 1. The-die here illustrated supports the sides of the boards to prevent them from bulging during compression. This arrangement consists of the upper die 02 which is provided with a projection 83 which corresponds in width to the width of board desired. The lower die 64 is firmly secured to the bolster plate by any convenient means and is provided with the movable slide plate 65, which is given a. horizontal motion by means of the rod 86. which is provided 81, which bears against'the surface 48 to force the plate'inwardly while the cam surface 89 gives the plate an outward movement near the an of the upward stroke of the press. 1 [represents a sectional view of the board in place in.the die. From this construction it will be ward stroke of the press the of the cam by the comcam 61 engages the left bringing it in close contact with the side of the board which is approximately the same width as the portion 03 of the upper die. As the downward stroke progresses the plate 45 is firmly held against the board by the flat surface 12 beaning against the straight side 13 of the opening through-plate 4!. while the plate CI is thus Held in close contact with the board the part compression and when the upper die 43 returns to a point near the up per end of its stroke, the cam surface 68 pushes the plate 85 outwardly to the position indicated in the drawings. The arrangement of the plate 45. as described, not only tends to straighten lumber by forcing it into a perfectly straight The lower die 33 may be,

. graduated in thickness seen that in the early part of the downposition during; the application of pressure, but

wseryes the further purpose of releasing the board the upper die 62, the plate 65 is free to move sideways in accordance with the pressure of the cam surface 61 which forces the plate inwardly during the down stroke of the die. Similarly the plate 65 is forced outwardly by the pressure of the cam surface 89 during the upward stroke of the die. Therefore the motion of the side plate 65 is automatically co-ordinated with the motion of the die 62 so that the inner surface of the plate always bears against the board while it is subjected to pressure by the projection 63, and is released to the position shown in Figure 2 during the upward stroke of the die. While the plate 65 is free to slide sideways, means (not shown) is provided to prevent it from being lifted out of position during the upward stroke of the press.

Referring to Figure 3, this diagrammatically represents a series of presses operating upon the same board lll'whereby each press further reduces the thickness and increases the hardness of the board, until it is finally discharged as a been previously planed) would be to reduce the finished product. In this view the lower toggle of the press is represented by the numeral 43a; the upper die by Mia and the lower die-by 33a. In this case both the upper and lower dies are sloped 'at the forward end to make the compression of the boards more gradual, the sloping surfaces being represented by the numerals l5 and I8;

Figure-4 diagrammatically represents a pair of boards being fed between the dies together whereby the thickness of the boards is reduced and at the same time the hard portions of one board are impressed into the softer portions of the opposite board to produce a smooth undulating surface upon the face of the boards which lends itself to artistic treatment as ,will hereafter be described. If desired the pattern of a fabric such as canvas or wire screen or like materials may be impressed in the board surfaces by placing such a fabric between the boards during compression.

lip carrying out the objectsof my invention the process is substantially the same whether dies as illustrated in Figure 1 are used or whether the type of dies illustrated in Figures 2 and 3 are used. In either. event the press may be set to reduce the thickness of the boards by about 10% during the first one or two passes through the press. If extreme hardness is desired the amount of reduction may be reduced with each successive pass. A typical operation where pine or fir lumber having an original thickness of l% inch is used (the boards preferably having thickness of an inch the first pass, of an inch the second pass and inch each for the third and fourth passes thus reducing the thickness of the board from H to 1"; of an inch. I have found that for a short time after the compression there is a slight expansion of the wood, increasingnthe thickness to a small degree but after the compressed lumber is seasoned for a few hours orat the most for a few days it holds its size without further change unless subjected to the action of dampness or liquids.

Ordinary commercial lumber either with or without kiln drying may be used in carrying out 3 the purposes of my invention. It is preferable to have the lumber planed on all four sides prior to compression but this may be dispensed with to obtain certain effects. The treatment is ordinarily carried on at normal room temperature withentirely satisfactory results although in certain cases I have found it advantageous to warm the boards prior to compression, whereby the resinous material within the board structure is softened with certain beneficial effects.

A typical method of operating the apparatus shown in Figure 1 would be as follows: The boards are fed on to the rollers 54 either manual'y or automatically, the machine being operated at a speed which may vary to suit the work in hand. A speed of about 40 strokes per minute gives satisfactory results although this may be greatly varied in either direction. The dies 33 and 35 in a typical instance may be 24 inches in length with the sloping portion extending over about 6 inches of the length of the die, leaving the parallel surfaces about 18 inches long. With this arrangement a forward feedof 12 to 15 inches may be used. In any event the feed forward should be somewhat less than the length of the-parallel portion of the dies so that there is a certain amount of overlapping of compression at each stroke. It will be understood, however, that these figures are all subject to wide variation which depends more or less upon the hardness of the lumber and the power of the press. For instance, soft pine boards receiving or 4 inch compression may readily be fed 15 or 16 inches at each stroke of the press without drawing excessively upon the power of the machine; but if oak planks are under treatment either the amount of compression or the amount of feed should be reduced as the power required to'compress oak planks is obviously greater than that required for soft pine. I

' If it is desired to reduce the thickness of the board to a large extent in a single pass through the machine then the sloping portion 40 of the die 35 may extend. almost the entire length of the die and the forward opening in the die may be half an inch or more wider than the parallel surfaces of the die. In this instance the feed of the board is reduced so that it is always somewhat less than the length of the parallel surfaces of the die. Therefore if the die is'24 inches long and the sloping portion extends for a distance of 18 inches. the feed should be reduced to 3 or 4 inches. In this case a board of an inch thick may readily be reduced to half of its original thickness at a single pass through the machine. The same principles apply when both the upper and lower dies have inclined surfaces at the forward end'as illustrated in Figures 3 and 4. Thus it will be seen that the desired result may be obtained either by rapid feeding with a small amount of compression or by slow feeding witha large amount of compression at As soon as the boards are advanced upon the rollers 54 far enough to. be engaged by the dogs 53 automatic feeding takes place. The flat portion of upper die 35 at all times maintains its parallel relation with the die 33 and in its downward stroke com m the board to the reby" the polished surfaces of the dies. Birtwhen quired extent, then as the die I! recedes from it is desired to obtain an irregular surface on the board the 'cam it forces the follower 46 and the face of the boards for antique or rustic ef-' the feed rod 41 forward and the board is thus fects the arrangement illustrated in Figure 4 advanced by the dogs It. It should be noted is used. In this instance the upper diel'lb 5 that the cam 45 is keyed to the shaft-Bil to which and the lower die-33b are mounted in a p'ress the gear wheel 38 is also fixed. Thus the crank similar to that shown in Figure 1 and all of the pin 30, which is carried by the gear wheel 38, operations are substantially the same except and the cam 48 maintain a fixed relation to each that two boards 82 and 83 are placed face to face other such that the cam 4! always acts upon and fed through the machine simultaneously. the follower l6 and rod 41 to feed the lumber By this process the lumber'is hardened as-it'is during the upward stroke of die 35. The board in the instances previously described, but the $2 in 'the drawings is represented ,as being in. harder portions of one board tend to'make deprogress of advancing in preparation for the pressions in the softer-portions'of the oppodte next stroke. The longitudinal lines on the side board and vice versa, in amanner that gives each 15,; of the board represent the harder grain of the 1 P r undulating u f ce wh h. wood which, as will be noted at the point indiwhen stained and otherwise decorated, produces cated by the numeral II, are not disrupted by pleasing and interesting effects with patterns the gradual process of compression but are forced are peculiar to each individual board and; closer together as the softer portions of the which never'repeat themselves. A knot in one wood yield 'to compression. when a considerable board makes a depression in the opposite one degree of compression is to be used on the lumand the varying densities of the'two boards, which her it is desirable to use the type of die iilusare not obvious before compression is applied,

' trated in Figure 2 which, as previously excauses the contours of the boards to vary and plained, supports the sides of the board and at the same time the surfaces are made ex- '25 prevents bulging or splitting. tremely hard, thus reducing the absorptive qual- The type of die illustrated inFigure 2 is parities of the boards and thereby minimizing the ticularly important when it is desirable to quantity of materials required for staining, varstraighten the lumber simultaneously with the nishing etc. Both boards are hardened and the hardening. For instance, narrow boards that tendency is for their hardness'to be equalized. are warped in a sidewise direction may in some As. hardening of the bda ds tends to reduce cases be straightened by compression in a die the amount ofstain which t y will absorb, it is of this type. This straightening is accomplished sometimes desirable, in order to give contrast in by reason of the rearrangement of fibers within color, to apply stain and allow it to dry prior to the board during heavy compression, while the compression. This applies to the treatment de- 5 board is'forcibly held inastraight position by'the scribed with reference to Figures 1g 2, and 3, side plates of the die. as well as to Figures and 5. I

The arrangement shown in Figure 3 repre- In the modification hown in Figure 5the dies sents a plurality of similar dies operating in 40c and 330 are used as previously described, but series each pair being somewhat closer together in this instance the fate of the die 330 is covered 4 than the preceding pair. The series of dies are 1 withrubber. fa r c. r a y r resilient ma assumed to be operated in timed relation with "as indicated by the numeral 84. In this each other so that the board 52a is released by all of the dies of the series simultaneously and is singly and the effect of the resilient su'rfed forward'with a single feed mechanism. In face'f'on the die is to compress certain grains of this figure the amount of compression of the thew'ood while others are brought 'out in relief. board is somewhat exaggerated for. purposes of The same result may be producedby placing a illustration, and it will be noted that in this loose ,sheet of rubber between the board and figure both the upper and lower dies have the die. I sloping forward surface as shown at I! and It 4 If it is desired to hardenboards with an 1r- 0 which makes it possible to compress the boards regular surface on both sides, then both the dies with less disturbance to the fiber structure than "c and "c may be covered with resilient maa when only the upper die is tapered as shown in terial the hardness of which is varied to suit the Figure l. type of lumber being treated and if desired cer- It should be noted that the results obtained tain patterns or undulating surfaces may be 55 with a' single pair ofdies as shown in Figure 1 provided. in any of the dies herein described to is ultimately the same as the results produced produce special efl'ects on the surfaces of the with the seriesarrangement shownin Figure 3, lumber.

but when a single press as shown in Figure 1. In Figure 6 the numeral 85 represents-a sec- -i'ication the boards are fed through the is used, a single batch of lumber is run through tion 'of an upper die corresponding to 83 in 50 the same dies several times, the dies being ad- Figure 2, upon which the beads 86 are an examiusted closer together after each operation. This ple of one form of pattern or decoration that adjustment may be accomplished through the be pressed upon the lumber during comscrew adjusting means customarily *used in pressing,

punch presses for' regulating the distance be- Obviously three or more boards may be passed o5 tween the dies. or one of the dies as I! or 35 through any of the dies at a time, in which inmay be replaced by a thicker one after each stance all of the boards except the upper and reduction in thickness of the batch. In some lower ones will have both of'their surfaces imcases I have found it convenient toreduce the pressed with theirregular pattern produced by space between the dies and thus increase comthe adjacent board. 7 pression .by securing one or more fiat spacing From the foregoing it will be understood that plates to the tgpof the lower 'die a. I boards or timbers of any size and length may be In the p 7 description it was assumed hardened by the use of a simple machine which that the to come'from the press can readily be adjustedto'sult any size material. 4 with a sm hardened surface as Any chemical or. other, treatment applicable to either before or after treatment by my process.

For instance a quantity of lumber may be placed in a vacuum chamber to remove the air from the cells after which, it may be submerged in a preservative such as creosote or a liquid such as linseed oil, varnish, sodium silicate or any other liquid which may be forced into the chamber under pressure to completely impregnate the pores of the wood, after which theboards are subjected to the compression herein described which will remove the surplus liquid and leave the boards in a hardened condition thoroughly impregnated for whatever purpose such special treatment may be desired.

The boards may be steamed or subjected to treatment in hot or cold water prior to treatment to obtain special effects.

. Boards of veneer or plywood may be successfully compressed after such veneer or plywood is manufactured or the individual layers which make up the product may be compressed prior to being glued together. In either instance a veneer or plywood of superior hardness is obtained.

One of the advantages of my process for producing an irregular surface as described in connection with Figures 4 and 5 is that the surface produced, While ,irregular, is still smooth and pleasing to the touch. However, when it is, desired toproduce certain rustic effects, and particularly where it is desired to open the pores of the wood to make it more receptive to stain, the surfaceof the compressed board, whether it is compressed with a smooth finish or with an uneven surface, may be treated with water or with a water stain, cr other liquid. This causes an opening of the pores at the surface and swelling of the grain which lends itself to a great variety of decorative eifects' well known in the arts, Ordinarily it is desirable to waterproof the lumber after compression as the surface of the lumber treated by my process is more susceptible to the action of water than ordinary lumber. This, however, is not essential so longv as the compressed lumber iskept in a reasonably dry place;

From the foregoing it will be understood that soft wood in the form of commercial lumber may be hardened to any'desired degree up to a point where it equalsor exceeds the hardness of the so-called hard woods such as oak, maple, hickory, etc, and the natural hard woodswhen treated by my process are greatly increased in strength and wearing qualities and decorative effects are produced by the methods herein described that have heretofore been unattainable in commercial lumber. r

1. A method of simultaneously hardening and producing an irregular surface on boards having hard and relatively soft portions which comprises placing a plurality of boards together with their adjacent surfaces in contact, subjecting said boards to a compressive pressure sufficient to permanently reduce the thickness thereof, said thickness varying moderately in different portions of said boards in accordance with the compressibility of said hard and relatively soft portions and the extent to which the hard portions of one board have been impressed into therelatively soft portions of the adjacent board, and then separating said boards to expose said adjacent surfaces.

2. A method of hardening wooden boards and the like by compression comprising, subjecting a section of a substantial area of a board to a substantially uniform compressive pressure sufficient to permanently reduce the thickness thereof and simultaneously subjecting a second section of a substantial area adjoining said firstmentioned section to compressive pressure such that the stress in said section gradually decreases in degree in a.direction away from said firstmentioned section, releasing the pressure on said sectionsjand then subjecting said second-mentioned section to a substantially, uniform compressive pressure equal to that previously applied to said first-mentioned section to permanently reduce its thickness .to a substantially uniform thickness corresponding to that of said firstmentioned section.

3. A method of simultaneously compressing and producing an irregular surface on boards having alternate hard and relatively soft portions which comprises, compressing aboard against a substantially flat resilient surface by applying compressive pressure thereto in excess of the elastic limit of said soft portions to thereby compress said portions to different degrees to form a board of varying thickness with certain parts of the hard portions standing out in relief relatively to compressive pressure sufficient to permanently reduce the thickness of said section of said boards and, simultaneously subjecting a second section of a substantial area of said boards adjoining said first-mentioned section" to compressive pressure such that the stress in said second section of said boards gradually decreases in degree in a- 7 direction away from said-first-mentioned section of said boards, whereby the soft portions of said boards are compacted and certain of the grains of said hard portions are forced against certain of said soft portions to form indentations therein,

releasing the pressure on said boards, then subjecting said second-mentioned section of said boards to a substantially uniform compressive pressure equal to that previously applied to said first-mentioned section of said boards to permanently reduce the thicknessthereof to a substantially uniform thickness corresponding to that of said first-mentioned, section. of said boards, and then separating said boards to expose said indentations to view.

5. The method of simultaneously hardening and producing an irregular surface on boards which-comprises, placing a board upon a resilient surface, applying a compressive pressure to a section constituting a substantial area of said board, said compressive pressure beingsufficient to permanently reduce said section to a substantially uniform thickness, simultaneously coinpressing a contiguous section of said'board to different degrees of compression to produce a longitudinally varying thickness in said contiguous section, releasing said pressure, and then app ying compressive pressure to said contiguous section to permanently reduce its thickness to a substantially uniform thickness corresponding to that of said first-mentioned section.

6. The method of hardening wooden boards by compression which comprises, supporting the opposite longitudinal edges of a board to prevent expansion of said board when compp y s a compressive pressure to a substantial portion of said board sufficient to permanently reduce said portion to a substantiallyuniform thickness and simultaneously oompras a contiguous portion of said board todifferent degrees of compression to produce a longitudinally varying thickness in said contiguous portion, releasing saidpressure, then applying compressive pressure to said contiguous portion to permanently reduce its thickness to a substantially uniform thickness corresponding to that of said first-mentioned portion.

'7. A method of filling, hardening and producing an irregular surface on boards having hard and relatively soft portions which comprises, apply ng sealing material to at least one surface of a plu rality of boards to fill the pores thereof, placing said boards together so that two iilledsurfaces are adjacent and in contact, subjecting said boards to a compressive pressure sufilcient to enclose in the pores of said boards the sealing materiai which has penetrated below the surface of said boards and to permanently reduce the thickness of said boards, said thickness vary ns moderately in different portions of said boards in accordance with the compremibility of said hard and relatively soft portions and the extent to pressive pressure which the hard portions of one board have been impressed into the relatively soft portions of the adjacent board, and then separating said boards to expose said adjacent surfaces,

8. A method of treating wooden boards and the like by compression, comprising, impregnating,

at least one face of a board with a sealing material, subjecting a section of a substantial area of said board to a substantially uniform comsufiicient to permanently reduce the thickness thereof and to .enclose within the board structure the sealing agent which has penetrated beneath the surface of said board, and

thickness corresponding to that of said first men- 25 tioned section.

ERNEST J. SWEE'I'LAND.

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