US2191099A - Blackboard and improved process of making the same - Google Patents

Description

Feb. 20, 1940. R. w. SHENTON BLACKBOARD AND IMPROVED PROCESS OF MAKING THE SAME Filed June 27, 1938 m m w 0N P. rm m M V. W WW W Y 4 R a r w H 6 i m V. J

Patented Feb. 20, 1940 :UNiTED. STATES BLACKBOARD AND IMPROVED PROCESS or l MAKING THE SAME Ralph W. ShentonQSlatedalc, Pa. Application Ju eau, 1938, Serial No. 215,998

10. Claims.

My invention relates to improved blackboards and to improved processes of making the same,

and this application for patent thereon is a con- 1 tinuation in part of my pending application Serial .6 No. 110,887. Particularly, the invention relates to blackboards having a base or body member of suitable material, such. as plywood, which serves as a backing-support for a facing of slate veneer utilized as the writing surface.

-39 blackboards I mean the various articles which have a natural slate writing surface, suchas the wellknown school slates, school blackboards, conference blackboards, bulletin boards, drafting v boards, etc. By slate veneer I mean a layer of 4. natural slate smoothly finished which is thinner rian has been considered practicable in the past for. any sheet of machined or polished slate. The

slate sheet which I term veneer does not exceed one-sixteenth inch thickness and, in the most usual adaptations of my invention, is of a thickness of the order of one-thirtysecond inch.

, It is well known that blackboards, bulletin boards, conference boards, school slates, and analogous articles are commonly made of natural slate. Natural slate has a surface texture which is particularly adaptable to highly satisfactory blackboard surfaces. It is well known that ithas nite' advantages and utility over all other known materials for this purpose. Numerous artificial substitutes, and coatings upon foundation bases, have been triedas blackboard surfaces, without being found to be as successful or useful as natural slate. However, natural slate a material which easily fractures and breaks.

Due to its peculiar. composition, it withstands without injury only very slight stresses'of certain nature. Furthermore, natural slate is a comparatively heavy material and thus involves considerable labor in handling and high charges for otransportation. The use of slate for blackboards involves considerable difficulty in distr'ibutingand mounting boards because of the great weight of the slate, and the liability of breakage. Also,

slate is quite a costly material, and its supply in 4,5 many parts of the country is limited. Thus, the cost of a suitable supply to such parts of the country is prohibitive, particularly when the transportation charges thereto are taken into account. lVly invention is designed to eliminate to a large extent the aforesaid disadvantages in. the use of natur al slate for blackboards, and: make natural slate for this purpose practicably available. For usein blackboards it has been necessary to have natural slate of from oneeighth inch thick ness up, depending upon the size of the black board. My invention is designed'to provide an efficient and wholly satisfactory blackboard having a natural slate writingsurface by the use of a natural slate veneer for they writing surface, .5 of a final thickness not exceeding one-sixteenth inch, and. preferably of a finalthickness of the order of onc-thirtynecond inch. Slate veneer of this character is utilized by me as a Writing surface. upon a suitable backing-support, such as 10 plywood. This veneer thickness is obtained by machining down. thin sheets securelyheld to a flat base which acts as chuck. The blackboard when fully completed comprises the slate veneer secured, preferably cemented, to a.backing-sup-Al. portc," l l In producing my improved slate veneer, 1 sub}- stantially discard all the slate, with the exception of a machined surface, and then buildupthe. necessary backing-support so that the final prod- 20 not possesses the characteristics of the hackingsupport with the exception of the natural slate Writing surface which is preserved. In fact, only enough slate is preserved to insure that the writing surface will not be worn through by scratching; .25 for instance, when rehoning the slate writing surface. This veneer thinness of the slate becomes evident as the thinness passesbelow onesixteenth inch and reaches its practicable limit at about one-thirty-second inch. Such a thin- I3 0 ness in the slate veneer results in its losing its dominant characteristics of a stone, such as its weight and rigidity, and the peculiar susceptibility of slate to cracking and splitting, so that there is 'preserved of the natural slate qualities 35,

only its superior quality as aawriting surface. The combination of the veneer and its backingsupport has the dominant characteristics of the backing material, such as lightness, toughness, and reasonable subjection to bending and Warp- 33,0 ing. This resultant. product is subject to carpentering by ordinary carpenters tools and can be, supported y a y a l pp rt by bein nailed thereto. The veneer facing is amenable tobenoling andwarping and follows the backing- 4 5 support when the latter is bent or warped and consistently conforms. to all portions thereof, so that at all times the veneer facing hugs itsbacklug-support. At the veneerthinness, the slate has become readily pliable, and the bonded joint 5,0 between the facing and the support is subjected to no serious mechanical stress by the bending or Warping of the backing-support.

. In the production of my improved blackboards, I first split, the rough natural block into sheets ,oti

as thin as can be practicably produced by slatesplitting operations. Then I produce the thinness, which I term a veneer, by machining the thin split-sheet while this thin sheet is securely held to a fiat backing which serves as a chuck for the machining, and any desired polishing, thus rendering possible the practicable finishing of the thin sheet down tothe thinness which I term veneer. i

The annexed drawing and the following de- 'scription set forth in detail certain means con,- stituting my improved blackboard, and certain improved processes of making the same, such disclosed meansconstituting, however, onlya few of the various forms in which the improved blackboard may be embodied, and only a;fevv of the.

various series of steps by which the improved processes may be worked. h r

by the line 33, Figure 2;

Figure 4: is a side elevation of the conference board shown in Figure 2, the View being taken from the side opposite that from which Figure 2 is taken and showing for purposes of illustration the slate veneer writing surface of my invention as comprised of a plurality of slatepieces jointed together to provide a smooth continuous slate surface and suitably secured. to thebacking support; and

' Figure 5 is a perspective of a drafting board provided with my improved slate veneer writing surface.

One method of making my improved blackboard consists in, first, splitting a rough slate block into sheets thicker than the desired thickness of the final slate veneer. These slate splitting operations are well known in the art. Secondly, I hold the split slate sheet aforementioned tothe surface of suitable fiat supporting material which acts as a chuck on which the thin split slate sheet can be machined, without any considerable slate breakage, and form the desired veneer surface by machining. Any desired polishing or other finishing of the veneer sheet can also be effected. The finished veneer sheet which is so thin and fragile that it can be handled in material sizes only with difficuity without its breaking under its own weight is then slid upon and secured to, preferably bycementing, a suitable backing-support which forms a body member for the blackboard, one such desirable body member being comprised of plywood l2, Figures 2 and 3, of any desired thickness. Another way of securing the finished veneer sheet to the backingsupport consists in spreading cement upon one face of the veneer sheet and pressing the backing support onto said veneer face.

Another method of forming the slate veneer sheet, and combining the same with the backingsupport, consists in cementing the split slate sheet to any suitable platen, such as a planing machine bed, using a thermo-cement, such as beeswax or shellac, for this purpose, then planing down the split slate sheet to the veneer thinness, and then reheating so that the veneer can backing-support.

against a fiat surface, I avoid cutting the slate across the grain of its natural split. Thus, the

veneer facing, facing which I provide, in the manner hereinbefore described, is such thateven moderate ham- Then the veneer sheet can be cemented to a suitable backing support to form the final product.

If desired, the final backing-support of the blackboard, such as the plywood l'2, can be utilized as the chuck uponwhich the thin split slate sheet is machined and finished, so that it is then unnecessary to transfer the finished'veneer sheet from a chuck base to the final blackboard body. Inthis event, the thin split slate sheet is firmly secured, asby cement, to the support which acts both as a chuck and a final blackboard body, before the machining and finishing are effected.

For purposes of illustration, the blackboard structure made as described is shown in Figure 1 nailed to a building Wall I. This method of mounting the blackboard 2 is effected by an ordinary nailing operation, and the nails 4 can be freely driven through the slate veneer 3 and the backing-support without injury to the veneer facing.

It will-beunderstood, of course, that if the improved slate veneer writing surface is desired upon both sides of the backing-support, the latter can be so provided, and such a showing is presented in Figures 2, 3, and 4, the slate veneer upon one side being a single slate sheet 6, and the slate veneer upon the other side being comprised of aplurality of small sections I3 cemented to the backing-support l2, the edges [4 of adjacent veneer sections I 3 being jointed to provide a smooth continuous slate surface. Thus, a plurality of thin split slate sheets can be used, scrap slate'if desired, cut to suitable sizes and shapes and machined to the veneer thinness, and secured to the supporting material and jointed to form the complete slate veneer writing surface."

It is well known in the art that the formation of natural slate is such that the sheets thereof obtained bysplitting, both the thinnest and the comparatively thick sheets, are not ,perfectly so as to conform to its shape and so as to conform to any changes in the shape of the backingsupport caused by bending or, warping, thus obviating any fracturing or breaking of the veneer sheet by reason of the bending or warping of the By so planing the slate pressed resulting planed sheet, while its resistance to bending is now very greatly reduced, still conforms with the natural plane of cleavage, with the resulting better writing surface which is incident to this condition. The improved veneer sheet is subject in use to blows upon its but the'character of the veneer mer blows. thereon will not fracture the slate, but

will leave only slight dentstherein.

The conference blackboard 5, shown in Figures 2 and i, is shown, for purposes of illustration, as

"being mounted upon a suitable standard having the feet I, the upright stanchions 8, and the strengthening cross frame member 9. The latter serves also as a suitable support for chalk and 'erasers "The conference blackboard 5 is secured be removed from the platen in finished form. to its supporting frame by clamps ill, the latter HOW.-

having journal portions which are pivotally mounted in the supporting frame, by means of which the blackboard can. be swung from side to side and secured in its desired pivotal position through the use of the binding nutsl l.

I illustrate in Figure 5 the application of my invention tc a drafting board iii. A suitable working board it is provided with a thin slate top surface ll cemented thereto and suitably mag chined and polished to form the slate veneer writing surface, and the slate-veneered board maintained at a suitable working height by the supporting pedestal l8.

Although my improved blackboard may be provided with a border frame, for any desired purpose, such as ornamentation, such a border frame is not necessary for the protection or proper functioning oi the slate veneer writing surface, or for the mounting of the blackboard. The finished product is a unitary composite article comprised of the backing-support and its natural slate writing surface, having the characteristics of the backing-support, with the exception of the writing surface which retains its superior writing qualities, and can be simply fastened by nails 4 to a building wall 5, such as shown in Figure l, or clamped to a support, such as shown in Figures .2 and e, or mounted upon a pedestal, such as shown in Figure 5. Ordinary school slates of sizes suitable for individual use, and requiring no mounting or special support, consist only of a suitable body member having a side or sides provided with the natural slate veneer.

What I claim is: l 1. An improved blackboard consisting of a backing-support having a veneer of natural slate cemented thereto of the order of one-thirty-sec-- 0nd inch thickness.

2; An improved product having a natural slate writing surface, comprising a support amenable to bending and warping and having a natural slate veneer facing cemented thereto and con-- formable to the bending and warping of the support, whereby all parts of the facing permanently hug the support.

3. An improved process of making blackboards consisting in cementing thin split slate material toa suitable base capable of serving asa backingsupport, and also serving as a chuck for s1atemachining, and then machining the slate mate-.

rial to form slate veneer on the base of the order of one-thirty-second inch thickness.

4. An improved blackboard consisting of a bendable and warpable support and a thin natural slate sheet secured thereto having the said characteristics of the support.

5. An improved blackboard consisting of a backing-support having a facingof natural slate secured thereto, saidfacing being in the nature of a veneer not exceeding one-sixteenth inch thickness.

'3. An improved blackboard consisting of a composite structure comprised of superimposed united layers of natural slate and slate-supporting material, the slate being of such a thinness that its natural toughness predominates over its natural brittleness, whereby it is amenable, without fracturing or splitting, to any reasonable bending and warping.

7. An improved blackboard consisting of a tough, fracture-resistant backing-support and a machined writing surface secured thereto and comprised of a plurality of edge-jointed natural slate sections, said slate sections being of a thinness sufiicient to partake of said characteristics of the support.

8. An improved process of making blackboards consisting in securing a sheet of natural slate throughout its area to a deformable support, and then machining the slate sheet to a thinness at which it will follow the deformations of the support without cracking or splitting.

9. An improved process or making a slate blackboard surface consisting in positively holding a natural-split natural slate sheet tightly against themachining area of a support, and

then machining the slate sheet to a thinness at

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