US2158995A - Method of manufacturing anodes - Google Patents

Description

METHOD OF MANUFACTURING ANODES Filed Oct. 3, 1935 2 Sheets-Sheet l INVENTOR I Jo/m/ A Z/TZLEE.

ATTORN EYJ y 1939; J. A. ZITZLER 2,158,995

METHOD OF MANUFACTURING ANODES Filed Oct. 3, 1935 2 Sheets-Sheet 2 INVENTOR (/b/Y/VA. Z/TZLER ATTORN EYS Patented May 23, 1939 PATENT OFFICE METHOD OF MANUFACTURING ANODES John Augusta Zitzler, St. Marys, Pa., assignor to Speer Carbon Company, St. Marys, Pa., a corporation of Pennsylvania Application October 3, 1935, Serial No. 43,450

7 Claims.

This invention relates to methods of manufacturing anodes. The invention relates more particularly to methods of manufacturing unitary or one-piece carbon anodes of generally hollow cylindrical or box-like'form, and especially anodes of that type having a flattened or oblate cross-sectional shape, adapted to enclose the electronemitting cathode, and useful in vacuum tubes for radio work, and in similar electron-discharge or 10' thermionic devices.

With anodes of the foregoing type, whatever the material of which they are made or their particular structural form, it is highly important that they be dimensioned with great accuracy, and

16 especially so with respect to their inner or electron-collectingsurfaces, and that they shall undergo the minimum-amount of distortion under conditions of use.

With a view to meeting these important requirements, a common practice in the manufac ture of anodes of the flattened cylindrical or boxlike type hasb'een to make them of sheet molybdenum or other suitable refractory metal, in two or more pieces, bent into the desired shape and held against separation and distortion aswell as might be by suitable fastening means. But aside from being undesirably expensive, such anodes were more or'less unsatisfactory because of their sectional or jointed construction.

30, In addition to its being less expensive material,

carbon, especially artificial graphite (i. e. electrographite, produced in an electric furnace at the very high temperature necessary to graphitize carbon), possesses certain properties rendering it distinctly more advantageous than molybdenum or other refractory metal as a material for anodes, particularly in power tubes. -However, if carbon is to be used as the anode material; and particularly foran anode of the flattened or oblate hollow v cylindrical or box-like type, the anode should be of one-piece construction not only to avoid the objections inherent in the sectional or jointed construction but also to adequately realize the advantages of carbon as the anode 'material.

5 But the relatively frangible nature of this material, coupled with the necessity for accurate dimensioning of cylindrical anodes as mentioned above, as well as other exacting requirements that have to be met in producing them commercially,

50 have combined to render the manufacture of such anodes from carbon or artificial graphite dif-.

ficult and largely impracticable under the methods of working this material commonlyprevailing in anode manufacture prior to my invention.-

Objects. ofthe present invention are to overcome the foregoing difficulties in the utilization of carbon (especially artificial graphite) in making anodes of the hollow cylindrical or box-like type, and, in particular, to provide a relatively simple and inexpensive method of making such 5 anodes in a variety of forms and each as one continuous piece or body of carbon, without any joint whatsoever, so as to give the marked advantages, both mechanical and electrical, of such an anode over the built-up or sectional box-like 10v anodes heretofore customarily employed. These and other objects and advantages of the invention are achieved through the use of a novel method of machining carbon that enables the safe working of that frangible material all in one 15 piece to give the finished anode and in a manner to attain'a high degree of accuracy in the anode surfaces both internal and external and in their arrangement and relation to one another.

Hollow cylindrical anodes of the type with 2 which the present invention is concerned may vary considerably in cross-sectional configuration. That is, although the right cross-section is always in the general form of a flattened or elongated annulus, the inner and outer figures 25 bounding it may be curved or polygonal, or both curved and polygonal; and they may or may not be alike. It is to be understood, therefore, that the terms cylinder, cylindrical and box-like, as employed herein. are used in a correspond- 30 in'gly broad or generic sense.

For the manufacture of the anode as one piece of carbon, the initial carbon material is formed into a flattened right cylindrical body whose over-all dimensions are slightly greater than those 5 desired in the finished anode. 'I'hat body or block of carbon may be one contoured to approximate more or less roughly the external shape of the finished anode, in which case it will have wholly curved or partly curved and partly plane 40 or approximately plane sides. Or it may be, and preferably is, formed as a quadrangular right prism, which may but need not have truly square corners and opposite truly plane and parallel sides, it being suflicient if this body be of generally rectangular shape in right section, with corners not more than approximately square and opposite sides only approximately plane and parallel. In any case, as already stated, the block is in the form of a flattened right cylinder, as the 5 term cylinder is here broadly used, and, most desirably, is also approximately symmetrical about its major and minor transverse or rightsectional axes.

According to the method of the present inven- 5 tion, a flattened or oblate cathode-enclosing chamber is first roughly drilled out and then completely machined to the exact desired dimensions within the carbon block, and with these inside operations completed the finished chamber surfaces are utilized as surfaces of reference or gauging surfaces in machining the outer lateral faces of the block so as to accurately locate and form the external anode surfaces in relation to the internal anode surfaces.

Referring to the method of the invention somewhat more in detail, upon completion of the cathode-enclosing chamber the chambered block or partially finished anode is so held up to the grinding wheel employed in machining its outer lateral surfaces as to definitely locate the chamber surfaces as surfaces of reference or gauging surfaces with respect to the grinding faces of the Wheel while at the same time the chambered block is rigidly supported interiorly. This method enables the attainment of a high degree of accuracy in both the internal and external anode surfaces and with maximum protection against failure of the frangible and relatively weak carbon material, that protection being due in substantial part to rough boring out and machining the cathode-enclosing chamber before the carbon block has been reduced from its initial over-all dimensions by any milling operations on its boundary surfaces and to rigidly supporting the chambered block interiorly during the machining of its outer lateral surfaces.

The general principles of the invention and its advantages as well as its detailed features will more fully appear from the following description illustrating, by way of a specific example, how the method of the invention may be employed in the manufacture of a one-piece carbon anode of the type to which the invention pertains.

In the accompanying drawings, which form a part of the description:

Fig. 1 is a perspective view of a carbon block from which an anode of the form illustrated in Fig. 6 may be made in accordance with the method of my invention;

Fig. 2 illustrates the step of roughing out by drill the internal chamber of the anode in the required relation to the transverse rectangular axes and the central longitudinal axis of the finished anode;

Fig. 3 illustrates the operation of accurately surfacing the inner walls of said chamber to finish the same to the desired dimensions, to give the required degree of accuracy to the internal anode surfaces, and to enable those surfaces to be used as surfaces of reference for machining the outer lateral surfaces of the block;

Figs. 4 and 5 illustrate the steps of machining lateral faces of the block into accurate relationship with the inner boundary surfaces of the chamber;

Fig. 6 is a perspective view of the finished anode mounted on supporting wires; and

Figs. 7 to 10 inclusive are perspective views of further typical forms of hollow cylindrical onepiece carbon anodes to which the same general method of manufacture is applicable.

- As already stated, the anode is formed from a flattened right cylindrical body of carbon which may be a quadrangular right prism having opposite plane and parallel or approximately plane and parallel sides and an oblong shape at any right section thereof or one having its sides contoured to approximate more or less roughly the shape of the finished anode; but in either case this body is approximately symmetrical about its major and minor transverse or right sectional axes and of over-all dimensions somewhat greater than those desired in the finished anode. For convenience in securely holding it during the initial operation of forming the cathode-enclosing chamber therein, the flattened right cylindrical carbon body preferably employed is a block, such as the block l0 shown in Fig. 1, of oblong shape in right section.

To obtain the general shape of block shown in Fig. l, a convenient length may be extruded from the desired carbon mix contained in an appropriate carbon press or jumbo having such die shape as to form the exterior surface shown in Fig. 1. As the material is extruded through the die the green carbon rod is cut into short lengths and these rods are baked to the desired temperature in ways well understood in the carbon industry to ensure that the resulting stock rod is either an amorphous carbon or artificial graphite, depending upon the final baking temperature. For most anode-making uses it is desirable to give the extruded rods a final bake at such high temperature as to convert the carbon into electrical or artificial graphite, although of course the method is not limited to this. After the rods have been baked to their final desired condition they are cut into blocks having the desired anode length, Fig. 1 showing one of these blocks.

It will be understood, of course, that with the carbon block f ormedin the manner described above, it is only approximately rectangular in right section, that is, its corners are only approximately square and its opposite faces only approximately plane and parallel; and to make this fact clearly apparent from the drawings the deviations from the angle and surface characteristics marking the true rectangular form are exaggerated somewhat in the views of the block. Of course, before proceeding further to the formation of the anode the carbon block may be machined externally to accurately parallel its opposite lateral faces and to dispose each of them in true rectangular relation to the adjacent lateral faces of the block. But the only advantages this preliminary machining of the carbon block gives in the formation of the anode under the principles of the present invention is that of greater convenience in securely holding that block in the rectangular recess of a jig or die block preferably employed as the holding fixture while performing the operations on the block which form the cathode-enclosing chamber; and it has the disadvantage of increasing the number of machining operations for the formation of the anode. While in some cases the foregoing advantage of the preliminary machining of the carbon block may outweigh the disadvantage, and the invention is not to be understood as excluding that operation on the block, it is generally preferable in the practice of the invention to forego that operation and employ additional means, not required when the block is thus externally machined, to securely hold it in the jig or die block.

A detailed illustrative example will now be given showing how the principles of the invention can be applied to the manufacture from the carbon block of an anode of the hollow cylindrical or box-like type, in this instance the specific form of anode shown in Fig. 6. In the specific example here described, the anode is to have a single fiattened or oblate right cylindrical chamber, coaxial with the outer cylindrical surfaces of the finished anode and with its major and minor axes pair of faces loa 'determine the initialaover-all, dimensions of'theblock'alongits minor transverse 2,168,996 .1 or center lines at: any: right section. substantially coincident with 'those of: the finished anode.

The anode chamberto be formed in this carbon block I is one' to extend longitudinally therethrough, and,;'as-'ltheublock is shown in' Fig. 1,.

this means; that the anode chamber will extend as'a bore through the block from. top to bottom. Also, as the block isshown in Fig. 1, the angularly related pairs of faces Illa and lb are the lateral facesor surfaces of the block :tobe' machined after thelanode'chamber has been formed. The

axis :and. the pair of faces I 0b? determine the initial over-all dimensions oftheblock along its ma-..

jor transverse axis, andv for convenience otreference, th'e pair-of faces Illa will'betermed the side faces of the block'and the pair. of faces lllbr the end faces;

The carbon-block is =first bored longitudinally ina straight-line series of drill'holes to rough outthe cathode-enclosing chamber, and for this operation the major and minortransverse axes or center lines of the chamber maybe arbitrarily determined and -marked on -'the carbon block,- as

shown, for example; by the broken-lines II and I! on the top face of the block in Fig. 1. The major transverse axis line I I will. then be the line along which the holes'are to be drilled in roughing out the chamber on opposite sides of the minor transverse axis line l2. These lines II and I2 may but need not precisely correspond with the major and minor transverse axes or center lines of the rough carbon: block itself, for-if that block is properly formed itwill'have sufiicient stock and over-all dimensionsto allow some appreciable variation in thelocation of the chamber from an exactly centered location-in the block which may occur when theline of the drilling is determinedwithout referenceto the major and minor transverse axes or center lines of :the rough block itself, and yet enable'the anodeto be finished to the desired ex ternal shape and size. Also, andas will later more fully appear, upon completion of the chamber its surfacesare used asgauging surfaces to machine theouter surfaces of theblock'into parallelism with" the chamber surfaces; so'that the major and minortransverse axesorcenter lines and the central longitudinal axisi'of the chamber then substantially coincide with thecorresponding axes of' the finished anode.

For theoperation of boring the carbonbl'ock longitudinally to rough out the cathode-enclosing chamber, that block may be rigidly'held up to the drilling toolby any suitable means. Preferably, however, the means employed comprises a jig or dieblock such as shown in Fig, 2 having a rectangular die aperture to receive the carbon block. When the carbon block is externally machined to true its angles :and sides inthe manner mentioned above, the die block,- with adie aperture dimensioned to snugly receive the carbon .block, is alone sufiicient as the holding means for the carbon block, but when the'rough carbon block of Fig; l is employed additional holding means are provided. "Fig.2 illustrates the equipment used and the operations on the rough, carbon block of Fig. 1 informing thecathode-enclosing chamber within the block. In this figure, I3 is a dig in the formof a blockxhaving a rectangular die.

aperture orrecess of somewhat greater transverse dimensions-than those of the 'rough carbon threaded bore in" the block-:of: the jig; from an outer'corner edge thereof diagonally into the die apertureadjacent the corresponding corner of that aperture to engage the adjacent corner edge x of the carbon block when the latter is properly inserted in the jig. The carbon block is so inserted in the die aperture of the jig-as to dispose its'opposite corner edge 3/ as far removed as possible from the end of the. pressure screw and thereby bring the corner edge at of the carbon block into position within the die aperture to be engaged by the notched end of that screw. With this'arrangement, operation of the pressure screw against the adjacent corner edge x of the rough carbon block clamps that block rigidly within the die aperture of the jig between the end of the screwand the remote side and end faces of the die aperture.

This jig may be accurately set and held in any desired position on movable carriage block I by means of side stop l5 and end stop IS. The carriage block I4 is rectilinearly movable between parallel ways I! and I8, secured to the bed plate I9 of a drillpress, and is held in any adjusted position by a spring-pressed plunger 20in the way I8 which snaps into any one of the notches 2| when the carriage block is moved along between the ways, the notches being spaced apart the distance of the roughing holes to be drilled in the carbon block.

Thorough carbon block having been clamped in the jig in the manner already described, the jig is then so positioned on the carriage block I4 aszto present the line H on the carbon block, which the drill is to follow in its successive operations, parallel to ways I! and 18 and vertically belowthe drill 2L; As the carbon block is a right cylindrical body, or more specifically, in this instance, a quadrangular right prism, and its base and top face are disposed horizontally in the jig and the drill operates vertically downward, it follows that in the successive operations of the drill the carbon block is longitudinally bored in a series of holes extending along the line H.

The cathode-receiving chamber having been thus roughed out, the next step is to machine the chamber smooth and to the exact desired dimensions. This is accomplished by milling the inner walls while the carbon block is still tightly and rigidlyheld against yielding movement by the enclosing jig or die-block l3 and the pressure screw l3. The jig or die block with the partially completed anode still clamped therein is removed from the drill press (Fig. 2) and is mounted upon the bed plate 23 of a suitable milling machine (Fig. 3) in the position illustrated, in operative relation to the horizontal rotary milling tool 24 extending longitudinally into the chamberin parallelism with the central longitudinal axis of'the chamber in the partially completed anode body. This rotary milling tool is mounted upon a .carriage (not shown) whose movement is accurately and precisely adjusted and controlled to givethe tool the exact cutting path, indicated by the arrows in Fig. 3, which will dimension thechamber symmetrically about the median planes passing through the cross-sectional axes ll andlZ of the chamber. The axis of rotation of the milling tool being parallel to the central longitudinal axis of the chamber, and remaining so throughout its travel in the indicated cutting path, the inner walls of the anode chamber are thus machined smooth and true to the precise dimensions desired- The chamber is'thusfinished as a flattened or oblate 1 true-right. cylindrical .chamber..

As a modification of the foregoing procedure, in respect to the milling equipment used and the manner of its use, the carbon block with the roughed-out chamber therein is removed from the jig l3 of the drill press (Fig. 2), and is mounted, in the same upright position it occupied in that jig, in a movable jig of a routing machine having a routing tool disposed over the jig to extend downwardly into the roughed-out chamber of the carbon block. With the routing tool rotating on a fixed axis, the jig is moved with its carrier block over the table of the machine, in contact with stop or guide pins adjustably set in that table, in a manner causing the routing tool to perform the same character of milling operations on the chamber wall performed by the milling tool 24 in the operations illustrated in Fig. 3.

The further operations upon the carbon block pertain to the machining of its lateral surfaces to accurately dimension the anode exteriorly, the required accuracy being attained as already mentioned, by utilizing the accurately machined internal anode surfaces as surfaces of reference or gauging surfaces for the exterior machining operations.

Having formed and accurately dimensioned the anode chamber, to finish the partially completed anode to the form shown in Fig. 6 its lateral surfaces must be shaped to provide the central longitudinal ribs I and 2 of the anode shown in that figure, the adjacent side faces 3, 4, 5 and B and the end faces 1 and 8 with their corner curvatures merging into the side faces. In this connection, it is also to be noted that in the finished anode (Fig. 6) the side faces 3, 4, 5 and 6 are plane faces in parallelism with the plane side faces of the anode chamber, the faces I and 8 which mark the outer boundary surfaces of the anode in its major transverse dimension are parallel with the corresponding inner boundary surfaces of the anode chamber, and all the lateral boundary surfaces of the anode are parallel, in their longitudinal dimensions, with the central longitudinal axis of the anode. That parallelism also, of course, characterizes the boundary surface of the anode chamber. It is further to be noted that the walls of the finished hollow cylindrical anode, except in the region of the ribs, are commonly quite thin (e. g. on the order of 0.05 inch) and that because of this fact and the frangibility and relative Weakness of the carbon material, special precautions have to be taken in order not only to avoid failure of the material while being worked but also to ensure attainment of the necessary degree of accuracy in dimensioning (e. g. within tolerance limits of plus or minus 0.002 inch in practice). Therefore the chambered carbon block or partially finished anode must be tightly and rigidly supported interiorly during the machining operations on its outer lateral faces.

Figs. 4 and 5 show the equipment .used and illustrate these further operations upon the carbon block to complete the anode shown in Fig. 6 The carbon block with the finished anode chamber therein is removed from the machine which completed the milling operations on that chamher, and is slipped over a supporting core or mandrel 25 formed to fit snugly and accurately within the chamber at all points except where the man.- drel is chamfered slightly for clearance as indicated at 25a and 25b, the portions 250 between the chamfered portions fitting snugly against the rounded inner surfaces of the chamber. "I'he mandrel is clamped in the split yoke member or part 26 of the laterally projecting head of the movable holder 21, a pair of adjustable screws 28 being employed to secure the forward separable part of the split yoke member to the part of the head of the holder to the rear of it and thereby to securely clamp the mandrel upon the head of the holder so as to extend it rear- Wardly therefrom truly parallel to the holder and its line of movement. Each of the opposite end portions of the mandrel may be transversely bored to provide two pairs of holes, as shown in Fig. 4, for the extension of the screws loosely through the holes of either pair at either end portion of the mandrel, depending upon the part of the mandrel in the clamp. As shown, the holder is channelled for longitudinally sliding movement upon the stationary guide or base rail 29 of the grinding machine employed so that a forward movement of the holder may be effected which will carry the chambered carbon block or partially completed anode into engagement with the grinding wheel, indicated at 30, whose arbor is normal to themedian plane passing through the major transverse axis of the anode and the anode chamber and, of course, also normal to the parallel plane surface portions of the anode chamber on opposite sides of that median plane.

The contour of the grinding faces of the grinding wheel will, of course, depend upon the desired shaping of the outer surfaces of the anode body. To shape the outer surfaces of the chambered carbon block to the finished form of the anode shown in Fig. 6, the grinding wheel 30 is provided with a hub-like grinding face 30a concaved rearwardly of its free inner edge, a plane side grinding face 3% normal to the arbor of the wheel and extending radially outward from the first-mentioned grinding face, and aperipheral grinding face 30c of concavo-convex curvature. The hub like grinding face 353a of the wheel functions to grind off the end faces lflb of the anode body sufficiently to properly dimension the anode along its major transverse axis and to round off the corners of those faces on an arc of the same radius as that of the adjacent inner wall of the chamber. The plane side grinding face 3%, normal to the arbor of the wheel, and the peripheral grinding face 300, together function to grind off the side faces Illa of the anode body sufiiciently to properly dimension the anode along its minor transverse axis and to form the ribs I and 2 of the finished anode (Fig. 6). It is to be understood, of course, that with the partially completed anode held on the mandrel as shown in Figs. 4 and 5, the grinding wheel 30 is vertically and horizontally adjustable to its work on the outer surfaces of the anode body.

In using the apparatus shown in Figs. 4 and 5 for the purpose stated, the chambered carbon block or partially completed anode is forced over the clamped supporting mandrel 25 until the anode abuts and is stopped by the clamp 26; and as the central longitudinal axis of the chamber in the carbon block is coincident with that of the mandrel and the mandrel extends from the clamping head of the holder truly parallel to the line of movement of the holder, it follows that, upon movement of the holder, the chambered carbon block describes a fixed path of movement in the direction line of its central longitudinal axis. Also, as the chambered carbon block is rigidly held by the mandrel from all movement save that in the direction line of its central longitudinal axis, that block may be said to be so held --gitudinal axis and'the right sectional axes-of the chamber of theblock. It'follows-that the inner boundary surfaces of the anode chamber on opposite sides of thoseplanes, which surfaces are 1 parallel to the central longitudinal axis of the chambenmay be utilized as set guides for adjust- *ing the grinding wheel to determine the points of This enables the machining of the lateral faces ofthe anode body in a manner attaining therequired accuracy in the external anode surfaces and in their arrangement and relation to the intern-a1 anode surfaces.

The grinding wheel having been properly adjusted with reference to the surfaces of the anode chamber or to the mandrel, the grinding wheel may be applied to the anode body as shown in Figs. 4 and 5 to thereby'grind a half portion of one of the end faces to partially completethe form shown for the faces! and 8 ofthe finished anode of Fig. 6. This application of the grinding wheel will also'form'one of the side surfaces 3, 4,

5 and 6 and a half portion of one of the ribs of the finished anode of Fig. 6. Upon reversing the anodebody end for end upon the.mandrel-but keeping the same side applied to the grinding wheel, a half portion of the opposite end face and anotherof the sidesurfaces 3, 4, 5 or 6 .of the j finished anode will be formed and the theretofore partially formed rib will be completed. Then, a

' turning of the anode side for side and again end 1 for end, with accompanying applications'of the a grinding wheel as before, will finish the remaining lateral surface portions of the anode and present itin the finally finished form shown in Fig. 6.

The foregoing procedure may be modified, with instead of the one grinding wheel 30 with a pluplied to the end faces of the carbon block to grind them downto the desired extent asparallel plane 1 faces normal to the major transverse axis of the chamber inthe anode body, a single grinding to thearbor' of the wheel may be applied to the side faces of the anode body to finish the side surfaceson opposite sides of the longitudinal ribs as plane faces in true rectangular relation to the end faces, and then grinding wheels with peripheral edge grinding faces of the required contours contour the longitudinally extending ribs.

Since this particular form of anode, when be taken in order to avoid shattering the thin walls of the anode shell, and to maintain the required accuratesymmetrical spacing of the wiresupport holes from: the major. transverse axis of the cathode-enclosing chamber.

ing operation upon the anode while it is rigidly held by the mandrel after the manner of its holding shown in Fig. 4. For example, the drilling 'the carbon rod stock solid, block, as illustrated in Fig. trude or otherwise form the stock hollow in the first place, so as to initially provide, when the attainment of substantially thesame results, by

s using several grinding wheels each having a single grinding face differing in contour from theothers the cathode-receiving chamber required, it ,-bei ng only necessary to mill the chamber walls, as indicated in Fig. 3, in order to dimension the chamber precisely and to smooth But these requirements are well met by performing the drilla operation may be performed in a drilling machine having a carrier block for advancing the work to the drillequipped with a clamping member of the against the drill.

It will be evident from the foregoing that the principles underlyingthe novel method of manapplication of its grinding faces to the anode body and the precise depth of the grinding to be done.

ufacturing carbon anodes are applicable to forms 10 The anodes shown in Figs. '7, 8 and 9, like that of Fig. 6, are single-chambered,

-the'single chamber being in each case coaxial with the cylindrical anode considered as a whole. The anode shown in- Fig. 10 hastwo chambers .20

both of which, however, are elongated in the direction of the major axis of any right section through the, anodecylinder and parallel to that axis and to the plane outer faces of the anode; and the longitudinal axis and inner walls of each .25

chamber are parallel with the central longitudinal axis of the cylindrical anode as a whole. Their structural features are therefore such that these anodes can readily be made in accordance with the principles'of the invention as exemplified ,30

by the applicationof those principles to the man ufacture of the particular form of anode shown in Fig. 6.

It may. further be noted that in practicing the method of my invention, instead of forming ;35

so as to give a solid 1, it is feasible to exblock is cut'therefrom, a central chamber in the 740 block approachingin general form and location that which is roughly drilled out, as illustrated .in Fig.2, where the block is initially solid. W'hen hollow stock is used, the step of rough drilling out is therefore not and aline its walls accurately and thereby also obtain the trueinner surfaces of reference or wheel having a plane side grinding face normal gauging bywhich to locate and form the finished outer surfaces of the anode.

enclosingtype which comprises machining to desired dimensions within a carbon block a fiat may be applied to round off the comers between the end and side faces of theanode body and to tenedor oblatecathode-enclosing chamber having its bounding surfaces accurately parallel with a line, through the; chamber corresponding to;;,e0

; piece, carbon anode of the box-like 0r cathode- I ienclosing type which comprises machining to de- .,=sired'idimensions within a. carbon block a' flat-.170

'ten'ed or oblate cathode-enclosing chamber extending-longitudinally through the block and having its bounding surfaces accurately parallel with a line through the block corresponding to the longitudinal central axis of the finished an- 7 ode, mounting said block on a mandrel snugly fitting the bounding surfaces of said chamber, and, while said block is thus mounted, machining outer bounding surfaces of said block while using the machined faces of said chamber as gauging surfaces to determine the desired outer contour and over-all dimensions of the finished anode.

3. The method of making a unitary or onepiece carbon anode having the general form of a hollow cylinder and adapted for use in a vacuum tube to enclose a cooperating cathode, which comprises preliminarily forming a solid carbon block with over-all dimensions somewhat exceeding those of the finished anode and having the general shape of a right prism whose right section is approximately symmetrical about two rectangularly intersecting axes corresponding approximately to such right-sectional axes in the finished cylindrical anode, boring the block 1ongitudinally to rough out a right cylindrical chamber, then machining the inner surfaces of the chamber into substantial parallelism with the longitudinal axis of the chamber, and, while so holding the block as to rigidly back inner bounding surfaces thereof and use them as gauging surfaces, machining outer lateral surfaces of said block into substantial parallelism with the said gauging surfaces.

4. The method of making a unitary or onepiece carbon anode having the general form of a hollow cylinder and adapted for use in a vacuum tube to enclose a cooperating cathode, which comprises preliminarily forming a carbon block with over-all dimensions somewhat exceeding those of the finished anode and having the general shape of a flattened right cylinder approximately symmetrical about its major and minor transverse or right-sectional axes, machining to exact dimensions within said block a right cylindrical chamber extending longitudinally therethrough and having its inner bounding surfaces in substantial parallelism with a line through said chamber and its open ends corresponding to the central longitudinal axis of said chamber, and, while so holding said block as to fix the planes passing through said longitudinal axis and the right-sectional axes of said chamber and also to rigidly back said inner bounding surfaces, accurately machining said block externally into a true right cylinder having at least two angularly related sets of truly plane lateral faces with the faces of each set in substantial parallelism with the central longitudinal axis of said chamber.

5. The method of making a unitary or onepiece carbon anode having the general form of a flattened or oblate hollow cylinder and adapted for use in a vacuum tube to enclose a cooperating cathode, which comprises preliminarily forming a carbon block with over-all dimensions somewhat exceeding those of the finished anode and having the general shape of a flattened right cylinder any right section of which is approximately symmetrical about two rectangularly intersecting axes of unequal length corresponding approximately to such right-sectional axes of the finished cylindrical anode, so machining'within said block a right cylindrical chamber extending longitudinally therethrough and elongated transversely in the direction of the longer of the right-sectional axes of the finished anode as to provide said chamher in its said transverse elongation with opposite block on opposite sides thereof lying transversely to the shorter axis of said block to provide plane outer faces accurately parallel to said inner faces and at distances therefrom determining the desired over-all dimensions of the finished anode along the shorter of its right-sectional axes andthe thickness of the anode wall.

6. The method of making a unitary or one-piece carbon anode having the general form of a fiattened or oblate hollow cylinder and adapted for use in a vacuum tube to enclose a cooperating cathode, which comprises preliminarily forming a carbon block with over-all dimensions somewhat exceeding those of the finished anode and having the general shape of a right cylinder any right section of which is approximately symmetrical about two rectangularly intersecting axes of unequal length corresponding approximately to such right-sectional axes of the finished cylindrical anode, so machining within said block a right cylindrical chamber extendinglongitudinally ber faces and at distances therefrom determining the desired over-all dimensions of the finished anode along the shorter of its right-sectional axes, and machining opposite outer lateral faces of said block lying transversely to the longer of said rightsectional axes thereof, while using adjacent inner faces of said chamber as gauging surfaces, to determine the over-all dimensions of said anode along the longer of its said right-sectional axes.

7. The method of making a unitary or onepiece carbon anode having the general form of a hollow cylinder and adapted for use in a. vacuum tube to enclose a cooperating cathode, which comprises preliminarily forming a carbon block with over-all dimensions somewhat exceeding those of the finished anode and having the general shape of a right cylinder any right section of which is approximately symmetrical about twosaid block as to rigidly back opposite inner bound-1' ary surfaces thereof and use them as gauging surfaces, machining said block externally to form a rib on each of at least two opposite sides thereof with opposed ribs parallal to each other and to the longitudinal axis of said chamber..

JOHN AUGUSTA ZITZLER.

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