US 3639990 A
The disclosure concerns automatic drafting apparatus incorporating a drafting table in the form of a stone block with interior channels through which air is removable to apply suction to the underside of a worksheet placed on the table surface; the method of forming such channels in the block, with channel inserts; and provision for highly accurate driving and guiding over the table of a marking head supporting crossarm.
Claims available in
Description (OCR text may contain errors)
O Umted States Patent [151 3,639,990 McInnis et al. Feb. 8, 1972  DRAFTING TABLE AND METHOD OF 3,110,107 1l/l963 Wilhelm ..33/21 A PRODUCING SAME 3,307,817 3/1967 Cocito ..248/362 3,359,879 12/1967 Hamlin ..269/21  Inventors: Andrew M. Mclnnls, Covma; LOUIS M. 3 396 679 8/1968 Little et aL 269/2 Ballard; Waldo I. Rogers, both Of Arcadia; G be t a] l David C. Kramer, Redondo Beach; Robert er r e 35/ Nielsell, na, all of Calif. FOREIGN PATENTS OR APPLICATIONS 1 1 Assignee= California Computer Products, 641,201 1/1937 Germany ..33/l74 H Anaheim, Calif. OTHER PUBLICATIONS  Filed: Apr. 14, 1969 American Machinist,.lune 3, I948 Page 148 ] Appl- N05 815,697 Primary Examinerl-larry N. Haroian Att0rneyWhite & Haefliger  US. Cl ..33/l8 R, 33/1 M, 33/76 R  Int. Cl ABSTRACT  Field of Search ..33/l8, 189, 184.5, 1 M; The disclosure concerns automatic drawn I g apparatus l1'lCOl- 312/231 243/362 318/20 235/151 269/21 porating a drafting table in the form of a stone block with interior channels through which air is removable to apply suc-  References C'ted tion to the underside of a worksheet placed on the table sur- UNITED STATES PATENTS face; the method of forming such channels in the block, with channel inserts; and provision for highly accurate driving and 2,317,348 4/ 1 943 guiding over the table of a marking head supporting crossarm. 2,410,877 11/1946 3,032,881 5/1962 Fengler ..33/23 C 26 Claims, 23 Drawing Figures PATENTEDFEB 8l972 SHEET 010? N llllllllllllllllllllllllllllllllllllllllllllllllllllllllll ll P wmmsw w MIMGW w W m I .BBKH 7 Mi M 5 ws mfi fi NbWD fl W m M PATENTEUFEB am: 3.839.990
sum ow n I N VEN 702.5. fl/voesw M. M: INN/.5 low: M. BALL. 020
7727400 I. B 0654.5 Dpwo C. KEQMEe 06927 1 7. MELJEA/ PATENTEU FEB 8 I972 SHfET 05 OF H IZIG. 8.
INVENTOEJ. /VOEEW Al. MCI/V/V/J low: M. Bang/e0 WPLDO I. Bass/e:
PATENTEU FEB 8 l5?! SHEET 08 0F 11 fin v N U. $22 5 EIAEML m vcLens a L fin w J? MMJCWM 1Q? ZZZ wunnfl w 6% W pbw PATENTEUFEB 81972 SHEET 08 0? H DUDE! UEIEI RUN L. rwaszN 2 mmmz v w 2 w WM W. a M ca. w 5 007% eu W 00 L v a w W aV HZ D3 PATENTEUFEB 8m 3,839,990
sum mar 11 MODE r-VACUU qwq l'irm'l tsfifff urz'aszrkma 143 0-0 P05] uP on C I l D I O'OCONF CLOSE SIZE SIZE 149 I LAMP 00 E FULL OWER OPEN 5 I z 5 TABLE .7: TLJJLLL "".Z-:HW l
74 17v VEN roves low: M- 34 41. QED 77221.00 I. Rosa-es DA V/O C. KfiQME/e 06527. MELJE/V 80 65/Q/VPEE/VM. Mei/WW:-
DRAFTING TABLE AND METHOD OF PRODUCING SAME BACKGROUND OF THE INVENTION This invention relates generally to drafting equipment, and more particularly concerns automatic drafting apparatus of high precision and employing an extremely stable drafting table over which a drafting head is moved with great precision.
Prior automatic drafting devices have not, to our knowledge, enjoyed the benefit of those combinations and subcombination of structure and modes of operation which characterize the present invention. For example, such prior devices lack the stability and uniformity of a stone drafting table which is not readily affected by temperature changes, which is vibration free and easily cleanable, which is accurately flat and yet incorporates a vacuum holddown system for holding a worksheet to the stone surface of the table. One reason for this lack in the prior art has been the difficulty of working a stone block to provide vacuum holddown coupled with extreme surface flatness for drafting purposes. Prior automatic drafting equipment is also characterized as lacking provision for extremely accurate guiding of a drafting head over the drafting table; as an example, a lateral crossarm carrying the head is commonly driven longitudinally at its opposite ends in such a way as can result in racking or backlash upon any unequal advancement of such opposite ends. Finally, prior equipment lacks the simplicity and precision of the present invention. Great accuracy is commonly required in the making of printed circuit diagrams, as well as in many other instances.
SUMMARY OF THE INVENTION It is a major object of the invention to provide automatic drafting apparatus characterized as overcoming the above and other problems and disadvantages associated with prior devices as mentioned. As respects the stone table aspect of the invention, the apparatus may be considered to comprise a frame; a heavy stone (as for example granite) block carried by the frame and having a flat upper surface to receive a worksheet, the block containing interior channels communicating with that upper surface and from which air is removable to apply suction to the underside of the sheet for holding the sheet to that surface; and means movable over and relative to the block surface for controlling marking the sheet. As will be seen, the frame may support the block by means of three horizontally spaced supports for twist-free stability. Also, the channels may be cut into the block upper surface to extend horizontally below and parallel to that surface.
An important aspect of the invention has to do with the provision of inserts carried by the block to cover the channel interiors, the tops of the inserts being made flush with the block upper surface by grinding and polishing of the entirety of that upper surface after the inserts are in place. Thereafter, small suctions openings are formed in the inserts to be spaced along the length of the channels for establishing communication between the table surface and the interiors of the channels. As will be seen, the inserts may advantageously consist of comminuted stone, or stone dust, in a resin binder which cures in place in the channels and bonds to the channel walls. In this regard, the channels may extend longitudinally and laterally in intersecting relation, and plugs may be located in certain channels to block airflow lengthwise of the channels past the plugs, whereby nonintercommunicating channel sections are formed to which suction may be controllably applied. In this way, intercommunicating lateral and longitudinal channel runs of different lengths are formed to correspond to different sizes of worksheets to be held down to the block surface.
The invention is also directed to the method of forming the drafting table block as described. As will be seen, the method contemplates sinking the elongated channels in the block upper surface; placing certain elongated spacers into certain of the channels (as for example the longitudinal channels) to extend in one direction below the plane defined by the block surface; then placing the insert material into those channels to cover the elongated spacers; and finally removing the spacers endwise from those certain channels. Thereafter, other elongated spacers are placed in others of the channels (as for example the lateral channels) to extend below the block upper surface, and insert material is filled in those channels, following which such other spacers are removed endwise, from those other channels. The channels may then be plugged at their ends, and intermediate the ends, to form the sections as referred to. Prior to drilling the small suction openings through the cured inserts, the block surface and protruding insert material may be ground and lapped.
As respects that aspect of the invention having to do with accurate guiding of the worksheet marking head; the invention contemplates the provision of an assembly including a frame and a table supported on the frame and having a flat upper surface for receiving a worksheet; an elongated linear way carried by the assembly; a carriage movable along the way in gripping engagement with same for accurately guiding carriage movement along the way; a cantilever unit or crossarm supported proximate one end thereof by the carriage to project laterally over the table surface; means to drive the carriage along the way so as to impart through the carriage the sole force for driving the unit lengthwise of the way; and marking head means on the unit to produce markings on the worksheet surface. As will be seen, when the table comprises a stone block, the way may be anchored to the block by means of a metal anchor member to which the way is fastened, that member being received in a groove sunk in the block and retained therein as by a stone dust and resin bonding agent. Further, a second elongated way may be provided to be spaced laterally from the first way, and to receive loading transmitted from the crossarm unit via a roller seated downwardly upon the second way to roll therealong, that end of the unit not being separately driven, longitudinally.
The carriage mounting the driven end of the crossarm may be advantageously supported on the first mentioned way by means of structure including rollers having close guiding engagement with opposite sides of that way, with certain roller axes of rotation offset from vertical and with certain rollers tapered so that adjusted gripping of the way by the rollers creates forces acting to eliminate all looseness as between the carriage and way, both horizontally and vertically.
These and other objects and advantages of the invention, as well as the details of an illustrative embodiment, will be more fully understood from the following detailed description.
DESCRIPTION OF THE DRAWINGS FIG. I is a plan view showing the drafting table; FIG. 2 is an end elevation taken on line 2-2 of FIG. 1; FIG. 2a is an enlarged section taken on line 2a-2a of FIG.
FIG. 3 is a side elevation taken on line 3-3 of FIG. 1; FIG. 3a is an enlarged section taken on line Zia-3a of FIG.
FIG. 4 is an enlarged plan view taken on line 4-4 of FIG. 3; FIG. 5 is an elevation taken on line 5-5 of FIG. 4; FIG. 6 is an enlarged fragmentary vertical section taken on line 6-6 of FIG. 5;
FIG. 7 is an enlarged fragmentary vertical section taken on line 7-7 of FIG. 4;
FIG. 8 is an enlarged fragmentary vertical section taken on line 8-8 of FIG. 4;
FIG. 9 is an enlarged elevation taken on line 99 of FIG. 1; FIG. 9a is a horizontal view taken on line 9a-9a of FIG. 9; FIG. 19 is an enlarged section taken on line l0l0 of FIG.
FIG. 1 l is an enlarged section taken on line llll of FIG. I;
FIG. 12 is an enlarged fragmentary plan view similar to FIG.
FIG. 13 is a vertical section taken on lines 13-13 of FIG. 10;
FIG. 14 is a horizontal view taken on line 14-14 of FIG. 13;
FIG. is a view showing the control panel in detail;
FIG. 16 is anelevation showing a photoexposure head supported on the cross-slide carriage;
FIG. 17 is a plan view showing the carriage for the crossarm;
FIG. 18 is an elevation of the FIG. 17 carriage;
FIG. 19 is a schematic showing of spacer placement in the channels; and
FIG. is a section showing attachment of the X-axis way to the stone drafting table.
DESCRIPTION OF PREFERRED EMBODIMENT Referring to FIGS. 1, 2, 3, 3a, 4 and 5, a heavy rectangular stone block 10 is shown as supported by a metal frame 11. The block has a ground, lapped and polished upper surface 12 to receive a work sheet 13 such as paper or film upon which markings are to be produced, as for example by controlled local exposure of a photographic film sheet or by inscription upon a paper sheet. It has been determined that a black granite surface 12 affords that extreme temperature-stability and uniformity needed for close tolerance marking of the worksheet. Also, such a surface is very easily cleaned. The heaviness of the stone block, which may for example be in excess of 3 inches thick, contributes to the vibration-free character of the work surface 12.
The block is supported by the frame 11, as for example on three horizontally spaced discs 14 carried by frame channel members 15. Those members are in turn supported by legs 16 adjustable vertically for horizontal leveling of the block surface 12. Frame 11 also includes longitudinally spaced lateral members 17 and 18 extending at opposite ends of the block and supporting housing structure 19 and 20 at laterally opposite sides of the block. Note also the longitudinal frame member 20a in FIG. 3, and the block corner locating structure 28 in FIG. 4. A lower portion 19a of the housing 19 receives the slide cabinets 21, 22 and 23 which respectively mount control structure such as a servo power supply 24, servocontrol unit 25 and a lamp power supply 26. Electrical power cables for such control structure are seen at 27 in FIG. 3.
In accordance with one important aspect of the invention, the block 10 contains interior channels communicating with the surface 12, air being removable from the channels to effect application of suction to the underside of sheet 13 for holding the latter firmly against the block surface 12, as during marking of the sheet by marking means to be described. The provision of such channels, with small auxiliary holes as more particularly to be described, overcomes the difficulty of providing the desired very small openings in the stone itself, it being a fact that to accurately drill holes smaller than about one-eighth inch diameter in granite is, for all practical purposes, impossible due to the problem of narrow drill breakage in the stone. Also note vacuum line 27a in FIG. 3.
More specifically, and as shown in FIGS. 4 and 6, the longitudinal and lateral channels 30 and 31 which may be groove cut by narrow bladed rotary saw discs, extend generally horizontally below and parallel to the block upper surface 12. The channels may typically have greater depth than width, representative width and depth dimensions being about oneeighth and one-fourth inches respectively, it being understood that other suitable dimensions may be used.
The tops of the channels are closed as by means of inserts 32 in channels 30 and 33 in channels 31, with the tops of the inserts being flush with the upper surface 12 of the block. Further, the inserts contain small openings 34 spaced along the lengths of the channels and communicating between the tops of the inserts and the open lower interiors of the channels, as designated at 31a in FIG. 6 for example. Such openings 34 may be much smaller in cross section than the widths of the channels, and may for purposes of illustration be characterized as pinhole" openings which are impossible to drill in granite or similar stone, as a practical matter. On the other hand, such openings effectively communicate channel suction to the work sheet, for holding same downwardly on surface 12. In this regard, the insert material may, with unusual advantage, consist of granite (or similar stone) dust mixed with an epoxy resin binder to form a paste filled into the upper channel region so as to cure or harden therein above a spacer 37 extending lengthwise of the channel. After such curing, the surface 12 of the block is lapped and polished to bring the insert tops (of hardened stonelike consistency) flush with the stone surface, and holes 34 arethen formed (as by drills 35) at spaced locations along the inserts after cleaning of the surface 12 so that stone dust does not clog these tiny holes.
FIG. 19 illustrates a cutter 36 which has been used to cut the channels in the block 10. Thereafter, a spacer in the form of a tetrafluorethylene rod 37 is placed in the channel 30 to extend longitudinally therein below the level of the block upper surface 12, and insert material is packed in the channel as described. After endwise withdrawal of the rod, the cured insert material is chipped away from the intersection location 38, and a second spacer in the form of a rod 39 is placed in channel 31 to extend laterally below surface 12. Insert material is then packed into that channel over the rod, following which the rod is withdrawn endwise. Of course, there may be multiple rods 37 and 39 and of sufficient length to extend throughout the lengths of multiple channels 30 and 31 and across their intersections.
The invention also contemplates the provision of plugs in certain channels to block air flow therein past the plugs, whereby nonintercommunicating channel sections are formed to which suction may be applied. In this regard, FIG. 4 illustrates the further step of plugging the thus-formed channels, proximate the ends of the channels at the block edges. For this purpose, holes larger than the channel widths may be drilled into the block and across the channels to intercept them, and insert material as described may be filled into such holes at locations as indicated at 40 and 41 in FIG. 4 and also HO. 8. Other plugs are located at 42a, 42b, etc., between channel intersections, as illustrated, and characterized in that separate intercommunicating channel runs are established to correspond to differently sized worksheets applicable to the block surface. For example, a vacuum line 44 may be connected to the block, at the location indicated to apply suction to one section of channel runs, i.e., those between plugs 40 and plugs 42a and 42b, and the lateral channels intersecting those runs. At the same time, no suction may be applied via a connection 45 to another section of channel runs i.e., those between plugs 42a and 42c, plugs 42b and 42d, and the intersecting run to the right of a plug 41. A third suction connection 46 is made to a third section of channel runs, i.e., those between plugs 42c and 42a, the run above plug 42d in FIG. 4, and the lateral run intersecting those runs. These plug and run locations are illustrative only, and other such locations may be selected within the purview of the invention, it being the purpose of same to facilitate holding down of different sizes of paper, applying suction to only such channels as are necessary to form a suction, grid corresponding generally to the size and location of the work sheet to be held down. See for example paper sizes A-E in FIG. 1.
FIG. 7 indicates the manner of connection of line 44 to the block. An opening 44a is drilled between the underside of the block and a channel as at 31, and then counterbored at 44b to receive a sleeve 44c. The latter is threaded to connect to the terminal of line 44. Note the cap 44d for opening 44a.
Another important aspect of the invention has to do with the accurate guiding of the automatically controlled drafting head over the drafting surface. Generally speaking, this portion of the invention is embodied in the provision in combination with the frame and table (as for example the block 10) of an elongated linear way such as seen at 50 in FIGS. 1, 10, 12, 17 and 18, carried by the assembly; a carriage movable along that way in gripping engagement with same for guiding carriage movement, an illustrative carriage being indicated at 51; a cantilever unit as at 52 supported at one end by the carriage to project laterally over the table surface 12; means to drive the carriage along the linear way so as to impart through the carriage the sole force for driving the cantilever unit lengthwise of the way; and marking head means (as for example the head 53) and supported at 54 on the cantilever unit to produce markings on the worksheet. In this regard, the marking head may comprise a multiple pen turret, one advantageous form of which is described in that certain David C. Kramer et al. application for US. Letters Pat., Ser. No. 724,183, filed on Apr. 25, 1968, for producing pen-inscribed markings on a worksheet as the head is moved laterally and longitudinally; FIG. 2a shows a pen turret at 201 and pen 202. As another alternative, the marking head may comprise a photoexposure device wherein a beam of light is directed downwardly for exposing portions of a sheet of film, as described in that certain Armin J. Hill application for US. Letters Pat. Ser. No. 717,159, filed on Mar. 29, 1968. FIG. 16 herein indicates the general outline form of such a photoexposure device at 53a, producing a directed beam at 200.
The referred to means to drive the carriage longitudinally may advantageously include a lead screw 55 driven in rotation by a servocontrolled drive motor 56 through a coupling that includes a bellows 57, as seen in FIGS. 9 and 9a. Suitable bearing support for the screw is provided at 58 and 59, such structure being attached at 60 and 61 to the side 62 of heavy block so as to benefit from block stability.
It will be appreciated that the opposite end of cantilever unit 52, that is end 63 remote from the way 50 and drive screw 55, is neither guided horizontally nor driven during longitudinal translation thereof, the sole driving force originating at screw 55. As a result, there is no possibility for the creation of racking or backlash in the movement of the cantilever unit, whereby the marking head is not subjected to erratic movement which would result from such racking or backlash. This benefit is given further implementation through the provision of a second elongated way, as at 66, carried by the assembly and spaced laterally from way 50 to receive weight imposed by the cantilever unit 52. In this regard, a roller 67 carried by unit 52 engages the top of way 66 and simply rolls therealong as the unit 52 is displaced longitudinally, the sole function of the roller being to transmit loading from unit 52 to way 66. Roller 67 is suitably carried by the terminal structure 68 of unit 52, as seen in FIG. 11.
Referring to FIGS. 10, 12 and 13, arm unit 52 may advantageously include a frame comprising horizontal inverted channel members 70 and 71 forming a housing attached to horizontal beams 72 and 73. The latter carry a pair of ways 74 and 740 which extend laterally and are spaced longitudinally. Terminal structure 68 is attached to the beams 72 and 73, and carries bearings 75 which in turn support one end of a laterally extending lead screw 76 for rotation beneath the lower channel 70. The opposite end of that screw is supported by bearings 77 carried by terminal structure 78 in the carriage 51. A rotary drive, servocontrolled for lead screw 76 is indicated at 78 as supported by unit 52, the latter also supporting a tray 140.
A laterally movable carriage 80 extends generally beneath channel member 70 and is connected to screw 76 to be driven laterally thereby, as by means of a nut 81 threaded on screw 76 and fastened at 82 to the carriage 80, as seen in FIG. 14. That carriage is accurately guided for travel along ways 74 and 74a as by means of rollers 83 and 84 engaging the tops of those ways; rollers 85 and 86 engaging the undersides of those ways; and rollers 87 and 88 engaging opposite edges of way 74a. All such rollers are carried by the carriage, as indicated. The carriage 80 projects at 89 from beneath the way 74a for attachment to a mount 54 for the marking head. The advantageous mount shown has dovetailed vertical recesses at 90 to interflt matching tongues on the head when dropped into place, a stop shoulder 91 on the mount seating the head for vertical locating purposes. If desired, the head may be adjusted vertically, as by means of the taper 92 on wedge block 93, the latter being horizontally movable under the control of an actuator 94 having a screw with vernier 95. A spring 96 acts as a return for the block 93, all of such structure being carried by the mount 54 as seen in FIG. 10. A tightening knob 97 is operable to lock the head in position on the mount.
As the carriage travels to the left in FIG. 12, it may suecessively engage or actuate a slowdown" switch 100, a 0-0 switch 101 and a STOP" switch 102, such switches being electrically connected to the drive 78 for deactivating same. As a last resort, the carriage will strike a limit stop 103 provided on a collar 104 on screw shaft 76a. Similarly, as the carriage moves to the right, it ultimately actuates a limit switch 105 to deactivate the drive. A safety stop 106 on collar 107 acts as a last-resort stop.
Turning back to FIG. 9, it will be seen that longitudinal travel carriage 51 is advanced as by means of a nut 110 threaded on screw 55 and attached to that carriage. Structure on the latter may successively operate the slowdown," 0 0, and safety-stop" switches 1 1 l, 1 l2 and 1 13 connected to drive 56, as the carriage approaches the last-resort stop 1 14 on collar 1 15. A single safety stop switch 1 16 serves to deactivate the drive as the carriage travels to the right in FIG. 9. and a last-resort stop appears at l 17 on collar 1 18.
Referring to FIGS. 12, 17 and 18, the carriage 51 is shown as comprising an elongated body supporting top rollers 121, rollers 122 to engage one side 123 of way 50, and rollers 1220 to engage the opposite side 123a of that way. Rollers 122 have their axes 124 offset at a slight angle a from a plane 125 parallel to side 123 of the way; and rollers 1224 have their axes 126 offset at a slight angle [3 from a plane 127 parallel to side 123a of the way. Bores and counter bores to receive the roller mounts and rollers are seen at 128132. It will also be noted that the carriage body contains longitudinal splits 133 and 134 between the rollers 122 and 122a of each pair. In this regard, an adjustable tensioning member as for example a threaded fastener 135, extends between the sections of the body at laterally opposite sides of each split to exert force acting to deflect those cantilever beam sections toward one another, thereby to cause the rollers 122 and 122a to forcibly grip the opposite sides of the way. The rollers themselves have such taper that their faces are brought into flat engagement with the way sides 123 and 123a only after slight bending deflection of the rollers relative to their mounts in response to tightening of the fasteners 135 to create the gripping action referred to. As a result, when the carriage moves along the way, there is no resultant looseness, either horizontally or vertically, the carriage tending to pull down toward the way due to the forces created. Rollers 121 spaced along the carriage and carried thereby engage the top of the way and transmit thereto part of the weight of the unit 52. Angles a and B may each typically be less than about 1, and the taper angularity of each of the rollers 122 and 122a may be less than about 2.
The metal ways 50 and 66 may be anchored securely to the top of the block 10 in the manner now to be described, with reference to FIG. 20. A recess or groove 230 is formed in the block 10 as by drilling into the top 12 thereof. A metallic anchor member 231 is then placed in the groove and retained therein as by the insert material 232 which may advantageously consist of stone dust in an epoxy binder, as described above. Note the sides 2310 of the anchor member which taper toward the outside of the groove, to block withdrawal of the member, as by positive engagement with the material 232. After lapping and polishing of the block surface and that of the resin-stone insert 232, the metal way 50 is placed thereon and held in position by a fastener 234 extending downwardly through the way and into a tapped opening in member 231. Accordingly, the longitudinal ways and screw are carried by the stone block for maximum stability.
Finally, FIGS. 1, l2 and 15 illustrate the provision of a control panel 240 on the structure 19, and operable in conjunction with the controls 141 (seen in FIG. 3) to command and control operation of the longitudinal and lateral drives as well as the marking head. One such control for the head is described in the above referred to Kramer et al. application. Manual or automatic control buttons appear at 142 and 143.
Button I44 activates the timed exposure functioning of the photoexposure disc 53a. Button 145 controls application of vacuum to various channels which may be selected (by buttons as indicated) to correspond to A-E size drawing sheets placed on the drafting table to be held in place by such vacuum in those channels. When a sheet is to be removed, the vacuum inhibit button 146 is pushed. A main power control is seen at 147, and the drives for the marking head may be deactivated at any time by pushing button 148. Power to the photoexposure head 53a is controlled by button 149; and up and down status of the multiple pens at head 53 may be controlled by buttons 150 and 151.
1. In automatic drafting apparatus, the combination comprising,
a. a frame,
b. a heavy stone block carried by the frame and having a flat upper surface to receive a worksheet, the block containing interior channels communicating with said surface and from which air is removable to apply suction to the underside of said sheet holding the sheet to said surface, and
0. means movable over and relative to said surface for controllably marking the sheet,
d. said channels extending generally horizontally below and parallel to the block upper surface, the block being downwardly grooved to form said channels and including inserts carried by the block covering the channel interiors, the tops of the inserts being flush with the upper side of the block, the inserts containing small suction openings spaced along the lengths of said channels and communicating between the tops of the inserts and the channel interiors.
2. The combination of claim 1 including three horizontally spaced block supports on the frame and through which all block weight is transferred to the frame.
3. The combination of claim 1 wherein said inserts consist of comminuted stone in a hardened resin binder.
4. The combination of claim 3 wherein said stone block and said comminuted stone both consist of granite.
5. The combination of claim 1 including elongated spacers extending in certain of said channels, the inserts consisting of curable material filled into the channels over the spacers, the spacers being removable endwise from said channels after at least partial curing of said insert material.
6. In automatic drafting apparatus, the combination a. a frame,
b. a heavy stone block carried by the frame and having a flat upper surface to receive a worksheet, the block contain ing interior channels communicating with said surface and from which air is removable to apply suction to the underside of said sheet holding the sheet to said surface, and
c. means movable over and relative to said surface for controllably marking the sheet,
d. said channels extending longitudinally and laterally in intersecting relation,
e. the block being downwardly grooved to form said channels, and including inserts carried by the block covering the channel interiors, the tops of the inserts being flush.
with the upper surface of the block, the inserts containing small suction openings spaced along the lengths of the channels and communicating between the tops of the inserts and the channel interiors.
7. The combination of claim 6 including plugs in certain of the channels to block airflow lengthwise of the channels past the plugs, whereby nonintercommunicating channel sections are fonned to which suction may be controllably applied.
8. The combination of claim 7 wherein some of said plugs are located proximate the ends of said channels at the edge of the block.
9. The combination of claim 8 wherein others of said plugs are located between certain longitudinal and lateral channel intersections and characterized in that separate intercommunicating channel runs are established to correspond to different size worksheets applicable to the block surface.
10. The combination of claim 7 including means to selectively apply suction to different of said channel sections.
11. In automatic drafting apparatus, the combination comprising,
a. an assembly including a frame and a table in the form of a heavy stone block supported on the frame and having a flat upper surface to receive a worksheet,
b. a first elongated linear way carried by said block to project upwardly therefrom,
c. a carriage movable along said way in gripping engagement therewith for guiding carriage movement along said way, there being grip structure on the carriage gripping opposite lateral sides of said way,
. a cantilever unit supported proximate one end thereof by the carriage to project laterally over the table surface,
e. means to drive said carriage along said way so as to impart through said carriage the sole force for driving said unit lengthwise of said way,
f. marking head means on said unit to produce markings on the worksheet g. and a second linearly elongated way carried by said block and spaced laterally from the first-mentioned way, and a roller engaging the top of the second way to constitute the only means for transmitting loading imposed by the cantilever unit to the second way,
h. the block being downwardly grooved to form elongated intersection channels, there being inserts covering the channel interiors, the tops of the inserts being flush with the block upper surface, the inserts containing small suction through openings.
12. The combination of claim 11 wherein said stone block anchors said ways.
13. The combination of claim 12 wherein said block contains a groove sunk downwardly therein from the surface thereof, and including a metallic anchor memberretained in said groove, and a fastener connecting said way to said anchor member.
14. The combination of claim 13 wherein said member is tapered upwardly and including comminuted stone in a hardened resin binder in said groove and bonding said member to said block.
15. The combination of claim 11 wherein said means to drive said carriage includes a longitudinally extending lead screw offset from said first way at one side of the block, and second drive means including a second lead screw extending laterally on said unit and operable to displace said marking head means laterally.
16. The combination of claim 11 wherein said unit includes a laterally extending way, and structure suspending said marking head means to said lateral way and including rollers having guiding engagement therewith.
17. The combination of claim 11 wherein said grip structure includes rollers on the carriage and having forcible guiding engagement with laterally opposite sides of the first way, the rollers at at least one of said sides being frustoconical.
18. The combination of claim I7 wherein two longitudinally spaced rollers engage one of the way sides and two longitudinally spaced rollers engage the opposite side of such way, and means in the carriage transmitting force acting to urge the rollers into flat face-to-face engagement with said way sides.
19. In the method of making a drafting table, the steps that include a. providing a heavy stone block having a working surface adapted to receive a worksheet,
b. sinking spaced elongated channels in said surface, and
c. placing curable inserts in said channels to cover the channel interiors and providing small openings through the insens to communicate the channel interiors with the outer sides of said inserts, whereby suction applied to said chan nel interiors is communicable via said small openings to the underside of said worksheet for holding said sheet on said surface,
d. said insert placement being carried out by first placing certain elongated spacers into certain of the channels extending in one direction so that the spacers are below a plane defined by the working surface, then carrying out said curable insert placement to cover the spacers, and then removing the spacers endwise from said certain channels.
20. The method of claim 19 wherein said sinking step is carried out by cutting said channels to extend laterally and longitudinally with multiple intersections.
21. The method of claim 20 wherein said sinking step is carried out to extend said channels to the edge of the block, and including the step of plugging said channels proximate the block edge.
22. The method of claim 19 wherein said inserts consist of comminuted stone in a resinous binder.
23. The method of claim 19 including the further step of placing other elongated spacers into others of said channels, then carrying out said insert placement to cover said other spacers, and thereafter removing said other spacers endwise from said other channels.
24. The method of claim 19 including the step of plugging certain of said channels to block airflow lengthwise therein past the plug locations, thereby to form nonintercommunicating channel sections to which suction may be controllably applied.
25. The method of claim 24 including the step of selectively applying suction to said channel sections.
26. The method of claim 19 including the step of grinding the working surface of said block after said insert placement but before providing said small openings through the inserts, thereby to prevent access of stone dust to said channel interiors during said grinding.