US2484906A

US2484906A - Terrazzo grinder

Info

Publication number: US2484906A
Application number: US756156A
Authority: US
Inventors: Harold J Pond; Daniel A Arones
Original assignee: Advance Machine Co
Current assignee: Nilfisk Inc
Priority date: 1947-06-21
Filing date: 1947-06-21
Publication date: 1949-10-18
Anticipated expiration: 1966-10-18

Description

Oct. 18; 1949. H.;J.I POND ETAL TERRAZ Z0 GRINDER 5 Sheecs-Sheet 1 Filed June 21, 1947 lNVENTOR HAROLD J. POND DANIEL A. ARONES ATTORNEY. S

Oct. 18, 1949. H. J. POND ETAL TERRAZZO GRINDER 5 Sheets-Sheet 2 Filed June 21, 1947 FIG. 2

36|NVENTOR HAROLD JIPOND DANIEL A. ARONES W 9 AT Tb fiEYs H. J. POND'ETAL Oct. 18', 1949.

TERRAZZO GRINDER Filed June 21'. 1947 5 Sheets-Sheet 3 POND AT TO "Oct. 18, 1949. H. J. POND EIAL 2,484,906

TERRAZZO GRINDER Filed June 21, 1947 5 Sheets-Sheet 4 I ll FIG. 4

INVENTOR HAROLD J. POND DANIEL A. ARONES ATTOR YS Filed June 21, 1947 III H.'J. POND ET'AL.

vIIIllllllllll lllllllllllll INVENTOR HAROLD J. POND DANIEL A. ARONES g AT??? EYS Patented Oct. 18, 1949 UNITED ES PAT OFFICE.

apolis, Minm, assignors to Advance Machine Company, Minneapolis, Minna, a corporation ofi Mizmesota;

ApplicationJime 21. 1947', Serial No. 7562156 13 Glaims.

Our invention relates to terrazzo grinders and has for anobject to provide" a. grinder whichcan be conveniently used for grindingvertical surfaces such as. stair risers, baseboard's, Wainscot borders. and other terrazzo wall surfaces.

An object of the invention resides inproviding a. grinder which will cover an extended area Without resetting.

A still further object resides. in providinga grinder having, a grinding wheel which. may" be; easily moved toward and from the work' without: resetting. the machine.

Another object of. the. invention resi'desin providing. a grinder which will follow. the wall surface. without. the. necessity of setting the. machine accurately with respect to the surface to be ground;

An. object ofthe. invention resides in providing agrinder which may be. used for grinding inclined surfaces or surfaces. out of plumb.

A still further object of. the invention resides in providing. a grinder. inwhich. the grinding wheel when moved toward the, surface to be ground will be, maintained paraliel tosaid surface.

Other objects of. the. invention. reside in the. novel. combination and arrangement of parts. and. in the details. of construction hereinafter illustrated and/or described;

In the drawings.

Fig. is a front elevational view of a terrazzo. grinder illustrating an embodiment of our. invention.

Fig.. 2. is. a side. view or the structure shown in Fig. 1 with. certain of the. parts in altered position..

Fig. 3. is. aside view similar to. Fig. 2lshowing the parts in still. diflerent. positions.

Fig. 4 is a fragmentary iron-t elevational view of. a. portion at one: of the arms of the invention and showing the method of mounting. the. wheel head, said view being drawn to. a greater scale than Figs- 1, 2. and 3..

Fig. 5' is a. sectional view taken an line. 5.-5 of Fig. 4'.

Fig. 6.- is a longitudinal side elevational sectional view of the joint of the arms. of. the invention and the power transmission mechanism. therein, said. view being drawn tothe. same scale as Fig. 5..

Fig. 7 is a plan sectional view taken on line i of Fig. 6.

Fig. 8 is. a. cross. sectional view taken on. line 8.8 of Fig. 6..

The invention. proper comprises. a base. [0 on which. is mounted a motor ll. Motor H has connected to it an arm ['2 which in turn has pivotally connected to it by means of. a joint 2. 20 another arm 3i Theamm 153 has attached to it at its free; end a grinding heart M which. sup.- ports: a grinding wheel: 53 These partsxwilt now be described? in detail.

The base Ml compnisestwom-shaped endframes it and Il which are identical inconstruction. Onlythe A'- frame I 8 which is: shown in: Fig. 1

will be described in detail'i This frame consists ofparallel frame members.- IB converging frame members I 9, and a horizontall frame member 2|. connected theretol A cross frame member 22 is weldedtothe parallel frame members: l8. The base H1- further includes two l'ong itudinal frame members 23 whichare welded to the frames l t and I 1 The base A is-supported on four wheels 24' and- 25' which extend transversely of said base and of whichthe wheels: 25- are disposed inwardly of the frame-members P8 of the frame I1. These-wheels are mounted on lugs- 26 which extend downwardly from the framemembenfl of'said frame; Bolts 21 extend throughsaid Wheels and are attached tothe lugs- 26 and form axles on which said wheels-are rotatably mountedl The wheels 2'4 are similarly'mourrted on bolts ZB which are attached to lugs- 29*. These lugs are welded to extensions 3 II formed on: the cross frame member 22 of frame [6. This construction brings; the said wheels 24 outwardly near the outermost edges of the base I0 By means ofi this construction the entire grinder'may be moved laterally when resting on the wheels 2'4 and 25 whichpermits ofmoving the grinder along the surface tobe ground in amanner which will be presently more fully described.

The base- I'U may be moved longitudinally by means of the following construction. Pivotedto thetwo parallel frame members It of" the frame H are twol'evers 32 These levers have bolts 33 extending through the same and which are screwed intothe said frame members. The upper ends of the levers3-2 haveweid'ed to them a handle 34' by means of which the said levers may be moved from the fullline position" to" the. dotted line position shown in Fig: 2; The lower ends 35 of the-levers- 32 havemounted on them wheels 36. Bolts 31'' extend through these wheels and are screwed into the. ends 35 of the levers 37;" and formaxleson which said wheels rotate. The. ends 35- of said l'evers are angularly' disposed with relerence to the levers. proper so that the. wheels. 36 when the said levers are in the position. shown in full lines in Fig. 3" become; raised. above the level' of the surface of which the device rests. When the handle 3 is moved to its dotted line position its wheels 36 are swung downwardly to floor level as shown in Fig. 2. Stops 38 on the end frame I! limit the swinging movement of the lower ends 35 of the levers 32. Further swinging movement of the handle 34 causes the

wheels

24 and 25 to become raised off from the surface on which the device is disposed and permits of wheeling the device longitudinally by means of the wheels 36. A clip 30 holds the lever 32 in its retracted position.

The motor II of the invention is supported by means of a shaft 39, which is flattened at its ends as designated at 4| in Fig. 1. Pivotally secured to the ends of the said shaft by means of bolts 42 are two

legs

43 and 44. These legs are provided with slots 45 which are adapted to receive bolts 46 extending through the same. 46 are threaded into brackets 41 welded to the horizontal frame members 2| of the frames I6 and If. The bolts 42 extend through off-sets 48 formed on the legs 43 whereby the

legs

43 and 44 straddle the two end frames I 6 and I1. By means of this construction the shaft 39 may be main tained horizontal as shown in Fig. 2 or the same may be raised at either end and tilted to the positions shown in full and dotted lines in Fig. 3. By tightening the bolts 46 the shaft 39 may be held in any angular adjusted position within the limits afforded by the lengths of the slots 45.

Mounted on the shaft 39 are two bearings 49 which are secured together at their lower ends by means'of a flange This flange is bolted by means of bolts 52 to the motor II. The upper ends of the bearings 49 have secured to them by means of screws 53 a longitudinally extending bar 54. Mounted between the bearings 49 and secured to the shaft 39 is a sleeve 55. This sleeve has bolted to it two blocks 56 which support a longitudinal bar 51.

Bars

54 and 51 are substantially the same width and overlie one another when the arm I2 is in elevated position. A torsion coil spring 58 encircles the sleeve 55 and has its ends 6| and 62 crossed and straddling the two

bars

54 and 51. Spring 58 is normally under tension so that when the parts are normally at rest the ends 6| and 62 of said spring engage the bars or opposite sides and hold the parts in upright position. When the arm I2 is normally swung from one side tov the other bar 54 is disengaged from one end of the spring 58 and engages the other end to further tension the said spring. This end of the spring then leaves the bar 51. It will thus become readily comprehended that the weight of the arm and the structure supported thereby is counterbalanced through the spring 58.

The arm I2 as shown in Figs. 1 and 2 is constructed from two channel members 63 which at their lower ends are welded to two cross bars 64. These cross bars are secured to the end bell. 65 of the motor I I by means of cap screws 66. The said channel members are attached at their other ends to a case 67 by means of cap screws 68. These cap screws extend through slots 69 in the webs of the channel member 63 and are threaded into the case Bl. The case 61 has two flats II on which the channel members 63 rest. By means of this construction the case 67 may be moved toward and from the motor II to adjust the belt and held in adjusted position by means of the cap screws 68.

Within the case 61, as shown in detail in Fig. 6, is rotatably mounted a shaft 12. This shaft is journaled in two ball bearings I3 and 14 which are mounted in said case. The bearing I3 is received in a bore in the case 61 and butts The bolts against a shoulder I6 formed in said case. A look nut TI clamps the said bearing against the shoulder I6. Bearing I4 is received in a bore I8 in said case in alignment with the bore 75. This bearing is however free to move within the bore I8. A cover I9 closes the bore I8 and when removed gives access to the bearing 74. Mounted on the shaft I2 between the two bearings I3 and I4 is a sheave 8| which receives a belt 82 disposed within the interior of the arm I2. This belt passes over another sheave 83 on the rotor shaft 84 of the motor II. By means of this construction the shaft I2 is driven from the motor II. The bearing I5 butts up against a collar 85 of the shaft 82. Sheave 8| butts up against the bearings I3 while a sleeve 89 lies between the bearing I4 and said sheave. A nut 81 screwed on the end of the shaft 12 holds the parts in proper assembled relation and retains the bearing I4 in operative position within the bore I8.

The arm I3 includes a housing 88 having a transverse bore 89 in the same. In this bore are mounted two ball bearings 9| and 92 which are held in spaced relation by means of a sleeve 93 disposed between the same. The bearing 9| butts up against a shoulder 94 formed in the housing 88 at the end of the bore 89. A nut 95 screwed into the end of said bore holds the two bearings in place therein. The shaft I2 extends into the housing 88 and extends through the two bearings 9| and 92. Bearing 9| fits up against a sleeve 96 which fits against a shoulder I on the shaft I2. A bevel gear 91 butts up against the said bearing and is held in position by means of a key 98 and a lock nut 99 screwed upon the end of the shaft 12. By means of the housing 88, the case 67, the shaft 12 and the various bearings associated with said shaft the joint 20 previously referred to is formed between the two arms I2 and I3 permitting the said arms to swing relative to one another about the axis of the shaft 72.

The housing 88 has a branch I02 extending at right angles to the axis of the joint 20. This branch has a chamber I03 within the same and in which the bevel gear 97 is disposed. The said branch has two bores I04 and I05 formed therein which are co-axial and which communicate with the chamber I03. In the bore I04 is mounted a ball bearing I06 while in the bore I05is mounted a ball bearing I01. The bearing I01 butts against a shoulder I08 in the branch I02 of housing 88 and is held in place therein by means of a sleeve I09 which is threaded to screw into the outer end of the bore I05 and which is held in fixed relation therein by means of a lock nut I I I. Journaled in the bearings I 06 and I07 is a shaft II2. This shaft has a shoulder II 3 against which the bearing I0! butts. A bevel gear I I4 extends up to the bearing I01 and is held from rotation by means of a key I I5. This bevel gear meshes with the bevel gear 9'! on shaft l2. A sleeve I I6 on the shaft I I2 lies between the gear H4 and the bearing I06. A nut II! on the end of the shaft I I2 holds the parts in assembled relation on said shaft.

The arm I3 in addition to the housing 88 includes a mounting II9 which is disposed at the end thereof opposite said housing. This mounting is in the form of a yoke having two side members I2I and I 22 and a connecting member I 23 therebetween best shown in Fig. 4. A bolt I24 connects the two side members I2I and I22 together and holds them in proper spaced relation. The arm I3 further includes three parallel links I25, I26, and I21. The links I25 and I26 are pivoted to the side members P24 and I2? of the mounting IFBby'meansTOfIoolts I28 which extendv through. said side: members and are screwed into blocks I29 secured to. the ends of said links. The. other ends of the said li'n'kshave attached to them blocks I 3 f which straddle a; lug I32 formedonthe branch I62" ofhousi'ng'88. Apin' I3? extends through said blocks and boss and" pivotally' connects the ends of the said links to the housing 88' which forms a portion of" the joint 20. A plate I36 extends. across the blocks IS'I and is secured to said blocks by means of cap screws I34 which extend through said plate andare threaded into the said? blocks. By means of this construction the ends of the links IZE'I'- and I26 are securely tied together: The link I2? is connected to the mounting I I9' and to the housing 88 in much the samemamrer as. the links I and I26. The link IZI is constructed with a block I35 at its upper end which extends between the two side members I2I and M2 of mounting H9.

A pintle I36 extends through said side members By means of theconstructi'on forming the arm- I6 I the mounting I'll may be moved in any direction from left toright and vice versa as viewed in Fig. 2 from the-dotted line position to-full line position. The arm I3 may beswung about the axis of the joint 20 and the mounting may be moved toward and from the surface of the wall being worked by means of handle I 42. This handle is attached toa cross bar I13 extending between the two sidemembers I 2 I and I22 of mounting H9. The weight of the arm counter-balanced by means of a counter-bal anced weight I44 which is slidably mounted on arod I45 and held in positionth'ereon by'means' of a set screw I46. Ihe rod I45 is attached" to a boss I I'I by means of a set screw I 48a Boss In has a flange I49 formed on the same which is se cured to the end of thebranch I 02" of case 88 by means of screws I5 I as-best shown in Fig. 6.

Supported by themounti'ng I I 9 is the grinding head I4 which includes a housing I 53- best shown in Fig. 5. This housinghas atransverse portion I54 and a longitudinal portion P56. Said housing has a chamber I-5'6-' within the same; In the transverse portion I53 are formed two co-axial bores I5'I and I 58 which receive ball bearings I6I and I62. The ball bearing I-Ii Z- butts up against a shoulder I63 in the: housing I53 and projects outwardly beyond the end of said ho ns-- ing. E'ncircling said bearing upon the projecting portion thereof a collar [64 which has a shoulder I65 butting against the outer end of the bearing I62. This collar is secured to: the housing I by means of screws I 66 shown in detail in Fig. 4. Mounted for rotation in the bearings IBI and I62 is a shaft I166. This shaft has an enlarged head I68 iormed= on; the outer end of the same. Encircling the said shaft and dis posed adjacent said head is acollar I69 which has a slinger I I I formed onthe outer portion of the same. A spacer I'I 2 also encircles the shaft I66 and butts against the bearing- I 62 mounted on the. shaft I66. Mounted on theshaf-t- I66 and disposed within the chamber I 56 is: a bevel gear I13 This gear iskeyed to the shatit by means of' a key I l 4 and extendsup to the bearing: I62.

.includes a ring armature shaft 815 of motor II.

A sleeve I 15 encircles the said shaft I66" and is disposedbetween the end of the gear I73 and the bearing I6I. A nut I1 6 screwed upon the end of the shaft I-66-hold'stheparts-inassembled relation. Mounted upon the end of the shaft I66 is the grinding wheel: I 5 is cuppedshapcd in form; This wheel is mounted upon the'head I68 of shaft I 66 and butts against thecollar I69. I66 by means of ascrew IT8= which has a flangedhead Ilii engaging the innermost portion of said wheel. The screw we screws into threads I B-I formed in the end of the shaft I66 In this manner the wheel I5 is" held mounted upon the end of the'shaft I66;

The-grinding head M is mounted for universalmovement with respect to the mounting II-9- by means of auniversal joint indicated in its entirety by the reference numeral I82. This jointi8-3 which encircles thecollar I64. Screws ass are threaded into the ring and pivots let formed on the ends of the same are received in sockets I66 formed in the collar I 64. This construction is best shown in Figs. 4 and 5-.

. The two side members IZ'I- and I2? of the mounting Ii't have threaded in them screws I81 which are-similar to the screws I84 and which havepivots ltiireceived within'sockets- I69 in the-ring I83. These pivots are at right angles to the pivots- !8'5'; By means of this construction the head Ill may be moved about to cause the grinding surface I9I to conform to the plane of the surface'being ground.

For the purpose of manipulating head I52 aknob- I92 is employed. This knob has a boss- I '63 which is received in the outermost end of the bore I5? of housing I53i holds the said knob in place.

Water is furnished to the grinding wheel IT! by means of the following construction. A wa-- ter pump I95 is mounted on the arm I2. This water pump has a pulley I66 mounted on the drive shaft I96 of the same. A belt I91 passes over this pulley and another pulley I98 on the The pump I95 has an inlet tube I98 connected to it which in turn is connected to a water tank 261. Tank 2ilI ismounted on brackets 262 secured to the A-frame Ii. Pump I65 has an outlet tube 203 A set screw I94 connected to it which in turn leads the water to the grinding head I52.

For the purpose of conducting the water to the wheel I5 the knob I92 is constructed with a water passageway 26E having a nipple 20E screwed into the same. The tube 263- is con-- nected to the said nipple. The shaft I66 ingrindinghead I52 is formed with a;v bore 206 ex-- tending completely through the same. This bore communicates with a bore 201 in the screw I18; A tube 1286 is disposed withinv the bores 2:66; and 261. This tube has an enlarged portion 206 at its innermost end which is screwed intothreads 2II formed in the knob I92. The interior oi the tube 266 communicates with the: passageway 264. A felt washer 2I'2 encirclesthe tube 2538 and forms a. fluid. tight connection between the nut I16 and the enlarged portion 269 of said' tube. By means or thisv construction water is prevented from entering the interior of the housing I53.

The shaft IE6 is. driven in the. following manner. In the longitudinal portion I55- of housing 153 is formed a: bore 213. In this-bore is mounted two ball bearings 2M and 2115. Bearing 2H3- bears against a shoulder: 216- formed in the: said Said wheel is held in place on shaft portion of the housing. A spacer 2|! holds the two bearings in proper relation within the bore 2I3. A threaded sleeve H8 is screwed into the end of the portion I55 of housing I53 and holds the various parts in position. Rotatably mounted in the bearings 2Iil and 2H) is a shaft 2l9. This shaft has a shoulder 22l against which the bearing 2M butts. A bevel gear 222 is mounted on the end of the shaft 2I9 and is keyed thereto by means of a key 223. This gear is held in place upon the end of said shaft by means of a nut 224 which is screwed upon said shaft. The gear 222 meshes with the gear H3.

The two shafts 2ft and H2 are connected together by means of a flexible shaft 225. This shaft has secured to it at its lower end a connector 225 which is formed with a fiat 227. Connector 226 is adapted to be received within a socket 228 in the end of the shaft II2. A slot 229 milled in the end of the shaft H2 receives a key 23I which engages the flat I2? and holds the shaft 225 from rotation. A collar 232 encircles the shaft H2 and has a set screw 233 in the same which engages the said shaft and clamps the parts in position. By means of this construction the one end of the shaft 225 is connected to the shaft H2 and may slide longitudinally relative thereto. The other end of the shaft 225 has secured to it a connector 230 which is connected to the end of the shaft 2I9. This connector has a tongue 239 which fits into a slot 24l in the end of the shaft 2I9. A collar 2 12 similar to the collar 232 holds the parts assembled. Encircling the shaft 225 is a flexible tubular case 234. This case has attached to the ends of it nipples 225 and 232 which are secured to the sleeve I59 and the sleeve 2| 8 respectively. A screw 23? holds the nipple 235 attached to sleeve I59 while threads 238 on the end of the nipple 23% attach the same to the sleeve 2I8.

The method of using the invention is as follows. The handle 3:3 is first tilted back to the position shown in dotted lines in Fig. 2 and until the lower end 35 of the lever 32 engages the stop 38. Wheels 38 are now in a position to engage the ground. Further movement of the handle 34 in a downward direction tilts the base I upwardly and raises the wheelsM and 25 above the floor on which the machine is setting. The grinder may now be convenientl wheeled about to the position where the same is to be used. Upon movement of the handle 34 in the opposite direction support of the grinder is transferred to

wheels

24 and 25 and the wheels 35 raised above the floor. When in such position the lever 32 is held in place by clip 35. The motor II is now energized and the handle I42 grasped by one hand and knob I92 by the other. Movement of the arms I2 and I3 is now controlled by the handle I42 and the locality of grinding determined thereby. By moving the handle I42 toward the surface to be ground and by manipulating knob I92 the actual grinding is controlled.

The advantages of the invention are manifest. With our improved terrazzo grinder, grinding may be easily and quickl accomplished. Extended areas may be ground without moving the entire machine. The machine does not have to be positioned closely to the surface to be ground. The grinder does not have to be accurately aligned with the surface to be ground. The parts of the grinder are counterbalanced in a manner such that the grinding wheel may be moved about during grinding without undue effort. In the movement of the grinding Wheel toward and from the wall or surface being ground the wheel travels in a parallel direction. The angularity of the plane of movement of the grinding wheel may be easily varied within considerable limits. The wheel is mounted rigidly on the spindle, with the spindle floating, thu permitting the wheel to run at the high speeds necessary for maximum efiiciency. This also allows the wheel to be dressed to the desired shape without removing it from the spindle, and permits the us of a round edge wheel for grinding of cove bases.

Changes in the specific form of our invention, as herein described, may be made within the scope of what is claimed without departing from the spirit of our invention.

Having described our invention, what we claim as new and desire to protect by Letters Patent is:

1. In combination, a support, an arm, a pivotal connection between said arm and said support, a second arm, a joint between said arms, the axis of said joint being parallel to the axis of said pivotal connection, said joint including a member movable with said second arm, said second arm including a mounting at the end thereof opposite said member and parallel links pivoted to said member and to said mounting for swinging movement about parallel axes disposed at right angles to a plane containing the axis of said joint, a grinding head carried by said mounting and including a grinding wheel and power transmission means for driving said grinding wheel.

2. In combination, a support, an arm, a pivotal connection between said arm and said support, a second arm, a joint between said arms, the axis of said joint being parallel to the axis of said pivotal connection, said joint including a member movable with said second arm, said second arm including a mounting at the end thereof opposite said member and parallel links pivoted to said member and to said mounting for swinging movement about parallel axes disposed at right angles to a plane containing the axis of said joint, a

grinding head including a shaft having its axis parallel to the axis of said joint, a bearing for said shaft carried by said mounting, a shaft carried by said joint, means for rotating said second shaft, and a flexible shaft extending along said links, said flexible shaft being driven from said second shaft and driving said first shaft.

3. In combination, a support, an arm, a pivotal connection between said arm and said support, a second arm, a joint between said second arm and said support, the axis of said joint being parallel to the axis of said pivotal connection, said joint including a member movable with said second arm, said second arm including a mounting at the end thereof opposite said member and parallel links pivoted to said member and to said mounting for swinging movement about parallel axes disposed at right angles to a plane containing the axis of said joint, a grindin head including a shaft having its axis parallel to the axis of Said joint, a bearing for said shaft, a ring encircling .said bearing, pivot means between said ring and bearing having its axis at right angles to the axis of said shaft, other pivot means' between said ring and mounting and having its axis at right angles to a plane containing the axis of said shaft and said first named pivot means and power transmission means for driving said first named shaft.

4. In combination, a support, an arm, a pivotal connection between said arm and said support, a second arm, a joint between said arms, the axis of said joint being parallel to the axis of said pivotal connection, said joint including a member movable with said second arm, said second arm including a mounting at .the ,end thereof op osite said member and parallel links pivoted ItO said :memberand to said mountinglfor swinging move- :ment about parallel axes disposed at ri ht angles .to a :plane containing the raxispf said joint, said links being spaced longitudinally of the :axis of said joint, a grinding wheel .at the end of said second arm and having its axis parallel to the axis of said joint and power transmission means for driving said grinding wheel.

5. In combination, a support, an arm, a pivotal connection between said arm and said support, a second arm, a joint between said arms the axis of said joint being parallel to the axis of said pivotal connection, said joint including a member movable with said second arm, said second arm including a mounting at the end thereof opposite said member and three spaced parallel links, pivots between said links and member and between said links and said mounting, the axes of said pivots being parallel and being disposed at right angles to a plane containing the axis of said joint, the pivots at each end of two of said links being co-axial, a grinding head carried by said mounting and including a grinding wheel and power transmission means for driving said grinding wheel.

6. In combination, a support, an arm, a pivotal connection between said arm and said support, a second arm, a joint between said arms, the axis of said joint being parallel to the axis of said pivotal connection, said joint including a member movable with said second arm, said second arm including a mounting at the end thereof opposite said member and three spaced parallel links arranged in the form of a triangle, pivots between said links and member and between said links and said mounting, the axes of said pivots being parallel and being disposed at right angles to a plane containing the axis of said joint, the pivots at each end of two of said links being coaxial, a grinding head carried by said mounting and including a grinding wheel and power transmission means for driving said grinding wheel.

7. In combination, a support, an arm, a pivotal connection between said arm and said support, a second arm, a joint between said arms, the axis of said joint being parallel to the axis of said pivotal connection, said joint including a member movable with said second arm, said second arm including a mounting at the end thereof opposite said member and three spaced parallel links arranged in the form of a triangle, pivots between said links and member and between said links and said mounting, the axes of said pivots being parallel and being disposed at right angles to a plane containing the axis of said joint, the pivots at each end of two of said links being coaxial, a grinding head carriedby said mounting and including a grinding wheel and a power transmission shaft for driving said grinding wheel, said shaft being disposed substantially within the confines of said triangle.

8. In combination, a support, comprising two spaced supporting members, a shaft extending across said supporting members, guide means acting between each of said supporting members and the shaft for guiding either end of the shaft for up and down movement to an extent greater than the other end of the shaft, clamp means for holding the shaft in any of its positions, a pair of jointed arms, pivot means between said shaft and one of said arms, a grinding wheel .carriedby the other of. said arms and power transmission ,means for driving said grinding wheel.

19.. .In combination, a supporta fixed shaft carried by said support, a pair of jointed arms, pivot means betweensaid shaft and one of said arms, a ,grinding wheel carried by the other of said arms, an abutment on said shaft, a coil spring encircling said shaft, .the ends .of said spring engaging said abutment on opposite sides thereof and in a manner to cause tensioning of-the spring 10. In combination, a support, an arm, a pivotal connection between said arm and said support, a second arm, a joint between said arms, the axis of said joint being parallel to the axis of said pivotal connection, said joint including a member movable with said second arm, said second arm including a mounting at the end thereof opposite said member and parallel links pivoted to said member and to said mounting for swinging movement about parallel axes disposed at right angles to a plane containing the axis of said joint, a grinding head, including a shaft having its axis parallel to the axis of said joint, a bearing for said shaft, a universal joint between said bearing and mounting and power transmission means for driving said shaft.

11., In combination, a support, an arm, a pivotal connection between said arm and said support, a second arm, a joint between said arms, the axis of said joint being parallel to the axis of said pivotal connection, said joint including a member movable with said second arm, said second arm including a mounting at the end thereof opposite said member and a link pivoted to said member and to said mounting for swinging movement about parallel axes disposed at right angles to a plane containing the axis of said joint, a grinding head carried by said mounting and including a grinding wheel and power transmission means for driving said grinding head.

12. In combination, a support comprising two spaced supporting members, a shaft extending across said supporting members, guide means acting between each of said supporting members and the shaft for guiding either end of the shaft for up and down movement, clamp means for holding said shaft in angularly adjusted position and a grinder 'pivotally mounted on said shaft and having a grinding wheel disposed remotely from said shaft and adapted to be shifted in position upon swinging of the grinder about said shaft.

13. In combination, a support, an arm, a pivotal connection between said arm and said support, a second arm, a joint between said arms, the axis of said joint being parallel to the axis of said pivotal connection, said joint including a member movable with said second arm, said second arm including a mounting at the end thereof, a grinding wheel carried by said mounting and a pivot between the second arm and said member, said pivot having an axis at right angles to a plane 2,484,906 11 containing the axes of said pivotal connection and said joint and guiding said grinding wheel The following references are of record in the 10 file of this patent:

UNITED STATES PATENTS for movement toward and from the surface being Number Name Date ground 181,715 Perkins Aug. 29, 1876 HAROLD POND, 5 405,961 Kampfe et a1 June 25, 1889 DANIEL A. ARONES. ,8 9 Gall June 19, 1917 1,308,933 Cavicchi July 8, 1919 REFERENCES CITED 1,776,110 Dina, Sept. 16, 1930 2,298,228 Pond et a1 Oct. 6, 1942