US2345189A - Grinding machine - Google Patents

Description

March 1944- w. F. FRASER GRINDING MACHIDUE:

Original Filed Aug. 29, 1940 5 Sheets-Sheet l 0 Ma M a O liiniiilm n 3 km March 28, 1944. w, FRASER GRINDING MACHINE Original Filed Aug 29, 1940 I -5 Sheets-Sheet 2 March 1944- w. F. FRASER I GRINDING MACHINE 5 Sheets-Sheet 5' Original Filed Aug. 29, 1940 28, 1944. w. F. FRASER GRINDING MACHINE Original Filed Aug. 29, 1940 5 Sheets-Sheet 5 .Ill i llln-E v Inl enfor:

Patented Mar. 28, 1944 UNITED STATES PATENT GFF IC'E r 2,345,189. GRINDING MACHINE WarrenKF. Eraser, Westboro, Mass Original application August 29, 1940, Serial No.

Divided and this-application March 1942, Serial No. 436,130

1 Claim.

This invention relates tosurface: grinding machines and is more especiallyconcerned with those factors affecting the accuracy ofthe surface produced by the grinding operation.

A typical machine of'this type includes a work support, a wheel head carrying-a revolving grinding wheel, and means supporting saidhead for reciprocating'mcvement to carry said wheel'backward and forward across thesur-faceof the work. While machines of this typ are old and well known and they have been widely used; they always have a tendency to produce a wavy surface in the work. In some cases, also, there is n. discernible difference in the cut produced on the forward stroke as compared'with that on the return stroke. Of course any such irregularity in the surface is noticeable only upon very careful inspection, but nevertheless machine manufacturers are quite conscious. of this fault. This effect often is referred to as chatter, although no audible chatter is discernible, and. it isdue to some relative vibration between the ,Work support and the Wheel spindle. While it isnot customarily troublesome it does become important when extreme accuracy, say down to a fraction of one ten-thousandth of. an inch; and fineness of finish are-required.

The present invention is especially concerned with these considerations, and it aims to im-l prove the organization of machines of this type with a view to minimizing these difficulties.

The nature of the invention will be readily understood from the following description when read in connection with the accompanying drawings, and the novel features will be particularly pointed out in the appended claim In the drawings,

Figure 1 is a side elevation of a surface grinder embodying features of this invention;

Fig. 2 is an elevation of the opposite side of the machine from that shown in Fig. 1;

Fig. 3 is a rear elevation of the machine with parts broken away;

Fig. 4 is a vertical; sectional view through the wheel head and adjacent parts, the section being taken approximately inthe vertical plane of: the axis of the wheelspindle and Fig. 5 is a vertical, sectional view approximately on the line 5-5ofFig. l. 7

Referring first to Figs. 1- and 2, the machine there shown includes a rotary chuck 2 partlyenclosed in a casing I, this chuck being mounted to revolve around a vertical axis, together with a wheel head 3, and a grinding wheel mounted in said head. So far as this general organization is concerned; the machine is likethcse common. ly used heretofore.

As better shown in Figs. 3 and 5", the Wheel head 3 is provided with guiding surfaces designed to slide horizontally on ways: 5 and B which are formed in the upper part of the section I of the machine frame orbase. In the preferred ernbcdiment of the invention thewheel' head is reciprocated backward and forward in these ways to carry-the wheel across the surface-of the work by means of an hydraulic mechanism including a cylinder 8. A unique feature of the invention resides in the fact that the axis of'this cylinder is located approximately in the same horizontal plane with theways 5 and 5. This relationship is better-illustrated in Fig. 5'. Consequently; the thrust exerted on the head tov move it in either direction is in the plane of the frictional resistance which this thrust must overcome. Preferably this thrust is exerted approximately midway betweenthe two longitudinal. pairs: of surfaces between which this frictional resistance is generated.

It will further be seen from an inspection of Figs. 3 and ithat the wheel? spindle Ill. ismounn ed in axial alignment with the cylinder 8 so that it also is in approximately the same horizontal plane with the ways 5 and 6. Atv its rearward end this spindle is belt-connectedito the driving shaft of anelectric motor lz whi'chismounted on. the Wheel head directly above the cylinder and the axis of its shaft preferably is in substantially the vertical plane passing through the axes of the spindle Ill and cylinder 8.

By making the base section 1 heavy, stiff and rigid and supporting the cylinder, and Preferably also the spindle, approximately in the horizontal plane of the ways, any leverage effect of those forces tending to produce relative vibration betweenthe wheel and the work is. reduced? to a minimum, with a consequent substantial improvementin the operating characteristics of the machine. The fact, also, that this arrangement permits the lowering of the center of gravity ofthe wheel head to a point close to the: horizontal plane of the ways, as will be evident from an inspection or Fig. 5, assists. in producing this desirable'result.

Afurther'novel feature contributing to this result is the fact that the frame or base of the machine is made in two sections, as illustrated'ineach of Figs. '1 to 5, inclusive. The lower section l3, orthe main part ofthebase, consists-of a heavy, stiff casting designed" to rest on the floor and to support and house certain of the-- driving mechanisms, as is customary in machines of this type. This section is provided with a vertical dove-tail guide 55 on which the bracket 53 that supports the chuck 2 and the driving and adjusting means therefor is mounted for vertical adjustment.

The upper section 1 also consists of a heavy, stiff casting reinforcedboth longitudinally and transverselyby ribs, shown at l4. and lin, Figs. 4 and 5, integral with the sides and horizontal bottom web of the casting. These two sections are,

secured together at three points only forming the corners of a triangle.

machine frame near opposite edges thereof, while the third point I9 is at the rear of the frame Two of these points, I1 and [8, Fig. 5, are located at the front of the the oil or other liquid used in the hydraulic .mechanism for reciprocating the wheel head inand is located approximately midway between the vertical planes of the ways 5 and 6.

These connections of the upper frame section to the lower section may conveniently consist simply of bolts passing loosely through the lowermost web or plate of the upper section and threaded into the metal of the lower section. Each of these bolts extends through a bearing area, preferably includinga series of spacing washers or shims. Such a three-point support for the upper frame section reduces the distorting effects of expansion and contraction of the base on the upper frame section and the ways which area part of it. It isolates the uppersection from the lower and thus renders the former substantially unaffected by changes in the latter, such'as those due to mechanical stress set up in or through the chuck slide 56,,or stresses caused by forces inthe castings, or by the driv- .ing mechanism in the lower section, and which stresses and strains would be likely to spring or warp the ways 5 and 6 sufficiently to cause chatter or vibrations of the character above de-- scribed.

This construction also permits the designing of the upper frame section so that it is of a more nearly uniform thickness, is less liable to warp, and its-tendency to change dimensions in ways that will affect the operation of the wheel on the work are reduced. This result is further aided by the fact that the motor is located overhead and moves with the wheel head so that no slots are made through the main plates of either base sectiomas is'customarily required for the passage ofthe driving belt.

The arrangement for reciprocating the wheel head further is unique in that the cylinder 8 is fastened securely to the wheel head and moves therewith, the piston being stationary. As best shown'in-Figs. 1, land 5, the cylinder fits snugly into axbore formed for it in the frame portion of the wheel head,'and a circumferential flange 2|, integral with the cylinder, is secured: to the adjacent portion of the wheel head frame by bolts or screws, such as those shown at 22;.

Fig. 5. The oil or other fluid used in thismechanismis conducted to: and from the cylin-' and from the cylinder 4 is produced in properly timedrelationship to the cycles of operations of the machine. So far as this supply and the,

valve. mechanism are concerned, they may be.

like those heretofore used in hydraulically opcludes a rotary pump 26 drawing oil through the pipe 21' from the supply tank 30 and forcing it through the pipe 28 into the valve mechanism 25 and thence into the cylinder 8 when allowed to do'so bythevalve mechanism. The exhaust oil is returned from the valve mechanism to the tank through the pipe 3|.

For the purpose of driving both this pump and also the rotary chuck 2, an electric motor 32, a

Fig. 3, is mounted on the machine frame at the rearward end thereof where it drives a variable speed mechansm mounted in the housing 33. As better shown in Fig. 1, the particular variable speed mechanism used in this machine is of the Reeves type including two pulleys, each pulley including two reversely positioned cones which are adjustable toward and from each other. The pulleys are connected by a belt of frusto-conical form in cross-section so that the operating ratio may be varied through a wide range by the adjustment of these conical pulley sections toward and from each other. In Fig. 1, this variable speed mechanism is indicated at 34. The adjusting shaft for the mechanism is shown at35, and the power output shaft is shown in Figs. 2 and 3 at 36. A long belt 31, Fig. 2, connects the pulley 38 on the shaft 36 with a driven pulley 40 on a jack shaft 4|, mounted in the chuck bracket 4?, and this belt not only drives that pulley but also the pulley 43 of the pump 26, an idler 44 resting on the belt between the pulley 43 and 38 to keep it taut. At the front of the machine the pulley 40 is belted to another pulley 45 on the driving shaft 46 for the chuck 2, this chuck drive, for example, being like that shown in my patent above referred to. In order to provide for the convenient adjustment of the variable speed driving mechanism 34, the screw shaft or adjusting shaft 35 of this mechanism is connected by means of a sprocket and chain drive with a hand wheel 41, Fig. 1, mounted on the side of the'framaso that by turning this wheel the driving speedof both the chuck 2 and the pump 43 can be increased or reduced, as desired. An indicating disk 48 preferably is geared to the hand wheel 41 andis graduated in any convenient manner as, for example, to indicate chuck speeds.

With this arrangement the speeds of both the wheel head and the chuck can be varied through a wide range. In addition, it also avoids the necessity for operating the pump continuously at the maximum output which it must'be expected to deliver under some conditions. The normal relationship between the pump speed and the chuck speed is such that the wheel head is trav: ersed at the maximum speed required for that particular work'speed. -When it is desired to reduce the speed of traverse of the wheel. that result. isaccomplished by adjustment of a throttle valve which is actuated by turning the knob 50 attached to a shaft5l extending through the machine and having on the back thereof a lever 52 connected through a link 53 to a similar lever 54 on an extension of the throttle 55.

The long, horizontal belt 31, Fig. 2, accommodates the vertical adjustment of the chuck 2 without afl'ecting the driving connections between the chuck and the variable speed mechanism.

While I have herein shown and described a preferred embodiment of my invention, it will be evident that the invention may be embodied in other forms without departing from the spirit or scope thereof.

This application is a division of my copending application Serial No. 354,634, filed August 29, 1940, and is limited to that feature of the machine comprising the construction of the base in upper and lower sections and the means for securing these sections together at a plurality of bearing points, preferably three, with the sections spaced slightly apart.

Having thus described my invention, what I desire to claim as new is:

In a grinding machine, the combination of a grinding wheel, a work support, a wheel head including a horizontal spindle on which said wheel is mounted and a slide supporting said spindle, a machine base comprising heavy, stiif upper and lower frame sections, a bracket on which said Work support is mounted, vertical guides rigid with said lower frame section on which said bracket is supported for vertical adjustment, said upper section having horizontal ways on which said wheel head slide is mounted for reciprocating movement toward and from said work support and including a horizontal bottom web and stiffening ribs located between the sides of said upper section and integral with said sides and bottom web and extending both longitudinally and transversely of said upper section, means securing said sections together at three supporting points only located at the corners of a triangle and isolating said upper section from said lower section except at said points, two of said points being located at one end portion of the frame and spaced widely apart, while the third point ofsupport is at the opposite end portion of the frame and is located substantially midway between the vertical planes of said ways.

WARREN F. FRASER.

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