US2662352A - Precision grinding machine - Google Patents

Description

Dec. 15, 1953 2 Sheets-Sheet l Filed Feb. 1.6, 1951 Dec. 15, 1953 Filed Feb. 16, 1951 C. T. RHODES PRECISION GRINDING MACHINE 2 Sheets-Sheet 2 Patented Dec. 15, 1953 PRECISION GRINDING MACHINE Clement Tipton Rhodes, Ascot, England Application February 16, 1951, Serial No. 211,247

Claims priority, application Great Britain February 23, 1950 1 Claim. j (01. 51-103) This invention relates to precision grinding machines and has for its object to provide simple, accurate and reliable grinding machines for the precision grinding of parts which are required to have an accurately ground circular sectioned surface which is accurately concentric with a shank or other circular sectioned surface of said part. Though not limited to its application thereto the invention is primarily intended to provide machines capable of accurately grinding the needles of diesel engine fuel pumps and injectors and grinding laps for use for trueing the seats of such pumps and injectors after wear.

The well known diesel engine fuel injection pumps and injectors now in widespread use include needle valves the seats of which are re-- quired to be of a slightly different angle (say, half a degree) from that of the needle. For example it is common practice in atomiser needle valves to make the angle of the needle 60 and the angle of the seat Sil the diiference of being adopted to ensure the necessary narrow ring-like contact. Because of this difference of angle, slight as it is, it is not possible to grind the needle directly in to the seat as is done, for example, with internal combustion engine poppet valves. The usual practice therefore is to regrind the seats after wear by means of a grinding lap of the correct seat angle. Owing to the high degree of accuracy required and in particular owing to the high degree of concentricity required between the tapered end of such a 'lap and the body or shank thereof, the grinding of such laps presents a quite serious problem and has hitherto had to be done by expansive complex special grinding machinery. Also the needles themselves have to be re-ground after wear and here too, the need for high accuracy has hitherto involved the use of special grinding machinery. Indeed it has not been generally possible, hitherto, to regrind diesel engine pump needles or to make laps for re-grinding diesel engine pump seats satisfactorily by means of ordinarily available grinders and when Wear has taken place in the pumps of diesel engines in use in remote parts of the world or in country districts, it has usually been necessary to replace the needles and seats and send the worn parts back to the makers for regrinding. The present invention seeks to overcome this important practical disadvantage and to provide apparatus whereby laps and needle can be easily and accurately ground by machines which consist merely of more or less standardised grinding machines such as are to be found in most well equipped garages, with only relatively simple and cheap modification.

According to this invention a machine for precision grinding an article required to have a circular sectioned part accurately ground in accurate concentricity with another circular sectioned part comprises a hardened block having a recess adapted to receive the latter part with the former part in contact with a grinding wheel and friction means for pressing the said latter part in said recess and simultaneously rotating it by friction drive thereto. Preferably the recess in the block is a V sectioned recess.

A preferred form of precision grinder in accordance with the invention comprises a motor driven emery or other grinding wheel, a work holder carrying a hardened recessed block in which the shank of the work to be ground may be placed and a swivel work head adapted to carry and to drive a shank upon which is a rubber or similar disc or wheel which is adapted to press the shank of the work into the block and simultaneously rotate said work, the whole arrangement being such that the part of the work to be ground is held against the grinding wheel and rotated during the grindingby friction drive transmitted to the shank.

Preferably the work holder is angularly adjustable so that the angle at which the work is presented to the grinding wheel may be adjusted as desired.

Preferably also the work holder is fitted with a back stop (which may be adjustable) to define the longitudinal position of the work.

In order to prevent loss of accuracy, after long use of the machine, due to the wearing of a shallow or recess in the back stop it is preferred to make the said back stop with a bearing surface of substantial area and to mount it in adjustably rotatable fashion in a carrier member therefor, whereby, when wear of part of said surface has occurred, the back stop can be rotated into a position in which a new and hitherto unworn part of its bearing face is brought into use.

Preferably, the work holder is fitted with means for carrying a diamond tool for use for trueing the grinding wheel.

Not the least of the practical advantages of the present invention is the simplicity with which it enables an existing grinder to be adapted to carry out the said invention and in the description which follows a preferred adapting apparatus which may be used to adapt an existing known grinding machine will be set out.

The invention is illustrated in the accompanying drawings which show one embodiment thereof. In the drawings Figure 1 is an elevation, Figure 2 is a part plan view, Figure 3 shows in section the variable drive to the chuck and Figure 4 a detail of the back stop and work-holder.

Referring to the drawings the machine therein shown comprises a motor I driving an emery wheel 2 having a horizontal shaft 3, the emery wheel and motor being arranged as a unit upon a base 5 across which it may be traversed by means of the usual screw adjustment operated by a handle 5. Also mounted on the base plate is a swivel work head 6 carrying a chuck I which is rotated by the said motor through a flexible drive 8. This drive includes a reversible infinitely variable gear consisting of two parallel spaced friction wheels 9, IE) and a third friction wheel Ii driven by the motor and between the said wheels and at right angles thereto. Drive is efiected in one direction or the other by bringing the edge of the third wheel ll against the face of one or other of the first two wheels 9, l and variation of the speed ratio of the drive is effected by moving the third wheel I i vertically across the face of the wheel with which its edge contacts. The reversal of drive and variation of speed ratio are effected by a handle i2, the former by twisting it in one direction or the other and the latter by sliding it up or down. No claim is made per se in this specification to this speed varying and reversing mechanism. The swivel head is arranged to swivel about a vertical axis and may be adjusted and clamped in any position of angularity by any suitable known means e. g. an ordinary gripping clamp operated by a handle IS. The swivel head is also arranged to be adjusted longitudinally with regard to the base plate by means of a screw or other longitudinal feed operated by a handle M.

The machine as so far described is a known machine commercially available at the present time. If it were sought to use such a machine for the precision grinding of, for example, a fuel injection pump atomiser needle or a seat lap by gripping the shank of the lap in the chuck and using the various adjustments provided to grind the required taper, it would generally if not invariably be found that the required high degree of accuracy would not be obtained. This is mainly because the degree of concentricity required between the ground tapered end of the lap and the shank is greater than can be obtained by merely holding the shank more or less near one end in a chuck while grinding the tapered end.

To adapt this machine to carry out the present invention there is provided a work holder I which is mounted on a bracket l5a detachably fixed in an accurately predetermined position on the slide 6a or" the work head. In the machine shown the slide can be moved in the plane of Figure l by the usual handle M in a direction at right angles to the movement of the emery wheel unit given by operation of the handle 5. Thus as will be seen later the cut is adjustable by the handle 5 and the traverse of the work is given by the handle [4. The Work holder 15 is arranged to be swivelled about a vertical axis [6 and adjusted in any position of angularity with regard to a vertical axis being clamped in the chosen adjusted position of angularity. This work holder is positioned between and is oiT-set with respect to the centres of the grinding wheel and of the chuck I. Fixed on the work holder is a hardened V-recessed block H, the V-recess l8 being horizontal and on its side with the line of the apex in the common plane of the grinding wheel and chuck axes. The work holder with its V-recessed block constitutes one of the two main additions required to embody the present invention. The second main addition consists of a stiff shaft or spindle I9 carrying at its end a rubber or similar disc or wheel 20 the edge of which is rounded off as shown. In use the spindle I9 is fitted into and clamped by the chuck 1.

To use the machine to grind a needle or a valve seat lap, for example, as shown in Figure 2, the shank 22 thereof is placed longitudinally in the V-recess of the block the holder of which is adjusted so that the tapered end 23 to be ground is presented at the required angle to the grinding wheel. The longitudinal position of the lap or needle in the V block is adjusted as required and the swivel head is swivelled to bring the rubber wheel 26 against the shank 22. Preferably the work holder is fitted with a back stop 24 (which may be adjustable) and which comes against that end of the lap or needle whichis remote from the grinding wheel so as to fix the longitudinal position of the said lap or needle. When the motor is run the grinding wheel is of course rotated and in addition the lap or needle is rotated in the V block by friction drive transmitted to it by the rubber wheel 2!]. Owing to the curvature of the edge of the rubber wheel it will drive satisfactorily at any of a wide range of angles.

Preferably the work holder is also fitted, near the end of the V-recessed block and rather nearer to the grinding wheel, with a drilled hole adapted to receive the holder 25 of a diamond tool for trueing the emery wheel after use.

Owing to the fact that the shank of the work is pressed for a considerable part-in some cases the whole-of its length against the hardened V-recess of the block and is rotated in said block while grinding is in rogress a very high degree of accuracy and concentricity is obtained.

Any of the various adjustments provided may of course be arranged in conjunction with suitable adjustment reading scales in accordance with known high grade workshop practice.

The form of back stop illustrated is the preferred form since it allows of adjustment to obviate the effects of wear. As will be seen the back stop 24 is of cylindrical shape with a hardened end face 24a and is carried in a carrier member fitted to the block so as to extend horizontally in the bisecting plane of the V-recess. This plane member is bored with a hole '26 whose axis extends parallel or approximately parallel to the bottom of the V-recess--i. e. extends along said plane-and said carrier member is split at 21 from its free end at least as far as said hole. A clamp screw 28 or the like is fitted into the free end of the carrier member across the split so that by tightening the said screw the two portions of the carrier member, one on each side of the split, may be drawn together after the manner of a split clamp. The stop 24 is fitted in the hole 26 with its hardened circular end bearing face towards the work. As will be appreciated by slacking back the clamp screw 28 the longitudinal position of the stop 24 may be adjusted in the pillar and/or it may be rotated about its own axis. The area of the bearing face 24a is large in relation to the end cross sectional area of laps or needles to be ground by the machine. The whole arrangement is such that the longitudinal position of the stop may be adjusted so that the rear end of a lap or needle to be ground abuts against the hardened bearing face 240. eccentrically with respect thereto. Accordingly it is a simple matter to adjust the stop to a position in which it acts correctly as a stop and to clamp it in that position. When, after a certain amount of grinding, the hardened bearing face 24a shows unpermissible wear on a small area where work has been contacting with it, the clamp screw 28 may be slackened, the stop rotated to bring another part of its bearing face into play and the clamp re-tightened.

I claim:

A grinding machine comprising a driven grinding wheel, a block having a V-recess of substantial length adapted to receive a portion of circular cross section of an article to be ground with sides of said portion of the article in contact with the sides of said V-recess and with one end of the article in contact with said grinding wheel, a rotary friction wheel having a resilient rim engaging said portion of the article at the side thereof opposite said V-recess, the axis of said friction wheel and the axis of said portion of the article lying in a common plane and said axes diverging in a direction away from said 6 grinding wheel, and a back stop for the article at the end thereof opposite said grinding wheel, the angularity of the axes of said grinding wheel and said portion of the article providing a resultant force tending to move the article in the direction of and into contact with said back s op.

CLEMENT TIPTON RHODES.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,452,508 Hervig Apr. 24, 1923 1,497,951 Smith June 17, 1924 1,776,241 Caster et a1. Sept. 16, 1930 2,059,723 Briney -1 Nov. 3, 1936 2,156,970 Burns May 2, 1939 2,247,994 Fiedler July 1, 1941 2,411,972 Melin Dec. 3, 1946 2,508,102 Cupler May 16, 1950 2,544,318 Horberg Mar. 6, 1951

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