US3553894A - Apparatus and method for grinding notched knives - Google Patents

Abstract

APPARATUS FOR FACILITATING THE PROPER ADJUSTMENT OF THE CUTING EDGES OF WORKING DRESSING ROOLS, SUCH AS HARD STEEL, OR DIAMOND FACED, ROOLS OF THE TYPE USED IN DRESSING GRINDING WHEELS, OR ABRADING ROLLS. THE APPARATUS IS A DRESSING ROLL ASSEMBLY INCLUDING TEMPERATURE REGULATION MEANS WHEREBY MODIFICATION OF THE DIMENSIONS OF THE DRESSING ROLL SURFACES, SUCH AS CORRECTING ERRORS IN ROLL LENGTH, IS ACCOMPLISHED BY THE APPLICATION OF A CAREFULLY CONTROLLED AMOUNT OF HEAT OR COLD THERETO.

Description

Jan. 12, 1971 J. W. SJOSTROM APPARATUS AND METHOD FOR GRINDING NOTCHED KNIVES Filed Feb. 17, 1969 INVENTOR. John W. Sjos'rrom ATTORNEYS 3,553,894 APPARATUS AND METHOD FOR GRINDING NOTCHED KNIVES John W. Sjostrom, Salem, N.H., assigner to Bolton- Emerson, `Inc., Lawrence, Mass., a corporation of Massachusetts Filed Feb. 17, 1969, Ser. No. 799,866 Int. Cl. B24b 3/00, 9/00, 1/00 U.S. Cl. 51-5 8 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Many finished cutting tools must have precise dimensions on the cutting edges thereof. For example, sawtooth type cutting knives, with teeth very uniformly and exactly located, must be machined to a high tolerance. Variations in dimensions can lead to consequent variations in size of the cut product and to other problems.

Consequently, great care is taken to assure that the grinding wheels used to form toothed cutting edges on such knives are maintained in a sharp condition during the forming operation. Normally, this continuing sharpness is achieved by periodically sharpening the ridges and furrows of the grinding Wheel with a harder dressing roll. This harder dressing roll is configured to match any ridges and furrows o'f the grinding wheels and thereby maintain the grinding edges sharp and true. It has been found, however, to be most diiiicult to economically achieve sufficiently good tolerances on these hard faced dressing rolls to satisfy the demands of sharpening processes wherein the pitch tolerance of the grinding wheels must be maintained at the order of 0.0005 per foot. It would be most desirable and economical to be able to accept a hard faced dressing roll from its manufacturer with, say, tolerances of 0.002 or 0.003 inch.

SUMMARY OF THE INVENTION Therefore it is a principal object of the invention to provide an improved dressing roll assembly wherein dressing rolls with relatively wide tolerances on the sharpening surfaces thereof may be suitably utilized.

It is another object of the invention to provide a novel process for maintaining grinding wheels in a state of sharpness.

Other objects of the invention will be obvious to those skilled in the art on reading the instant specication.

The above objects have been substantially accomplished by a novel dressing roll assembly wherein the hard faced, working, dressing roll is provided with heating or cooling means and temperature-controlling means, thereby providing a dressing roll which may be minutely controlled with respect to its dimensions by making use of the coefficient of thermal expansion or contraction of materials from which such sharpening devices as dressing rolls are most often constructed. Although the particular method of achieving a temperature differential to bring about the required dimensional change is not critical, it is necessary that the means chosen be utilized in such a way that access to the dressing roll by the grinding wheel ignited States Patent O 3,553,894 Patented Jan. 12, 1971 be preserved, and it is desirable that the means selected be economical. In view of the fact that dressing rolls have a limited service life, it is preferred that the heating or cooling means be external to the roll proper.

It is particularly surprising that the apparatus of the invention functions well in the particular application for which it was designed because during the sharpening or dressing operations for which it is used a coolant is applied to the surfa-ce of the roll to avoid the local overheating of the roll by friction. It has been discovered that coolant is supplied for such a short period during dressing of the grinding wheel that the: dimensions of the roll are not substantially changed from the dimensions established by the temperature to which the roll was purposefully heated.

Thus, for the first time, it has become possible to utilize a hard faced dressing roll which has been manufactured to arelatively wide tolerance for refurbishing a grinding wheel which has been manufactured to a relatively narrow tolerance by selecting a dressing roll sized larger or smaller in length than the desired dimensions of the grinding wheel and adjusting its dimensions by heating or cooling as required to maintain close tolerance desired on the grinding wheel.

In the most advantageous embodiment of the invention, the improved dressing roll assembly includes an enclosure, i.e. a hood, for serving as a heat insulating barrier, and temperature control means operably connected to a heating means, and preferably also a cooling means, for maintaining a preselected temperature. This enclosure is preferably removable from the assembly so that the dressing roll can be made more accessible.

ILLUSTRATIVE EMBODIMENT OF THE INVENTION FIG. l is a schematic drawing of a machining operation in which the apparatus of the invention is utilized.

FIG. 2 is an elevational view of the apparatus of the invention.

FIG. 3 is also an elevational view of the apparatus of the invention taken at a -degree angle from FIG. 2.

Referring to FIG. 1, it is seen that a series of knife blanks 10 to be machined to a desired sawtooth edge are placed in a horizontal jig 12 with the edges 14 of blanks 10 facing upwardly. Jig 12, knife blanks 10= therein, is placed on reciprocating carriage 16 of grinding machine 18. Thus assembled knife blanks 10 may be moved back and forth beneath rotating grinding wheel 20. Surface 22 of grinding wheel 20l is, of course, shaped with ridges and furrows to impart the desired configuration to edges 14 of knife blanks 10. In such processes, it is necessary that grinding wheel 20 be frequently sharpened or dressed in order to be sure that the cutting surface 22 thereof is maintained in acceptable working condition. In order to accomplish this dressing of grinding wheel 20, the working dressing roll 24 is maintained at one end of grinding machine 18.

Of course, the configuration of hard surface 25 of dressing roll 24 must match that of :surface 22 of grinding wheel 20 in order to obtain an effective dressing action thereof.

Hard faced dressing roll 24 is normally enclosed in a heat insulated hood 28. On the inside of hood 28 are mounted heating means 30, such as four electrical resistance heaters 32. A temperature-sensing means 34, such as liqiud-filled bulb 35, is mounted Within insulated hood 28, and, through thermostat control 37, maintains the temperature within hood 28 at a predetermined level. Electrical connections to heaters 32 are brought into box 32 via conduit 39. Suitable refrigerant tubes 43 are also mounted within insulated hood 28 and connected to a commercially available refrigerant, or chilling device 44 of any well known type, the temperature of the tubes 43 being also controlled and regulated by the control 37.

The precise temperature at which the dressing roll 24 is to be maintained depends upon the precise material from which the roll is made, and on the difference between the desired roll dimensions and the dimensions of the roll as it is received from the manufacturer. For example, the coefficient of expansion of steel is about .000066 per degree Fahrenheit. Therefore, in an illustrative case, let it be assumed that the configuration being cut into knife blanks is a row of sawteeth forming a 90-degree angle at their tips and a 90-degree angle at their bases. Assume further that the pitch of these teeth, i.e. the distance between the most remote ridges thereof must be eleven inches within a tolerance of $0005 inch. In such a situation, of

course, the corresponding ridges 41 on surface 22 of grinding wheel must have a tolerance of i.0005 inch. Moreover, surface of dressing roll 24 must be fit to maintain the 1.0005 inch tolerance during the dressing operation. Thus, ideally, dressing roll 24 would have a surface configured to a tolerance of about 1.0005. However, since obtaining such tolerances on steel, or other hard faced rolls, is very expensive, it has now been demonstrated that a roll may be purchased having, say, a most remote ridge-to-ridge dimension of eleven inches with a r0.003 tolerance at 70 degrees F. or say 10.998 inches in length. Such a roll is relatively inexpensive and by operating the roll at a temperature of degrees F. above or below degrees F., i.e. at 115 degrees F. or 25 degrees F., the desired dimension of eleven inches can be readily achieved.

Because the normal dressing operation is only from about two to fifteen minutes in duration, and because the dressing roll has so much sensible heat, it has been found that this process of modifying roll dimensions is extremely efficient at temperatures up t0 about 50 degrees F. above or below the normal environmental temperature of the dressing operation, i.e. up to about 130` degrees F., or down to about 20 degrees F.

Preferably a master dressing roll 4.6 is mounted at the other end of milling machine 18, for dressing the working dressing roll 24 when required.

A tubular opening 48 may be provided in hood 28 for the introduction of a thermometer. 49 designates an oilproof, electric junction box, and 50 is a tubular conduit for the cables leading to heaters 32.

In operation, when grinding wheel 20 requires dressing, the thermal insulating hood 28 is temporarily removed and the roll 24 therewithin has been found to continue for about two hours to remain at the selected temperature and to remain at the desired dimensions. The grinding wheel 20 is moved into contact with dressing roll 24 for the two to ive minute dressing operation. When dressing roll 24 has been heat expanded, the heat generated in grinding compensates for any heat lost to the ambient temperature so that grinding wheel 20 is correctly cut by the heat expanded dressing roll. When dressing roll 24 has been cold contracted, the heat generated in grinding does not adversely affect the dimensions during the relatively short period required for the dressing operation.

What is claimed is:

1. A process for utilizing a hard faced dressing roll which has been manufactured to a relatively wide tolerance for refurbishing a grinding wheel which has been manufactured to a relatively narrow tolerance, comprising the steps of selecting said dressing roll manufactured to such relatively wide tolerance, subjecting said dressing roll to a predetermined temperature, substantially different from ambient temperature until the dimensions of said roll have changed from said relatively wide tolerance to conform to the desired dimensions of said grinding wheel and then refurbishing said grinding wheel with said dressing roll.

2. A process as defined in claim 1, wherein said dressing roll is heated to a temperature of up to about degrees F.

3. A process as defined in claim 1, wherein said dressing roll is cooled to a temperature of down to 20 degrees F.

4. The process of claim 1, wherein the step of subjecting said dressing roll to said temperature is achieved externally of said dressing roll.

5. An improved dressing roll assembly comprising a dressing roll,

a temperature regulation means mounted proximate to said dressing roll,

an enclosure for thermally insulating said dressing roll from ambient temperatures,

and control means operably connected to said temperature regulation means to maintain said dressing roll at a selected desired temperature relative to ambient temperature.

6. The dressing roll assembly of claim 5, wherein said enclosure is removably mounted about said dressing roll and said temperature regulation means is mounted on the inner surface of said enclosure.

7. The dressing roll assembly of claim 5, wherein said control means comprises a thermostat mounted on the inner surface of said thermal insulating enclosure.

8. Apparatus for accurately cutting a row of teeth in the edge of a cutting blade, said apparatus comprising:

powered, automatic cutting mechanism including a reciprocating table supporting said blade for movement along a path, and a rotating, grooved grinding wheel arranged to form said teeth as said blade moves back and forth on said path;

a hard faced dressing roll, grooved to conform to said grinding wheel, mounted on said mechanism at one end of said path for use in dressing said grinding wheel;

a thermal insulated enclosure on said mechanism normally enclosing said dressing roll;

temperature regulation means in said enclosure for treating said dressing roll to control the dimension thereof by temperature,

said enclosure being removable to enable said grinding wheel to engage said hard faced, temperature treated dressing roll.

References Cited UNITED STATES PATENTS 2,586,235 2/1952 Krafft 5l--5 2,815,744 10/1957 Crane l2511 2,824,556 2/1958 Bateman 125-11 OTHELL M. SIMPSON, Primary Examiner U.S. Cl. X.R.

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