Note: Descriptions are shown in the official language in which they were submitted.
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TOOL FOR TRUEING AND DRESSING A GRINDING
WHEEL AND h~ETHOD OF USE
3ackaround of the Invention
The present invention relates to a -nethod for trueing and dressing
grinding wheels and to a novel trueing and dressing tool. ~ore particularly,
the present invention relates to a -nethod for trueing and dressing grinding
wheels having vitrified-bonded cubic boron nitride (C8N) abrasive by use of
1û a fine point trueing disc mounted between the existing headstock and
tailstock of a grinding machine.
A number of grinding wheels are known to those skilled in the art
including, for example, conventional aluminurn oxide and silicon carbide
grinding wheels as well as resin-bonded and vitrified-bonded C8N grinding
15 wheels and diamond grinding wheels. Regardless of the type of grinding
wheel, it is necessary to true and dress the grinding wheel in order that it
may accurately form fine finishes or precise contours on workpieces.
A variety of methods for trueing and dressing grinding wheels are
known in the art, however, each has various drawbacks and disadvantages,
2û particularly with regard to trueing and dressing grinding wheels whose
abrasive material is vitreous-bonded C8N. One prior art method is disclosed
in U.S. Patent 2,79 1 ,2 11 to Nagy and involves periodical ly indexing a
diamond tipped dressing tool in relation to the grinding wheel so that in all
indexing positions the diamond is in contact with the wheel in a direction of
25 hard grain forming an angle of between 30 and 45 to a crystal axis of the
diamond. While such a single point tool is useful for dressing small diameter
grinding wheels, the diamond tip would wear much too rapidly to be useful in
dressing large diameter grinding wheels, especially vitrified-bonded CBN
grinding wheels.
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Alternatives to single point trueing and dressing tools include hand set
diamond and metal-bonded diamond rotary cup and straight wheel tools.
'~hile such rotary dressing tools are more effective than single point tools,
they have the disadvantage of being relatively expensive, and, furthermore,
they are used in conjunction with a relatively expensive electric or hydraulic
precision drive motor and spindle assembly. Consequently, small machine
shops are unable to avail themselves of rotary dressing technology. Another
disadvantage of rotary cup wheel dressing tools is the necessity of changing
the position or angle of the dressing wheel in order to present new, sharper
1û edges as the originally presented edges wear flat. Straight wheel dressing
tools suffer from the further disadvantage of having the abrasive applie~ to
the circumferential surface of the wheel in a band several milli,neters in
width. As a result, the operator has very little control over the dressed
surface of the vitrified-bonded C8N grinding wheels because a wide band of
abrasive, unlike a sharp point, generally leaves the wheel in a closed or dull
condition. Wheels in this condition generate excessive heat, which may
cause the wheel to burn the workpiece.
Whi le such prior art methods are general Iy considered to be
acceptable, manufacturers are always concerned with improving the trueing
and dressing process, such as by reducing the time required to true and dress
a grinding wheel and reducing the cost of the trueing and dressing tool.
Summary of the Invention
It is an object of the present invention to provide a fine point trueing
and dressing wheel.
It is another object of the present invention to provide a method for
making a fine point trueing and dressing wheel.
It is still another obiect of the present invention to provide a method
for trueing and dressing a grinding wheel with a trueing and dressing wheel
~hat can be mounted between the headstock and the tailstock of a grinding
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60SD00 319
machine in place of the workpiece.
In accordance with one aspect of the present invention, there is
provided a tool for trueing and dressing a grinding wheei, comprising a disc
having a thin layer of diamonds in a plane perpendicular to the rotational
axis of said disc. Preferably. the thin layer of diamonds is only a single
layer of diamonds in width and is disposed inside the trueing and dressing
wheel. In a less preferred embodiment, a single layer of diamonds is plated
or metal-bonded to at least one side of the trueing and dressing wheel.
In accordance with another aspect of the present invention, there is
provided a method for trueing and dressing a grinding wheel, cornprising
engaging the periphery of the rotating grinding wheel with a rotating trueing
and dressing wheel disposed intermediate the headstock and tailstock of a
grinding machine.
8rief Description of the Drawings
FIG. I is a front elevation view of a portion of one embodiment of the
trueing and dressing wheel; and
FIG. 2 is a front elevation view of one embodiment of the trueing and
dressing tool;
FIG. 3 is a front sectional view of the method of manufacture of the
portion of the trueing and dressing wheel shown in FIG. 2.;
FIG. 4 is an exploded front view of the trueing and dressing wheel and
its mounting assembly;
FIG. 5 is a front elevation view of the trueing and dressing wheel
mounted on a grinding machine.
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Description of the Invention
There is provided by the present invention a tool for trueing and
dressing a grinding wheel, cornprising a disc having a thin layer of diamonds
in a plane perpendicular to the rotational axis of said disc. Although the
5 trueing and dressing tool of the present invention is especially suited for
trueing and dressing large diameter vitrified-bonded CBN grinding wheels, it
may also be used effectively and efficiently on conventional grinding wheels
such as, for example, alurninum oxide and silicon carbide, as well as resin-
bonded CBN grinding wheels and diGmond grinding wheels.
Referring now to the drawing, FIG. I shows a segment l O of a
preferred embodiment of the present invention. Segment l O preferably
comprises a thin layer of diamonds l l disposed intermediate a first metal
section 12 and a second metal section 13. Inasmuch as diamond layer l l
functions to true and dress the grinding wheel, the more narrow the diamond
15 layer l l, the more closely the trueing and dressing tool of the present
invention will operate as a single point trueing device. Although it is rnost
preferred that diamond layer l l only be a single diamond in width, in some
instances it might be more practical to prepare tools wherein diamond layer
I l is several diamonds in width, for example, up to about 0.8 millimeters in
20 width, so as to provide a fine point trueing and dressing tool.
Diamond particles of any size may be ernployed in diamond layer I I,
depending upon the trueing and dressing requirements. Preferably, larger
size diamond particles, e.g., 20/25 to 30/40 U.S. mesh size, are otilized for
trueing and dressing vitrified_bonded C8N grinding wheels as they provide a
25 longer useful life. The artisan will be able to select suitable diamond
particle sizes for use in trueing and dressing other types of grinding wheels
without undue experimentation.
In an alternative, but less preferred embodiment (,not shown), it is
contemplated that diamond layer l l can be attached to one or both sides of
30 the trueing tool, for example, by plating or metal bonding. This
embodi nent, although simple to manufacture, suffers from the disadvantage
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60SD00319
that the diamond particles of the tool are not held in place
as firmly as in the preferred embodiment.
Sections 12 and 13 may consist of any suitable metal
bonding matrix with harder bonds such as those containing
iron or cobalt being most preferred. The most important
criteria in selecting the material for sections 12 and 13 is
that it be sufficiently hard to retain the diamonds of
section 11 in the trueing and dressing tool of the present
invention and will not deform or vibrate during use.
FIG. 2 illustrates one preferred embodiment wherein a
plurality of sections 10 shown in FIG. 1 are attached to disc
15, for example, by use of a suitable brazing material. Disc
15 can be any suitable, relatively stiff material and
preferably is a metal Qr metal alloy. Typically, the core or
disc 15 will be between 1/8 and 3/8 inch in thickness.
Brazing material can be any of the well known brazes, for
example, as described in U.S. Patents 4,396,577 and 4,414,178
to Smith, et al., both of which are assigned to the same
assignee as the present invention. Of course, other suitable
brazing materials will be obvious to those skilled in the
art.
There is no particular criticality regarding the length
of sections 10 or the spacing 16 between sections 10 shown in
the "sawblade" configuration of FIG. 2. The limiting
consideration is obtaining an effective and efficient trueing
and dressing tool while not utilizing an excessive amount of
diamonds. In a second preferred embodiment, not shown, the
diamond abrasive continues around the entire circumferences
of the trueing and dressing wheel of the present invention.
In general, there are no limitations regarding the diameter
of the trueing and dressing wheel other than it must be able
to be mounted between the powered headstock and tailstock of
a grinding machine s illustrated in FIG. 5. The optimum
diameter of the trueing and dressing wheel is most affected
by the grinding machine on which it is to be used, the
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available speed of the headstock, and the diameter of the grinding wheel.
Typically, the trueing and dressing wheel of the present invention will range
between four inches for use on small grinding wheels and ten inches or more
for use on large grinding wheels.
FIG. 3 illustrates a preferred method for making the fine point trueing
and dressing wheels of the invention. Initially, first section 12 is cold
pressed by means well known in the art in mold 17. If a sawblade type
trueing and dressing tool is to be manufactured, thin diamond layer l l is
applied across the entire upper surface of section 12 as shown in FIG. 3. On
1û the other hand, if the diamond abrasive is to continue around the entire
circumference of the truing and dressing tool, mold 17 would be the size of
the trueing and dressing wheel, however, diamond layer l l would only
extend partially towards the center of the wheel in order to minimize the
cost of the tool. Of course, there would be an opening at the center of the
mold which would correspond to the size of the wheel core as shown in FIG.
2. Following addition of the appropriate amount of diamond l l, an amount
of metal bond powder is added which is sufficient to form second section 13
upon hot pressing. If the unitary or second ernbodiment is being
manuftured, hot pressing is all that is needed to make the finished trueing
and dressing tool. If, however, ~nly a segment 10 as shown in FIG. I is
prepared by the hot pressing step, it is necessary to braze segment 10 to
disc 15 as the final step.
FIG. 4 illustrates one means for securing the trueing and dressing tool
18 of the present invention to a spindle and flange assembly 19 which can be
mounted between the headstock and tai Istock of a grinding machine.
13riefly, tool 18 is mounted through its central opening 2û onto spindle and
flange asse;nbly l9 and held in close contact with flange 21 by means of
threaded screws 22. The combined tool 18 and spindle and flange assembly
l 9 is then inserted into driving dog 23 in the same way as would a
3û workpiece. Alternatively, combined tool 18 and spindle and flange assembly 19 can be affixed to a headchuck, not shown.
In either case, the completed mounting nssembly is secured between
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the existing headstock 2~ and tailstock 25 of the grinding machine as shown
in FIG. 5 when mounted between centers. It would, of course, be highly
desirable to have a variety of spindle lengths available whicn qre
approximately eaual to the length of commonly encountered workpieces. In
this way, the operator can more easily substitute the trueing and dressing
wheel for the workpiece.
Trueing and dressing is effected by engaging the periphery of the
grinding wheel with the rotating trueing and dressing wheel. Rotational
power for the trueing and dressing wheel is supplied by the workhead of the
1û grinding machine and is transmitted to the trueing and dressing wheel via
driving dog 23 or the workpiece chuck assembly, not shown. Although
greater convenience is obtained when rotational power is provided to the
trueing and dressing tool in this manner, the tool is equally effective when
driven by a precision spindle and drive motor. Trueing and dressing is
accomplis'led by traversing the trueing wheel 18 across the grinding wheel
26 using the grinding machine's powered table and feed controls. The
surface condition generated on grinding wheel 26 can be control led by
increasing the trueing or dressing rate for a finer finish, i.e., increasing or
decreasing the machine table and/or infeed rate.
