US2264698A - Method of cutting quartz - Google Patents

Description

Patented Dec. 2, 1941 METHOD OF CUTTING QUARTZ Charles E. Johnson, Collingswood, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application September 30, 1939, Serial No. 297,410

6 Claims.

This invention relates to the art of cutting natural quartz crystals (or rock crystals as they are sometimes called) and has for its principal object to provide (a) a simplified, inexpensive, time saving method of cutting quartz, (b) one which permits the use of smaller, and consequently cheaper mother crystals in the production of piezoelectric and optical elements, and one which ensures minimum wastage of material.

The invention will be better understood from the following description considered in connection with the accompanying drawing and its scope is indicated by the appended claims.

In the drawing wherein like reference characters designate the same or corresponding parts in all figures,

Figure 1 is a view in outline and in perspective of a quartz mother crystal cut, in accordance with the prior art, in planes normal to its optic (Z) axis, to provide a plurality of sections,

Figure 2 is an elevational view of one of the sections of Fig. 1 showing subsequent cutting operations dictated by the later described prior art method of producing so-called V-cut piezoelectric quartz elements,

Figure 3 is a view in perspective of a quartz mother crystal which is marked to indicate another prior art method of cutting V-cut piezoelectric elements therefrom,

Figure 4 is a view in perspective illustrating subsequent cutting operations required by this prior art method,

Figure 5 is a view in perspective of a quartz mother crystal having cut therefrom (in accordance with the present invention) a single bar whose long dimensions are substantially parallel to the optic axis,

Figure 6 is a view in perspective of the bar of Fig. 4 removed and cut into a number of semifinished V-cut piezoelectric blanks,

Fig. 7 is a View in perspective of one of the blanks of Fig. 6, and

Fig. 8 is a view in perspective of the bar of Fig. 4 removed and cut into a number of semifinished X-cut and Y-cut piezoelectric blanks.

The term V-cut as used herein designates any crystal element whose thickness dimension is inclined at other than a right angle with respect to the optic (Z) axis of the mother crystal. The orientation of V-cut crystals of both the thickness mode and contour mode" types are described in considerable detail in British Patent 457,342 (1936).

The term X- cut or Curie cut as herein used designates any crystal element whose thickness dimension lies along an X axis of the mother crystal.

The term Y-cut or Tillyer-cut as used herein designates any crystal element whose thickness dimension lies along a Y-axis of the mother crystal.

The term Z-cut as used herein designates any crystal whose thickness dimension lies along the optic (Z-axis) of the mother crystal. As is known in the art, Z-cut crystals exhibit substantially no piezoelectric efiect, but may, when suitably ground and finished, be employed as optical lenses and the like.

In accordance with one widely used method of cutting V-cut, X-cut, Y-cut, and Z-cut crystal elements. the practice has been to cut as many slabs from the mother crystal in planes normal to the optic axis as the length of the crystal and the ultimate desired size of the finished element will permit. This is indicated in Fig. 1 of the drawing, wherein three sections I, 2 and 3, respectively, each, say, one-inch thick are shown cut from a mother crystal Q, whose optic axis is marked Z--Z. From these sections l, 2 and 3, bars 4 (Fig. 2) whose short dimensions may be parallel to an X-axis or to an X+0 axis are cut. From the bars 4, the crystal elements 5 are cut at an angle determined by the particular characteristic desired. Thus, referring to Fig. 2, if a V-cut crystal element having a zero or some low temperature coeflicient of frequency is required, the elements 5 may have their electrode faces inclined not only with respect to the Z axis and with respect to the major (M) and minor (N) apex faces but also with respect to the X-axes, all as described in detail in the above-mentioned British Patent 457,342.

One very real objection to the above described prior art method of cutting quartz is that it can not be practiced economically with mother crystals of small size (e. g. quartz candles" up to, say, mother crystals will result in the production of numerous useless fragments unless the mother crystal is carefully selected with a finished element of particular size in mind. In the case of the mother crystal here illustrated, the fragments 6, I and 8, or some of them, may be used in the production of very small piezoelectric elements (e. g. filter crystals) but are usually discarded in commercial production because of the difliculties incident to the identification of the natural axes of such fragments. Another objection to this method of the prior art resides in 2 diameter) and, in the case of larger the fact that the wastage at the areas 6, 1 and 8, Fig. 2, is duplicated in each central section I, 2 and 3. Further, each section and each bar 4 must be separately set up in the cutting machine before the separate semi-finished elements 5 can be realized. 7

Referring to Figs. 3 and 4, in accordance with another prior art method of cutting ,V-cut blanks. the mother crystal Q is first sliced, at the desired angle with respect to the Z-axis, into as many as possible slabs ID of a thickness approximating that of the finished elements. The

principal objection to this method is that each.

thin slab H) must be separately set .up in the cutting machine in the manufacture of the semi finished blanks ll (Fig. 4). Another difficulty which is especially apparent in the cutting of blanks of the indicated orientation is that in at-- I tempting to practice this method economicallythe corners l2 of the blanks may extend to the side faces M and Not the mother crystalwhere imperfections (such as twinning) in the crysbut little material need be removed from these semi-finished .blanks toprovide finished piezoelectric element of the desired dimensions the finishing operation may be accomplished by grinding .or lapping and without setting up the separate blanks in a sawor other cutting machine. w 7

It will. be observed that. the principal wastage in material resulting from thepractice of this method is. that which occurs at 23, 24, Fig. '7, adjacentthe side faces of the mother crystal .where,. as above pointed out, imperfections in the quartz are most likely to be present. It will alsoJ-be noted that there are. but .two end portions 5 and .26, (Fig. 6:) to be discardedinstead of six as in the .case of the method of Figs. 1 and 2.

There is another very real saving incident to the practice of the/present. method in that it permits. the economical use of mother crystals whose diameterissubstantially no greater than the diameter .of the elements to becut therefrom. v'I'heimportance of this. feature .of the invention will be appreciated by a reference to the .current price of quartz. The price .of: raw quartz candles, of a size. suitable for the cutting of blanks 11" square: in accordance with the present invention is currently about $4.00! per 1b.; the lar er pieces usually employed in practicing prior methods cost up to 5316.00.13.81 1b.

While the invention has thus far as applied :to. the cutting of a --V.cut piezoelectric element, the electrode faces. of which are substantially parallel. to an X-axis and inclined at an angle (the actual angle .of the V-cut blanks of Figs. 2,. .3, 6 and 7 is substantially 49) with respect in the optic axis in a direction towardparallelism with av major. (M) apex face of the mother crystal, it will be apparent the invention is, ,not'limited tothe cutting of crystal been described elements, useful for optical purposes, may be obtained from the elongated bar of Fig. 5 by cutting it in planes normal to the optic axis, in-' stead of askew with respect to it, as in the case of the V-cu elements 2| shown in Fig. 6. Such a Z-cutelement is shown at 21, Fig. 6.

Referring to Fig- .8. In applying the invention 7 to the cutting of X-cut and Y-cut blanks, the

bar 20 is'cut-in a direction parallel to the Z-axis so that, in the case of an X-cut blank, its thickness dimension is parallel to an X-axis and, in

the. case of a Y-cut blank, the thickness dimension is parallel to a Y-axis.

lOthehmOdificatiohg of the. invention will suggest themselve v.to :those skilled in the art. It is to be understood therefore thatv the foregoing is to :be interpreted. as illustrativeand not in a limiting sense except as requiredby the prior art and by the spirit of the appended claims.

What is claimed is:

LIMethOd of cutting a quartz crystal element from'natural quartz which comprise cutting directly from a mother crystal a bar whose long dimensions .aresubstantia'lly parallel to the optic axis and then cutting saidelement from said bar.

2. Method of cutting .a .quartz element from natural quartz which comprises cutting directly from a mother crystal 2. bar whose long dimensions are substantially parallel to the opticaxis and then cutting said element from said barin planeswhich are transverse with respect to said optic axis.

3. Method of cutting a quartzpiezoelectric element from natural .quartz which comprises cutting. directly from a mother crystal a .barwhose long dimensions are substantially parallel to the optic axis and then cutting. said piezoelectric element from said bar at a desired angle with re.- spect to said optic axis.

:4. Method of cutting a *V-cut quartz. piezoelectric element from natural. quartz which comprises cutting directly from a mother crystal a bar whose long dimensions are substantially parallel .to the optic axis. and then cutting said elementirom saidbarat an acute angle with respect to said optic axis.

. 5. h/Iethod of cutting a quartz piezoelectric element from natur l quartz which comprises cutting directly from a mother crystal a bar whose vlong dimensions are substantially parallel to the optic axis and whose short dimensions are only slightly greater than is required to produce a finished element of the required dimensions, then cutting a slab from said bar at a desired angle with respect to said optic axis, .and finally reducing the dimensions of said slab to the desired dimensions of said element.

B;'M&l7h0d of cuttingja. Z-cut crystal ,element from natural quartz which comprises cutting directly from a mother crystal a bar whose lon adimensions are substantially parallel to the optic axis and then cutting said element from said bar at arig ht angle with respect to said optic axis.

1 CHARLES JOHNSON...

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