US 3813101 A
A pickup needle having a diamond tip soldered by a hard solder to a shaft. According to the invention the shaft is formed of a material selected from silicon carbide, boron carbide, corundum, quartz and glass having a melting point exceeding 800 DEG C.
Description (OCR text may contain errors)
United States Patent 1191 Benz [ PICKUP NEEDLE  lnventor: Ernst Benz, Altweg 308. 7450 I Andelfingen, Switzerland  Filed: May 1, 1972  Appl. No.: 249,687
 Foreign Application Priority Data June 12. 1971 Switzerland 8605/71  US. CIL'. 274/38 [5 l] Int. Cl. Gllb 3/46  Field of Search 274/38; 29/1695, l69.5 S.
 References Cited UNITED STATES PATENTS l.l l(l.428 9/l9l4 Edison' 274/38 ll/l929 8/l9Sl 11/1953 ll/l960 7/l96l 9/l966 Primary E.raminerLouis R. Prince Assistant Examiner-Charles E. Phillips Attorney. Agent, or Firm-Werner W. Kleeman ABSTRACT A pickup needle having a diamond tip soldered by a hard solder to a shaft. According to the invention the shaft is formed of a material selected from silicon carbide, boron carbide, corundum, quartz and glass having a melting point exceeding 800C.
6 Claims, 2 Drawing Figures BACKGROUND OF THE INVENTION The present invention relates to a new and improved pickup needle having a diamond tip soldered by means of a hard solder to a shaft. I
With most of the pickup needles employed at the present time at least the tip is formed of diamond, since this material offers suffi cient wear resistance in order to be able to ensure satisfactory sound pickup over a longer period of time, and therefore playback at microgrooved-long playing records, especially stereo records.
Belonging to the class of prior art pickup, needles of this type are those where the shaft is formedof metal, for instance, aluminum, steel -or molybdenum. Such type pickup needles have been disclosed, for instance, in the following publications: German patent publication 1,552,160, Swiss patent 377,119, British patent 836,768, Dutch patent application 6l/268,734, Dutch patent, 101,167 and U.S. Pat. Nos. 2,961,750, 2,570,248 and 2,960,759. In these prior art disclosures the diamond tip is flanged-in or soldered. One of the drawbacks of such needles, is theirrelatively great 'weight which is essentially ascribed .tothe shaft. In fact the specific weight of such needles is in the order of magnitude of approximately 7.9 gmslcm tsteel) and l 1.0 gms/cm (molybdenum). Even if the dimensions of the needles are verysmall their weight hasa measurable influence upon theinertia of the sound pickupsystem, which is noticeable during pickup of-high frequencies in the region beginning approximately at l2-kHz.
Needles having a metalshaft possess the further draw back that they are susceptible to corrosion. This drawback is particularly then prevalent when therecord' to be played is wet or contains an anti static coating.
In this regard it should be mentioned thatthe equally known pickup needles embodying a diamond tip bonded upon orto an aluminum shaft are more favorable since they possess a considerably smaller specific weight, in the order of magnitude of 2.7 3.5 gms/cm. The drawback of such type needle resides in the unreliable connection joint between the shaft and the tip which, as a general rule,-does not possess any satisfactory prolonged alternating-stress strength inorder to be even able to approximately approach the longevity of the diamond tip.
Finally, there are also known to the art from German patent publication l,l80, l 56 pickup needles ground of one-piece from diamond. While such possess a low specific weight of 3.4 gms/cm they are however extremely expensive as concerns the raw material and machining.
SUMMARY'QF THE'INVENTION construction of pickup needle of the previously mentioned type which exhibits the advantages of the needles formed completely of diamonds and avoids the drawbacks of needles formed with metal shafts, without requiring as concerns the raw material or fabrication costs a' greater expenditure than with metal shafts.
Yet afurther significant object of the present invention relates to an improved construction of pickup needle having a diamond tip and a shaft formed of a material which imparts increased lightweight characteristics to the needle while improving upon the sound pickup characteristics thereof, especially at high frequencies.
Now in order to implement these and still further obl5 jects 'of the invention, which will become more readily apparent as the description proceeds, the proposed pickup needle of this development is manifested by the features that the shaft is formed of a material selected from silicon carbide, boron carbide, corundum, quartz and glass having a melting point exceeding 800C.
According to a particularly advantageous aspect of this development, there is preferably employed as the shaft material monocrystalline corundum, for instance ruby or sapphire, preferably synthetic colorless sapphire. This material possesses increased hardness and mechanical as well as chemical resistance and is extremely' well suited for subsequent mounting of the needle at the needle support.
Also suitable as the shaft material is glass, having a meltingpoint exceeding 800C., that is, SiO and A1 0 containing glass. Also suitable as the shaft material is quartz, especially monocyrstalline quartz, and silicon carbide, especially monocrystalline silicon carbide.
It hasbee 'n found that the hard soldered connection between the shaft material and the'diamond tip, even with a planar impact surface, possesses a higher mechanicalstrength than the shaft material. This is surprising since previously it was assumed that such was BRIEF DESCRIPTION OF THE DRAWING The invention will be better understood and objects other than those set forth above, will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawing wherein:
FIG. 1 is an exploded view of the components of a pickup needle designed according to the teachings of the present invention prior to final machining; and
FIG. 2 schematically illustrates a finished machined pickup needle produced according to the teachings of this invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Describing now the drawing, in FIG. 1 there is shown a blank 1 of a cylindrical shaft, formed of any of the materials heretofore disclosed, and which is provided at its upper end face with a slight depression or recess 2. Reference numeral 3 designates a layer of a hard solder and reference character 4 a raw or semi-finished diamond grain.
Soldering of the diamond grain 4 to the blank shaft 1 can be performed, for instance, by way of example but not exclusively, according to the techniques described in U.S. Pat. No. 2,570,248, so that no further discussion thereof would appear to be necessary. As a general rule, the blank shaft 1 possesses a diameter which is in the order of 0.6 and 1.0 mm. and in its raw or blank state its length, similar to the known pickup needles formed completely of sapphire, is in the order of 0.8 and 1.6 mm. However, in this respect it is to be mentioned that the selection of such dimensions depends to a large degree upon the machining means used for grinding the tip.
The finished machine tip has been illustrated in FIG. 2. it will be recognized that the blank shaft 1 of FIG. 1 is slightly conically pointed at its end carrying the diamond grain 4 and therefore has now become the needle shaft 1'. Similarly, the hard solder layer is apparent and has been designated by reference character 3' whereas the diamond grain 4 has been essentially ground into a cone 4' having a rounded tip 5 and further possesses a highly polished outer surface at least at the region of tip 5. The degree of finishing or machining of the pickup needle depicted in FIG. 2 corresponds to the needles employed in commercially available pickups, that is to say, possess a diameter in the order of magnitude between 0.4 and 0.8 mm., a length in the order of magnitude of 0.8 to 1.2 mm., a cone angle of the tip in the order of magnitude of 40 to 60, a radius of curvature of the tip in the order of magnitude of 0.012 to 0.025 mm (for long playing records).
it should be understood that for the described needle there can be also ground a so-called bi-radial tip, that is, a tip the cone of which at least at the region of the rounded portion of the tip possesses an elliptical outline so that the rounded portion of the tip in two axial cutting planes perpendicular to one another possesses a respective minimum value of for instance 0.012 mm. and a maximum value of for instance 0.025 mm.
It has been found that with the described pickup needle it is possible, without any greater expenditure, to reduce the needle weight from about 0.5 mg. (for known needles having a shaft formed of steel of molybdenum) to approximately 0.15 mg.
Such values could be only previously realized with noncomparable expensive needles formed completely of diamond or having a shaft formed of aluminum, which however owing to the lower prolonged alternating-stress strength and the difficulties arising during mounting at the pickup are not satisfactory.
Additionally, the described pickup needle is just as nonsensitive to corrosion effects of all types, such as those caused by humidity, smoke, human perspiration, anti-static agents, and so forth, as pure diamond needies, yet in contrast to such is a number of times cheaper. When forming the shaft from a material as proposed by this development for such diamond tip needle,' the pickup needle advantageously possesses a lower specific weight, which preferably amounts to about 4.00 gm/cm or less, depending upon the specific material selected for the shaft.
While there is shown and described present preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims. Accordingly,
What is claimed is:
1. A pickup needle comprising a non-metallic shaft, a diamond tip, and a hard solder layer therebetween bonding the diamond tip to such nonmetallic shaft, said non-metallic shaft being formed of a material selectedfrom the group consisting of silicon carbide, boron carbide, corundum, and quartz.
2. The pickup needle as defined in claim 1, wherein the shaft is formed of monocrystalline corundum.
3. The pickup needle as defined in claim 2, wherein the shaft is formed of synthetic colorless sapphire.
4. The pickup needle as defined in claim 1, wherein the shaft is formed of monocrystalline quartz.
5. The pickup needle as defined in claim 1, wherein the shaftis formed of monocrystalline silicon carbide.
does not exceed about 4.00 gms/cm.