JP2004098181A

JP2004098181A - Manufacturing method of electro-deposited grinding wheel

Info

Publication number: JP2004098181A
Application number: JP2002259753A
Authority: JP
Inventors: Tsukasa Horiuchi; 堀内　宰; Hideo Shibuya; 渋谷　秀雄
Original assignee: Japan Science and Technology Corp
Current assignee: Japan Science and Technology Agency
Priority date: 2002-09-05
Filing date: 2002-09-05
Publication date: 2004-04-02

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of an electro-deposited grinding wheel by a shape inverting method. <P>SOLUTION: A die having inner diameter equal to the outer shape of a grinding wheel is prepared, its inner surface is plated with copper, the copper plating is cut by diamond, abrasive grains are arranged on a surface of the copper plating in a contact state, copper plating is performed in this state to adhere the abrasive grains to the inner surface of the die, nickel plating is performed, a grinding wheel base metal is inserted into the inside thereof, low-melting-point metal or the like is filled between the nickel plating layer and the grinding wheel base metal to be integrated, and then the die and the copper plating layer are removed. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、形状反転法による高精密な電着砥石の製作方法に関するものである。
【０００２】
【従来の技術】
最近の生産技術に対する高精度高能率化の要求はますます激しくなってきている。現在、鉄鋼材料部品の研削加工では、切れ味がよく摩耗が少ないｃＢＮホイ−ルを使用することが増えている。しかし、ｃＢＮ砥粒が高価であるため、砥粒層が１層だけの電着ホイ−ルが使われることも多い。
また、通常の電着ｃＢＮホイ−ルの製作方法では、ホイ−ルベ−スとなる砥石台金を陰極とし、ニッケルメッキ浴に浸けて砥粒の電着を行っている。このとき、メッキ層が砥粒と砥石台金とを接合し砥粒を保持する。この製作方法では、砥粒突き出し量がバラツキ、作業面の砥粒高さがそろわないので形状精度が悪くなる。このため、この電着ホイールでは高い加工精度を得ることができないという問題点を抱えており、そのため、ツル−イングを行うことで形状精度を高めている。しかしこの方法では砥粒の最も尖った部分を落としてしまうので、砥石切れ味が低下することになる。
【０００３】
そこで本発明者らは、上記のような従来技術のもつ問題点を解決するために形状反転法を利用した電着ホイール（以下砥石という）の製作方法を提案してきた。
この形状反転法を図６を参照して説明する。電着ｃＢＮ砥石の製作方法は、図６に示すようにアルミニウムによって形成された金型２１を使用し、この金型２１の内面にエポキシ樹脂で砥粒径の１／３程度の薄い接着層２２で砥粒２３を接着し、その砥粒２３の残り２／３の部分をニッケルメッキ２４で保持し、その内側に砥石台金２６を挿入し、前記ニッケルメッキ２４と砥石台金２６との間に低融点金属結合剤２５等を充填して、メッキ面２４と砥石台金２６を結合する。そして、最後に金型と接着層を除去すれば金型の内径の大きさに砥粒の高さをそろえることができ、さらに砥粒突き出し量は、接着層の厚さの分とすることができる。この形状反転法によれば、砥石の外形は形状精度が良く、砥粒の突き出し量の均一な作業面を有する電着ｃＢＮ砥石とすることができる。
【０００４】
【発明が解決しようとする課題】
ところで、前記形状反転法で用いた金型の材料はアルミニウムである。その理由は、金型内面が、より精密に仕上げられなければならないので、軟質金属を材料に用い、ダイヤモンドバイトで仕上げる必要があるためである。しかしながら、アルミニウムの金型では、砥粒の突き出し量を均一にするということはできたものの、製作過程における熱の影響を受けた際に、金型、ニッケルメッキ層、および砥石台金の線膨張係数の違い（表１）により、金型の形状が変化してしまうという問題が発生した。即ち、形状反転法は金型の内面形状がそのままホイ−ルの形状となるので、前述のように金型の形状が歪んだ金型となると、ホイ−ル自体の形状が歪んでしまい真円とならず、形状精度が悪くなるという問題がある。
【０００５】
【表１】

【０００６】
本発明では、線膨張係数の違いに注目し、金型、ニッケルメッキ層および砥石台金の線膨張係数が近い値となる材料でホイ−ルを製作する新たな形状反転法を提供することにより、前記従来の問題点を解決し、形状精度の良い電着ｃＢＮホイ−ル（高精密電着砥石）を製作することを目的とする。
本発明では、砥石外形を内径とする炭素鋼製の金型（Ｓ４５Ｃ）を用意しその内面に砥粒を接した状態で配置しその状態で銅メッキし、砥粒を金型内面に固着させる。このときの銅メッキの厚さを砥粒径の約１／３とする。その後ニッケルメッキを２から３ｍｍ厚さまで行う。その内側にステンレス製の砥石台金を挿入し
、ニッケルメッキ層と砥石台金との間に低融点金属等を充填して一体化する。この製作法により高精度で安価な電着砥石を実現できる。
【０００７】
【課題を解決するための手段】
このため本発明が採用した技術開発手段は、
砥石外形を内径とする金型を用意しその内面に砥粒を接した状態で配置し、さらにその状態でメッキして砥粒を金型内面に固着させ、ついでニッケルメッキを行い、その内側に砥石台金を挿入し、ニッケルメッキと砥石台金との間に低融点金属等を充填して一体化し、その後金型および金型内面のメッキ層を除去することを特徴とする電着砥石の製作方法である。
また、砥石外形を内径とする金型を用意しその内面に銅メッキを施し、さらにその銅メッキをダイヤモンド切削したのち、その銅メッキの表面に砥粒を接した状態で配置し、さらにその状態で銅メッキして砥粒を金型内面に固着させ、ついでニッケルメッキを行い、その内側に砥石台金を挿入し、ニッケルメッキと砥石台金との間に低融点金属等を充填して一体化し、その後金型および銅メッキ層を除去することを特徴とする電着砥石の製作方法である。
また、前記銅メッキの厚さは砥粒径の約１／３であることを特徴とする電着砥石の製作方法である。
また、前記ニッケルメッキを２〜３ｍｍ程度の厚さで行うことを特徴とする電着
砥石の製作方法である。
また、前記砥石台金には非磁性のステンレスを使用したことを特徴とする電着砥石の製作方法である。
【０００８】
【実施の形態】
以下、本発明の実施形態を説明すると、図１は本実施形態の砥石の断面図である。
図中、１は炭素鋼製の金型（Ｓ４５Ｃ）、２は銅メッキ層、３は砥粒、４はニッケルメッキ層、５は結合剤、６はステンレス製のホイ−ル砥石台金（ＳＵＳ３０４）である。
本例では炭素鋼製の金型１を用いるので、内面の精密切削にダイヤモンドバイトでは工具寿命が著しく低下することとなる。そこで金型１の内面に線膨張係数でニッケルやＳ４５Ｃと近い値の銅メッキを施し、銅メッキ層部分をダイヤモンドバイトで精密に切削する。さらにその切削面に砥粒を配置して銅メッキで砥粒の突き出し量となる砥粒径の１／３の厚さを覆うメッキ層を形成し砥粒を固定する。そしてニッケルメッキ４で残りの２／３を保持する。ニッケルメッキ層と砥石台金を低融点金属で保持し、最後に金型１と銅メッキ層２を除去することで電着ホイ−ルが完成する。また、ステンレスを砥石台金の材料に用いた理由は、これまで砥石台金の材料にＳ４５Ｃを使用していたところ、研削実験を行う平面研削盤の電磁チャックに吸引され、研削力に影響が見られたからである。そこで今回は、非磁性のステンレス（ＳＵＳ３０４）を砥石台金の材料とした。
【０００９】
以下に本発明に係る電着砥石の製造工程を説明する。
〔メッキ工程〕
１．銅メッキ
ｉ）金型のマスキング
ｉｉ）金型を脱脂、脱錆、活性化のメッキ前処理を行う。
ｉｉｉ）銅メッキの下地として、ニッケルメッキを数分程度行う。
ｉｖ）金型内面を銅メッキする。銅メッキ浴の温度は２０°Ｃ前後の常温で行う。このとき加える電流を電流密度が１．５Ａ／ｄｍ^２となるようにすると、１時間当たり約２０μｍの厚さのメッキを行うことができる。
２．ニッケルメッキ
ニッケルメッキ浴は４０°Ｃ〜６０°Ｃと少し高めの温度とする。ニッケルメッキ浴に浸け、電流密度が１Ａ／ｄｍ^２となるようにすると、１時間当たり約１０μｍの厚さのメッキができる。
【００１０】
〔電着ホイ−ルの製作手順〕
▲１▼リング型の金型（Ｓ４５Ｃ）の内面へ、厚付け銅メッキ（約２００μｍ）を施す。
▲２▼金型をエアスピンドルに取り付け、内面をダイヤモンドバイトにより精密切削をする。
▲３▼金型の内面に砥粒を敷きつめて、もう一度銅メッキ（砥粒の大きさの約１／３の厚さ）を施し、砥粒を固定する。このときのメッキ厚さが金型と接着層を除去したときにホイ−ルの砥粒突き出し量となる。
▲４▼金型内面の銅メッキをされていない砥粒の部分をニッケルメッキで保持する。このニッケルメッキ層が砥粒保持部となる。
▲５▼ニッケルメッキ層と砥石台金を低融点金属で結合する。
▲６▼最後に金型を旋盤で削り、残りの銅メッキ部分をＷＡ砥石スティックでドレッシングすることにより除去する。銅メッキ部分が除去されるとホイ−ルの完成となる（図３）。
【００１１】
つづいて、上記製作方法による電着砥石の形状測定結果および研削実験結果を示す。
完成した電着ホイ−ルの形状を触針式表面粗さ計で測定した。
電着砥石の周方向形状については図２、幅方向形状については図３に示す。図２、図３から明らかなように砥粒の保持されている部分では均一な高さが得られ、本発明に係る電着砥石の形状が従来に比較して精度がよくなっていることが判る。
また、ワークの表面粗さについては周方向について図４、幅方向について図５に示す。これらの図から、研削仕上げ面の表面粗さは形状反転法を用いない通常の電着ホイ−ルのものよりも格段に向上させることが判る。
【００１２】
以上、本発明に係る形状反転法による電着砥石では、金型内面に厚付け銅メッキ（約２００μｍ）を施すが、必ずしも銅メッキに限定することなく、同様の機能を達成できるメッキであれば、他のメッキを使用することができ、また銅メッキの厚さも適宜選択できる。
さらに、本発明はその精神または主要な特徴から逸脱することなく、他のいかなる形でも実施できる。そのため、前述の実施形態はあらゆる点で単なる例示にすぎず限定的に解釈してはならない。
【００１３】
【発明の効果】
以上説明したように本発明によれば、
砥石外形を内径とする金型を用意しその内面に砥粒を接した状態で配置しその状態で銅メッキし、その後ニッケルメッキを行い、さらにその内側に砥石台金を挿入し、ニッケルメッキ層と砥石台金との間に低融点金属等を充填して一体化することで電着砥石を製造するため、高精度で安価な電着砥石（高精密電着砥石）を実現できる。また、金型内面に砥粒を敷き詰め、銅メッキすることにより、砥粒を固定することができ、さらに砥粒の突出し量が均一となり、砥粒先端の高さのバラツキを小さくできる。その結果、研削仕上げ面粗さも通常の電着砥石より格段に向上させることができた、等の優れた効果を奏することができる。
【図面の簡単な説明】
【図１】本実施形態の電着砥石の断面図である。
【図２】従来例および本実施形態の電着砥石の周方向の形状を示す図である。
【図３】従来例および本実施形態の電着砥石の幅方向の形状を示す図である。
【図４】ワークの幅方向の表面粗さを示す図である。
【図５】ワークの研削方向の表面粗さを示す図である。
【図６】従来の電着砥石の断面図である。
【符号の説明】
１　　　　　　金型
２　　　　　　銅メッキ層
３　　　　　　砥粒
４　　　　　　ニッケルメッキ層
５　　　　　　結合剤
６　　　　　　砥石台金[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a highly precise electrodeposited grinding wheel by a shape inversion method.
[0002]
[Prior art]
Demands for high precision and high efficiency in recent production technologies are becoming more and more intense. At present, cBN wheels with sharpness and low wear are increasingly used for grinding steel material parts. However, since cBN abrasive grains are expensive, an electrodeposition wheel having only one abrasive grain layer is often used.
In a conventional method of manufacturing an electrodeposited cBN wheel, a wheel base is used as a cathode, and the electrode is immersed in a nickel plating bath to electrodeposit abrasive grains. At this time, the plating layer joins the abrasive grains and the grindstone base and holds the abrasive grains. In this manufacturing method, the protrusion amount of the abrasive grains varies, and the height of the abrasive grains on the work surface is not uniform, so that the shape accuracy is deteriorated. For this reason, there is a problem that high working accuracy cannot be obtained with this electrodeposited wheel, and therefore, shape accuracy is enhanced by performing tooling. However, in this method, the sharpest part of the abrasive grains is dropped, so that the sharpness of the grinding stone is reduced.
[0003]
Therefore, the present inventors have proposed a method of manufacturing an electrodeposited wheel (hereinafter, referred to as a grindstone) using a shape inversion method in order to solve the above-described problems of the related art.
This shape inversion method will be described with reference to FIG. As shown in FIG. 6, a method for manufacturing an electrodeposited cBN grindstone uses a mold 21 made of aluminum, and a thin adhesive layer 22 of about 1/3 of the abrasive grain size is formed on the inner surface of the mold 21 with epoxy resin. The remaining two-thirds of the abrasive grains 23 are held by nickel plating 24, and a grindstone base metal 26 is inserted inside the nickel grains 24, and between the nickel plating 24 and the grindstone base metal 26 Is filled with a low melting point metal binder 25 and the like, and the plating surface 24 and the grindstone base metal 26 are bonded. Finally, if the mold and the adhesive layer are removed, the height of the abrasive grains can be adjusted to the size of the inner diameter of the mold, and the amount of abrasive grains projected can be set to the thickness of the adhesive layer. it can. According to this shape inversion method, the outer shape of the grindstone can be an electrodeposited cBN grindstone having a good shape accuracy and a work surface with a uniform protrusion amount of abrasive grains.
[0004]
[Problems to be solved by the invention]
The material of the mold used in the shape inversion method is aluminum. The reason for this is that since the inner surface of the mold must be finished more precisely, it is necessary to use a soft metal as the material and finish it with a diamond bite. However, in the aluminum mold, although the protrusion amount of the abrasive grains could be made uniform, the linear expansion of the mold, the nickel plating layer, and the wheel base metal when affected by heat during the manufacturing process. Due to the difference in the coefficients (Table 1), there was a problem that the shape of the mold changed. That is, in the shape inversion method, since the inner surface shape of the mold becomes the shape of the wheel as it is, when the shape of the mold is distorted as described above, the shape of the wheel itself is distorted, and the shape of the wheel itself becomes a perfect circle. However, there is a problem that the shape accuracy is deteriorated.
[0005]
[Table 1]

[0006]
In the present invention, attention is paid to the difference in the coefficient of linear expansion, and by providing a new shape reversal method for manufacturing a wheel with a material in which the linear expansion coefficients of the mold, the nickel plating layer, and the wheel base are close to each other. It is an object of the present invention to solve the above-mentioned conventional problems and to manufacture an electrodeposited cBN wheel (high-precision electrodeposited grinding wheel) having good shape accuracy.
In the present invention, a carbon steel mold (S45C) having an outer diameter of a grindstone is prepared, abrasive grains are arranged in contact with the inner surface thereof, and copper plating is performed in this state to fix the abrasive grains to the inner surface of the mold. . At this time, the thickness of the copper plating is set to about 1/3 of the abrasive grain size. Thereafter, nickel plating is performed to a thickness of 2 to 3 mm. A grindstone made of stainless steel is inserted into the inside thereof, and a low melting point metal or the like is filled between the nickel plating layer and the grindstone to be integrated. With this manufacturing method, a highly accurate and inexpensive electrodeposition whetstone can be realized.
[0007]
[Means for Solving the Problems]
For this reason, the technical development means adopted by the present invention are:
Prepare a mold with the whetstone outer diameter as the inner diameter, arrange it with the abrasive particles in contact with its inner surface, further plating in that state to fix the abrasive particles to the inner surface of the mold, then perform nickel plating, and then inside The electrodeposition whetstone is characterized by inserting a grindstone base, filling low-melting point metal and the like between nickel plating and the grindstone base and integrating them, and then removing the mold and the plating layer on the inner surface of the mold. It is a production method.
Also, prepare a mold with the outer diameter of the whetstone, apply copper plating to the inner surface, cut the copper plating with diamond, and then place the abrasive in contact with the surface of the copper plating, and then place it in that state Abrasive grains are fixed to the inner surface of the mold by copper plating, then nickel plating is performed, and a grindstone base metal is inserted inside, and a low melting metal is filled between the nickel plating and the grindstone base metal and integrated. And then removing the mold and the copper plating layer.
Further, in the method of manufacturing an electrodeposited whetstone, the thickness of the copper plating is about 1/3 of the abrasive particle diameter.
Further, there is provided a method for manufacturing an electrodeposited whetstone, wherein the nickel plating is performed with a thickness of about 2 to 3 mm.
Further, there is provided a method of manufacturing an electrodeposited whetstone, wherein non-magnetic stainless steel is used for the whetstone base.
[0008]
Embodiment
Hereinafter, an embodiment of the present invention will be described. FIG. 1 is a sectional view of a grindstone of the present embodiment.
In the figure, 1 is a carbon steel mold (S45C), 2 is a copper plating layer, 3 is an abrasive grain, 4 is a nickel plating layer, 5 is a binder, and 6 is a stainless steel wheel grindstone (SUS304). ).
In this example, since the carbon steel mold 1 is used, the tool life is remarkably reduced by using a diamond tool for precision cutting of the inner surface. Therefore, the inner surface of the mold 1 is plated with copper having a linear expansion coefficient close to that of nickel or S45C, and the copper plating layer is precisely cut with a diamond bite. Further, abrasive grains are arranged on the cut surface, and a plating layer is formed by copper plating so as to cover a thickness of 砥 of the abrasive grain diameter, which is the amount of the abrasive grains, and the abrasive grains are fixed. Then, the remaining 2/3 is held by nickel plating 4. The electrodeposition wheel is completed by holding the nickel plating layer and the grindstone base metal with a low melting point metal, and finally removing the mold 1 and the copper plating layer 2. Also, the reason why stainless steel was used as the material of the wheel base metal was that S45C was used as the material of the wheel base metal before, but it was attracted to the electromagnetic chuck of the surface grinder performing the grinding experiment, and the grinding force was affected. Because it was seen. Therefore, this time, non-magnetic stainless steel (SUS304) was used as the material for the grindstone.
[0009]
Hereinafter, the manufacturing process of the electrodeposition grindstone according to the present invention will be described.
[Plating process]
1. Copper plating i) Masking of the mold ii) Pre-plating treatment of degreasing, rusting and activation of the mold.
iii) Nickel plating is performed for several minutes as a base for copper plating.
iv) The inner surface of the mold is plated with copper. The temperature of the copper plating bath is set at a normal temperature of about 20 ° C. If the current applied at this time is set so that the current density becomes 1.5 A / dm ² , it is possible to perform plating with a thickness of about 20 μm per hour.
2. Nickel plating The temperature of the nickel plating bath is set at a slightly higher temperature of 40 ° C to 60 ° C. When immersed in a nickel plating bath so that the current density becomes 1 A / dm ² , plating with a thickness of about 10 μm per hour can be performed.
[0010]
[Production procedure of electrodeposition wheel]
{Circle around (1)} Thick copper plating (about 200 μm) is applied to the inner surface of the ring mold (S45C).
(2) Attach the mold to the air spindle and precision cut the inner surface with a diamond bite.
{Circle around (3)} The abrasive grains are spread on the inner surface of the mold, and copper plating (about 1/3 of the size of the abrasive grains) is applied again to fix the abrasive grains. The plating thickness at this time becomes the amount of protrusion of the abrasive grains of the wheel when the mold and the adhesive layer are removed.
{Circle over (4)} A portion of the inner surface of the mold that is not plated with copper is held by nickel plating. This nickel plating layer becomes an abrasive grain holding unit.
{Circle around (5)} The nickel plating layer and the grindstone base are combined with a low melting point metal.
{Circle around (6)} Finally, the mold is shaved with a lathe, and the remaining copper-plated portion is removed by dressing with a WA grinding stone stick. When the copper plating is removed, the wheel is completed (FIG. 3).
[0011]
Next, the results of measuring the shape of the electrodeposited whetstone and the results of the grinding experiment by the above-described manufacturing method are shown.
The shape of the completed electrodeposition wheel was measured with a stylus type surface roughness meter.
FIG. 2 shows the circumferential shape of the electrodeposition grindstone, and FIG. 3 shows the widthwise shape. As is clear from FIGS. 2 and 3, a uniform height is obtained in the portion where the abrasive grains are held, and the shape of the electrodeposition whetstone according to the present invention is improved in accuracy compared to the conventional one. I understand.
The surface roughness of the workpiece is shown in FIG. 4 in the circumferential direction and in FIG. 5 in the width direction. From these figures, it can be seen that the surface roughness of the ground surface is remarkably improved as compared with that of a normal electrodeposition wheel not using the shape inversion method.
[0012]
As described above, in the electrodeposition whetstone by the shape inversion method according to the present invention, thick copper plating (about 200 μm) is applied to the inner surface of the mold, but the plating is not necessarily limited to copper plating, and any plating capable of achieving the same function can be used. Other platings can be used, and the thickness of the copper plating can be appropriately selected.
Furthermore, the present invention may be embodied in any other form without departing from its spirit or essential characteristics. Therefore, the above-described embodiment is merely an example in all aspects and should not be interpreted in a limited manner.
[0013]
【The invention's effect】
According to the present invention as described above,
Prepare a mold with the outer diameter of the grindstone, arrange it in a state where the abrasive grains are in contact with the inner surface, perform copper plating in that state, then perform nickel plating, insert the grindstone base metal further inside, and place a nickel plating layer The electrodeposition grindstone is manufactured by filling and integrating a low-melting point metal or the like between the metal and the grindstone base, so that a highly accurate and inexpensive electrodeposition grindstone (high precision electrodeposition grindstone) can be realized. Further, the abrasive grains can be fixed by spreading the abrasive grains on the inner surface of the mold and copper plating, and the protrusion amount of the abrasive grains can be made uniform, and the variation in the height of the tips of the abrasive grains can be reduced. As a result, it is possible to obtain excellent effects such as that the finished surface roughness of the grinding can be remarkably improved as compared with the ordinary electrodeposited whetstone.
[Brief description of the drawings]
FIG. 1 is a sectional view of an electrodeposition grindstone of the present embodiment.
FIG. 2 is a diagram showing a circumferential shape of an electrodeposition grindstone of a conventional example and the present embodiment.
FIG. 3 is a diagram showing shapes in a width direction of an electrodeposition grindstone of a conventional example and the present embodiment.
FIG. 4 is a diagram showing a surface roughness in a width direction of a work.
FIG. 5 is a diagram showing a surface roughness of a workpiece in a grinding direction.
FIG. 6 is a cross-sectional view of a conventional electrodeposition grindstone.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Mold 2 Copper plating layer 3 Abrasive grains 4 Nickel plating layer 5 Binder 6 Grinding wheel base

Claims

Prepare a mold with the outer diameter of the grindstone, arrange it with the abrasive particles in contact with the inner surface, further plating the inner surface of the mold in that state, fix the abrasive particles on the inner surface of the mold, and then perform nickel plating Inserting a grindstone into the inside, filling low-melting point metal and the like between the nickel plating and the grindstone and integrating them, and then removing the plating layer on the mold and the mold inner surface. How to make an electrodeposited whetstone.

Prepare a mold with the inner diameter of the whetstone outer diameter, apply copper plating on the inner surface, further cut the diamond by diamond, then place it with the abrasive particles in contact with the surface of the copper plating, and further Plating to fix the abrasive grains to the inner surface of the mold, then perform nickel plating, insert a grindstone base into the inside, fill the low melting point metal etc. between the nickel plating and the grindstone base and integrate them. And thereafter removing the mold and the copper plating layer.

3. The method according to claim 2, wherein the thickness of the copper plating is about 1/3 of the abrasive grain size.

The method according to any one of claims 1 to 3, wherein the nickel plating is performed to a thickness of about 2 to 3 mm.

The method according to any one of claims 1 to 4, wherein a non-magnetic stainless steel is used for the grindstone base.