201244856 六、發明說明： 【發明所屬之技術領域】 本發明，係與直徑爲3.175mm(l/8英吋） 直徑鑽頭相關。 【先前技術】 傳統之小直徑鑽頭，例如，有如專利文獻1 亦即，專利文獻1之發明，具備相對於工具旋轉 對稱配置的二條溝，係於前端具備切刃及刀口之 3.175mm以下之小直徑鑽頭，相對於工具旋轉軸 稱形成削磨部。 專利文獻1:日本特開平7-164228號公報 【發明內容】 專利文獻1之小直徑鑽頭，尤其是，在安裝 及各種電子零件之印刷電路板鑽孔時，的目的係 孔之位置精度（以下，稱爲孔位置精度）。然而 獻1之小直徑鑽頭的削磨部加工所形成的切刃， 爲負角度，切削效能不足容易導致被削材出現較 衝擊。所以，專利文獻1之小直徑鑽頭，孔位置 善並不充份。此外，專利文獻1之小直徑鑽頭， 力集中於以削磨部之加工所形成的切刃，有容易 磨部周邊發生破損、或較大切削力導致折損之問 ，專利文獻1之小直徑鑽頭，隨著摩耗的增加， 以下之小 所示者。 軸線爲線 直徑爲0 線以線對 積體電路 提高加工 ，專利文 因爲傾角 大之結塊 精度之改 因爲切削 出現從削 題。而且 削磨部變 -5- 201244856 淺並導致面積縮小，失去了利用削磨部來改善孔位置精度 的效果。並且，由削磨部之加工所形成的切刃部分，因爲 很快就變磨圓，孔位置精度的改善效果很快就會減弱。 例如，使用於印刷電路板孔之鑽孔的小直徑鑽頭，在 工具壽命結束時，再硏磨前端並再使用數次是一般的做法 。然而，專利文獻1所示之削磨部形狀，難以再硏磨時來 再形成，再硏磨之前後，小直徑鑽頭的切刃形狀完全不同 。所以，有再硏磨前後之切削性能完全改變的問題。 本發明係提供一種，可提高孔位置精度，抑制摩耗進 行所導致之削磨部的面積縮小，不易破損及折損，容易再 硏磨，可維持一定之再硏磨後的切削性能，直徑爲 3 . 1 7 5 mm以下之小直徑鑽頭。 本發明之小直徑鑽頭，具備從前端面（3)朝向後端 側配設之至少一條溝（2 )、以及形成於該前端面（3 )之 切刃（4)及刀口（5)，且具有3.175mm以下之直徑（d )的小直徑鑽頭，其特徵爲，具有從前述前端面（3)朝 後端側延伸而於前述小直徑鑽頭之至少前端區域之刀葉厚 度變薄的方式所形成之凹部（6)，前述切刃（4)，含有 :形成於前述至少一條溝（2)所形成具有正傾角之刃面 與前述前端面（3)之交叉部的第1切刃部（4a);及形 成於前述凹部（6)所形成具有正傾角之刃面與前述前端 面（3)的交叉部之至少一部分的第2切刃部（4b)，前 述第2切刃部（4b) ’連接於前述第1切刃部（4a)，而 且，與前述刀口（5)交叉。 -6- 201244856 本發明之小直徑鑽頭，因爲對形成著第2切 部的刃面，賦予與第1切刃部之刃面的傾角相同 ，小直徑鑽頭之切削效能大幅提升。而且，降低 直徑鑽頭之切削阻抗（旋轉阻抗及旋轉軸方向推 ，而提高孔位置精度。並且，此處所指之孔位置 升，當然包含孔入口之位置精度（機械指令位置 孔位置的偏離）的提升，也包含孔彎曲的改善及 位置精度的提升在內。 此外’本發明之凹部，從小直徑鑽頭之前端 延伸，即使前端面之摩耗持續，從前端側觀察時 形狀也沒有變化，第2切刃部不易變圓。減緩孔 的劣化速度，大幅延長工具壽命。 而且，本發明之凹部，即使在切刃進行至少 磨時’也具有維持第2切刃之形狀的長度。所以 硏磨前端面’即可再生與新品相同之切刃形狀。 發明之小直徑鑽頭，在再硏磨之前後，切削性能 【實施方式] 一邊參照圖式，一邊針對本發明之實施方式 〇 第1圖係第1實施方式之小直徑鑽頭的右側 。第2圖係第丨圖之小直徑鑽頭的右側面圖。第 :圖之小直徑鑽頭的正面放大圖。第4圖係第 刃部之凹 之正傾角 施加於小 力阻抗） 精度的提 與加工之 孔出口之 朝後端側 之凹部的 位置精度 一次再硏 ，只要再 所以，本 沒有變化 進行說明 面放大圖 3圖係第 1圖之小直 201244856 徑鑽頭的IV-ΐν線方向剖面圖。第5圖係第1圖之小直徑 鑽頭的正面放大說明圖。第6圖係第2實施方式之小直徑 鑽頭的右側面放大圖。第7圖係第6圖之小直徑鑽頭的左 側面放大圖。第8圖係第3實施方式之小直徑鑽頭的正面 放大圖。第9圖至第11圖係小直徑鑽頭的實驗結果。 如第1圖至第4圖所示，在第1實施方式之小直徑鑽 頭1，形成有右旋之二條溝2。本實施方式時，二條溝2 係相對於工具旋轉軸線0爲線對稱配置。 前端面3，具有側腹面的機能，在該2個側腹面的交 叉部，形成刀口 5,在前端面3與形成於溝2之具有未圖 示之正傾角的刃面之直線狀交叉部，形成有第1切刃4a。 而且，刀口 5，在前端面3之中心附近，產生如前端切刃 之作用。 於二條溝2，形成有削磨部6。而且，「削磨部」係 指爲了在由二條溝2之溝底所形成之刀葉9(參照第4圖 )之前端形成切刃（第2切刃4b)而進行追加機械加工之 區域。削磨部6，從前端面3朝後端側延伸，係由以薄於 小直徑鑽頭1之至少前端區域之刀葉9厚度的方式所形成 之凹部來構成，以沿著削磨部6之旋轉軸線Ο的長度小於 溝2長度的長度來形成。 在削磨部6，形成具有未圖示之正傾角的削磨面，在 朝向該削磨面與前端面3之旋轉方向彎曲成凹狀之交叉部 的一部分，形成有第2切刃4 b。該第2切刃4b，連接於 第1切刃4a，而且，與刀口 5交叉。「與刀口 5交叉」， -8- 201244856 如本實施方式所示，除了第2切刃4b與刀口 5交叉時以 外，尙包含刀口 5之端點與削磨部6之削磨面及前端面3 之交點線的其中一方端點一致時，亦即，與第2切刃4b 之其中一端點一致時。 本實施方式時，削磨部6，係將前端面3部分相對於 小直徑鑽頭1之旋轉軸線Ο削除成線對稱形狀之方式來形 成。所以，削磨部6之加工所形成的第2切刃部4 b，係以 線對稱配置方式來形成。線對稱配置的話，容易取得旋轉 均衡，而且，也容易取得切削力均衡。削磨部6之形成範 圍，並無特別限制，然而，可以在考慮再硏磨之預定次數 及小直徑鑽頭1必要剛性等數個要素來設定* 小直徑鑽頭1之後端7側，形成有圓筒狀之柄部8。 本實施方式時，對應由小直徑鑽頭1所加工之孔徑的工具 徑（直徑）φ Dmm，約爲少0.250mm。柄部7之柄部徑， 約爲φ 3.175mm。削磨部6之長度，從小直徑鑽頭1之前 端面3朝後端7側沿著旋轉軸線Ο方向測定的話，約爲 0.8 mm。一般而言，約0.8 mm之長度的話，可以對應5次 程度之再硏磨^削磨部6之長度以0.5mm以上、以1.5mm 以下之範圍爲佳。例如，工具徑pDmm爲φ0.150mm時， 以約0.6mm爲佳。工具徑pDmm爲p 2.000mm以上時， 以約1.5 mm爲佳。而且，削磨部6之長度，一般而言，係 至削磨部6消失爲止之長度，然而，此處，係削磨部6之 形狀保持大致一定的長度。 溝2的溝長，可以對應工具徑p Dmm來適度決定。本 5 -9- 201244856 實施方式時，溝2的溝長，從小直徑鑽頭1之前端3側朝 後端7側方向測定的話，約爲3 .5mm。削磨部6之長度， 以溝長之一半以下爲佳。本實施方式時，約爲23%。 扭轉角，並無特別限制。印刷電路板用之小直徑鑽頭 時，本發明之小直徑鑽頭1之扭轉角以30°以上、60°以下 爲佳，最好爲40°以上、50°以下》本實施方式時，扭轉角 約爲45° (未圖示）。 而且，一般而言，工具徑pDmm爲1.500mm以上之 小直徑鑽頭時，剛性夠高，幾乎不會發生孔位置精度的問 題。本發明，對於工具徑pDmm爲φ 1.500mm以下之小直 徑鑽頭1時，孔位置精度的提升效果特別高。尤其是，工 具徑pDmm爲<p0.500mm以下時，孔位置精度的提升效果 特別高。例如，因爲於工具徑Dmm約φ 0.100mm之非常 細的小直徑鑽頭1，也可形成長度約0.6mm之削磨部6， 確認到孔位置精度的提升效果。 從前端面3側觀察到之削磨部6的形狀，利用第5圖 之正面圖來進行說明。各削磨部6之刃面與前端面（3) 所形成2之交點線之間的距離Amm，相當於小直徑鑽頭1 前端3的心厚，亦即，相當於前端面3之刀葉9的厚度。 如本實施方式之2片刃時，如第5圖所示，與2個削磨部 6與前端面3之2條交點線相切的圓當中，最小直徑之圓 的直徑Amm爲2個削磨部6之間的距離Amm。該距離 Amm愈短則切刃4愈接近旋轉軸線0，故可提供切削效能 良好之小直徑鑽頭1。 -10- 201244856 然而，一般而言，於小直徑鑽頭設置削磨面等之凹部 的話，可能有前端部分強度不足而發生破損或折損等之問 題。而且，因爲也有再硏磨之問題，小直徑鑽頭一般不實 施削磨面等。亦即，在不發生破損或折損等問題的情形， 提升孔位置精度之削磨面形狀，事實上應該難以實現》 本發明，爲了兼顧上述相反之2個課題（切削效能提 升及防止破損），苜先，著眼於距離Amm，了解其影響及 可適用範圍。 後述實驗之結果，得到以下之可適用範圍。以小直徑 鑽頭1之工具徑P Dmm作爲基準（100% )的話，2個削磨 部6之間的距離Amm，比率A/D以1 5%以上、35%以下之 範圍爲佳。該比率A/D未達15%時，前端部分強度不足， 加工開始之結塊容易發生破損及折損。相反的，比率A/D 超過3 5%的話，無法得到設置削磨部6的效果，孔位置精 度未提升。該比率A/D爲20%以上、25 %以下之範圍特別 好。本實施方式時，約爲20%。 此外，雖然並未圖示，然而，3片刃以上之小直徑鑽 頭時，描繪3個以上之削磨面當中之內切於3個削磨面的 最小直徑之圓時，該圓之直徑A m m作用如小直徑鑽頭1 之前端面3的心厚。而且，削磨部6以相對於旋轉軸線Ο 爲線對稱設置時，理論上，係描繪與3個以上之所有削磨 部6相切的圓。然而，實際上，因爲受到製造誤差等之影 響，以切於3個削磨部6之圓當中之最小直徑之圓來求取 。其他方法，也可以考慮以求取最接近旋轉軸線〇之削磨 -11 - 201244856 部6的距離之2倍的方法。此處，係考慮測定之容易度’ 而採用利用切於3個削磨部6之圓當中之最小直徑的圓之 方法。 不只是小直徑鑽頭，例如，於一般之金屬加工用鑽頭 等之工具徑爲p 3.20mm以上之鑽頭等設置削磨面時’該 比率A/D通常爲4%以上、1 5%以下。如前面所述’直接 以該比率A/D爲1 5%以下適用於小直徑鑽頭的話，削磨面 周邊強度不足而結塊時，容易發生破損或折損。所以’被 認爲難以在小直徑鑽頭設置削磨面。 第6圖，係第2實施方式之小直徑鑽頭1A的圖示。 此外，第6圖及第7圖中，與第1實施方式相同之構成部 分賦予相同符號。本實施方式時，於前端面3附近形成二 條溝2，該二條溝2係以朝後端7之中途合流成一條溝2 。合流方法，可以利用各種傳統技術。例如，可以從前端 面3開始逐漸改變各溝2之扭轉角來形成。或者，使其中 一方之溝2從中途開始改變扭轉角來形成，只要以使其合 流之方式進行調整即可。 是以，於中途使溝2合流的話，藉由在小直徑鑽頭1 之較細的根部側，使垂直旋轉軸線〇之剖面中的溝2剖面 積較小，來提高剛性。小直徑鑽頭1之根部側，因爲係有 較大彎曲力矩作用之部分，該處之剛性對鑽頭之彎曲十分 重要。使溝2合流的結果，可以得到更不易彎曲且孔位置 精度較高之小直徑鑽頭1。藉由與前述削磨部6之形狀的 相乘效果，實現更高之孔位置精度，且長期維持其高精度 -12- 201244856 。另一方面，切屑之排出性方面，例如，如本實施方式之 使溝2緩慢合流的話，沒有問題，且確保良好之切屑排出 性。 其次，針對刀口 5之長度Cmm之影響及可適用範圍 進行說明。如第5圖所示，因爲形成削磨部6而縮短之刀 口 5的長度Cmm，與前述複數削磨部6之間的距離Amm 相同，在前端面3，切刃4與旋轉軸線Ο有少許間隔。此 處，考慮測定之容易度，係以刃數爲偶數時，具體而言， 係以2片刃時來進行說明。此外，刃數爲4片刃時，以於 2處求取之距離中之較短一方的距離作爲Cmm。若刃數爲 奇數時，亦即，3片刃時，測定從工具旋轉軸線Ο至刀口 5之端點的距離，以相當於最短距離之2倍的長度作爲 Cmm。難以測定時，也可考慮描繪通過3個刀口之外側端 點的圓，以其圓之直徑作爲長度Cmm的方法。刀口之長 度 Cmm，係以工具徑φ Dmm作爲基準，其比率 C/D以 40%以上、70%以下之範圍爲佳。其比率C/D未達40%時 ，前端部分強度不足，發生破損或折損的問題。相反的， 超過70%的話，無法得到設置削磨部6的效果，未能提升 孔位置精度。其比率C/D，最好爲45%以上、60%以下之 範圍。本實施方式時，約爲50%。 其次’針對未設置削磨部6時之刀口 5的虛擬長度 Emm之影響及可適用範圍進行說明。如第5圖所示，未設 置削磨部6時，推測刀口 5係持續至從刀口 5延伸之虛擬 直線、及從第1切刃4a延伸之虛擬直線的虛擬交點P1爲 •13- 201244856 止。考慮測定之容易度，針對刃數爲偶數時，進一步針對 將刃數限定爲2片刃時來進行說明。設置前述削磨部6時 之刀口 5的長度Cmm、及長度Emm之比率C/E，係削磨 部6之有無之刀口 5長度的變化率。所以，其比率C/E愈 小，則削磨部6所產生之第2切刃4b的長度愈長。該比 率C/E，以65%以上、100%以下之範圍爲佳。該比率C/E 未達65%時，刀口之長度Cmm、及長度Dmm之均衡性較 差。此處說明之比率C/E爲100%之狀態，係指削磨部6 之其中一方端點、及刀口 5之其中一方端點一致的形狀。 亦即，係指雖然設有削磨部6但其未與刀口 5交叉之形狀 ，所以，此時，刀口 5未較短。設置削磨部6的效果，除 了縮短刀口 5之長度以外，也具有優良效果。亦即，即使 刀口長度Cmm相同，削磨部6之形狀也可進一步提升孔 位置精度。 以削磨部6縮短刀口長度Cmm時，不但希望具有相 乘效果，也希望能適度地保持均衡。比率C/E，最好爲 70%以上、80%以下之範圍。本實施方式約爲75%。 到目前爲止，係以形成二條溝之實施方式爲中心來進 行說明，然而，本發明，例如，也可適用於只形成1條溝 之小直徑鑽頭。形成~條溝之第3實施方式如第8圖所示 。如第8圖所示，一條溝2時，也以於刀口 5兩側實施削 磨部6爲佳。該實施方式時，削磨面形狀係形成爲相對於 旋轉軸線〇爲線對稱之形狀。然而，並未受限於該形狀。 削磨面形狀，例如，亦可考慮切削力之均衡等而形成爲非 -14- 201244856 對稱形狀。此外，溝，並未受到相對於旋轉軸線〇爲線對 稱形狀之限制。例如，以非對稱方式形成二條以上之溝的 小直徑鑽頭時，2個以上之削磨面形狀也可以非對稱方式 來形成。 從第9圖至第11圖，係包含第1實施方式在內之本 發明的小直徑鑽頭1實驗結果。此外，實驗結果如前述之 說明所示。參考該實驗結果，本發明之效果獲得驗證。比 率 A/D，如第9圖所示，15%以上、35%以下之範圍的實 驗結果良好。實驗條件，如以下所示。 加工基板，係將2片印刷電路板用之FR-4 (厚度 1 · 6mm之4層板）重疊加工。抵壓板係使用鋁板。主軸旋 轉數，係1 60,000min-l (旋轉/分）。饋送速度係 3.2 m/min 〇 切削性能之判定基準，以5000hits (孔）加工爲止之 孔位置精度爲〇 . 〇 5 0 m m以下時作爲合格判定（〇判定）。 此外’孔位置精度爲〇.〇45mm以下時，視爲特別良好範圍 (◎判定）。該孔位置精度之數値，係所謂平均値+3 σ之 數値。印刷電路板之孔位置精度的判定，一般而言，係利 用孔分析機（孔位置座標測定機），並以目標中心座標所 測定之孔中心座標値的分佈來表示從原來指令位置偏離多 少。孔位置精度，一般有2種評估方法，以距離中心之最 大値來表示的方法、及以對有誤差之平均値加上標準偏差 σ之3倍的値（平均値+3σ )來表示的方法。但是，最大 値評估方法’例如’有時會受到表面損傷等之突發問題的 -15- 201244856 影響。此處，選擇以平均値+3 σ之數値來評估孔位置精度 的方法。 另一方面，由相同實驗分析對工具壽命延長之影響的 話，得到以下之結果。例如，孔位置精度之判定基準爲 0.040mm以下時，第1實施方式之小直徑鑽頭1，相對於 相同形狀而未設置削磨面之小直徑鑽頭，得到約2倍之工 具壽命。如前面所述，第1實施方式之小直徑鑽頭1的比 率A/D約爲20% ^ 比率C/D，如第10圖所示，40%以上、70%以下良好 。實驗條件及判定基準，與比率A/D相同。如前面所述， 第1實施方式之小直徑鑽頭1的比率C/D約爲50%。 比率C/E，如第1 1圖所示，60%以上良好。實驗條件 及判定基準，與比率A/D等相同。如前面所述，第1實施 方式之小直徑鑽頭1的比率C/E約爲75%。 以上說明之小直徑鑽頭1，可自由裝卸於印刷電路板 等之孔專用工作機械，係對被加工物進行相對運動來實施 切削加工（孔）。工作機械，也可以使用搪床及切削機等 之可安裝小直徑鑽頭的工作機械。 本發明，並未受限於以上說明之實施方式者，只要未 背離發明之要旨範圍，可以進行適度之構成變更、追加、 及削除。例如，不但可以適用於印刷電路板，也可適用於 金屬之孔加工用小直徑鑽頭等。 【圖式簡單說明】 -16 - 201244856 第1圖係第1實施方式之小直徑鑽頭的右側面放大圖 第2圖係第1圖之小直徑鑽頭的右側面圖 第3圖係第1圖之小直徑鑽頭的正面放大圖 第4圖係第1圖之小直徑鑽頭的1V_IV線方向剖面圖 第5圖係第1圖之小直徑鑽頭的正面放大說明圖 第6圖係第2實施方式之小直徑鑽頭的右側面放大圖 第7圖係第6圖之小直徑鑽頭的左側面放大圖 第8圖係第3實施方式之小直徑鑽頭的正面放大圖 第9圖係小直徑鑽頭的第1實驗結果 第1 0圖係小直徑鑽頭的第2實驗結果 第1 1圖係小直徑鑽頭的第3實驗結果 【主要元件符號說明】 〇 :旋轉軸線 1 :小直徑鑽頭 1 A :小直徑鑽頭 2 :溝 3 :前端面 4 :切刃 4a :第1切刃部 4b :第2切刃部 5 :刀口 6 :凹部 7 :後端 -17- 201244856 8 :柄部 9 :刀葉 -18-201244856 VI. Description of the Invention: [Technical Field of the Invention] The present invention relates to a drill having a diameter of 3.175 mm (l/8 inch). [Prior Art] The conventional small-diameter drill, for example, is disclosed in Patent Document 1, which has two grooves arranged symmetrically with respect to the tool, and has a small cutting edge and a cutting edge of 3.175 mm or less at the front end. The diameter drill bit is said to form a sharpening portion with respect to the tool rotation axis. [Patent Document 1] Japanese Laid-Open Patent Publication No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. , called hole position accuracy). However, the cutting edge formed by the grinding part of the small-diameter drill bit of 1 is a negative angle, and the insufficient cutting efficiency is likely to cause a shock to the material to be cut. Therefore, in the small-diameter drill of Patent Document 1, the hole position is not sufficient. Further, in the small-diameter drill of Patent Document 1, the force is concentrated on the cutting edge formed by the machining of the sharpening portion, and there is a problem that the peripheral portion of the grinding portion is damaged or the cutting force is large, and the small diameter drill bit of Patent Document 1 is used. As the wear and tear increases, the following small ones are shown. The axis is the line diameter is 0 line to the line pair. The integrated circuit is improved. The patent is due to the large angle of the agglomeration. The accuracy is changed because the cutting occurs from the cutting. Moreover, the grinding part becomes -5- 201244856 and the area is reduced, and the effect of using the sharpening part to improve the hole position accuracy is lost. Further, since the portion of the cutting edge formed by the processing of the sharpening portion is quickly rounded, the effect of improving the positional accuracy of the hole is quickly weakened. For example, for small diameter drill bits used in the drilling of printed circuit board holes, it is common practice to honing the front end and using it several times at the end of the tool life. However, the shape of the sharpening portion shown in Patent Document 1 is difficult to re-form when it is honed, and the shape of the cutting edge of the small-diameter drill is completely different before and after honing. Therefore, there is a problem that the cutting performance is completely changed before and after honing. The invention provides a method for improving the position accuracy of the hole, suppressing the reduction of the area of the sharpening portion caused by the abrasion, and being easy to be damaged and damaged, and being easy to be honed, and maintaining the cutting performance after a certain honing, the diameter is 3 Small diameter drills up to 1 7 5 mm. The small-diameter drill of the present invention includes at least one groove (2) disposed from the front end surface (3) toward the rear end side, and a cutting edge (4) and a knife edge (5) formed on the front end surface (3), and having A small-diameter drill having a diameter (d) of 175 mm or less is characterized in that it has a shape in which a thickness of a blade extending from the front end surface (3) toward the rear end side and at least a front end region of the small-diameter drill is thinned. In the recessed portion (6), the cutting edge (4) includes: a first cutting edge portion (4a) formed at an intersection of the blade surface having a positive inclination angle and the front end surface (3) formed by the at least one groove (2) And a second cutting edge portion (4b) formed in the concave portion (6) and forming at least a part of an intersection portion between the blade surface having a positive inclination angle and the front end surface (3), and the second cutting edge portion (4b) 'Connected to the first cutting edge portion (4a) and intersecting the aforementioned cutting edge (5). -6- 201244856 The small-diameter drill of the present invention has the same inclination angle to the blade surface of the first cutting edge portion as the blade surface on which the second cutting portion is formed, and the cutting performance of the small-diameter drill is greatly improved. Moreover, the cutting resistance of the reduced diameter drill bit (rotational impedance and the direction of the rotation axis is increased, and the hole position accuracy is improved. Moreover, the position of the hole referred to here is increased, of course, including the positional accuracy of the hole entrance (the deviation of the position of the hole of the mechanical command position) The lifting also includes the improvement of the hole bending and the improvement of the positional accuracy. Further, the recess of the present invention extends from the front end of the small-diameter drill bit, and the shape does not change when viewed from the front end side even if the front end surface wears out continuously, the second cut The blade portion is less likely to be rounded, and the speed of deterioration of the hole is slowed down, and the life of the tool is greatly extended. Further, the recessed portion of the present invention has a length that maintains the shape of the second cutting edge even when the cutting edge is at least ground. 'It is possible to reproduce the cutting edge shape similar to the new one. The cutting performance of the small diameter drill of the invention before and after honing. EMBODIMENT> The embodiment of the present invention will be described with reference to the drawings. The right side of the small diameter drill bit of the embodiment. Fig. 2 is the right side view of the small diameter drill bit of the second drawing. The front side is enlarged. Figure 4 shows the positive inclination of the concave portion of the first blade portion applied to the small force impedance.) The accuracy of the position of the concave portion on the rear end side of the hole exit of the machining is improved once and again. Fig. 3 is a cross-sectional view taken along the line IV-ΐν of the drill bit of the straight straight 201244856. Fig. 5 is an enlarged front elevational view of the small diameter drill of Fig. 1. Fig. 6 is an enlarged plan view showing the right side of the small diameter drill of the second embodiment. Fig. 7 is an enlarged side view of the left side of the small diameter drill of Fig. 6. Fig. 8 is an enlarged front view of the small-diameter drill of the third embodiment. Figures 9 through 11 show the experimental results of a small diameter drill bit. As shown in Figs. 1 to 4, in the small-diameter drill 1 of the first embodiment, two grooves 2 which are right-handed are formed. In the present embodiment, the two grooves 2 are arranged in line symmetry with respect to the tool rotation axis 0. The front end surface 3 has a function of a side ventral surface, and a knife edge 5 is formed at an intersection of the two side ventral surfaces, and a linear intersection portion of the front end surface 3 and a blade surface having a positive rake angle (not shown) formed in the groove 2 is formed. The first cutting edge 4a is formed. Further, the knife edge 5, in the vicinity of the center of the front end face 3, acts as a front cutting edge. In the two grooves 2, a sharpening portion 6 is formed. In addition, the "grinding portion" is an area to be additionally machined to form a cutting edge (second cutting edge 4b) at the front end of the blade 9 (see Fig. 4) formed by the groove bottom of the two grooves 2. The sharpening portion 6 extends from the distal end surface 3 toward the rear end side, and is formed by a concave portion formed to be thinner than the thickness of the blade 9 at least in the distal end region of the small-diameter drill 1 to rotate along the sharpening portion 6. The length of the axis Ο is formed to be smaller than the length of the groove 2. In the sharpening portion 6, a sharpening surface having a positive inclination angle (not shown) is formed, and a second cutting edge 4b is formed in a part of an intersection portion that is curved in a concave shape in a direction of rotation of the grinding surface and the front end surface 3. . The second cutting edge 4b is connected to the first cutting edge 4a and intersects the cutting edge 5. "Crossing the knife edge 5", -8- 201244856 As shown in the present embodiment, the ridge includes the end of the knife edge 5 and the sharpening surface and the front end surface of the sharpening portion 6 except when the second cutting edge 4b intersects the knife edge 5. When one of the endpoints of the intersection line of 3 coincides, that is, coincides with one of the end points of the second cutting edge 4b. In the present embodiment, the sharpening portion 6 is formed such that the front end surface portion 3 is cut away from the rotation axis of the small-diameter drill 1 into a line symmetrical shape. Therefore, the second cutting edge portion 4b formed by the machining of the sharpening portion 6 is formed in a line symmetrical arrangement. In the case of line symmetry, it is easy to obtain the rotation balance, and it is easy to obtain the balance of the cutting force. The range in which the sharpening portion 6 is formed is not particularly limited. However, it is possible to set the front end 7 side of the small-diameter drill 1 in consideration of a predetermined number of times of re-honing and the required rigidity of the small-diameter drill 1 to form a circle. A cylindrical handle 8 . In the present embodiment, the tool diameter (diameter) φ Dmm corresponding to the hole diameter machined by the small-diameter drill 1 is approximately 0.250 mm. The shank diameter of the shank 7 is approximately φ 3.175 mm. The length of the sharpening portion 6 is approximately 0.8 mm as measured from the front end 3 toward the rear end 7 side of the small-diameter drill 1 along the rotational axis Ο direction. In general, when the length is about 0.8 mm, it can be re-honed for 5 times. The length of the sharpening portion 6 is preferably 0.5 mm or more and 1.5 mm or less. For example, when the tool diameter pDmm is φ0.150 mm, it is preferably about 0.6 mm. When the tool diameter pDmm is p 2.000 mm or more, it is preferably about 1.5 mm. Further, the length of the sharpening portion 6 is generally the length until the sharpening portion 6 disappears. However, here, the shape of the sharpening portion 6 is maintained substantially constant. The groove length of the groove 2 can be appropriately determined in accordance with the tool diameter p Dmm. In the embodiment 5-9-201244856, the groove length of the groove 2 is about 3.5 mm when measured from the front end 3 side of the small diameter drill 1 toward the rear end 7 side. The length of the sharpening portion 6 is preferably one or more of the groove length. In the present embodiment, it is about 23%. The twist angle is not particularly limited. In the case of a small-diameter drill for a printed circuit board, the torsion angle of the small-diameter drill 1 of the present invention is preferably 30° or more and 60° or less, more preferably 40° or more and 50° or less. In the present embodiment, the twist angle is about It is 45° (not shown). Further, in general, when a tool diameter pDmm is a small diameter drill having a diameter of 1.500 mm or more, the rigidity is high enough, and the problem of the hole position accuracy hardly occurs. According to the present invention, when the small diameter drill 1 having a tool diameter pDmm of φ 1.500 mm or less is used, the hole position accuracy is particularly enhanced. In particular, when the tool diameter pDmm is <p0.500 mm or less, the hole position accuracy is particularly improved. For example, since the sharp-cut portion 6 having a length of about 0.6 mm can be formed on the very small-diameter drill 1 having a tool diameter Dmm of about φ 0.100 mm, the effect of improving the hole position accuracy can be confirmed. The shape of the sharpening portion 6 as viewed from the front end surface 3 side will be described using a front view of Fig. 5. The distance Amm between the blade surface of each of the sharpening portions 6 and the intersection line formed by the front end surface (3) corresponds to the thickness of the front end 3 of the small-diameter drill 1, that is, the blade 9 corresponding to the front end face 3. thickness of. In the case of the two blades of the present embodiment, as shown in FIG. 5, among the circles tangent to the two intersecting lines of the two sharpening portions 6 and the front end surface 3, the diameter Amm of the smallest diameter circle is two grindings. The distance between the parts 6 is Amm. The shorter the distance Amm is, the closer the cutting edge 4 is to the rotational axis 0, so that the small-diameter drill 1 having good cutting performance can be provided. -10- 201244856 However, in general, when a small-diameter drill is provided with a recess such as a grinding surface, there is a problem that the strength of the tip end portion is insufficient and damage or breakage occurs. Moreover, because of the problem of re-honing, small-diameter drills generally do not apply the grinding surface. In other words, in the case where no problem such as breakage or breakage occurs, the shape of the sharpening surface for improving the positional accuracy of the hole is actually difficult to achieve. In order to achieve the above two opposite problems (improvement of cutting efficiency and prevention of breakage), First, look at the distance Amm to understand its impact and scope of application. As a result of the experiment described later, the following applicable range was obtained. When the tool diameter P Dmm of the small diameter drill 1 is used as a reference (100%), the distance Amm between the two grinding portions 6 is preferably in the range of 15% or more and 35% or less. When the ratio A/D is less than 15%, the strength of the tip end portion is insufficient, and the agglomeration at the start of processing tends to be damaged or broken. On the other hand, if the ratio A/D exceeds 35%, the effect of setting the sharpening portion 6 cannot be obtained, and the hole position accuracy is not improved. The ratio A/D is particularly preferably in the range of 20% or more and 25% or less. In the present embodiment, it is about 20%. Further, although not shown, in the case of a small-diameter drill having three or more blades, when a circle having a minimum diameter of three or more of the grinding faces is drawn, the diameter of the circle is A mm. The effect is as the thickness of the end face 3 of the small diameter drill bit 1. Further, when the sharpening portion 6 is disposed symmetrically with respect to the rotation axis Ο, a circle which is tangential to all of the three or more of the sharpening portions 6 is theoretically drawn. However, in actuality, it is determined by a circle having a minimum diameter among the circles of the three sharpening portions 6 due to a manufacturing error or the like. For other methods, it is also possible to consider the method of obtaining the distance of the grinding axis -11 - 201244856 part 6 which is closest to the rotation axis 〇. Here, a method of using a circle having a minimum diameter among the circles of the three sharpening portions 6 is adopted in consideration of the easiness of measurement. In the case of a small-diameter drill, for example, when a tool having a tool diameter of 3.30 mm or more is provided with a grinding surface, the ratio A/D is usually 4% or more and 15% or less. As described above, when the ratio A/D is 15% or less, it is suitable for a small-diameter drill. When the strength of the grinding surface is insufficient and the cake is agglomerated, it is likely to be damaged or broken. Therefore, it is considered difficult to set the grinding surface on the small diameter drill. Fig. 6 is a view showing the small-diameter drill 1A of the second embodiment. In the sixth and seventh embodiments, the same components as those in the first embodiment are denoted by the same reference numerals. In the present embodiment, two grooves 2 are formed in the vicinity of the front end surface 3, and the two grooves 2 are merged into one groove 2 in the middle of the rear end 7. The convergence method can utilize various conventional techniques. For example, the twist angle of each groove 2 can be gradually changed from the front end face 3 to be formed. Alternatively, one of the grooves 2 may be formed by changing the twist angle from the middle, and it may be adjusted so as to be merged. Therefore, when the grooves 2 are merged in the middle, the rigidity of the groove 2 in the cross section of the vertical rotation axis 〇 is made smaller by the thinner root side of the small-diameter drill 1 . The root side of the small-diameter drill bit 1 is very important for the bending of the drill bit because it has a large bending moment. As a result of the joining of the grooves 2, a small-diameter drill 1 which is more difficult to bend and has a high hole position accuracy can be obtained. By multiplying the shape of the aforementioned sharpening portion 6, a higher hole positional accuracy is achieved, and the high precision is maintained for a long period of time -12-201244856. On the other hand, in terms of the discharge property of the chips, for example, if the grooves 2 are slowly joined as in the present embodiment, there is no problem, and good chip discharge performance is ensured. Next, the influence of the length Cmm of the knife edge 5 and the applicable range will be described. As shown in Fig. 5, the length Cmm of the blade opening 5 which is shortened by the formation of the sharpening portion 6 is the same as the distance Amm between the plurality of sharpening portions 6, and the cutting edge 4 has a slight inclination with respect to the rotation axis at the front end face 3. interval. Here, in consideration of the easiness of measurement, when the number of blades is an even number, specifically, two blades are used for explanation. Further, when the number of blades is four blades, the distance from the shorter one of the distances obtained at two points is taken as Cmm. When the number of blades is an odd number, that is, when three blades are used, the distance from the tool rotation axis Ο to the end of the blade edge 5 is measured, and the length corresponding to twice the shortest distance is taken as Cmm. When it is difficult to measure, it is also conceivable to draw a circle passing through the outer end points of the three cutting edges, and the diameter of the circle is used as the length Cmm. The length of the knife edge Cmm is based on the tool diameter φ Dmm, and the ratio C/D is preferably 40% or more and 70% or less. When the ratio C/D is less than 40%, the strength of the front end portion is insufficient, and the problem of breakage or breakage occurs. On the other hand, if it exceeds 70%, the effect of setting the sharpening portion 6 cannot be obtained, and the hole position accuracy cannot be improved. The ratio C/D is preferably in the range of 45% or more and 60% or less. In the present embodiment, it is about 50%. Next, the influence of the virtual length Emm of the knife edge 5 when the sharpening portion 6 is not provided and the applicable range will be described. As shown in Fig. 5, when the sharpening portion 6 is not provided, it is estimated that the knife edge 5 continues until the virtual straight line extending from the knife edge 5 and the virtual intersection P1 extending from the first cutting edge 4a is •13-201244856 . In consideration of the easiness of measurement, when the number of blades is an even number, the description will be made with respect to the case where the number of blades is limited to two blades. The ratio C/E of the length Cmm of the knife edge 5 and the length Emm when the above-described sharpening portion 6 is provided is the rate of change of the length of the blade edge 5 in the presence or absence of the sharpening portion 6. Therefore, the smaller the ratio C/E, the longer the length of the second cutting edge 4b produced by the sharpening portion 6. The ratio C/E is preferably in the range of 65% or more and 100% or less. When the ratio C/E is less than 65%, the balance between the length Cmm of the knife edge and the length Dmm is poor. The state in which the ratio C/E is 100% as described herein means a shape in which one end of the sharpening portion 6 and one end of the knife edge 5 coincide with each other. That is, although the shape of the sharpening portion 6 is not intersected with the knife edge 5, the blade edge 5 is not short. The effect of providing the sharpening portion 6 has an excellent effect in addition to shortening the length of the knife edge 5. That is, even if the blade length Cmm is the same, the shape of the sharpening portion 6 can further improve the hole positional accuracy. When the cutting edge length Cmm is shortened by the sharpening portion 6, it is desirable not only to have a multiplication effect but also to maintain a proper balance. The ratio C/E is preferably in the range of 70% or more and 80% or less. This embodiment is approximately 75%. Heretofore, the description has been focused on the embodiment in which the two grooves are formed. However, the present invention is also applicable to, for example, a small-diameter drill which forms only one groove. The third embodiment for forming a groove is as shown in Fig. 8. As shown in Fig. 8, in the case of one groove 2, it is preferable to carry out the sharpening portion 6 on both sides of the knife edge 5. In this embodiment, the shape of the sharpening surface is formed into a line symmetry with respect to the axis of rotation 〇. However, it is not limited to this shape. The shape of the grinding surface can be formed into a non-14-201244856 symmetrical shape, for example, considering the balance of the cutting force. In addition, the grooves are not limited by the shape of the line symmetry with respect to the axis of rotation. For example, when a small-diameter drill having two or more grooves formed asymmetrically, two or more of the shape of the sharpening surface may be formed in an asymmetrical manner. From Fig. 9 to Fig. 11, the experimental results of the small-diameter drill 1 of the present invention including the first embodiment are shown. Further, the experimental results are as shown in the foregoing description. Referring to the results of the experiment, the effects of the present invention were verified. The ratio A/D, as shown in Fig. 9, is excellent in the experimental results in the range of 15% or more and 35% or less. Experimental conditions are as follows. The substrate was processed by superimposing FR-4 (4 layers of thickness 1 · 6 mm) for two printed circuit boards. The aluminum plate is used for the pressing plate. The number of spindle rotations is 1 60,000 min-l (rotation/minute). Feeding speed is 3.2 m/min 〇 The cutting performance is judged by the hole position accuracy of 5000hits (hole) machining. 〇 5 0 m m or less is used as the qualification judgment (〇 judgment). In addition, when the hole position accuracy is 〇.〇45 mm or less, it is regarded as a particularly good range (◎ judgment). The number of positions accuracy of the hole is the number 所谓 of the average 値+3 σ. In the determination of the hole position accuracy of the printed circuit board, generally, the hole analyzer (hole position coordinate measuring machine) is used, and the distribution of the center coordinates of the hole measured by the target center coordinates indicates how much deviation is from the original command position. Hole position accuracy, generally there are two methods of evaluation, the method represented by the maximum 値 from the center, and the method of expressing the mean 値 with error plus the standard deviation σ of 3 times 値 (average 値 + 3σ ) . However, the maximum 値 evaluation method 'for example' is sometimes affected by sudden problems such as surface damage, -15-201244856. Here, a method of estimating the hole position accuracy by the number of 値+3 σ is selected. On the other hand, the following results were obtained by the same experimental analysis on the effect of tool life extension. For example, when the criterion for determining the hole position accuracy is 0.040 mm or less, the small-diameter drill 1 of the first embodiment has a tool life of about twice as large as that of the small-diameter drill having the same shape without the grinding surface. As described above, the ratio A/D of the small-diameter drill 1 of the first embodiment is about 20% ^ ratio C/D, and as shown in Fig. 10, 40% or more and 70% or less are good. The experimental conditions and the criterion are the same as the ratio A/D. As described above, the ratio C/D of the small-diameter drill 1 of the first embodiment is about 50%. The ratio C/E, as shown in Fig. 1, is better than 60%. The experimental conditions and the criterion are the same as the ratio A/D and the like. As described above, the ratio C/E of the small-diameter drill 1 of the first embodiment is about 75%. The small-diameter drill 1 described above can be detachably attached to a hole-specific work machine such as a printed circuit board, and the workpiece is subjected to relative movement to perform cutting (hole). For working machines, it is also possible to use a working machine such as a boring machine or a cutting machine that can mount a small-diameter drill. The present invention is not limited to the embodiments described above, and may be appropriately modified, added, and deleted without departing from the scope of the invention. For example, it can be applied not only to a printed circuit board but also to a small-diameter drill for metal hole machining. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an enlarged view of the right side of the small diameter drill of the first embodiment. Fig. 2 is a right side view of the small diameter drill of Fig. 1. Fig. 3 is the first figure. Fig. 4 is a cross-sectional view of the small diameter drill bit of Fig. 1 taken along line 1V_IV of the first embodiment. Fig. 5 is a front enlarged view of the small diameter drill of Fig. 1. Fig. 6 is a small Magnification of the right side of the diameter drill bit Fig. 7 is an enlarged view of the left side of the small diameter drill of Fig. 6. Fig. 8 is a front enlarged view of the small diameter drill of the third embodiment. Fig. 9 is the first experiment of the small diameter drill Results Figure 1 shows the second experimental result of the small-diameter drill bit. Figure 1 shows the third experimental result of the small-diameter drill bit. [Main component symbol description] 〇: Rotation axis 1: Small-diameter drill bit 1 A: Small-diameter drill bit 2: Groove 3: front end face 4: cutting edge 4a: first cutting edge portion 4b: second cutting edge portion 5: knife edge 6: recessed portion 7: rear end -17-201244856 8: shank portion 9: blade -18-