201039948 六、發明說明： 【發明所屬之技術領域】 本發明是關於鑽孔工具。 【先前技術】 一般印刷配線板（P C B )用的鑽孔工具，例如第1圖所 示是以既定的扭轉角A ’設置一對的切削屑排出溝槽21、 0 22’在該切削屑排出溝槽21、22與第一刀腹面（funk) 23 、24的交叉稜線部25、26形成具有既定的前端角γ’之切刃 。圖中的符號28' 2 9代表第二刀腹面。 因此，第1圖的工具合計有4個前端面，藉由對各前端 面（刀腹面）分別賦予既定的角度，以在工具前端中央附 近形成鏊刃。第1 (a)圖爲俯視圖，第1 (b)圖爲前視圖 ，第1 ( c )圖爲右側視圖。 然而，隨著近年來電子機器的高集積化、高密度化， 〇 必須對PCB實施極小孔徑的加工，因此對鑽頭要求更加小 型化。 例如會有使用工具直徑〇.〇5mm左右的極小徑鑽頭的情 況，由於工具的剛性極小，發生折損的可能性高，必須頻 繁地更換工具，或必須減少將PCB重疊而同時加工的片數 〇 此外，在前端形狀的外觀檢查·時，是測定左右的平衡 (切刃的偏位及鑿刃的偏心）來判定良窳，若孔徑變小， 不僅是加工本身，連該檢查也變得很麻煩。 201039948 於是’例如在專利文獻1揭示一種即使是小徑的工具 也期望能確保其剛性之單切刃鑽頭的構造，但就現狀而言 ’尙無法獲得充分的折損壽命。此外，前端接觸面有複數 個’因此與習知同樣的要進行良窳判定檢查非常麻煩。 〔專利文獻1〕日本特開2003-3 1 1 522號公報 【發明內容】 本發明是有鑑於上述現狀而開發完成的，其目的是爲 了提供一種鑽孔工具，即使是極小徑的鑽孔工具也不容易 折損’不須頻繁地更換，形狀簡單且容易進行製造及檢查 ，而具備前所未有的優異實用性。 參照所附圖式來說明本發明的要旨。 本發明之鑽孔工具，係具備一個或複數個螺旋狀的切 削屑排出溝槽1、2之鑽孔工具，其特徵在於··工具前端面 是包含：朝與工具中心軸交叉的方向展開且沒有稜線之一 個前端接觸面5a、以不接觸該前端接觸面5 a所接觸的被切 削物的方式相對於與工具軸垂直的方向以既定角度傾斜且 設置成與該前端接觸面5 a相連之前端刀腹面5b。 此外，在請求項1記載的鑽孔工具中，前述前端接觸 面5a是相對於與工具軸垂直的方向以既定的傾斜角度α形 成傾斜。 此外，在請求項1記載的鑽孔工具中，在複數個前述 切削屑排出溝槽1、2之間設置島部3、4，在前述切削屑排 出溝槽1、2與前述前端接觸面5a的複數個交叉稜線部6、7 -6- 201039948 當中比較長的交叉稜線部6上具有最前端點，該交叉 部6可發揮切削作用。 此外，在請求項2記載的鑽孔工具中，在複數個 切削屑排出溝槽1、2之間設置島部3、4，在前述切削 出溝槽1、2與前述前端接觸面5a的複數個交叉稜線部 當中比較長的交叉稜線部6上具有最前端點，該交叉 部6可發揮切削作用。 q 此外’在請求項4記載的鑽孔工具中，前述前端 面5a相對於與工具軸垂直的方向的傾斜角度α設定;| (90°-扭轉角）。 此外’在請求項5記載的鑽孔工具中，前述傾斜 α設定爲1〇°~30°。 此外，在請求項5記載的鑽孔工具中，前述前端 面5b是設置在前述前端接觸面5a與前述島部3、4之間 此外’在請求項6記載的鑽孔工具中，前述前端 Q 面5b是設置在前述前端接觸面5a與前述島部3、4之間 此外，在請求項5記載的鑽孔工具中，前述前端 面5b是設置在具有前述最前端點之交叉稜線部6的工 轉方向後方側。 此外，在請求項6記載的鑽孔工具中，前述前端 面5b是設置在具有前述最前端點之交叉稜線部6的工 轉方向後方側。 此外，在請求項7記載的鑽孔工具中，前述前端 面5b是設置在具有前述最前端點之交叉稜線部6的工 稜線 前述 屑排 6 ' 7 稜線 接觸 10°~ 角度 刀腹 > 刀腹 > 刀腹 具旋 刀腹 具旋 刀腹 具旋 201039948 轉方向後方側。 此外，在請求項8記載的鑽孔工具中，前述前端刀腹 面5b是設置在具有前述最前端點之交叉稜線部6的工具旋 轉方向後方側。 此外’在請求項5〜I2中任一項記載的鑽孔工具中，是 具有二個前述切削屑排出溝槽1、2，前述前端刀腹面5b被 設置成：以不超過將交點A (在前述前端接觸面5a之前述 島部3、4與前述切削屑排出溝槽1、2的交點A、B當中位於. 工具旋轉方向前方側的交點）互相連結的直線L的範圍， 在具有前述最前端點之交叉稜線部6的工具旋轉方向後方 側，朝向與前述前端接觸面5a不同的傾斜方向。 此外，在請求項1 3記載的鑽孔工具中，工具直徑爲 0.2mm以下。 本發明由於採用上述構造，即使是極小徑的鑽孔工具 也不容易折損’不須頻繁地更換，形狀簡單且容易進行製 造及檢查，而具備前所未有的優異實用性。 【實施方式】 簡單地說明本發明的較佳實施形態並根據圖式來顯示 本發明的作用。 在工具前端設置沒有稜線之單一的前端接觸面5a，不 同於一般的鑽頭（例如在工具前端中央附近具有鑿刃，與 該鑿刃相連而形成具有既定的前端角之切刃），在工具前 端中央附近並不具備鑿刃，在鑽孔加工中的切削阻力的大 -8- 201039948 部分是由推力方向（工具軸方向）承受，如此可減輕工具 軸垂直方向的外力（鑽孔加工中的切削阻力）所產生的彎 曲應力，而不容易發生折損。 再者，是讓前端接觸面5a之最突出的部分（與島部3 、4或切削屑排出溝槽1、2的交叉稜線部）抵接於工件加 工面而逐漸進行切削，不同於上述一般的鑽頭，由於不容 易咬入加工面，在切削初期工具可稍微擺動而適度地擴大 0 入口側的孔徑以進行鑽孔，因此加工孔形狀在入口側的口 徑變大，工具的基端側不容易與加工孔內壁接觸，而能抑 制工具的基端側與加工孔內壁接觸所造成的折損。 此外，藉由形成以既定角度與前端接觸面5a相連之前 端刀腹面5b，就不會阻礙切削後的切削屑往切削屑排出溝 槽1、2的導出，而不容易發生切削屑的堵塞。 此外，由於形狀簡單，且只要將形成有切削屑排出溝 槽之工具材料的前端部以適當的位置及適當的角度除去即 〇 可’因此容易形成具有既定的截面形狀及期望的傾斜角度 α之前端接觸面5a。 此外’由於前端形狀單純，不容易像具有多數個前端 接觸面之習知工具那樣發生各前端面的左右失衡，其左右 平衡的檢查容易，能使檢查簡單化並提昇良率。 〔實施例〕 根據第2〜8圖來說明本發明的具體實施例。 本實施例，如第2圖所示，係具備二個螺旋狀的切削 -9- 201039948 屑排出溝槽1、2之鑽孔工具，其工具前端面是包含：朝與 工具中心軸交叉的方向展開且沒有稜線之一個前端接觸面 5a、以不接觸該前端接觸面5a所接觸的被切削物（工件） 的方式以既定角度傾斜且設置成與該前端接觸面5a相連之 一個平坦的前端刀腹面5b。 圖中’符號6、7代表切削屑排出溝槽1、2與前端接觸 面5a的交叉稜線部，符號8代表島部3與前端刀腹面5b的交 叉稜線部，符號9代表島部4與前端接觸面5a的交叉稜線部 ，符號10代表前端刀腹面5b與切削屑排出溝槽2的交叉稜 線部。第2(a)圖爲俯視圖，第2(b)圖爲前視圖，第2 (c )圖爲右側視圖。 具體而言，本實施例是將本發明運用於工具直徑（刃 部的最大外徑）〇.〇5mm之極小徑的雙溝槽鑽頭。但並不限 定於雙溝槽鑽頭，也能適用於單溝槽鑽頭等的其他鑽頭。 此外，並不限定於極小徑工具，也能適用於工具直徑超過 0.2mm之一般工具。 接著說明各部分。 前端接觸面5a相對於與工具軸垂直的方向以既定的傾 斜角度α形成傾斜。該傾斜角度α較佳爲設定成：與工具 軸垂直方向平行的角度以上（0°以上），且爲90°-切削屑 排出溝槽的扭轉角以下的角度。比90°-扭轉角（本實施例 爲45°)更大的角度，亦即比90°-45°=45°更大角度的情況 ，工具前端變得過尖而容易發生缺口，起因於前端缺口會 造成切削能力降低’而導致折損壽命減少。特別是設定在 -10- 201039948 10°〜3 0°時，不容易產生缺口，可發揮充分的切削能力且折 損壽命長。本實施例之前端接觸面5 a的傾斜角度α設定爲 20° ’又如第3圖所示設定其傾斜方向X，以從前端接觸面 5 a與島部4的交叉稜線部9到具有工具最前端點的交叉稜線 部6擦過的方式來與工件表面接觸。 此外’本實施例的前端接觸面5a，可在工具材料上形 成有切削屑排出溝槽1、2的狀態下，將該工具材料的前端 0 部以既定位置及既定角度除去，而形成期望的前端面形狀 及期望的傾斜角度α。 此外，在本實施例，在切削屑排出溝槽1、2與前端接 觸面5a的複數個交叉稜線部6、7當中比較長的交叉稜線部 6上具有最前端點（最先接觸工件的點），該交叉稜線部6 可發揮切削作用。因此，由於最前端點不在島部3、4(外 周）上，更不容易受到工具軸垂直方向的外力，而能穩定 地獲得充分長的壽命。 Q 此外，在本實施例，前端接觸面5a是由平滑之單一個 平面所構成。但並不限定於平面，亦可由不致對切削作用 產生不良影響的程度之平滑凹彎曲面或凸彎曲面所構成。 在前端接觸面5a和島部3之間設置前端刀腹面5b。前 端刀腹面5b，是和前端接觸面5a同樣的由平滑之單一個平 面所構成。前端刀腹面5b並不限定於平面’亦可由不致對 切削作用產生不良影響的程度之平滑凹彎曲面或凸彎曲面 所構成’又不限定於一面而能由多面所構成。但考慮到生 產性時，以由一面所構成較佳。 -11 - 201039948 此外，前端刀腹面51>是設置在：交叉稜線部6之最前 端點的工具旋轉方向（第3圖中的R方向）之後方側’如此 與交叉稜線部6接觸而被切削後的切削屑往切削屑排出溝 槽2的導出就不會受到阻礙，而能被良好地排出。 具體而言，前端刀腹面5b是如第3圖所示被設置成= 以不超過將交點A (在前端接觸面5a之島部3、4與切削屑 排出溝槽1、2的交點A、B當中位於工具旋轉方向前方側的 交點）互相連結的直線L的範圍，在具有前述最前端點之 交叉稜線部6的工具旋轉方向後方側，朝向與前端接觸面 5a的傾斜方向X不同的傾斜方向Y。 此外，前端刀腹面5b的傾斜角度，是設定成使該前端 刀腹面5b不致接觸工件的角度。具體而言，前端刀腹面5b 的傾斜角度，較佳爲設定成：與工具軸垂直方向平行的角 度以上（0°以上），且爲90°-切削屑排出溝槽的扭轉角以 下的角度。比9(Γ-扭轉角（本實施例爲45° )更大的角度， 亦即比90°-45° = 45°更大角度的情況，工具前端變得過尖而 容易發生缺口，起因於前端缺口會造成切削能力降低，而 導致折損壽命減少。本實施例設定爲30°。亦即，將前端 接觸面5a和前端刀腹面5b設定成不同的傾斜角度。 本實施例由於採用上述構造，前端尖銳部（鏊刃）或 一般具有前端角之切刃等的外力集中的部分並不存在，故 不容易發生咬入’另一方面，不容易受到工具軸垂直方向 的外力，前端接觸面5 a與切削屑排出溝槽的交叉稜線部可 逐漸將加工面加工，因此在工具前端不容易發生缺口。 -12- 201039948 再者，是讓前端接觸面5a之最突出的部分與切削屑排 出溝槽1的交叉稜線部6抵接於加工面而逐漸進行加工，由 於如上述般不容易發生咬入，工具可稍微擺動而適度地擴 大入口側的孔徑以進行鑽孔，因此加工孔形狀在入口側的 口徑變大，工具的基端側不容易與加工孔內壁接觸，而能 抑制工具的基端側與加工孔內壁接觸所造成的折損。 此外，由於形狀簡單，且只要將形成有切削屑排出溝 0 槽之工具材料的前端部以適當的位置及適當的角度除去即 可，因此容易製造。 此外，由於前端接觸面5a只有一個，不會像具有複數 個前端接觸面的情況那樣在各前端接觸面發生左右的失衡 ，因此不須進行左右的平衡檢查，能使檢查變簡單並提昇 良率。 此外，在工具直徑爲0.2mm以下的工具的情況，上述 效果可顯著發揮。亦即，在小徑工具的情況，在利用工具 Q 前端進行切削的初期，該工具前端容易發生缺口，因此可 將切削初期的外力儘量減低之本實施例的構造非常有用。 因此，本實施例之鑽孔工具，即使是極小徑的鑽孔工 具也不容易折損，不須頻繁地更換，形狀簡單且容易進行 製造及檢查，而具備前所未有的優異實用性。 接著說明可證實上述效果的實驗例。 第5、6圖是顯示第4圖所示的習知例、比較例和實施 例的工具壽命（根據對PCB之衝擊數）之比較結果；習知 例是習知之具有2個切削屑排出溝槽和2個切刃之一般鑽頭 -13- 201039948 ;比較例是如前端平坦（1面）欄所示’未設置本實施例 的前端刀腹面而僅設置前端接觸面的鑽頭；實施例是如前 端平坦（2面）欄所示，是使用本實施例的鑽頭。根據第5 、6圖可確認出，若前端接觸面是沒有稜線之平坦的單— 面，相較於習知例之具有複數個前端接觸面的構造’可大 幅延長工具壽命。 此外，第7、8圖是顯示比較例和實施例的孔位置精度 之比較結果。根據第7、8圖可確認出，實施例可改善比較 例的孔位置精度。其理由在於，從第4圖的加工後（1萬次 衝擊後）的相片可推知，在比較例，切削屑會踫撞前端接 觸面之無助於加工的部分（具有最前端點之交叉稜線部的 工具旋轉方向後方側的區域）而阻礙切削屑的排出’相對 於此，將該區域除去而設置刀腹面的實施例，可避免阻礙 切削屑的排出，因此能將切削屑順利地排出，可改善內壁 粗糙情形，而同時也改善了孔位置精度。 【圖式簡單說明】 第1圖係習知例的槪略說明圖。 第2圖係本實施例的槪略說明圖。 第3圖係說明本實施例的前端形狀之放大槪略說明圖 〇 第4圖係實驗例所使用的工具之加工前、加工後的前 端的相片。 第5圖係比較工具壽命的圖 -14- 201039948 第6圖係比較工具壽命的表。 第7圖係比較孔位置精度的圖。 第8圖係比較孔位置精度的表。 【主要元件符號說明】 1、2 :切削屑排出溝槽 3、4 :島部 0 5a :前端接觸面 5b :前端刀腹面 6、7 :切削屑排出溝槽與前端接觸面之交叉稜線部 α :傾斜角度 A :(工具旋轉方向前方側的）交點 B :(工具旋轉方向後方側的）交點 L :將交點A互相連結的直線 〇 -15-201039948 VI. Description of the Invention: [Technical Field to Which the Invention Is Ascribed] The present invention relates to a drilling tool. [Prior Art] A drilling tool for a general printed wiring board (PCB), for example, shown in Fig. 1 is a pair of chip discharge grooves 21, 0 22' at a predetermined twist angle A' in which the chips are discharged. The grooves 21, 22 and the intersecting ridge portions 25, 26 of the first flaps 23, 24 form a cutting edge having a predetermined leading end angle γ'. The symbol 28' 2 9 in the figure represents the second flank. Therefore, the tool of Fig. 1 has a total of four front end faces, and a predetermined angle is applied to each of the front end faces (the flank faces) to form a cutting edge near the center of the front end of the tool. The first (a) is a top view, the first (b) is a front view, and the first (c) is a right side view. However, with the recent high integration and high density of electronic equipment, 〇 has to perform extremely small aperture processing on the PCB, so that the drill bit is required to be smaller. For example, in the case of a very small diameter drill having a tool diameter of about 〇5 mm, since the rigidity of the tool is extremely small, there is a high possibility of breakage, the tool must be frequently changed, or the number of sheets to be processed while overlapping the PCB must be reduced. In addition, when the appearance of the front end shape is checked, the right and left balance (the offset of the cutting edge and the eccentricity of the chiseling edge) is measured to determine the good sputum. If the diameter is small, not only the processing itself, but also the inspection becomes very good. trouble. 201039948 Thus, for example, Patent Document 1 discloses a structure of a single-cutting drill which is capable of securing rigidity even with a tool having a small diameter. However, in the present state, a sufficient breaking life cannot be obtained. Further, there are a plurality of front end contact faces. Therefore, it is very troublesome to perform the good and bad judgment check as in the conventional case. [Patent Document 1] JP-A-2003-3 1 522 SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to provide a drilling tool, even a micro-diameter drilling tool. It is not easy to break. 'It doesn't need to be replaced frequently. It is simple in shape and easy to manufacture and inspect, and it has excellent practicality like never before. The gist of the present invention will be described with reference to the accompanying drawings. The drilling tool of the present invention is a drilling tool having one or a plurality of helical chip discharge grooves 1 and 2, wherein the tool front end surface includes: a direction that extends toward a center axis of the tool and A front end contact surface 5a having no ridge line is inclined at a predetermined angle with respect to a direction perpendicular to the tool axis so as not to be in contact with the object to be contacted by the front end contact surface 5a, and is disposed to be connected to the front end contact surface 5a. The front end of the knife face 5b. Further, in the drilling tool according to claim 1, the front end contact surface 5a is inclined at a predetermined inclination angle α with respect to a direction perpendicular to the tool axis. Further, in the drilling tool according to the first aspect, the island portions 3 and 4 are provided between the plurality of the chip discharge grooves 1 and 2, and the chip discharge grooves 1, 2 and the front end contact surface 5a are provided. The plurality of intersecting ridge portions 6, 7 -6 - 201039948 have a foremost point on the relatively long intersecting ridge portion 6, and the intersection portion 6 can exert a cutting action. Further, in the drilling tool according to the second aspect of the invention, the island portions 3 and 4 are provided between the plurality of chip discharge grooves 1 and 2, and the plurality of cutting grooves 1 and 2 and the front end contact surface 5a are cut. Among the intersecting ridge portions, the relatively long intersecting ridge portion 6 has a foremost end point, and the intersection portion 6 can exert a cutting action. Further, in the drilling tool of claim 4, the front end surface 5a is set at an inclination angle α with respect to a direction perpendicular to the tool axis; | (90°-twist angle). Further, in the drilling tool of claim 5, the inclination α is set to 1 〇 to 30°. Further, in the drilling tool according to the fifth aspect of the invention, the front end surface 5b is provided between the front end contact surface 5a and the island portions 3 and 4, and the front end Q is in the drilling tool described in the claim 6. The surface 5b is provided between the front end contact surface 5a and the island portions 3 and 4. In the drilling tool according to claim 5, the front end surface 5b is provided at the intersecting ridge portion 6 having the foremost end point. Turn the work direction to the rear side. Further, in the drilling tool according to the sixth aspect of the invention, the front end surface 5b is provided on the rear side in the direction of the working direction of the intersecting ridge portion 6 having the foremost end point. Further, in the drilling tool according to the seventh aspect, the front end surface 5b is a ridge line provided on the intersecting ridge portion 6 having the foremost end point, the chip row 6' 7 ridge line contact 10° to an angle knife blade> Abdominal > knives with a scalpel abdomen with a rotary knife abdomen with a spin of 201039948 turn to the rear side. Further, in the drilling tool according to the eighth aspect of the invention, the front end rake face 5b is provided on the rear side in the tool rotation direction of the intersecting ridge portion 6 having the foremost end point. Further, in the drilling tool according to any one of claims 5 to 2, there are two aforementioned chip discharge grooves 1 and 2, and the front end face 5b is provided so as not to exceed the intersection point A (in The range of the straight line L in which the intersections of the island portions 3 and 4 of the front end contact surface 5a and the intersections A and B of the chip discharge grooves 1 and 2 are located at the intersection on the front side in the tool rotation direction is the most The rear end portion of the intersecting ridge portion 6 in the tool rotation direction rear side faces an oblique direction different from the front end contact surface 5a. Further, in the drilling tool described in claim 13, the tool diameter is 0.2 mm or less. According to the present invention, even the extremely small diameter drilling tool is not easily broken. It does not need to be frequently replaced, and the shape is simple and easy to manufacture and inspect, and has excellent practicality as never before. [Embodiment] A preferred embodiment of the present invention will be briefly described, and the effects of the present invention will be described based on the drawings. A single front end contact surface 5a without a ridge line is provided at the front end of the tool, which is different from a general drill bit (for example, a chisel edge near the center of the front end of the tool, which is connected to the chisel edge to form a cutting edge having a predetermined front end angle), at the tool front end There is no chisel edge near the center, and the large cutting resistance in the drilling process is -8-201039948. The part is received by the thrust direction (tool axis direction), which reduces the external force in the vertical direction of the tool axis (cutting in drilling) The bending stress generated by the resistance is not easily broken. Further, the most protruding portion of the front end contact surface 5a (the intersecting ridge portion with the island portions 3, 4 or the chip discharge grooves 1, 2) is abutted on the workpiece processing surface to be gradually cut, unlike the above. Since the drill bit does not easily bite into the machined surface, the tool can be slightly oscillated at the initial stage of cutting to appropriately enlarge the hole on the inlet side to drill the hole. Therefore, the diameter of the machined hole on the inlet side becomes large, and the base end side of the tool does not. It is easy to contact with the inner wall of the machined hole, and it can suppress the damage caused by the contact of the base end side of the tool with the inner wall of the machined hole. Further, by forming the front end surface 5b adjacent to the front end contact surface 5a at a predetermined angle, the cutting of the chips after cutting into the groove discharge grooves 1, 2 is not hindered, and chipping of the chips is less likely to occur. Further, since the shape is simple, and the tip end portion of the tool material on which the chip discharge groove is formed is removed at an appropriate position and an appropriate angle, it is easy to form a predetermined cross-sectional shape and a desired inclination angle α. Front end contact surface 5a. Further, since the shape of the front end is simple, it is not easy to cause left and right imbalance of the front end faces like a conventional tool having a plurality of front end contact faces, and it is easy to check the left and right balance, and the inspection can be simplified and the yield can be improved. [Embodiment] A specific embodiment of the present invention will be described based on Figs. 2 to 8. This embodiment, as shown in Fig. 2, is a drilling tool having two helical cutting -9-201039948 chip discharge grooves 1 and 2, the tool front end surface including: a direction crossing the tool center axis a flat front end blade that is unfolded and has no front end contact surface 5a of the ridge line and is inclined at a predetermined angle so as not to be in contact with the workpiece (workpiece) that the front end contact surface 5a contacts, and is disposed to be connected to the front end contact surface 5a. Ventral surface 5b. In the figure, the symbols 6 and 7 represent the intersecting ridge portions of the chip discharge grooves 1, 2 and the front end contact surface 5a, the symbol 8 represents the intersection ridge portion of the island portion 3 and the front end face 5b, and the symbol 9 represents the island portion 4 and the front end. The intersecting ridge portion of the contact surface 5a, the reference numeral 10 represents the intersecting ridge portion of the leading end rake face 5b and the chip discharge groove 2. Fig. 2(a) is a plan view, Fig. 2(b) is a front view, and Fig. 2(c) is a right side view. Specifically, the present embodiment is applied to the present invention to a double-groove drill having a tool diameter (maximum outer diameter of the blade) 极. 5 mm. However, it is not limited to a double groove drill bit, and can be applied to other drill bits such as a single groove drill bit. In addition, it is not limited to the extremely small diameter tool, and can also be applied to general tools with a tool diameter of more than 0.2 mm. Next, each part will be explained. The front end contact surface 5a is inclined at a predetermined inclination angle α with respect to a direction perpendicular to the tool axis. The inclination angle α is preferably set to be equal to or greater than an angle (0° or more) parallel to the direction perpendicular to the tool axis, and is an angle of 90° or less than the torsion angle of the chip discharge groove. More than an angle of 90°-torsion angle (45° in this embodiment), that is, a larger angle than 90°-45°=45°, the tip of the tool becomes too sharp and is prone to a gap, resulting from the front end. The gap will result in a decrease in the cutting ability' and the loss life will be reduced. In particular, when it is set at -10-201039948 10° to 30°, it is not easy to form a notch, and it can exhibit sufficient cutting ability and long service life. The inclination angle α of the end contact surface 5 a before the present embodiment is set to 20° 'and the inclination direction X thereof is set as shown in Fig. 3 to have the tool from the front end contact surface 5 a and the intersection ridge portion 9 of the island portion 4 The intersecting ridge portion 6 of the foremost end point is wiped in contact with the surface of the workpiece. Further, in the state in which the front end contact surface 5a of the present embodiment is formed with the chip discharge grooves 1 and 2 in the tool material, the front end portion 0 of the tool material is removed at a predetermined position and a predetermined angle to form a desired one. The shape of the front end face and the desired angle of inclination α. Further, in the present embodiment, among the plurality of intersecting ridge portions 6, 7 of the chip discharge grooves 1, 2 and the front end contact surface 5a, the longest intersecting ridge portion 6 has the foremost point (the point at which the workpiece is first contacted) The cross ridge portion 6 can exert a cutting action. Therefore, since the foremost point is not on the island portions 3, 4 (outer circumference), it is less likely to be subjected to an external force in the vertical direction of the tool shaft, and a sufficiently long life can be stably obtained. Further, in the present embodiment, the front end contact surface 5a is constituted by a smooth single plane. However, it is not limited to a flat surface, and may be constituted by a smooth concave curved surface or a convex curved surface which does not adversely affect the cutting action. A front end rake face 5b is provided between the front end contact surface 5a and the island portion 3. The front end face 5b is composed of a smooth single flat surface similar to the front end contact face 5a. The distal end surface 5b is not limited to the flat surface. It may be formed of a smooth concave curved surface or a convex curved surface which does not adversely affect the cutting action. It is not limited to one surface and can be composed of a plurality of surfaces. However, in consideration of productivity, it is preferable to constitute one side. -11 - 201039948 Further, the front end rake face 51 is disposed on the side of the tool rotation direction (the R direction in FIG. 3) at the foremost end point of the intersecting ridge portion 6, and is thus cut in contact with the intersecting ridge portion 6 so as to be cut. The subsequent cutting of the chips into the chip discharge grooves 2 is not hindered, and can be discharged well. Specifically, the front end face 5b is set as shown in Fig. 3 so as not to exceed the intersection point A (the intersection point A of the island portions 3, 4 of the front end contact surface 5a and the chip discharge grooves 1, 2, The range of the straight line L that is connected to each other at the intersection of the B on the front side in the tool rotation direction is inclined toward the rear side in the tool rotation direction of the intersecting ridge portion 6 having the foremost end point, and is inclined to the inclination direction X of the front end contact surface 5a. Direction Y. Further, the inclination angle of the front end face 5b is set such that the front end face 5b does not contact the workpiece. Specifically, the inclination angle of the tip end face 5b is preferably set to be equal to or greater than the angle parallel to the vertical direction of the tool axis (0° or more) and is 90° - the angle below the torsion angle of the chip discharge groove. When the angle is larger than the angle of 9 (Γ-twist angle (45° in this embodiment), that is, more than 90°-45° = 45°, the tip of the tool becomes too sharp and is prone to a gap, resulting from The front end notch causes a decrease in the cutting ability, and the wear life is reduced. This embodiment is set to 30. That is, the front end contact surface 5a and the front end rake face 5b are set to different inclination angles. The sharp portion of the tip end (the edge of the blade) or the portion of the external force having the cutting edge of the tip end does not exist, so that it does not easily bite. On the other hand, it is not easily subjected to the external force in the vertical direction of the tool shaft, and the front end contact surface 5 a and the intersecting ridge portion of the chip discharge groove can gradually process the machined surface, so that no gap is likely to occur at the tool tip. -12- 201039948 Furthermore, the most prominent part of the front end contact face 5a and the chip discharge groove The intersecting ridge portion 6 of the groove 1 is gradually processed by abutting against the machined surface, and since the biting does not easily occur as described above, the tool can be slightly swung to appropriately enlarge the diameter of the inlet side to perform drilling. The diameter of the machined hole on the inlet side becomes large, and the base end side of the tool does not easily come into contact with the inner wall of the machined hole, and the damage caused by the contact between the base end side of the tool and the inner wall of the machined hole can be suppressed. Further, it is only necessary to remove the tip end portion of the tool material in which the cutting dust discharge groove 0 is formed at an appropriate position and an appropriate angle, and thus it is easy to manufacture. Further, since there is only one front end contact surface 5a, it does not have a plurality of In the case of the front end contact surface, the left and right imbalances occur at the front end contact surfaces. Therefore, it is not necessary to perform the left and right balance check, and the inspection can be simplified and the yield can be improved. Further, in the case of a tool having a tool diameter of 0.2 mm or less, the above In the case of the small-diameter tool, the tip of the tool is likely to be notched at the beginning of the cutting by the tip of the tool Q. Therefore, the structure of the present embodiment can be minimized by minimizing the external force at the initial stage of cutting. Therefore, the drilling tool of the embodiment does not easily break even a very small diameter drilling tool, and does not need to be frequently replaced. The shape is simple and easy to manufacture and inspect, and has excellent practicality as never before. Next, an experimental example in which the above effects can be confirmed will be described. Figs. 5 and 6 show conventional examples, comparative examples, and examples shown in Fig. 4 . The comparison of the tool life (according to the number of impacts on the PCB); a conventional example is a conventional drill bit with two chip discharge grooves and two cutting edges - 1339939948; the comparative example is as flat as the front end (1 side) In the column, the drill having the front end face of the present embodiment is not provided, and only the front end contact surface is provided; the embodiment is as shown in the front end flat (two faces) column, and the drill bit of the embodiment is used. According to the fifth and sixth It can be confirmed that if the front end contact surface is a flat single surface having no ridge lines, the structure having a plurality of front end contact faces as compared with the conventional example can greatly extend the tool life. Further, Figs. 7 and 8 are comparison results showing the hole positional accuracy of the comparative example and the embodiment. It can be confirmed from the Figs. 7 and 8 that the embodiment can improve the hole positional accuracy of the comparative example. The reason is that, from the photograph after the processing of Fig. 4 (after 10,000 impacts), it can be inferred that in the comparative example, the chips will collide with the portion of the front end contact surface that does not contribute to the processing (the cross ridge line having the foremost point) In the case where the tool is rotated in the direction of the rear side of the tool, the discharge of the chips is inhibited. In contrast, the embodiment in which the region is removed and the blade surface is provided, and the discharge of the chips can be prevented from being hindered, so that the chips can be smoothly discharged. It can improve the roughness of the inner wall while improving the hole position accuracy. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic explanatory diagram of a conventional example. Fig. 2 is a schematic explanatory view of the present embodiment. Fig. 3 is an enlarged schematic view showing the shape of the front end of the embodiment. Fig. 4 is a photograph of the front end of the tool used before and after processing of the tool used in the experimental example. Figure 5 is a comparison of tool life -14-201039948 Figure 6 is a table comparing tool life. Figure 7 is a graph comparing the accuracy of the hole position. Figure 8 is a table comparing the accuracy of the hole position. [Main component symbol description] 1, 2: Chip discharge groove 3, 4: Island portion 0 5a: Front end contact surface 5b: Front end flank surface 6, 7: Cross ridge portion α of the chip discharge groove and the front end contact surface : inclination angle A: (the front side of the tool rotation direction) intersection B: (the rear side of the tool rotation direction) intersection point L: a line connecting the intersection point A to each other 〇-15-