錨栓的設計，最基本當然是要符合歐盟對於攀岩錨栓的規範：EN959 標準 (感謝博文提供相關資訊)。不過，EN959 只是最低標準，因此我們需要在這標準上再強化我們的需求：增加抗腐蝕的耐用度。抵抗腐蝕有許多手段，除了材料選擇外，還可藉由設計來進行加強。鈦只是相當不易生鏽，並不是真的不會鏽，這個世界上目前還不存在「完全不會生鏽」的金屬或合金。

從設計上的強化，至少有兩個方向可下手：其一，一體成型，即減少bolt總體的表面積，降低鏽蝕反應速率，而且不會存在焊接等可能造成易腐蝕的弱點。加上是以鑄造方式成形，不會存在如彎折等方式所殘留的內應力 (造成鏽蝕的原因之一)；其二，加粗直徑，越粗就撐越久。基本上是以「過頭」的方式，來提高三四十年後所能保有的強度。大部分型號的鈦金屬只要 8mm，即已超過 EN959 的強度要求，市面上就有一款鈦合金錨栓是以 8.8mm 的鈦條彎折製成。廠商有成本考量，每多粗一點，成本就更高一些，售價就得上調。鈦合金錨栓的售價在市場上的接受度已不高，因此廠商也必須在其間取得平衡。然而，我們的成品並不販售，因此在這方面有更多彈性。我們的鈦合金錨栓設計直徑最後決定以 12mm 為基調，因為除了強度考量外，我們也希望能夠為未來保留沿用舊孔的機會。當然，設計上還有許多其他考量，比如 P 型、T 型與 U 型的決擇：由於 U 型要鑽兩個孔，因此我們決定不考慮；而 P 型，部分方向受力較強，部分方向受力卻會較弱；因此，最後我們決定採用可多方向受力的 T 型做為版本。

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整個設計過程是在不斷的討論、檢討中改進，一點一滴逼進最適合的平衡點。其中，不可或缺的另一位關鍵岩友，即是熱心的小傑；發揮了他機械專家的本領，為我們進行一次又一次的電腦應力分析，並接下繪製3D檔案的工作。另外，也感謝岩友 Jamy 提供我們 3D 列印的服務。

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In designing a bolt, a primary consideration is that the bolt must conform to international safety standards, particularly EN959 (special thanks to Bowen Cheng for providing a copy of EN959). However, EN959 should be considered merely the minimum standard, and additional features, particularly the bolt’s ability to resist corrosion, must also be taken into account. There are a variety of approaches to optimizing the corrosion resistance of a bolt design. In addition to the type of material selected, bolt design is also a key factor. Even titanium alloys are not truly immune to corrosion, but instead achieve relatively high levels of corrosion resistance. In fact, there is no known material that is completely immune to corrosion.

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Beyond meeting the EN959 standard, it was determined that the ideal bolt design should meet two additional objectives. First, the bolt should be of a one-piece design, in order to minimize total exposure area, thereby slowing the corrosion reaction process, if any; and, due to the cast, one-piece design, reducing or eliminating the residual internal stress that occurs in forged, bent designs and that is known to be one of the contributing factors of SCC. Second, the bolt’s diameter should be as large as practical, so that it can last longer, following a principle of ‘over-designing’ such that a bolt can last at least 30 or 40 years and its strength will remain intact. Most titanium bolts currently on the market are formed of bent 8.8 mm stock. This is done mainly due to cost considerations: larger stock is more costly to make and results in a pricier product. However, we decided to make our titanium bolt 12 mm, for two reasons: first and obviously, we want a stronger bolt, and second, we want to make the bolt hole reusable, in order to simplify any replacement, of even the titanium bolt, that might need to be performed by future climbers. There are other considerations as well: for example, there are several popular configurations of glue-in bolts: P-shape, T-shape, and U-shape. A U-shaped bolt requires two drilled holes, doubling the damage to the rock wall; therefore, U-shaped designs were eliminated from consideration. Meanwhile, a P-shaped bolt has problems in handling different loading directions, and was therefore also dropped from our consideration. Finally, only the T-shaped bolt, with its ability to withstand multi-directional loading forces and its need for only one hole, was determined satisfactory for our needs.

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The design process benefitted from continuous discussion and idea exchange among many local climbers as we worked toward a consensus. During the discussions, Xiao Jie, an active climber and important contributor who is familiar with mechanical engineering, performed the necessary stress analysis, shared the results, and helped finalize the computerized 3D graph of the titanium bolt that has existed today. Special thanks also go to Jamy Chen, who made the 3D print of the bolt possible.