We do all our models "Top-Down" and here iswhat we found so far to be the best (in

我們發(fā)現(xiàn)下面所介紹的“自頂向下”設計方法對大多情況是最好的（適用
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most cases, since there are some assemblies that willrequire another structure).

于絕大多數(shù)情況，除了某些特殊結構的裝配體）：
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1.- Create a Part inside your Top-Level Assembly andcall it "Ref_Geometry" and define it as "not show on BOM"

1.在頂層裝配體中新建一零件后把它命名為“參考幾何體”，并在屬性中設置成“不在BOM表中顯示”* |* r2 Z% Z9 {! l

2.- Inside that Part, create all the sketches, planes,axis, points, etc. you need to drive your entire assembly. Aslo you can driveall that geometry from a single DT inside that part

2.在這個零件中，創(chuàng)建要驅動整個模型的所有草圖，平面，軸，點等，當然也可以用這個零件中的設計表來驅動裝配體$ e. n% o# Z3 u- v

3. Create Sub-assemblies as you need to create yourparts and insert a copy (an instance) of the Ref_Geometry" part on thosesub-assemblies.

3.創(chuàng)建所必須的子裝配體并把“參考幾何體”插入到這些子裝配體中。
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4.- Create parts inside the sub-assemblies, and relatethe sketches needed to create the parts to the geometry on the"Ref_Geometry" part (that way all the in-context relations will be"inside" each sub-assembly level.

4.在這些子裝配體中創(chuàng)建零件并將零件中的草圖參考到“參考幾何體”的元素中。（這樣做的話就可以使頂層零件的參考約束也可以作用到子裝配單元）
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5.- This will create a Top-Down structure that willallow you top work with a single sub-assembly open, but on which any changesmade to the referencial geometry (or to the DT) will be reflected on any othersub-assembly and on the complete assembly when opened.

5.這種自頂向下的結構可以做到：僅在子裝配體打開的情況下編輯子裝配體而不會使參考失效。但是參考幾何體如有任何改動，都會影響到任何子裝配體以及打開時的整個裝配體。: u& k6 W2 L! w  m; X% {% y+ H

You need to create referencial geometry sketches assimple as possible in order to not create a "monster referencial geometrypart" that will degrade machine performance. That is, just create theesential geometry (for example to define a rectangular shape do not draw therectangle, just draw two points positioned with relations to another geometryor by dimensions, To define a circular shape, just define the points needed tocreate the circle at the part that will use that shape. Remember that you arecreating "referencial geometry" not a drawing.

創(chuàng)建的參考幾何體要盡量地簡單，一個復雜的“參考幾何體”會使運行速度變慢.這樣的話，只要創(chuàng)建一些關鍵的元素就可以了（比如說畫一個直角形而不是矩形，只要畫兩個點，用尺寸或其它幾何體定義位置，通過定義幾個模形中要用到的點來定義一個圓）要記住你畫的是參考幾何體而不是工程圖！
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Do not do large referencial geometry sketches withlosts of relations, divide the referencial geometry in smaller sketches relatedone to each other (since they are inside the same part will not increase the"load", but when you open one for editing you will not be working ona 2000 entities sketch that will take 15 minutes to close and rebuild.

不要在一個大的草圖里設置大量的幾何關系，把這些參考幾何分散到相互聯(lián)系的小草圖里，（這樣的話因為這些幾何體都在一個個小的草圖內，從而不會增加模型載入的時間，從而不發(fā)這樣的事：打開一個包含一個兩千個實體的草圖，并且需要花15分鐘關閉與重建）" w3 H2 c; q9 z

One last issue, try to avoid as much as possible"global variables", use "equal" relations between sketchesand place a dimension on one of the entities, that one will drive all theothers without getting into the "inefficient" Equations SW module. Ifyou have a DT on the Referencial Geometry part do all your complex calculationsinside the DT (Excel is a lot more powerfull that the VB equations ability ofSW.